High-load silver nanowires, dispersions and pastes, conductive materials and corresponding methods

Abstract

Concentrated dispersions of silver nanowires are used to produce qualitatively distinct silver structures with various properties. The concentrated dispersions may contain a high weight percent of silver nanowires and can be formulated to be a fluid liquid or a non-fluid paste. The concentrated dispersions may be stable for up to a week without visible sedimentation, may have non-Newtonian rheology, and can be diluted to a desired weight percent of silver nanowires without adversely affecting the uniformity of the dispersion. The concentrated dispersions may be formulated with or without polymer or prepolymer components. The concentrated dispersions may be formulated with silver salts to adjust the dispersion of silver nanowires and to improve the conductivity of the hardened silver structures formed from the dispersions. Methods for forming concentrated dispersions are described as methods for forming silver structures from dispersions.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to the concurrently pending U.S. Provisional Patent Application No. 63 / 459,495, filed on 14 April 2023, entitled “High Loadings of Silver Nanowires Dispersions and Conductive Pastes; and Corresponding Methods,” which is incorporated herein by reference.

[0002] This invention relates to a high-concentration silver nanowire dispersion, a method for producing the dispersion, and the use of the same. This invention further relates to the use of silver salts to improve the dispersion of highly conductive silver nanowire deposits and silver nanowires, and to significantly improve the conductivity of hardened metal structures. [Background technology]

[0003] Silver nanowires have been explored for a variety of applications since the development of suitable solution-based synthesis methods for commercial-scale synthesis. Particular interest lies in the formation of transparent conductive films due to the nanowires' ability to be coated as a sparse metallic layer that allows light transmission while providing useful conductivity. The conductive properties of metallic nanowires, along with their flexibility, suggest potential applications in devices such as sensors and current collectors.

[0004] Silver and other metal nanoparticles and other forms of microparticles have found usefulness as conductive fillers for inclusion in composite materials, etc. Such materials can be used to form conductive metal traces, shields, grounding elements, and the like. [Overview of the project] [Means for solving the problem]

[0005] In a first aspect, the present invention relates to a fluid concentrated dispersion comprising silver nanowires and a polymer dispersant in a polar solvent, wherein the dispersion exhibits non-Newtonian viscosity, does not show visible sedimentation over a week, and is stable when diluted with isopropyl alcohol to a concentration of 0.1% by weight. The fluid concentrated dispersion may contain at least about 8% by weight, at least 15% by weight, or at least about 20% by weight of silver nanowires, and the aspect ratio may be greater than 25. The polar solvent may include volatile polar solvents and / or solvents such as monomers, oligomers, or polymers that can be polymerized and / or crosslinked during further processing such as drying, heating, irradiation, blending with additional reactants, combinations thereof, or other suitable methods. Non-Newtonian viscosity may include shear reduction without the addition of a thickener. In some embodiments, salts such as silver salts may be included in the dispersion. The silver salt may be included in any amount, for example, such that the dispersion contains up to about 50% by weight of silver ions relative to the weight of the silver nanowires. The fluid concentrated dispersion may contain a reducing agent if silver salts are present. The reducing agent may be an additive such as an inorganic salt, an organic salt, or other organic component. The reducing agent may also contain a volatile polar solvent and / or a solvent containing monomers, oligomers, or polymers. The fluid concentrated dispersion exhibits fluidity when placed on a surface at an angle of 60 degrees from the horizontal.

[0006] In another aspect, the present invention relates to a fluid concentrated dispersion used to form conductive composite materials and adhesives. The dispersion has a flow rate of 0.1 s -1 When subjected to shear rates, it may exhibit a viscosity of at least about 100 cP or about 500 cP to about 5000 cP. Conductive composite materials and adhesives or other solid materials may be formed during further processing as described above. Curing may further involve the reduction of metal salts, such as silver salts, when present in a dispersion.

[0007] In a further embodiment, the present invention relates to a fluid dispersion comprising silver nanowires, a polymer dispersant, and a silver salt in a polar solvent, wherein the dispersion has a flow rate of 0.1 s -1It exhibits non-Newtonian viscosity at a shear rate of . Silver nanowires have an average aspect ratio of about 30 to about 1000 and are present in an amount of at least about 5% by weight of the fluid dispersion. Silver salts are present in an amount of at least about 1% by weight of the silver nanowires. The fluid dispersion does not need to show visible sedimentation over a week and can be a stable dispersion when diluted to a concentration of 0.1% by weight with isopropyl alcohol. The polar solvent can be any of those described above for the fluid concentrated dispersion. The fluid dispersion can be further processed as described above for the fluid concentrated dispersion. The fluid dispersion may contain at least about 8% by weight, at least about 15% by weight, or at least about 20% by weight of silver nanowires. Silver salts may be included in any amount, for example, such that the dispersion contains up to about 50% by weight of silver ions relative to the weight of silver nanowires. The fluid dispersion may contain at least about 8% by weight of silver nanowires and about 5% to about 50% by weight of silver ions relative to the weight of silver nanowires. The fluid dispersion may contain a reducing agent. The reducing agent may be an additive such as an inorganic salt, an organic salt, or other organic component. The reducing agent may also contain a volatile polar solvent and / or a solvent containing monomers, oligomers, or polymers. The fluid dispersion exhibits flow when placed on a surface at an angle of 60 degrees from the horizontal.

[0008] In further embodiments, the present invention relates to a conductive material comprising at least about 95 wt% silver, wherein the silver has a structure formed from the reduction of a silver salt in the presence of a silver nanowire deposit comprising at least about 50 wt% silver nanowires having an aspect ratio of at least about 30. In some embodiments, the silver is formed from the reduced silver salt and at least about 75 wt% silver nanowires having an aspect ratio of at least about 50. In some embodiments, the silver is formed from at least about 90 wt% silver nanowires. The conductive material comprises about 1 × 10⁻¹⁶ 4 Ohms-cm or less, or approximately 5 x 10⁻¹ -5 Ohm - cm ~ approximately 4 x 10 -6 It may have a resistivity of ohms-cm.

[0009] In further embodiments, the present invention relates to a silver paste essentially comprising a uniform distribution of silver nanowires and optionally additional silver nanostructures, a polymer dispersant, an optionally selected salt providing up to about 50% by weight of metal ions relative to the weight of the silver nanowires, and a polar solvent, wherein the dispersion is stable with respect to phase separation and does not flow under zero shear, and dilution and harmless mixing of the conductive dispersion to a metal concentration of 0.1% by weight with isopropyl alcohol results in a well-dispersed solution. In some embodiments, the silver nanowires have an average aspect ratio of at least about 250, and the total metal concentration may be at least about 12% by weight, with at least about 80% by weight of the metal being silver nanowires. In some embodiments, the silver nanowires have an average aspect ratio of about 15 to about 250, and the total metal concentration is at least about 25% by weight, with at least about 80% by weight of the metal being silver nanowires. The silver paste may contain a salt providing up to about 50% by weight of silver ions relative to the weight of the silver nanowires. The silver paste can be spread by applying shear and does not flow on a surface inclined at 60 degrees from the horizontal. The silver paste is approximately 5 × 10 -2 It may have a resistivity of ohms-cm or less.

[0010] In a further aspect, the present invention relates to a method of forming a concentrated silver nanowire dispersion. The method includes evaporating a low-boiling point temperature solvent component of a silver nanowire dispersion that includes a polar solvent, the low-boiling point solvent temperature component having a boiling point of about 125° C or less at atmospheric pressure, and removal of the low-boiling point temperature solvent component results in the formation of a well-dispersed concentrated silver nanowire dispersion having a solid concentration of at least about 5 wt%, and prior to evaporating the low-boiling point temperature solvent component, the silver nanowire dispersion is a stable dispersion that includes about 10 wt% or less silver nanowires. The silver nanowire dispersion may include a silver salt along with the polar solvent that is the low-boiling point solvent, and the silver salt is present in an amount that provides from about 1 wt% to about 50 wt% silver ions relative to the weight of the silver nanowires. In some embodiments, after removal of the low-boiling point temperature solvent component, the concentrated silver nanowire dispersion includes from about 10 wt% silver nanowires to about 70 wt% silver nanowires. The concentrated silver nanowire dispersion may be fluid. The concentrated silver nanowire dispersion may be a paste. The method may further include curing the concentrated silver nanowire dispersion to form a conductive silver-based material.

[0011] In a further aspect, the present invention relates to a method of forming a conductive solid structure that includes silver. The method includes heating a three-dimensional deposit that includes silver nanowires and a silver salt at a temperature of at least about 120° C for at least about 5 minutes to reduce the silver salt and form a conductive solid structure, and the deposit prior to curing has at least about 25 wt% silver nanowires and at least about 1 wt% silver ions relative to the weight of the silver nanowires. The three-dimensional deposit may include a concentrated silver nanowire dispersion and a polar solvent, and the polar solvent may be removed by blowing a gas across the three-dimensional deposit. The conductive solid structure includes a cured material that includes at least about 25 wt% silver or at least about 95 wt% silver. The conductive solid structure may have a resistivity of about 1×10 4 ohm-cm or less or about 5×10 -5 ohm-cm to about 4×10 -6 ohm-cm. The conductive solid structure may be opaque and may have an average thickness of at least about 2 microns.

[0012] In a further aspect, the present invention relates to a composite material comprising an opaque structure of at least about 5 wt% polymer matrix and at least about 25 wt% silver, the silver being formed of agglomerates of three-dimensional silver nanowires through which a silver salt is reduced to silver metal and contributes to the conductive composite material. The composite material can contain at least about 50 wt% silver or from about 75 wt% silver to about 90 wt% silver. The silver formed by reducing the silver salt can provide from about 2 wt% to about 40 wt% silver relative to the silver nanowires. The composite material can have a resistivity of about 1×10 -3 ohm-cm or less or from about 5×10 -5 ohm-cm to about 4×10 -6 ohm-cm.

[0013] In a further aspect, the present invention relates to a dispersion of silver nanowires consisting essentially of a uniform distribution of silver nanowires and optionally additional silver nanostructures, a polymer dispersant, optionally a salt providing up to about 0.5 wt% metal ions, and a polar solvent, the dispersion being stable with respect to phase separation and dilution and innocuous mixing of the conductive dispersion to a 1 wt% metal concentration with isopropyl alcohol resulting in a well-dispersed solution. The dispersion can be fluid. The dispersion can be a non-fluid paste.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram showing how much the number density changes depending on the particle size at the same weight density by comparing the number density of dispersed nanowires having different physical dimensions. [Figure 2] It is a schematic plot of viscosity as a function of the volume fraction of solid spherical particles at a set low shear rate showing a transition to non-Newtonian behavior and subsequent rapid increase in viscosity as the packing density of the particles approaches the densest packing density. [Figure 3] It is a schematic plot of viscosity as a function of the nanowire density showing the change between different densities exhibiting different material behaviors. [Figure 4]A representative plot of the volume percentage of silver as a function of the weight percentage of silver for a dispersion assuming an organic density of 1.19 g / ml. [Figure 5] (FIG. 5A) A plot of resistivity as a function of weight percentage (wt%) for a dispersion containing H nanowires (H-NW) in propylene glycol (PG), and (FIG. 5B) a plot of resistivity as a function of volume percentage (vol%) for the H-NW dispersion of FIG. 5A. [Figure 6] Shows the normalized UV-Vis absorption spectra for selected H-NW dispersions in PG at concentrations ranging from 60 wt% to 20 wt%. [Figure 7] Shows a plot of viscosity as a function of shear rate for selected H-NW dispersions in PG. [Figure 8] Shows a plot of storage modulus (dark gray) and loss modulus (light gray) as a function of angular frequency for selected H-NW dispersions in PG. [Figure 9] (FIG. 9A) Shows plots of resistivity and viscosity as a function of weight percentage for a continuously diluted dispersion containing H-NW in PG, and (FIG. 9B) shows plots of resistivity and viscosity as a function of weight percentage for a dispersion containing H-NW in PG. [Figure 10] Shows a continuously diluted dispersion. [Figure 11] (FIG. 11A) An image at 10 times magnification of H-NW dispersed in PG at 70 wt% (H70-PG) and formed as a film approximately 25 microns between two glass substrates, (FIG. 11B) an image at 10 times magnification of H70-PG continuously diluted to 30 wt% and formed as a film approximately 25 microns between two glass substrates, (FIG. 11C) an image at 10 times magnification of H70-PG continuously diluted to 20 wt% and formed as a film approximately 25 microns between two glass substrates, and (FIG. 11D) an image at 10 times magnification of H70-PG continuously diluted to 10 wt% and formed as a film approximately 25 microns between two glass substrates. [Figure 12](Figures 12A and 12B) Plots of viscosity as a function of shear rate for dispersions containing N-nanowires (N-NW) in PG. [Figure 13] The plots of the storage modulus (dark gray) and loss modulus (light gray) as functions of each frequency for an N-NW dispersion in PG are shown. [Figure 14] The UV-Vis absorption spectrum of the N-NW dispersion in PG is shown. [Figure 15] The UV-Vis absorption spectra for N-NW dispersions containing 15% by weight of polyvinylpyrrolidone (PVP) in PG, expressed as an organic-to-silver ratio (O / Ag), are shown, with O / Ag values ​​of 0.13, 0.26, and 0.39. [Figure 16] Figure 15 shows a plot of O / Ag as a function of recovery rate for the dispersion described. Recovery rate is the ratio of the expected weight to the actual weight, expressed as a percentage. Values ​​greater than 100% indicate the amount of EtOH remaining in the dispersion after rotary evaporation. [Figure 17] Figure 15 shows the dispersions, with O / Ag values ​​of 0.13, 0.26, and 0.39 from left to right. [Figure 18] The U-Vis absorption spectrum of the H-NW dispersion in ethyl lactate (ELA) is shown. [Figure 19] These are images of H-NW in ELA at 10x magnification at concentrations of 50 wt% (Figure 19A), 60 wt% (Figure 19B), and 70 wt% (Figure 19C), respectively. [Figure 20] The UV-Vis absorption spectrum of N-NW in IPA prepared by redispersing a dried N-NW film is shown. [Figure 21] The UV-Vis absorption spectrum of H-NW in IPA prepared by redispersing a dried H-NW film is shown. [Figure 22] These figures show the redispersibility and sedimentation of H-NW in IPA prepared by redispersing dried H-NW films dispersed in triethylene glycol (Figure 22A) and ethylene glycol butyl ether (EGBE; Figure 22B), respectively. [Figure 23] The viscosity as a function of shear rate is plotted for an N-NW dispersion containing 3.5% by weight of N-NW in hydroxyethyl methacrylate. [Figure 24] (Figure 24A) shows an image at 10x magnification of an H-NW dispersion containing 60% by weight of H-NW in N-methyl-2-pyrrolidone, and (Figure 24B) shows an image at 10x magnification of an H-NW dispersion containing 60% by weight of H-NW in dimethyl sulfoxide. [Figure 25] The UV-Vis absorption spectra of a dispersion containing 60% by weight of H-NW and 15% by weight of N-NW in dimethylacetamide are shown. [Figure 26] The UV-Vis absorption spectra of dispersions containing 80% to 30% by weight of H-NW in EGBE are shown. [Figure 27] This is a plot of resistivity as a function of weight percentage for dispersions containing 80% to 20% H-NW in EGBE. [Figure 28] The UV-Vis absorption spectra of dispersions containing 15% to 7% by weight of N-NW in EGBE are shown. [Figure 29] The images, from left to right, show dispersions containing 55% by weight of H-NW (H55-PG), H55-PG containing silver heptafluorobutyrate, and H55-PG containing silver fluoride, respectively. [Figure 30] The UV-Vis absorption spectra are shown for dispersions containing silver trifluoroacetate (TFA) or silver perchlorate, prepared in different solvents, at a concentration of 50% by weight and containing H-NW. [Figure 31] These are 50x magnification images of H-NW in 50% by weight of butoxytriglycol before (Figure 31A) and after (Figure 31B) heating in an oven at 150°C for 5 minutes. [Figure 32] The plots show the average resistivity as a function of temperature for H-NW(H2) with an average length of approximately 2 microns, at 60 wt% in various solvents, with or without TFA. [Figure 33]The average resistivity as a function of temperature is plotted for H-NW(H5) with an average length of approximately 5 microns at 30% by weight in various solvents, with or without TFA. [Figure 34] Figures 32 and 33 show combined plots illustrating the resistivity for both H2 and H5 nanowires. [Figure 35] These are 25,000x magnification images of H2 nanowires in butyl carbitol at 60% by weight, before (Figure 35A) and after (Figure 35B) heating at 150°C for 5 minutes. [Modes for carrying out the invention]

[0015] The formation of materials containing high concentrations of silver nanowires is described as forming a series of qualitatively distinct material types. Based on an understanding of the rheology and properties of the dispersion components, product materials using dispersion formation and concentrated dispersions can be derived using achievable concentrations in appropriate solvents. The dispersions can be stable in that they avoid non-dispersible aggregates, and appropriate methods for evaluating stability are elucidated. Dispersions, which can take the form of high-concentration fluid liquids or non-fluid pastes, can be free of dispersants and resins other than residual polyvinylpyrrolidone derived from silver nanowire synthesis, or high-concentration dispersions can be formed in liquid polymer matrix precursors. In other embodiments, high concentrations of silver nanowires can be used to formulate high-metallic-load composite materials with polymers or solid materials with large amounts of silver nanowires and small amounts of polymer, in either case forming materials with moderate to high conductivity. Silver salts have been found to provide a remarkable effect on high-concentration dispersions, and subsequent reduction of silver ions can improve conductivity. When high-fill materials are cured with silver salts to reduce silver ions to silver metal, conductive materials with significantly increased conductivity due to the reduced salts can be formed, adapted from the applicant's Nanoglue® technology. Processing with silver salts to improve the conductivity of dry-deposited materials involves applying more heat over longer periods compared to previous studies with transparent conductive films, which appears to be related to the slower reduction rate of silver ions. Electrical resistivity comparable to that of metals such as iron has been achieved from cured fluid deposits. These materials provide alternative commercially available materials for forming highly conductive structures applied in fluid forms and introduce novel paste-like conductive materials for various conductive applications. Unless otherwise specified, conductivity as used herein refers to electrical conductivity, although high thermal conductivity can also generally be obtained.

[0016] High concentrations of dispersions exceeding 10% by weight can be stably formed with long, thin silver nanowires, while even higher concentrations can be achieved using silver nanowires with lower aspect ratios, although the aspect ratios suitable for nanowires to form highly conductive structures remain relatively high. A paste can be formed that does not flow in a suitable solvent but is stretchable, easily processable, and dispersible in a stable, diluted dispersion. The paste is stable but can still retain a large proportion of solvent. Some of the concentrated dispersions and auxiliary materials formed from them may essentially consist of a solvent, silver nanowires, optional additional metal nanostructures, a polymer dispersant soluble in the solvent at about 0.1% to about 60% by weight relative to the weight of silver, an optional polymer matrix precursor, and an optional salt having a metal cation. These compositions may lack the polymer matrix and other additives that substantially alter the conductivity rheology of the listed components. As the concentration of silver nanowires in the paste increases, transitions occur that are reminiscent of exceeding the percolation threshold, where the resistivity drops significantly. The processing may be based on forming a good diluted dispersion in a preferred low-boiling point solvent, followed by the desired solvent transfer and concentration by removing at least a large portion of the original solvent.

[0017] Polymer dispersants are generally solid polymers that dissolve in a solvent and are commonly incorporated into the final material as processing aids, often as organic components. Polyvinylpyrrolidone is a common polymer dispersant used in silver nanowire synthesis. Polyvinylpyrrolidone copolymers may also be useful. Other polymer dispersants include, for example, polysaccharides such as cellulosic polymers, e.g., cellulose ethers and / or cellulose esters. Some solvents may be liquid polymer precursors or oligomers that can be cured into polymers during final product formation. Thus, the solvent may or may not be removed during processing. High-concentration dispersions and pastes offer remarkable properties, but the final dried and further processed compositions formed from the dispersions offer a potential area for new products. In suitable embodiments, the polymer matrix may be formed from polymer matrix precursors such as monomers, oligomers, soluble binder polymers and / or crosslinkable resins.

[0018] The use of metal salts, particularly silver salts, has been found to reduce the curing of materials by converting silver ions into metal, thereby significantly lowering electrical resistivity. How the reduced silver metal is positioned within the final conductive structure remains unclear. It has also been found that metal salts, when heated more gently than those used to reduce silver, can bring about surprising material changes in paste-like dispersions. The reason why silver salts appear to dissolve or soften materials with shorter durations and relatively gentle heating at higher concentrations of silver nanowires is unknown.

[0019] Silver nanowires have been of great interest due to their ability to form transparent conductive structures. Silver is particularly interesting due to its high conductivity. Based on their effective one-dimensional properties, silver nanowires can be spread across a surface to form a sparse layer through which visible light can pass. Nevertheless, long lengths result in many intersections of nanowires, which provide potential conduction pathways. Due to the two-dimensional nature of the sparse layer, the junction resistance to conduction between adjacent silver nanowires can be significant. Chemical fusion of silver nanowire junctions, based on thermodynamic priorities for metal deposition at the nanowire junctions, may be effective in reducing or eliminating junction resistance through the formation of a unitary structure. See, for example, U.S. Patent No. 10,029,916 to Virkar et al., entitled "Metal Nanowire Networks and Transparent Conductive Material" and U.S. Patent No. 10,020,807 to Virkar, entitled "Fused Metal Nanostructured Networks, Fusing Solutions With Reducing Agents and Methods for Forming Metal Networks," both of which are incorporated herein by reference.

[0020] In relation to opaque conductive materials, silver nanowires can be loaded into polymers such as adhesives to form conductive fillers, adhesives, and the like. For example, see, for instance, the concurrently pending U.S. Patent Application No. 18 / 376,952 to Virkar et al., entitled “Silver Nanowire and Noble-Metal Coated Silver Nanowire Conductive Polymer Composites With Low Loading Percolation Conduction,” which is incorporated herein by reference. The use of silver nanowire-filled composite materials for forming adhesives is described in the U.S. Patent Application Publication No. 2016 / 0177146A (hereinafter referred to as the '146 application) to Mun et al., entitled “Adhesive Film and Display Member Including the Same,” which is incorporated herein by reference. Based on the applicant's previous research on melting, soluble metal salts, such as silver salts, can be added to concentrated dispersions. These salts appear to affect the rheology of these concentrated dispersions, and therefore they can be used to adjust the rheology and may be useful in affecting conductivity. Metal salts can generally be added in amounts of up to approximately 60% by weight relative to the weight of silver nanowires.

[0021] Silver nanowires are generally synthesized by solution reactions involving diols as solvents and reducing agents, and polyvinylpyrrolidone as a capping agent, which is preferred for nanowire formation over other nanoscale particle shapes under appropriate conditions. To form transparent conductive layers, it has generally been desirable to form thinner nanowires with longer lengths. Thinner nanowires have less scattered light and are therefore optically superior to thicker nanowires, and two-dimensional films composed of longer nanowires are typically desirable because they form films with fewer junctions for a given amount of silver and therefore lower junction resistance. Transparent conductive layers require thin coatings and low silver content to achieve good optical properties. To form a silver nanowire-based transparent conductive layer, the substrate is typically coated with a relatively dilute ink having low viscosity and a low weight percentage of silver (typically <0.2 wt%). Therefore, much of the effort in the field of silver nanowires has been directed towards optimizing thin, long silver nanowires dispersed at low loadings (i.e., low weight and low volume ratios of high aspect ratio nanowires). The synthesis of thin silver nanowires on a commercial scale is described in U.S. Patent No. 10,714,230B2 (hereinafter referred to as the '230 patent) to Hu et al., entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed from the Nanowires," which is incorporated herein by reference. The nanowires formed in the '230 patent were found to result in transparent conductive films with good sheet resistance and excellent optical quality. In these transparent conductive films, the resistivity is limited by the amount of silver present, as the intrinsic resistivity of silver provided the boundary for electrical conduction.

[0022] The large aspect ratio of nanowires is a crucial factor in establishing conductive paths, and while narrower diameters may help achieve desirable optical quality, for opaque applications, it may be beneficial to deviate from nanowire dimensions that are highly desirable for transparent conductors. While significantly concentrated samples were formed with state-of-the-art silver nanowires for transparent conductive applications (the applicant's C3 nano Activegrid® GEN7 and GEN8 inks), higher concentrations of dispersions and pastes were achievable with nanowires having smaller aspect ratios. This may be due to rheological issues to some extent. With longer and thinner nanowires, viscosity increases to very high values ​​even at relatively low loadings. The rheology of spherical particle-based dispersions, e.g., silver nanoparticles in solvents, has been studied in great detail and can fit very well into existing models and theoretical equations and frameworks; however, the 1-D related complexity and considerable aspect ratio characteristic of silver nanowires introduce novel and unexpected features and behaviors in higher loading dispersions where solid-particle interactions can dominate the rheology.

[0023] This dichotomy can be understood by examining the properties of dispersed nanowires. Referring to Figure 1, the comparison is schematically shown for longer and thinner nanowires and shorter and thicker nanowires. The Type 2 version of the shorter and thicker nanowires still has an aspect ratio of approximately 100, and therefore the nanowires are long enough to establish a conductive path. The cartoon in Figure 1 does not emphasize the aspect ratio, and the distinction regarding the amount of silver loaded in the dispersion is clear. It is easy to imagine that a dispersion with a larger number of longer and thinner nanowires will have a higher viscosity, either thinner or thicker, compared to a dispersion with shorter nanowires. The following examples demonstrate this effect very clearly. Researchers studying dispersions of one-dimensional structures such as AgNW can gain some insight into the system properties by estimating the dimensionless number β (which is defined below and reflects the non-spherical nature of the nanowires convolved in concentration in a way that is reflected in the resulting rheology). The importance of this parameter in relation to polymer solutions is discussed in Wierenga et al., “Low-shear viscosity of isotropic dispersions of (Brownian) rods and fibers; a review of theory and experiments”, Colloids and Surface A:Physicochemical and Engineering Aspects 137(1998)355-372, which is incorporated herein by reference. The rheology of formulated screen printing inks containing an additional polymer with silver nanowires at a concentration of up to 7 wt% is described in Hemmati et al., “Rheological behavior of silver nanowire conductive inks during screen printing”, J Nanopart Res(2016)18:249, which is incorporated herein by reference. This parameter supports the observed significance of the aspect ratio of silver nanowires.

[0024] Diluted particle dispersions in Newtonian fluids (the most common solvents) generally exhibit Newtonian rheology, with viscosity proportional to the volume fraction of particles in the solution. For spherical particles of equal size, the opposite limit is a densely packed system. If particle-particle interactions do not inhibit particle packing, the most densely packed structure of spherical particles of equal size has a volume fraction of 0.52% to 0.74%, depending on the stacking order of the particles. At such densities, the solvent can only exist in the gaps between particles. However, from the viewpoint of dispersion, viscosity increases abruptly, making mixing somewhat below the nearest packing volume fraction extremely difficult. This is schematically shown in Figure 2. Non-Newtonian rheology has been shown to be far below the volume fraction limit. Non-Newtonian viscosity was theoretically predicted for concentrated solutions of flexible rods. See Doi and Edwards, "Dynamics of Rod-like Macromolecules in Concentrated Solution, Part 2," J. Chem. Soc., Faraday Trans. 2, 1978, 74, 918-932. Non-Newtonian behavior is generally a form of shear-induced viscosity reduction where viscosity decreases as a function of shear rate. In the case of shear-induced viscosity reduction fluids such as honey, viscosity decreases as the mixing rate increases. On the other hand, shear-induced viscosity increase is another form of non-Newtonian fluid behavior where viscosity increases when shear is applied. The following examples provide results that demonstrate either shear-induced viscosity reduction or shear-induced viscosity increase. Generally, fluids under extreme shear exhibit nonlinearity, but non-Newtonian behavior is observed at 0.1s -1 This can be demonstrated at low shear rates such as those mentioned above.

[0025] Figure 3 schematically shows the qualitative rheological behavior of silver nanowires. However, the rheological behavior depends on the shape of the nanowires. For longer and thinner nanowires, the viscosity becomes too high to effectively mix the dispersion with a relatively low metal load. By appropriately adjusting the dimensions of the silver nanowires, it is possible to obtain a high metal load that allows for the formation of a highly conductive paste. To our knowledge, nothing close to these systems has been formed or even considered before the current research. These highly conductive pastes are remarkable materials that appear to involve a surprising stabilization mechanism, which, due to their similarity to hydrogels, seems to involve some form of physical crosslinking, possibly due to the entanglement of the nanowires. The electrical conductivity with percolation appears to depend on the ability to form a highly concentrated dispersion, thereby allowing the metal nanowires to interact sufficiently to achieve good conductivity without removing the solvent, despite the presence of relatively large amounts of solvent and insulating organic material.

[0026] The applicant has gained considerable understanding of the formation of transparent conductive films using silver nanowires. In two-dimensional transparent films, electrical resistance is governed by the junctions between nanowires, and the two-dimensional morphology imposes the formation of many junctions due to the large aspect ratio of the silver nanowires. In this regard, the applicant has developed a melting technique that enables the formation of a single structure called a molten metal nanostructure network, which provides electrical conduction directly along the structure. This melting technique is based on in-situ reduction of the metal salt in contact with the silver nanowires and inducing reduction in the thin film to preferentially provide thermodynamic drive at the nanowire junctions. Direct electrical conduction along the molten single structure avoids the need for electron percolation. The transparent structure is essentially a two-dimensional structure with a sparse metal layer to allow light transmission through the film.

[0027] Three-dimensional opaque materials can introduce different metal nanowire configurations. In composite materials with high metal content or materials with less organic content compared to silver, three-dimensional opaque materials also have many interaction points between silver nanowires. With low metal nanowire content in three dimensions accompanied by a polymer matrix, the interactions between metal nanowires become less distinct. While we do not wish to be limited by theory, as in the applicant's research on more two-dimensional transparent conductive films, deposited metals formed from the reduction of metal salts such as silver salts can be thermodynamically driven to interconnect particles and contribute particularly to the formation of conductive networks. As used herein and fairly consistently in the art, a three-dimensional conductive structure refers to a structure in which any cross-section passing through the material in the deposit has many times the diameter of the silver nanowires, such that many nanowires pass through along a thickness parallel to the conceptual cut.

[0028] A transparent conductive film can be porous to allow light to pass through the material, but the transparency of the structure imposes limitations on its thickness, and correspondingly, limits the resistance of electrical conduction through the material. Generally, greater thicknesses to provide a greater current flow are associated with a corresponding loss of transparency. Highly conductive material structures are generally opaque, but materials of intermediate thicknesses can provide some degree of light transmittance, and translucent materials are conceivable. Generally, highly conductive silver-based materials may have an average thickness of at least 1 micron, at least 2 microns in further embodiments, at least 5 microns in some embodiments, and about 10 microns to about 5 mm in other embodiments. Generally, there is no upper limit to the thickness, but there is a practical limit to reduce revenue and cost. Those skilled in the art will recognize that additional thickness ranges within the express range described above are contemplated and within the scope of this disclosure.

[0029] At higher loading levels, the nanowires appear to be entangled within the material. At lower metal loading levels, a more random orientation of silver nanowires seems more likely, although detailed investigations of such materials are unknown. The incorporation of reducible metal ions has demonstrated that composite materials with low resistivity can compete with commercially available adhesives that utilize substantially more metal or other conductive fillers to achieve the same resistivity, as further described below, with <5 wt% silver. Reducible metal ions can be provided using a suitable silver composition. The silver composition must be soluble in any solvent involved in the formation of the ink. The properties of the silver composition dissolved in the solvent are not particularly important, as long as the silver can be reduced during the processing of the composite material. Solubility provides proper mixing in the ink, but the solvation properties of the metal composition can be complex, especially in non-aqueous solvents. It also seems plausible that in three-dimensional structures, the activation energy for diffusion is higher and the general reaction rate is substantially slower compared to transparent conductive film structures, and this distinction may also explain why potentially longer times and higher temperatures may be required to achieve the lowest resistivity. Furthermore, a catalyst and / or reducing agent different from the solvent can be added to reduce the activation barrier and decrease the amount of soluble silver ions.

[0030] Similar highly conductive silver structures have been discovered by the present applicant in the form of dry, low-polymer silver structures. These high-density silver deposits have been found to have resistivity in proportion to that of bulk silver. See, by reference, the concurrently pending U.S. Patent Application No. 18 / 422,732 (hereinafter referred to as the '732 application) to Yang et al., entitled "Formation of Electrically Conductive Layers At Near Ambient Temperature Using Silver Nanoparticulate Processing and Inks for Forming the Layers," which is incorporated herein by reference. A common feature appears to be the formation of structures having densely packed silver nanoparticles. These structures were formed with a moderately concentrated silver nanowire dispersion and a small amount of polymer binder to improve adhesion properties. In these systems, it was found that the use of silver salts in the dispersion (Nanoglue®) resulted in a slight change in conductivity. The studies in the '732 application with silver salts proved to be very effective for forming transparent conductive films with short processing times and room temperature at low heat levels. Based on the research described herein, it has been found that metal reduction involving silver salts in high-density or low-sparse metal layers may involve higher temperatures and longer durations, and therefore, the silver reduction results in the '732 application may not fully utilize this potential conductivity-improving technique.

[0031] In contrast to the applicant's research in application '732, this study achieves high conductivity by introducing a silver salt that is reduced after deposition. This also achieves resistivity several times lower than that of bulk silver, comparable to the resistivity value of metal. The amount of silver from the reduced silver salt can range from a few percent to a considerable proportion of the total silver amount. Slightly higher resistivity values ​​were obtained by the applicant using silver nanowires mixed with silver flakes and / or silver micron particles, and silver nanoparticle blends, along with up to 50 wt% polymer binder and the reduced silver salt. See, by reference, the concurrently pending U.S. Provisional Patent Application No. 63 / 540,772 to Virkar et al., entitled “Silver Nanowire Based, Electrically Conductive Inks, Pastes and Electrically Conductive Adhesives.” In contrast, the highly conductive dry deposits in this study essentially aim for materials having primarily silver nanowires, optionally reduced metal salts, and optionally silver nanoparticles for nucleation of salt reduction. After solvent removal, the materials of this specification may, in some embodiments, contain little to no binder and have small amounts of polymer dispersants and reduced silver salts to improve conductivity, while in other embodiments they may be highly loaded in a polymer matrix having at least about 25% by weight of metal.

[0032] The processing to reduce silver salts in these higher-density metal deposits to form highly conductive structures generally involves heat treatment at a temperature of at least about 115°C for at least about 5 minutes. This processing is described in detail below. In contrast to previous studies involving transparent conductive films for forming molten metal nanostructured networks, metal deposition may not occur, mainly or even more significantly, in relation to drying, although this may not be clear as some solvents boil at fairly high temperatures. The reducing agent may be a higher-boiling point solvent, a specially added reducing agent, or a polymer such as a polymer or polymer precursor used to form a polymer matrix. Higher-boiling point solvents can be used so that the solvent persists to carry out silver reduction over a longer time frame involved in the metal reduction process in these three-dimensional materials.

[0033] The ability to form high-concentration silver nanowire dispersions expands the possibilities for forming a variety of important novel materials. In some embodiments, high-concentration dispersions of silver nanowires can be formed directly into highly conductive silver deposits, with or without the use of reduced silver salts. Nevertheless, it may be useful to form silver nanowire composites in a polymer matrix, such as for the formation of conductive adhesives or other composite materials, to create materials with desirable mechanical properties and good adhesion for specific applications. Surprisingly, using reduced silver salts yielded low resistivity values ​​over a wide range of silver loading levels in the polymer matrix. These novel materials can then provide desirable mechanical properties due to the polymer matrix, while also offering good conductivity. At lower metal loading levels of 25 wt% or less, these remarkable novel materials are described in the concurrently pending U.S. Provisional Patent Application No. 63 / 551,737 (hereinafter referred to as the '737 application) to Virkar et al., entitled "Conductive Composites, Inks and Adhesives, With Low Silver Nanowire Loading and Low Resistivity and Methods for Forming Conductive Features," which is incorporated herein by reference. These lower metal loading materials are noteworthy for having good conductivity obtained at metal loading levels of 5 wt% or less. This study extends the study in the '737 application to higher silver nanowire loading levels to achieve even lower resistivity and generalizes the low polymer embodiment to provide composite materials with a remarkable polymer matrix, enabling a wider range of material properties.

[0034] As described above, the commercial synthesis of silver nanowires generally relies on the use of polyvinylpyrrolidone as a capping agent. Standard nanowire purification can remove at least some of the excess polyvinylpyrrolidone (PVP), but a considerable amount of PVP, including some more tightly bound PVP, generally remains without more aggressive processing to remove it. A moderate amount of PVP may be beneficial because PVP tends to inhibit nanowire aggregation, and residual PVP is found in silver nanowires and their dispersions as described herein. The applicant's proprietary melting process for forming a molten metal nanostructured network having a single conductive transparent structure is not inhibited by PVP, and once a single conductive structure is formed, the presence of PVP does not hinder electrical conduction. As it stands, some PVP does not appear to significantly interfere with conductivity, even without in-situ metal deposition.

[0035] Because the density of silver is significantly higher than that of the organic component containing the solvent, the comparison of relative deposition percentage to relative weight percentage differs significantly with respect to the comparison of the silver component to the organic component. Therefore, the dispersion can generally be divided into solid and solvent. The solid may include silver nanoparticles as well as organic materials such as polymers, monomers, and oligomers. For the purpose of identifying the components of the material, components that are solid in an isolated form are still referred to as solids after being dissolved in the solid; therefore, for convenience, PVP is generally referred to as a solid. Note that the solvent is a liquid in an isolated form, although in some cases the solvent does not need to be volatile and may include monomers, oligomers, other polymers that are liquid within a suitable processing range, or non-volatile ionic liquids. This definition of solvent may be contrary to that used in the applicant's previous studies, but the applicant acknowledges that at some point during processing, some liquids may polymerize or crosslink, and as a result, potentially volatile liquids may be converted to non-volatile solids during processing. Therefore, liquids can be further divided into non-volatile liquids, volatile liquids that are converted into non-volatile compositions during processing, and volatile liquids that remain volatile. The specific relative amounts of these components will be further discussed below and in the examples. A typical paste may contain approximately 60 wt% solids and 40 wt% solvent, with 50 wt% silver and 10 wt% PVP. This corresponds to approximately 10 wt% silver. In the case of high aspect ratio silver nanowires, the paste is observed with a remarkably small weight percentage of solids, and as a result, the weight percentage of solvent can be approximately 75 wt% or more. A paste that does not flow and has high resistance to deformation, even with a liquid solvent of about 70 wt% or even 90 wt%, is somewhat surprising. This also highlights the unique characteristics of the 1-D structure of NW, where the excluded volume can be significantly larger than the actual physical volume (which is conceptually similar to the excluded volume fraction common in polymer physics developed by Werner Kuhn and Paul Flory). Perhaps the closest equivalent would be an organic hydrogel or organic gel that can exhibit very high liquid swelling while maintaining good structural integrity.However, in hydrogels or organic gels, the polymer is crosslinked, so the polymer itself provides an integral mass for absorbing the liquid. While there is no corresponding integral mass in the current paste, the entanglement of nanowires may provide physical crosslinking. The cohesive forces that hold the paste together are still not fully understood. Although we do not wish to be limited by theory, PVP can have a relatively low molecular weight, so it is not expected that PVP will form significant physical crosslinking, however, silver nanowires, in combination with other components including swollen dissolution in the stabilized polymer, are thought to contribute to a form of physical crosslinking. Other analogous examples that may explain these systems to some extent include concrete and damp beach sand, where solid particles may be involved in aggregating and holding liquid molecules, enabling some properties intermediate between pure liquid and pure solid.

[0036] The remarkable properties of silver nanowire paste extend even to concentrated dispersions. Starting from dilute solutions, conceptually, as the concentration increases, the nanowire clumps should collide due to interparticle forces exceeding solvating forces. This expected view has been found to be somewhat inaccurate. Based on the studies herein, five distinct domains can be identified for the material as a function of concentration with respect to the specific characteristics of the dispersion components, silver nanowires, PVP, and solvent. Before further detailing these domains, the inventors consider expectations from the art.

[0037] Please consider the discussion in the paper “Formulation of concentrated and stable ink of silver nanowires with applications in transparent conductive films”, RSC Advances 2017, 7, 1936 (hereinafter referred to as Chen's paper), which is incorporated herein by reference. Chen's paper discusses the difficulty of forming a stable dispersion system of silver nanowires. Chen's paper discusses the formation of a silver nanowire ink of approximately 0.5 wt%. Several issues from Chen are worth considering: silver nanowires, processing to stabilize their dispersion, definition of their stability, and their considerations in related research on higher concentration silver nanowire inks. Chen's silver nanowires had an average diameter of 36 nm and an average length of 72 microns and were synthesized using a mixture of PVPs with molecular weights of 360,000 and 55,000. Thus, Chen's nanowires have an average aspect ratio of approximately 2000.

[0038] Regarding stability, Chen refers to the absence of sedimentation as a basis for evaluating stability. The applicant's commercially available inks for forming transparent conductive films are stable against sedimentation for months, and these inks also contain other polymer components that increase viscosity, network structure, and can prevent sedimentation of relatively thin, low-concentration nanowires. While this is reasonable for dilute dispersions, it may be overly limited for more concentrated silver nanowire dispersions. In particular, a more useful tool has been found for evaluating the stability of concentrated dispersions. In this regard, sedimentation does not necessarily involve the avoidance of hard aggregate formation. As used herein, hard aggregates refer to nanowire aggregates that cannot be redispersed without breaking the nanowires. Therefore, sedimentation without hard aggregates can be diluted and mixed to reproduce stable dilute dispersions. The absence of hard aggregates can be confirmed by diluting to lower concentrations of dispersions to check for any sedimentation and to check the ultraviolet / visible absorption spectrum, which can provide characteristic spectra based on the nanowire morphology. Absorption spectra have been shown to be distorted in the presence of hard aggregates. Irreversible aggregation of nanowires alters their plasmonic response, which can be measured using a UV-Vis spectrophotometer. Visual observation and microscopic examination can also provide useful information.

[0039] Regarding the processing, Chen uses a portion of high molecular weight PVP in its nanowire synthesis. Higher molecular weight PVP can be expected to provide improved dispersion stability compared to lower molecular weight PVP, as well as steric hindrance, which helps increase stability along with polymer molecular weight. Higher molecular weight PVP is also associated with higher viscosity. On the other hand, the applicant has not found the molecular weight of PVP to be a very important factor in the processing of silver nanowires. As is commonly done, the purification of silver nanowires at the end of synthesis partially removes a portion of the PVP that was started at a relatively high weight percent relative to silver. Chen has made considerable efforts to obtain a stable dispersion with 5 milligrams of Ag (mg / ml) per milliliter of dispersion. In particular, Chen et al. use 30 mg of PVP / ml. This is a very large amount of PVP, and in terms of volume percentage, the volume of PVP in the dispersion is much larger than that of the silver nanowires. Based on the results herein, it can be understood that Chen needs to use such a large amount of PVP to obtain a good dispersion, and that it is to stabilize the nanowire dispersion.

[0040] Studies of the formation and rheological properties of silver nanowire dispersions at approximately 1 wt% are incorporated herein by reference, as described in Fang et al. (hereinafter referred to as Fang's paper), “Effects of inclusion size on thermal conductivity and rheological behavior of ethylene glycol-based suspensions containing silver nanowires with various specific surface areas”, International Journal of Heat and Mass Transfer 81(2015)554-562. The experiments in Fang's paper were based on commercially available silver nanowires obtained in very long lengths as advertised. According to Fang's paper, the obtained silver nanowires were sonicated to first disperse non-dispersible aggregates, and the sonication fragmented the nanowires to an average length that was only a fraction of their initial size. Rheological results are presented in Fang's paper for three silver nanowires at four different concentrations (with a maximum concentration of 10 mg / ml). For silver nanowires (250) with the highest aspect ratio at a maximum concentration of 10 mg / ml, they observed shear-thinning behavior, while other samples exhibited Newtonian rheology. Reports of higher concentration silver nanowire dispersions generally involve forming dispersions from purified synthetic silver nanowires and using them as inks without significant storage, so that stability is not an issue. See, for example, Li et al., ACS Appl. Mater. Interfaces 2014, 6, 21721-21729 (5 wt%) and Tao et al., Nanoscale Research Letters 2013, 8:147 (15 wt%), both of which are incorporated herein by reference. Wu et al. formed 10 wt% and 20 wt% silver nanowire dispersions using a silane surface modifier (Thin Solid Films 544 (2013) 427-432, incorporated herein by reference).When used herein, silane surface modifiers are not considered dispersants, and such agents may covalently bond to metal surfaces. Unless otherwise specified, silver nanowires described herein are considered unmodified. It is unclear whether surface modification impairs conductivity.

[0041] Silver nanowires are generally synthesized using the chemical reduction of silver salts with glycol, along with PVP capping polymers and various salt catalysts. Basic synthesis was pioneered by DuCamp-Sanguesa et al. ("Synthesis and Characterization of Fine and Monodisperse Silver Particles of Uniform Shapes," Journal of Solid State Chemistry, Vol.100(2), 1992, 272-280) and Xia and collaborators (Sun et al., "Uniform Silver Nanowire Synthesis by Reducing AgNO3in Ethylene Glycol in the Presence of Seeds and Poly(Vinyl Pyrrolidone)," Chemical Materials, 2002, 14:4736-4745) (both incorporated herein by reference). The applicant has developed a commercial-scale synthesis of silver nanowires with an average diameter of less than 20 nm and possesses commercially available inks suitable for forming transparent conductive films using state-of-the-art technology. See U.S. Patent No. 10,714,230 to Hu et al., entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed From the Nanowires," which is incorporated herein by reference. While optical properties have been found to improve with thinner nanowires in the formation of transparent conductive films, the improvement may gradually decrease as the nanowires become thinner, because the plasmonic response remains in the visible region of the spectrum regardless of the nanowire diameter. The applicant has found that further elongation across a given length of nanowire does not result in a significant improvement in conductivity.

[0042] The transparent conductive film is based on the formation of a sparse metal coating through which light can be transmitted via gaps within the nanowire film. Good optical properties can be achieved due to the small ratio of nanowire diameter to visible light wavelength. The applicant has developed a melting process for converting a sparse metal layer into a single molten metal nanostructure network, which is effective in reducing or eliminating bonding resistance between adjacent metal nanowires. The applicant holds extensive patent protection in the United States and internationally for this technology. See the references above.

[0043] In opaque conductive structures formed from silver nanoparticles, the design of desirable materials presents significant challenges. Therefore, optical properties are irrelevant. The aspect ratio has been found to be a crucial parameter in influencing the rheology of concentrated silver nanowire dispersions. While the "one-dimensional" aspect ratio of nanowires remains important in providing good conductivity, the results still suggest that balancing the significant rheological effects associated with aspect ratio distorts the parameter balance for the use of intermediate aspect ratios, leading to desirable dispersions for further use. The desire for better transparent conductive films is driving the formation of narrower and longer silver nanowires, while the design of good high-concentration dispersions and pastes is leading to the use of lower aspect ratios. Therefore, much of the effort in the field of silver nanowires and existing paradigms focuses on creating and synthesizing very thin, high-aspect-ratio silver nanowires.

[0044] For highly transparent conductive films, uniform deposition is a crucial consideration, and consequently, dispersion uniformity is important. The concept of a good dispersion can have different views in relation to concentrated dispersions. When silver salts are introduced into the dispersion, it is observed that the coating formed by the dispersion is more uniform. In addition, the applicant has discovered significant unexpected behavior regarding concentrated silver nanowire dispersions as the concentration increases. To maintain the desired material, it is important that the nanowires remain substantially free of hard aggregates that cannot be dispersed by non-destructive mixing. When the dispersion is used to blend with other materials, such as for the formation of conductive adhesives or polymer composites, concentrated dispersions can be mixed with other components, and therefore, it may not be necessary to maintain a higher degree of dispersion without any sedimentation. The higher the concentration of silver nanowires in the dispersion, the simpler and more applicable the further processing and compounding of the dispersion becomes, which can be important for the commercial and technical implementation of nanowires. Prior to the applicant's research, high concentrations of silver nanowires resulted in the formation of unstable dispersions consisting of hard aggregates. Hard aggregates can also hinder several attractive deposition methods due to clogging and defects.

[0045] Using conventional formation protocols for dispersions, purified, moist silver nanowire pellets are diluted and mixed to form the desired concentration. As the concentration increases, the viscosity increases accordingly, and forming a well-mixed dispersion can become difficult as viscosity increases. It has been found that the formation of a well-dispersed, initially diluted dispersion allows for the formation of a uniform, high-concentration dispersion that can behave as a paste at sufficiently high concentrations. Thus, starting from a good diluted dispersion, it appears to provide a foundation for maintaining properties associated with a good dispersion, even with materials of very high viscosity. As the concentration increases, significant non-Newtonian behavior is observed, and in particular, the dispersion exhibits significant shear reduction unless a specific thickener is added to induce this behavior. The nanowires themselves appear to induce this behavior. In some solvent systems, once non-Newtonian rheology is achieved, the dispersion no longer exhibits sedimentation. As the concentration increases further beyond the concentration at which the nanowires sediment, the material becomes a non-flowing paste. Even though the material looks almost like clay, the solvent plays a crucial role, allowing the material to be redispersed into a good quality dilute dispersion. This behavior, related to the ability to redisperse, indicates that the nanowires do not form a significant number of rigid aggregates. This behavior is truly surprising even to the inventors who have been studying this field for over a decade.

[0046] The applicant has found that the rheological properties are highly dependent on the aspect ratio of the silver nanowires. The applicant is aware of one previously reported instance of non-Newtonian behavior of a simple silver nanowire dispersion in a solvent. See Fang above. Fang reports that he has fabricated three sets of nanowires purchased in very long lengths, and that the resulting nanowires were highly aggregated. To disperse the nanowires, Fang discloses the use of extensive ultrasound to fragment the nanowires and enable their dispersion. At three different nanowire diameters, they form dispersions at a maximum concentration of 10 mg / ml. Fang et al. study the rheology of these dispersions. Fang's first dispersion using nanowires with an average aspect ratio of 250 and an average diameter of 40 nm yields shear-thinning rheological properties as plotted in Figure 8. Fang did not associate the connection between the nanowire morphology and concentration dependence, rheology, and silver nanowire morphology. The applicant has found that at lower aspect ratios, non-Newtonian rheology is magnified to a higher degree. An example is presented below with two nanowire dimensions, one nanowire being thin with a high aspect ratio, and the second nanowire having a larger diameter and a lower aspect ratio.

[0047] The applicant has found that achieving a concentration of silver nanowires sufficient to produce shear-thinning non-Newtonian rheology results in stabilization of the dispersion against sedimentation without any additional surface modification of the nanowires or the inclusion of specific solvents to modify the rheology. Controlling the dimensions of the silver nanowires allows for the achievement of high silver concentrations for specific rheologies. This result is contrary to expectations based on the conventional view that higher concentrations would result in greater aggregation and expected sedimentation. The applicant has found that the exact opposite occurs in some systems. This conventional view is expressed in Chen's paper, “Reported AgNW dispersions with a high concentration usually suffer from aggregation under a long-term storage condition.” See the introduction to Chen's paper and the relevant papers cited after this quote by Chen. As stated in the previous paragraph, the applicant has found that the achievable concentrations in these high-concentration stabilized silver nanowire dispersions can be transitioned to higher concentrations at lower aspect ratios. An extension of this understanding leads to a discovered paste, which may be non-flowing, redispersible, conductive, and processable.

[0048] As the concentration of the dispersion increases, it transitions from a fluid state to a non-fluid state, and as the concentration increases, it transitions to a spreadable paste state. As a paste, the concentrated material can be redispersed in a good quality diluted dispersion, indicating that minimal irreversible aggregation has occurred. At even higher concentrations, it reaches a concentration where irreversible changes are eventually observed, and the solid material cannot be dispersed in a stable dilute dispersion. At lower aspect ratios of silver nanowires, the paste can reach concentrations high enough to be conductive with the silver nanowires in configurations above the percolation threshold, where a significant decrease in resistivity is observed. This represents a unique composition in which the dispersion or paste remains conductive despite high levels of solvent. The applicant is not aware of any other prior studies demonstrating conductive pastes before solvent removal or further concentration for solvent removal.

[0049] Based on conventional silver nanowire synthesis using the polyol method, the as-synthesized nanowires contain associated PVP. If aggressive methods are used to remove all PVP, the silver nanowires tend to form rigid aggregates that cannot be redispersed. More conventional purification of silver nanowires leaves a reasonable amount of PVP behind, some of which appears to adhere more strongly to the nanowire surface, while other amounts of PVP remain in the solution. Silver nanowire dispersions with lower PVP levels while maintaining good dispersion have been achieved. Perhaps not by coincidence, the solvents that provide good nanowire dispersions are also solvents in which PVP is soluble.

[0050] In summary, the applicant identified five states of silver nanowire dispersions, differing depending on the silver concentration: 1) dilute, stable dispersions; 2) higher but still low concentrations, showing some sedimentation even after standing for a period of time; 3) intermediate concentrations, fluid but exhibiting shear-thinning rheology; 4) high-concentration pastes, non-fluid but spreadable in accordance with shear-thinning behavior; and 5) solids of irreversible aggregates. When properly prepared, states 1) to 4) can be stable, as identified by the ability to dilute the sample to low concentrations using non-destructive mixing to achieve stable dispersions substantially free of hard aggregates and exhibiting the expected absorption spectra. As will be further discussed below, the boundaries and concentration ranges between these states depend heavily on the silver nanowire dimensions.

[0051] Some of the remarkable properties of the morphologies of silver nanowire materials described herein suggest that time will be needed to grasp their potential applications, although some applications already suggest them themselves. The ability to blend silver nanowires by starting with a more concentrated solution to incorporate them into composite materials offers a potentially significant processing advantage and may enable the formation of composite materials such as polymers loaded with silver nanowires in formulations that would be difficult or impractical if dilute dispersions of silver nanowires were required. Of interest herein are polymer composite materials, which generally have a high silver loading of at least about 25 wt%, and as stated above, the applicant has other studies involving lower loadings of less than about 25 wt% silver, which offer very unique properties. These polymer composite materials may substantially contain silver salts that can be reduced during processing to improve conductivity, resulting in a resistivity reduction of an order of magnitude or more. In these high-density three-dimensional systems, the reduction of the silver salts involves heating to a temperature of at least about 125°C for at least about 5 minutes. With or without the silver salts, these dispersions can be used to form highly conductive metallic structures.

[0052] Regarding the paste, if these can be localized in a structure that prevents the evaporation of the solvent, the paste can be used as a conductor molded into the desired shape and position. Although its conductivity is somewhat lower than that of liquid metal, silver nanowire paste is non-toxic and can be formed for convenient placement while providing high conductivity. The solvent can be selected to have a relatively low vapor pressure at room temperature. Furthermore, non-toxic gallium-based liquid metals form a solid oxide layer when exposed to the ambient environment, which makes practical applications and large-scale commercial processing extremely difficult. Liquid metals also exhibit very high surface energies, further complicating their processing. Conductive pastes manufactured from nanowires described by the applicant are not affected by any of these major drawbacks. More concentrated dispersions can be conveniently transported for use in forming transparent conductive films and can also be diluted to the desired concentration for printing. This can significantly reduce transport costs and the effort required for the process is minimal. The discovery of these new materials opens up the possibility of exploring a variety of additional new applications for exploration.

[0053] In some applications, the concentrated dispersion is deposited using appropriate techniques such as any reasonable coating or printing process. The deposited material can then be dried and cured. Curing may involve polymerization and / or crosslinking of polymers or polymer precursors in the composition. Curing may further involve reduction of metal salts, such as silver salts, in the composition. Since the concentrated silver nanowire dispersion may contain solvents with higher boiling points, solvent removal may require higher temperatures than those used to dry transparent conductive films, which can be performed at room temperature or with some heat. Drying may be accelerated using radiation such as intensity pulsed light or other light sources. Polymerization and / or polymer crosslinking, if carried out, may be driven thermally or using radiation such as UV radiation. In principle, these processes, solvent removal, polymerization / crosslinking and / or silver ion reduction, can be carried out in a single process step or using multiple process steps. In this way, a desired dried material specific to a particular desired application can be formed. Examples of product materials include metal-filled composite materials (conductive adhesives) generally comprising a polymer matrix containing at least 10% by weight of organic matter and at least 25% by weight of silver, with at least 75% of the silver provided as a starting material in the form of silver nanowires. For materials with a low organic content, very high conductivity was found when the material was dried and the silver salt was reduced in situ to deposited silver. The resistivity of bulk silver is 1.59 × 10⁻⁶. -6 It has been reported as Ωcm, and the resistivity of bulk iron is 9.7 x 10⁻⁶. -6 The values ​​are reported as Ωcm. The values ​​are obtained for dried, highly loaded composite materials having resistivity values ​​between bulk iron and bulk silver, as reported below. Silver paste with a considerable amount of solvent remaining in the material is approximately 1 × 10⁻⁶ -1 It can have a resistivity of less than Ωcm.

[0054] Synthesis and Characterization of Silver Nanowires Silver nanowire synthesis involves adjusting reaction conditions to guide crystal growth along a single crystal axis. Silver nanowires are generally single-crystal objects. Polyvinylpyrrolidone (PVP) and its copolymers are known to preferentially associate with specific crystal planes of silver, resulting in preferential crystal growth along a single axis. Although non-PVP synthesis has been reported, the synthesis of good quality nanowires on a commercial scale to date has relied on PVP. While other reducing agents, such as sugars in aqueous solutions, have been used, commercially available silver nanowire synthesis generally relies on ethylene glycol or other glycols as both solvent and reducing agent. Salts are generally added to help influence the nanowire dimensions of the product. The desire to produce thinner nanowires to improve optical quality for the production of concentrated dispersions is no longer the dominant driving force for many applications. Therefore, thicker silver nanowires with smaller aspect ratios may be potentially more desirable for some applications, as they are found to yield high density and desirable rheology. However, the silver nanowires should have a length long enough to provide the establishment of conduction pathways and a diameter that is not too large so that a dilute dispersion can be formed with high stability.

[0055] The properties of nanowires for forming dispersions described herein primarily involve the ability to form stable, dilute dispersions of silver nanowires in low-boiling point solvents such as ethanol. This goal provides for avoiding non-dispersive aggregation and for imposing constraints on the nanowire diameter. The silver nanowires should remain well-dispersed when diluted, and this should be possible up to a relatively large average diameter.

[0056] The average diameter of the nanowires should generally be approximately 250 nm or less at most, 200 nm or less in further embodiments, 150 nm or less in other embodiments, 15 nm to 125 nm in some embodiments, 20 nm to 100 nm in additional embodiments, and 35 nm to 80 nm in further embodiments, and embodiments having alternative ranges for these lower boundaries (15, 20, or 35) with any of the specific upper boundaries (250, 200, 150, 125, 100, or 80), e.g., 20 to 150. For opaque, high-concentration materials of primary interest in this specification, having very thin nanowires may not be a major concern, although some applications may still desire the use of thinner nanowires. The average length of silver nanowires may generally be 80 microns or less, 50 microns or less in some embodiments, and 35 microns or less in additional embodiments. With regard to processing into concentrated dispersions, perhaps a particularly important parameter is the average aspect ratio, i.e., the average length divided by the average diameter. The demand for more electrical conduction paths suggests longer nanowires, but rheology suggests that higher dispersion concentrations can be more easily achieved with smaller aspect ratios, as will be discussed further in the following sections. Therefore, there may be trade-offs in nanowire dimensions, and the choice of average aspect ratio may be influenced by the intended application of the product and the desired conductivity, whatever it may be. Generally, the average aspect ratio is at least about 15, at least about 25 in some embodiments, about 30 to about 3000 in further embodiments, about 40 to about 1000 in other embodiments, about 50 to about 750 in additional embodiments and about 75 to about 250 in some embodiments, and embodiments having alternative ranges for these lower boundaries (15, 25, 30, 40, 50 or 75) with any of the specific upper boundaries (3000, 1000, 750, 250), e.g., 25 to 750. As mentioned before and discussed in detail in the following sections, the dispersion properties depend heavily on the dimensions of the silver nanowires, particularly their aspect ratio.Those skilled in the art will recognize that an additional range of silver nanowire dimensions beyond the express range described above is intended and falls within the scope of this disclosure. Unless otherwise specified, references to nanowire dimensions generally refer to average values.

[0057] Silver nanowires are commercially available from various suppliers, including Sigma / Aldrich, NanoCintech, ACS Materials, Cheaptubes.com, Novarials, and C3nano (the applicant). The applicant fabricated the silver nanowires used in the following examples. Previous efforts have generally aimed to form thinner nanowires, but such efforts may be hindered from synthesizing thicker and shorter nanowires. In addition, sonication has been found to be effective in breaking silver nanowires into shorter nanowires. Ultrasonic mixers are commercially available. The applicant's results using sonication are consistent with previously reported results in that the breaking of metal nanowires can result in considerable uniformity in the length of the broken nanowires. Silver nanowires broken by sonication appear to exhibit the same properties as nanowires synthesized directly in shorter lengths.

[0058] As described above, silver nanowires are primarily synthesized using polyol processes employing glycols such as ethylene glycol as solvents and reducing agents. Polyvinylpyrrolidone is commonly used as a polymer capping agent. While various molecular weights of PVP are used, they are mostly in the moderate average molecular weight range of approximately 10,000 g / mol to approximately 100,000 g / mol, although higher molecular weights can be used, and suitable average molecular weights of PVP can be up to 2,000,000 g / mol or sometimes higher. For a description of silver nanowire synthesis using the copolymer poly(vinylpyrrolidone-co-diallyldimethylammonium nitrate), see U.S. Patent Application Publication No. 2014 / 0178247 to Alsayed et al., entitled "Process for Making Silver Nanostructures and Copolymer Useful for Such Processes," which is incorporated herein by reference. In this specification, references to polyvinylpyrrolidone also refer to suitable copolymers unless otherwise specified.

[0059] Purification of nanowire products generally removes excess PVP but retains a considerable amount. Empirically, it is suggested that some PVP binds more closely to the nanowire surface, while some remains in the solution. Additional purification steps can remove more PVP, which are illustrated below to better understand the role of PVP. No experiments have been conducted to completely remove PVP. Several examples of adding more PVP are presented below, primarily in relation to investigating its effect on electrical conductivity. The amount of PVP across the range considered does not qualitatively alter the rheology. The range of PVP is discussed further below. Naturally, the final ratio of PVP bound to the silver surface to PVP free in solution establishes equilibrium over time and is influenced by various factors including PVP concentration, silver concentration, silver nanowire size, shape, purification process, and solvent type. PVP also functions as a dispersant.

[0060] Silver nanowires can be coated with noble metals to enhance their corrosion resistance. The applicant has developed an improved, scalable synthesis method as described in U.S. Patent No. 9,530,534B2 to Hu et al., entitled “Transparent Conductive Films,” which is incorporated herein by reference. These noble metal-coated silver nanowires are used similarly to silver nanowires in forming transparent conductive coatings. The noble metal-coated silver nanowires must function equivalently to silver nanowires in forming the concentrated dispersions described herein. The noble metal coating should be relevant to any desired silver nanowire dimensions.

[0061] For example, other metal nanowires such as copper nanowires, gold nanowires, platinum nanowires, and cobalt nanowires are known in the art. These nanowires can be dispersed with PVP or similar types of polymers that can bond to the surface of the metal nanowires. These other nanowire types exhibit the observed behavior of silver nanowires as described herein, but their conductivity is generally somewhat lower. There is nothing about the chemical properties of specific metal nanowires involved in the formation of silver nanowire dispersions. Sigma Aldrich sells a variety of metal nanowires, including gold, copper, and cobalt.

[0062] The results in the examples suggest that, as long as the nanowires can be sufficiently dispersed at low concentrations, it is possible to process them into more advanced dispersions and gels. Stable low-concentration dispersions of nanowires are thought to exhibit Brownian properties. The dispersions will be discussed in detail in the following sections.

[0063] Dispersion and Formation Method Advances in the processing of silver nanowire dispersions have led to the formation of previously unimaginable materials exhibiting remarkable properties suited to novel compositions. The incorporation of silver salts provides the ability to reduce metal salts to form in-situ volume metals, which has been shown to potentially significantly reduce the resistivity of the formed metallic structures, while also enabling process improvements. As described above, five distinct silver nanowire dispersion domains with progressively increasing concentrations of silver nanowires relative to the solvent have been identified. Four of these domains can be called stable dispersions, but only three are fluid. The concentration division between domains has been found to be highly dependent on the silver nanowire dimensions and to some extent on the solvent. The properties of the dispersions can be evaluated using rheology, observation of sedimentation or lack of sedimentation, and dilution to low-concentration states, along with evaluation of low-concentration dispersions using UV / Vis absorption and stability assessment. The five dispersion domains are as follows: I - A stable dispersion at a low concentration. II - Medium concentration, Newtonian rheology with some sedimentation over time, and redispersible into Domain I. III - Fluidity at moderate to high concentrations but non-Newtonian rheological, no sedimentation observed over a reasonable period, and redispersible into Domain I. IV - High concentration, paste-like, non-flowing, shear-thinning, spreadable and moldable, and redispersible into Domain I. V - A non-flowable solid that cannot be redispersed with respect to domain I.

[0064] In the case of a particular aggregate of silver nanowires, the concentration determines the specific domains exhibited by the dispersion. As mentioned above, the concentration of nanowires moving between different domains depends on the properties of the nanowires, particularly the aspect ratio. As the aspect ratio decreases, it becomes possible to achieve higher nanowire concentrations for a particular dispersion domain, and thus fluid dispersions can be at higher concentrations, however, the conductivity of the structure formed by the nanowires may be affected by the change in aspect ratio.

[0065] The ability to form five domains presupposes the ability to form domain I from silver nanowires, which requires some minimum quality of the silver nanowires. If the silver nanowires are nondispersible due to aggregates, they should be processed, purified or otherwise cleaned up, or may not be suitable for processing as described herein. The following considerations assume that nanowires of sufficient quality are obtained and used.

[0066] Domain I is well known in the art and is the primary focus of commercially available basic nanowire inks. The concept of transition to other silver nanowire domains is not considered to be recognized in the art. In Domain I, silver nanowires can generally be considered Brown particles in the sense that, with a suitable solvent, the silver nanowires remain stably dispersed and substantially do not exhibit any observable sedimentation over long periods, generally several months. During storage, the dispersion should be protected from solvent evaporation and other improper destruction. In Brown systems, diffusion for the generation of any concentration gradient compensates for any effect of gravity, and therefore the particles remain suspended. There is no lower limit to the concentration of silver nanowires in this domain. The upper limit of the concentration in this domain generally depends on the nanowire size and the solvent, and some care has been taken in the art to explore the limits of this domain without recognizing the distinction between domains or the influence of dispersion behavior.

[0067] Regarding the applications of silver nanowires, dilute dispersions can be combined with other processing aids such as surfactants and / or binders to make the ink suitable for various coating methods and / or suitable for the resulting components that form the material. In some embodiments, silver nanowires can be blended as fillers with polymers and the like. The focus here is on dispersions that do not contain significant additives, although small amounts of additives generally do not disrupt the dispersion. Additives may also interfere with electrical conductivity depending on the circumstances. The dispersions described herein can, of course, be blended with a variety of materials.

[0068] Generally, the dispersion comprises silver nanowires, a solvent, a polymer dispersant, an optional surfactant, an optional polymer matrix composition or precursor thereof, an optional silver salt, and metal nanoparticles. Generally, the silver nanowires do not contain surface modifications that may reduce conductivity. The concentration of silver nanowires determines which dispersion domain is relevant, and once other components are selected, the amount of solvent provides the remainder of the composition. The average aspect ratio of the silver nanowires and potentially other dimensional parameters help determine the concentrations that divide the domains. For domains I to IV, the silver nanowire concentration can be up to about 75 wt%, in other embodiments it can range from about 0.01 wt% to about 65 wt%, and in further embodiments it can range from about 0.05 wt% to about 60 wt%. A concentrated silver nanowire dispersion can generally be considered to contain at least about 8 wt% silver nanowires, in further embodiments it contains at least about 10 wt% silver nanowires, in additional embodiments it forms about 12 wt%, and in other embodiments it forms at least about 15 wt% silver nanowires. In some embodiments, the fluid concentrated dispersion may have a silver nanowire concentration of up to about 75% by weight, in other embodiments about 10% to about 70% by weight, in additional embodiments about 15% to about 65% by weight, and in further embodiments about 20% to about 60% by weight of silver nanowires. As stated throughout this application, the fluidity with respect to a particular concentration of silver nanowires depends largely on the aspect ratio of the nanowires. The dispersion may contain at least about 0.01% by weight of a polymer dispersant, in some embodiments at least about 0.1% by weight, and in further embodiments about 0.2% to about 60% by weight, in other embodiments about 0.25% to about 50% by weight, in additional embodiments about 0.3% to about 20% by weight, and in some embodiments about 0.35% to about 5% by weight of a polymer dispersant, relative to the weight of the silver nanowires. A suitable polymer dispersant is, for example, polyvinylpyrrolidone. As described above, the silver nanowires generally retain some PVP from the nanowire synthesis, which is carried out through purification. Exemplary silver nanowires generally maintain approximately 5–20% by weight of PVP relative to the silver nanowire.Examples are presented in which the range of PVP is adjusted by additional purification to reduce retained PVP, or in which additional PVP is added to the dispersion. In these operations, the range of PVP may be about 0.5 to 35% by weight of PVP relative to the silver nanowires. Various surfactants can be used in principle. A wide range of surfactants are commercially available, including nonionic surfactants, cationic surfactants, anionic surfactants, zwitterionic surfactants, and gemini-type surfactants. Fluorosurfactants are popular for various practical reasons. The surfactant is optional, but when used, the dispersion generally contains about 0.05% to about 3% by weight of the dispersion relative to the weight of the dispersion. Those skilled in the art will recognize that further ranges of dispersion component concentrations within the express ranges described above are intended and within the scope of this disclosure. In addition, the limiting ranges of the intervals excluding and including the express endpoints presented above may also be considered appropriately disclosed as other alternative intervals excluding and / or including the endpoints, with their respective limited exchanges.

[0069] The dispersions described herein generally contain about 50% by weight or less of the solid organic composition, about 40% by weight or less in further embodiments, about 30% by weight or less in some embodiments, and about 5% to about 20% by weight of the solid organic composition in additional embodiments. The solid organic composition refers to a composition whose isolated form is solid, and generally does not consider solubility in a desired solvent. The solid organic composition may be a polymer for silver nanowires or a precursor for an adhesive matrix, formed upon removal of the solvent. The solvent may include a polymer matrix precursor that can be cured, polymerized and / or crosslinked to form a polymer matrix that may be present in addition to or alternative to the polymer dissolved in the ink. Accordingly, suitable matrix polymers include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyamide, polyimide, polysulfone, polysiloxane, polyester, epoxy, polyurethane, polyvinyl alcohol, polyvinyl acetate, copolymers thereof, or blends thereof. The corresponding ink may include a dissolved polymer or polymer precursor or mixture thereof, referring to a possible mixture of polymers, a mixture of polymer precursors, or a mixture of polymers and precursors. As stated above, the polymer binder may be provided in the ink as a monomer, oligomer, dissolved polymer, or mixture thereof, which can be further polymerized or crosslinked later. Those skilled in the art will recognize that a further range of solid concentrations within the express range above is contemplated and falls within the scope of this disclosure.

[0070] The solvent and solvent concentration are selected to provide the desired processing and material properties of the dispersion. For certain silver nanowire shapes, the solvent concentration influences the formation of that type of dispersion. If the product material contains a polymer matrix, the solvent may contain precursors, which may be monomers, oligomers, or crosslinkable liquid polymers, capable of reacting to form the polymer matrix. The solvent may be volatile or inert in the sense that it can decompose before evaporation. The solvent may include a solvent blend.

[0071] In relation to solvent transfer to higher boiling point solvents, PVP has been found to play another role in the resulting material. PVP is known to potentially retain at least ethanol from the lower boiling point solvent in the polymer, as ethanol is favorably removed for the transfer solvent. During solvent transfer, ethanol is generally removed using gentle heating and reduced pressure. Under these process conditions, a considerable amount of ethanol may be retained, as described in the following examples. As seen in the examples, adjustments to the PVP level may or may not proportionally change the amount of retained ethanol. Since ethanol can reduce viscosity to a degree that it can diffuse into the solvent after solvent transfer, the retained ethanol is an underlying issue in explaining the observed rheological behavior. The retained ethanol can be removed during the complete drying process of the material.

[0072] In contrast to the solid organic compositions mentioned above, as used herein, “solvent” refers to a liquid composition at room temperature. The process techniques used herein are based on initial dispersion in a low-boiling point solvent, followed by a transfer to a higher-boiling point solvent as needed, although the dispersion may be maintained in the low-boiling point solvent. This suggests that this relationship may not be particularly limited to the transfer solvent, as the solvent transfer is to a higher-boiling point solvent, but the initial solvent may be processed under low-temperature or high-pressure conditions. Regarding the initial solvent, the solvent needs to be suitable for forming a dilute and stable silver nanowire dispersion, with water and low molecular weight alcohols being particularly suitable for forming good dispersions at low concentrations. Where good solvent transfer is present for the formation of more concentrated dispersions, the transfer solvent should generally be highly soluble or miscible with the initial dispersion solvent and a solvent in which PVP is soluble to avoid PVP phase separation. Suitable volatile solvents for dispersions include, for example, water, alcohols, glycols, amides, glycol ethers, dimethyl sulfoxides, and other sufficiently polar aprotic solvents, several additional polar solvents, and mixtures thereof. Specific volatile solvents include, for example, water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof. In some embodiments, it may be desirable to use non-volatile solvents. Suitable non-volatile liquids include, for example, silicones, mineral oils, and ionic liquids such as 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0073] The term "solvent" refers to a liquid composition, but the solvent may also be a direct precursor for potential further processing. For example, the solvent may be a monomer or oligomer or a polymer that can be polymerized and / or crosslinked during further processing, such as heating, irradiation, blending with additional reactants, combinations thereof, or other suitable methods. Suitable monomers or oligomers include, for example, acrylic types such as hydroxyethyl methacrylate, diol or polyol types which are precursors of polyurethanes such as hydroxyethyl acrylamide, tetraethylene glycol, and 1,3-propylenediol, epoxy precursors such as DGEBA (bisphenol A diglycidyl ether), Celloxide 2021P (Daicel USA, Inc.), or YX8000D (Mitsubishi Chemical Group), radiation-curable liquid adhesives such as optical adhesive NOA 85 (Norland Optical), and combinations thereof, which can be cured by heat, radiation, or chemical means. These polymer precursor solvents may or may not be volatile. These polymer precursor solvents can be blended with the volatile solvents mentioned in the previous paragraph, which are generally inert under the relevant process conditions.

[0074] For a particular batch of silver nanowires, the dispersion properties depend on the concentration, as described above. It has been found that certain parameters can be used to help estimate the dispersion properties based on concentration and nanowire dimensions. In particular, for the dispersion of one-dimensional structures such as silver nanowires, some insight into system specificity can be gained by estimating the dimensionless number β, which is defined below and reflects the non-spherical nature of the nanowires convolved at the concentration in a way that is reflected in the resulting rheology as described above. This parameter supports the observed importance of the aspect ratio of silver nanowires: β=νL 3 (1) In the formula, ν = #NW / unit volume (cm³) 3 ) and L = the length of NW (cm). As β increases due to higher number density, longer nanowires, or both, the dispersion tends to increase in viscosity as a result of increasing solid-state interactions. While not limited by theory, it should be shown that for similar systems (e.g., the same solvent), a larger number of β indicates higher viscosity, and as β→∞, the system progresses from "liquid-like" to more "solid-like." Analysis of equation (1) also shows why, for a fixed amount or quantity of silver loading, the viscosity of a dispersion of longer and thinner nanowires increases at lower concentrations than that of shorter and thicker nanowires, because both terms in β increase (higher aspect ratio) as the nanowires become thinner and longer. Assuming the nanowire shape is cylindrical, the following relationship holds: β = C·a 2 The equation / B is found, where B is a constant, C is the concentration expressed as (mg / ml), and a is the aspect ratio. Therefore, for approximations, the properties of the dispersion are independent of the average diameter and average length.

[0075] Silver salts may be included to provide reduction of silver salts and improve electrical conductivity and / or thermal conductivity. The presence of silver salts has also been observed to enhance coating properties with respect to the smoothness of the coating. Silver salts may be provided so that the reduced silver forms a substantial portion of the final metal in the hardened deposit of the ink. Reduction of silver salts has been found to involve significantly higher temperatures and longer times than the reduction of the corresponding silver in transparent conductive films. The reasons for this can be speculated to include improvements in dispersion quality and electrostatic properties due to the presence of charged species, but the exact reasons remain unclear. Suitable reducible silver compositions include, for example, silver acetate (Ag(O2CCH3)), silver trifluoroacetate (Ag(O2CCF3)), silver heptafluorobutyrate (Ag(O2CC3F7)), silver lactate (Ag(O2CCH(OH)CH3)), silver hexafluoroantimonate (AgSbF6), silver fluoride (AgF), silver tetrafluoroborate (AgBF4), silver nitrate (AgNO3), silver perchlorate (AgClO4), or mixtures thereof, which are generally soluble in the solvent of choice. Process conditions may be influenced by the selection of a specific silver salt, as will be further described below.

[0076] Generally, the ink may contain a silver salt or other reducible metal salt, and the weight ratio of metal / silver from reducible metal ions to silver nanowires is generally about 50% by weight or less of the silver nanowire, about 2.5% to about 40% by weight in some embodiments, about 5% to about 30% by weight in further embodiments, and about 8% to about 26% by weight in other embodiments. The weight of the complete salt depends on the weight of the anion relative to the metal cation. The metal salt should be soluble in the solvent, and the concentration of silver or other metal salts can be relatively high in the case of large silver nanowire loadings. Those skilled in the art will recognize that additional ranges of component concentrations and relative weights within the express ranges above are contemplated and within the scope of this disclosure.

[0077] Silver salts can be reduced to silver based on a solvent such as alcohol or glycol, or a polymer such as a matrix polymer or a dispersant polymer such as cellulose. In additional or alternative embodiments, additives can be added as reducing agents. Suitable reducing agent additives include, for example, salts of ammonium or other oxidizing anions, such as sulfites, hydrosulfites, thiosulfites, phosphites, hydrogen phosphites, oxalates, etc.; phenolic compounds, such as phenol, aminophenol, hydroquinone, pyrogallol, catechol, phenidone, 4-amino-3-hydroxy-1-naphthalenesulfonic acid, etc.; polyols containing sugar alcohols; sugars such as monosaccharides and disaccharides; hydroxyamines and derivatives; aldehydes; α-hydroxycarbonyl compounds such as benzoin, froin, and hydroxyacetone; hydrazide derivatives such as phthalhydrazide, adipic acid dihydrazide, and phenidone; reducing aromatic compounds such as 1-methyl-1,4-cyclohexadiene and dihydrodiazine, and combinations thereof. In some embodiments, reducing agent additives are incorporated into the dispersion at concentrations of about 0.001 mM to about 1000 mM, in further embodiments about 0.01 mM to about 100 mM, and in additional embodiments about 0.1 mM to about 10 mM, and the desired concentration is generally influenced by the chemical properties of the selected agent or combination of agents, and those skilled in the art can empirically assess these issues based on the teachings herein. Those skilled in the art will recognize that an additional range of reducing agent concentrations within the express ranges described above is intended and falls within the scope of this disclosure.

[0078] Regarding Domain I, there is no lower limit to the silver nanowire concentration. In practical terms, inks with silver nanowire concentrations below a certain value will have decreased value. As the ink concentration increases, it reaches Domain II. When the aspect ratio "a" is smaller, the concentration at the transition from Domain I to Domain II is C IIThe nanowires can become larger, which may be desirable for certain applications. In domain II, the dispersion generally becomes more viscous due to the increasing nanowire concentration. The higher the nanowire concentration, the more pronounced the interactions between nanowires. In this domain, in contrast to domain I, some sedimentation of nanowires may be observed after standing for 24 hours. Visual observation of sedimentation is accompanied by a turbid, isolated domain near the bottom of the storage container. No attempts have been made to isolate or quantify the "settled" nanowires. There is some separation of the dispersion that can be clearly identified, but the dispersion can be mixed and returned to a well-dispersed, visible, homogeneous dispersion that does not separate again without standing for a considerable period of time. It is unclear what happens if left undisturbed for a long period of time, but even after a week of sedimentation, the dispersion can still be returned to a well-dispersed state. The absence of significant hard aggregation can be confirmed by diluting the dispersion to a low-concentration dispersion by dilution with a solvent, as described in the following section, and it is confirmed to be a well-dispersed, dilute dispersion. These results confirm that any sedimentation in Domain II is reversible.

[0079] As the concentration of silver nanowires in the ink increases further, it reaches domain III. Here again, domains II and III, C IIIThe concentration of silver nanowires at the boundary between domains depends on the dimensions of the silver nanowires. The properties of the dispersion in domain III are noteworthy. As mentioned above, the properties in domain I can be understood in terms of Brownian motion and interparticle interactions. In domain III, although we do not wish to be limited by theory, it is reasonable that the interaction between nanowires limits the effectiveness of the Brownian force counteracting gravity, and thus heterogeneity results. In general, for dispersions of solid particles in a liquid, Stokes' law can be used to estimate the diffusion rate that affects sedimentation. Although we still do not wish to be limited by theory, generally, sedimentation is inversely proportional to the difference in particle and fluid densities, inversely proportional to viscosity, and as the NW concentration increases, viscosity increases, which further reduces sedimentation. In domain III, it is expected that the interaction of nanowires will grow more dominantly to induce sedimentation, while the increase in viscosity may slow down sedimentation. However, the exact opposite phenomenon is observed. Here again, though we do not wish to be limited by theory, the interactions between nanowires appear to result in stabilizing effects that may be enthalpy, entropy, or a combination of these. The stabilization of the dispersion corresponds to a transition to non-Newtonian rheology, which will be further described in the following sections. Since it is still undetermined whether the transition to non-Newtonian behavior precisely coincides with stabilization against sedimentation, there may be small intermediate domains II-III that have some properties of each region, some sedimentation and non-Newtonian behavior, or sedimentation and Newtonian behavior. If the same force is involved in both the change in rheological behavior and stabilization against sedimentation, then no intermediate region may exist. As will be further discussed below, confirmation of the maintenance of highly dispersible silver nanowires can be confirmed by mixing and diluting the domain III dispersion to form a stable dilute dispersion with the expected properties of well-dispersed dilute silver nanowires.

[0080] As the concentration of silver nanowires increases, the dispersion reaches domain IV, where the dispersion is no longer fluid. As a result, it exhibits shear-thinning behavior, meaning it does not flow on a gravity-affected inclined surface, but can flow when shear is applied. As used herein, paste refers to a non-flowing solid that is shear-thinning, meaning it can flow when shear is applied. Again, the concentration at which the dispersion becomes a paste (C) IV The conductivity depends on the dimensions of the silver nanowires and the solvent. For high aspect ratio silver nanowires, the concentration may be relatively low. The solvent volume fraction can be very high. Despite the high solvent volume fraction, the paste can exhibit relatively low electrical resistivity values. Even in this paste region, as will be further explained below, the paste can be redispersible as a dilute dispersion with the expected properties of a stable dilute dispersion. A very interesting observation is found at sufficiently high silver concentrations that the dispersion itself becomes an efficient electrical conductor. This is quite remarkable, as the paste still contains a considerable amount of insulating liquid solvent molecules and organic matter. The concentration at which the paste becomes particularly conductive, with the percolation threshold being exceeded, depends on the shape of the silver nanowires. Note that it is possible to form a paste that is conductive and dispersible in a dilute, non-aggregated dispersion.

[0081] At a certain threshold, the mass of the silver nanowire becomes such that it is no longer possible to dilute and redisperse it into a stable, dilute material; it becomes a solid material. As a function of concentration, this is referred to herein as domain V. The resulting material can have high conductivity. Domain V(C V The concentration during the transition to the non-mold material depends on the size of the silver nanowires. During this transition to the non-mold material, the silver nanowire dispersion exhibits irreversible aggregation.

[0082] Figure 4 plots the relationship between weight percentage and volume percentage of the dispersion. The remaining volume consists of the solvent, PVP, and a small, permissible amount of optional additional organic solid.

[0083] The material is very new, and no similar material is known; therefore, the boundaries between domains are still being explored for further dimensions and properties, although some information has been obtained from the samples. Firstly, NW can exhibit excellent non-aggregating dispersions over a wide concentration range. Depending on the aspect ratio, solvent, and PVP, the dispersion shows dramatic changes in physical properties such as viscosity over silver nanowire weight ratios of less than 10 times (e.g., 10 times). 6 Centipoise or bulk resistance of 10 8 It can demonstrate (exceeding) the limit.

[0084] Methods for effectively forming dispersions within the above concentration range are described. Given the recognition of the existence and general properties of these materials, it is likely that other formulation protocols may be developed in the future. Successful processing methods developed to date are described below, illustrating these methods as follows. To form a concentrated dispersion, an initial dilute dispersion can be formed using a suitable solvent and non-destructive mixing. As mentioned above, ultrasonic mixing for considerable time has been found to fragment silver nanowires; therefore, appropriate mixing generally involves grinding-style mixing at low to moderate shear without a mixing medium. Those skilled in the art can adjust the mixing time and conditions based on the properties of the supplied silver nanowires to ensure that significant nanowire fragmentation does not occur.

[0085] Once a good dispersion is formed, the solvent is removed by evaporation to concentrate the nanowires. If a more concentrated dispersion is formed in the same solvent as the initial dilute dispersion, the solvent can be removed using heat and / or vacuum to remove any remaining non-volatile components. Solvent removal is continued until the desired solid concentration is reached. If necessary, the removed solvent can be recovered and recycled. For solvent transfer, one or more high-boiling point solvents, non-volatile solvents, or mixtures thereof are added and mixed with the initial dilute dispersion. The amount of transfer solvent added can be based on the desired dispersion concentration, taking into account any expected losses due to evaporation during the solvent removal process. After mixing with the added solvent, the low-boiling point initial solvent can be removed by evaporation. In solvent transfer, the goal is generally to remove all of the initial solvent, although a small amount may remain depending on design or practical processing considerations. By selecting the amount of solvent added, the desired silver nanowire concentration can be achieved.

[0086] While highly concentrated dispersions are appealing based on their inherent properties, their commercial value ultimately lies in their applications for creating desired final products. The ability to form concentrated dispersions offers direct advantages in simplifying transport by reducing the volume required to transport a given weight of silver nanowires and simplifying the addition of silver nanowires to various composite materials where silver nanowires are introduced at higher concentrations. As described above, dispersions can be directly formulated as precursors for desired composite materials by introducing a polymer precursor as a solvent and / or dissolving the desired polymer in the solvent. These materials can then be processed by drying and curing, as further described below. In particular, curing may involve the reduction of silver salts to deposited silver metal in situ.

[0087] Characterization of dispersions Dispersions can be characterized in various ways to define their properties. Some properties of a dispersion are visual, such as the evaluation of sedimentation and fluidity. Other properties involve measurements using analytical instruments, such as rheology and light absorption. Rheology follows the general trend described above, where Newtonian behavior is observed in domains I and II, non-Newtonian rheology in domain III, and qualitative characterization in domains IV and V. Concentrated dispersions may exhibit significant conductivity that is more dependent on the weight percentage of silver than on rheology. As described above, the evaluation of the reversible properties of a dispersion has proven to be a good method for evaluating the properties of the material. As described above, several specific properties are evaluated to classify dispersions. These are described in more detail below.

[0088] With respect to sedimentation, this feature may be important for silver nanowire dispersions in domains I, II, and III as specified above. Since domain IV is a paste and domain V is a solid, sedimentation is a somewhat irrelevant concept. Broadly speaking, sedimentation can be considered heterogeneity. If particles are governed by Brownian motion and viscous forces govern gravity, then once sufficiently dispersed in a dilute dispersion, they should remain suspended. Particles can remain suspended for long periods, and commercially available nanowire inks can be stable for long periods, although subtle changes over time can disrupt this situation. However, domain II is characterized by sedimentation. In the following examples, sedimentation in domain II is characterized by heterogeneity that appears as a separate substance at the bottom of the storage container. The separate substance that settles does not look like aggregated nanowires, but rather like a colloid separated from the homogeneous dispersion. The composition and mass of the separated substance have not been determined.

[0089] In Domain I, far from the boundary with Domain II, most of the processing of the transparent conductive film takes place, and therefore its properties and stability are well known. However, near the boundary between Domain I and Domain II, there is a transition from the familiar to the unfamiliar. To be more specific, sedimentation can be specified in terms of visible phase separation by a person with average visual acuity looking through a transparent glass storage container, evaluated after 24 hours without mixing. The exact boundary between the domains is not particularly important at present, as there is no clear reason for this transition to be at work, and the transition may be slightly sensitive to room temperature fluctuations and other environmental variations, so that any boundary concentration can be adequately identified within a range similar to error bars. Since the rheology remains Newtonian through Domain II, changes in rheology do not provide any information about the transition from Domain I to Domain II.

[0090] The transition between domain II and domain III involves a surprising transition accompanied by final sedimentation at higher concentrations. At similar concentrations, the rheology becomes non-Newtonian as the concentration increases. Specifically, higher concentration dispersions exhibit shear thinning. While not wishing to be limited by theory, the shear thinning behavior may be attributable to the untangling and alignment of nanowires under shear. In that case, it is unclear why the entanglement of nanowires inhibits rather than promotes sedimentation at concentrations containing large amounts of solvent, and that the viscosity may increase sufficiently with increasing nanowire concentration to dominate sedimentation, and surprisingly, this appears to be due to interparticle interactions that do not result in larger mass particles having a higher sedimentation tendency. Regarding stability against sedimentation, this can be reassessed after 24 hours without mixing.

[0091] Upon achieving Domain IV, the dispersion becomes a paste, and as used herein, this indicates that the material does not flow without shear; therefore, it is a solid without shear and a fluid liquid under shear. Thus, from a practical standpoint, the material remains where it is deposited, but it can form or diffuse. Flow is an everyday experience, but it is useful to think about and express it in a way that avoids the messy beading caused by surface tension due to the lack of flow. If a 5-gram quantity is placed on a surface with a diameter of 1 centimeter and inclined at a 60-degree angle to the horizontal, and does not flow across the surface, the material is considered non-flowing. Obviously, this is a qualitative test and cannot be expected to have mathematical precision. As with other transitions between domains, the exact boundary may be affected by environmental conditions, and it may be useful to consider the boundary as a small range.

[0092] The concentrated dispersion is observed to exhibit a remarkable degree of conductivity. Migration is observed in the domain IV paste, suggesting the arrival of a percolation threshold, indicating the availability of a novel conduction pathway corresponding to a sharp decrease in electrical resistance. The decrease in electrical resistance depends on the length and concentration of the silver nanowires. Higher loadings of shorter nanowires are achievable with an appropriate aspect ratio, while longer nanowires at lower concentrations may result in greater conductivity. Therefore, depending on the intended use of the material, there are significant material design options.

[0093] As described above, the recognition of new forms for silver nanowire dispersions allows for the determination of stability in an appropriate manner to reflect these new materials. When used herein, stability is determined by the absence of hard aggregates, and consequently, the material can be redispersed in the original volatile solvent in a harmless mixture to achieve a stable low-concentration dispersion. Thus, in a sense, the dispersion is reversible and therefore stable in the concentrated state. Dilute dispersions can be characterized by properties expected to achieve a well-mixed dispersion. While the exact concentration is not critical from a property standpoint, concentrations of 0.1 wt% solids, 1 wt% solids, or similar concentrations can be used for dilute reconstituted dispersions to provide some specificity to the evaluation process. A reconstituted dilute dispersion should not show hard aggregate formation even after standing for 3 days without stirring, although this period is likely to be much longer, and the 3-day selection provides a practical period for testing. In addition, optical spectroscopy can be used to evaluate the absence of aggregation of dispersed nanowires.

[0094] Electrical resistance is measured in ohms. The measured resistance depends on the conduction path and the shape of the conductor. For materials, resistivity is an inherent parameter that does not depend on size and has units of ohm-time length. For a uniform material, resistivity ρ can be estimated from the formula ρ = RA / l, where R is the resistance measured in ohms, A is the area of ​​the conductor edge perpendicular to the conduction path, and l is the length of the conduction path. To obtain resistivity (in units of ohms·cm), A = cm 2 The unit l must be in units of cm. The electrical resistance of a thin coating can be expressed as sheet resistance (Rs) and is reported in units of square ohms (Ω / □ or ohms / sq) to distinguish the value from the bulk electrical resistance value according to the parameters related to the measurement process. Sheet resistance along a surface can generally be measured using four-point probe measurement or another suitable process. If the thickness of the structure is known or measurable, the resistivity (ρ) is given by ρ = R s It can be evaluated as t (where t is the average thickness).

[0095] The concentrated dispersion is 10 6 It is known to be conductive with a resistivity of approximately ohms-cm. At higher concentrations corresponding to the paste, the resistivity value decreases moderately until it reaches a certain concentration, at which point the resistivity decreases significantly, which appears to indicate a change in the conductivity mechanism. For one type of silver nanowire, this transition appears to occur at about 60 wt% nanowire with a resistivity of less than 1 ohm-cm. The paste is generally less than or equal to about 1 Ωcm, less than or equal to about 0.1 Ωcm in further embodiments, and less than or equal to about 5 × 10⁻¹⁶ in other embodiments. -2 Ωcm ~ approx. 5×10 -4 Resistivity of Ωcm can be observed. Since rheological properties and electrical conductivity do not coincide with respect to nanowire dimensions, this transition to lower resistivity values ​​may occur at significantly different loading amounts. The applicant has measured resistivity <10 Ω-cm in various concentrated dispersions—i.e., different solvents. Those skilled in the art will recognize that an additional range of resistivity within the express range described above is intended and falls within the scope of this disclosure.

[0096] UV / Vis spectra can be used to diagnose the properties of silver nanowires and the quality of dispersions. Generally, absorption spectrum evaluation is performed in dilute dispersions to obtain meaningful spectral measurements. As described above, a stable dispersion can be diluted to form a dilute dispersion. The UV-Vis spectrum of the obtained dilute dispersion can be used to evaluate the dispersion. Thin, uniform silver nanowires dispersed in DMSO solvent were characterized by the UV-Vis absorption spectrum in the '230 patent cited above. Characterizing the diameter and quality of nanowires using UV-Vis absorbance is well known to those skilled in the art.

[0097] The UV-Vis absorption spectrum in isopropyl alcohol was used to characterize a concentrated dispersion diluted with 0.005 wt% silver, although at low concentrations, the normalized spectrum is generally not very sensitive to concentration. As used herein, the normalized absorption spectrum is set to 1 for the highest value and 0 for the lowest value in the wavelength range of 300 nm to 800 nm. As the average nanowire diameter decreases, the absorbance maximum tends to shift to lower wavelengths (blue shift). As the silver nanowires become more uniform, the absorbance peak tends to narrow. The tail of the absorption spectrum at higher wavelengths appears to be sensitive to dispersion quality, as it indicates a degradation in quality related to aggregation and the plasmonic response associated with well-dispersed individual nanowires.

[0098] To reduce the possibility of misinterpretation of the absorption spectrum due to solvent or nanowire dimensions, the spectrum can be compared to the absorption spectrum obtained from a dilute dispersion formed with silver nanowires, thereby allowing for direct evaluation of the absorption spectrum of a sample diluted from a concentrated dispersion. It is known that nanowire aggregation alters the longer wavelength tail of the absorption spectrum, and well-dispersed nanowires should exhibit very similar absorption spectra across the entire spectrum.

[0099] When the solvent is completely removed, the resulting aggregate reaches a point where the material can no longer be redispersed. The aggregation hardens and is irreversible. The point at which the irreversible state is reached also depends on the shape of the nanowires and the solvent. Conductivity can be further improved in these aggregates. In such extreme cases, the nanowires aggregate so much that they completely lose their plasmonic properties, and the characteristic absorbance peaks associated with surface plasmons can disappear. When the material is in a paste state, if desired, it can be molded into the desired shape to dry completely. This is domain V and is unique in that it is not stable in the sense currently used. When all the solvent is removed, the conductivity increases, and the resistivity value is about 1 / 100th of that of bulk silver.

[0100] Beyond a considerable concentration domain, dispersions can be characterized using viscosity and rheological behavior. However, by adjusting the concentration, solvent, and potentially additives, a desired value of viscosity can be achieved. Beyond a certain value, viscosity is generally non-Newtonian. From these perspectives, viscosity is selectable over a reasonable range. The Newtonian properties of viscosity are as follows: -1 Viscosity can be evaluated at low shear values. Viscosity can be evaluated using a commercially available rotary rheometer such as Brookfield or Haake. In some embodiments, the viscosity of the fluid concentrate dispersion may be at least about 500 cP (cP = mPa·s), in further embodiments at least about 750 cP, in other embodiments about 1000 cP to about 1250 cP to about 50,000 cP, and in additional embodiments about 1500 cP to about 40,000 cP. Viscosity and other parameters herein are evaluated at room temperature at about 25°C. Those skilled in the art will recognize that an additional range of viscosities within the express ranges above is intended and falls within the scope of this disclosure.

[0101] Qualitatively, concentrated dispersions can be characterized as flowable or non-flowable. As described above, flowable dispersions can be characterized by flowing down a surface with a 60-degree angle. For use, flowable dispersions offer desirable versatility with respect to delivery at various desired locations. Concentration and viscosity can be adjusted to suit selected delivery methods such as injection, distribution, printing, or coating. In some embodiments, paste dispersions are suitable for spreading at specific locations to form devices or structures incorporating the paste dispersion. At some point, in most coatings, the dispersion after coating is dried or dried by a curing process to remove any remaining solvent and / or convert the dispersion into a solid. Curing may involve reducing crosslinked polymer components, polymer monomers, oligomers, or small polymers, silver salts to silver metal, or a combination of these two or more effects.

[0102] Within one limitation, the dry solid material may take the form of an essentially metallic mass containing embedded polymer dispersants and optionally other trace organic components. Within another limitation, the dry material may be a polymer-metal composite, and in some embodiments, a conductive adhesive in acceptable terms, having a metal load that can range in value. Once the dispersion is dried, cured, and so on, there may be no direct remnants of the initial state of the composition at the time of delivery, if any. Nevertheless, the concentration of the dispersion at the time of delivery to a deposit that is subsequently further processed to form a material may affect the material properties depending on the material composition.

[0103] With regard to materials that are substantially metallic, primarily formed from silver nanowires, previous work has involved forming these deposits using moderately concentrated silver nanowire dispersions. See application '732 cited above. These deposits may contain about 25% by weight or less of organic matter, in further embodiments about 15% by weight or less of organic matter, in some embodiments about 0.025% to about 10% by weight of organic matter, and in other embodiments about 0.1% to about 7.5% by weight of organic matter. Potential organic components are discussed above in relation to dispersions, and the material includes non-volatile organic matter as well as organic matter that polymerizes or crosslinks to become non-volatile before their evaporation. With regard to metallic components, generally, at least about 75% by weight of the metal in the material originates from silver nanowires, and the remainder of the metal potentially originates from reduction from other metal nanoparticles or metal salts such as silver salts. Even well-purified silver nanowires co-purify other particle shapes, mainly nanoparticles, but may have other shapes such as nanocubes, nanorods or nanoplates. While accurately quantifying contaminant levels in nanowire collections can be challenging, reasonable limits can be established. As described above, silver salts can be reduced to silver metal, which contributes to the material's overall metallic content. In some embodiments, the metallic portion derived from silver nanowires may be about 75% to 99.5% by weight, in further embodiments about 80% to 99% by weight, and in other embodiments about 82.5% to 95% by weight. In additional embodiments, all of the silver may be provided by refined silver nanowires having a degree of co-refined metallic contaminants. Those skilled in the art will recognize that an additional range of material components within the express range described above is contemplated and falls within the scope of this disclosure.

[0104] The materials described in the previous paragraph may contain various organic components, but particular interest is focused on composite materials containing a polymer matrix surrounding the metallic elements of the structure. Low resistivity values ​​were obtained with small amounts of metal loading from silver nanowires supplemented with metal from reduced silver salts. See application '737 cited above. The procedure for forming higher concentration dispersions described herein can be adapted to form composite materials having higher metal loading in the polymer matrix. Generally, these composite materials have at least about 25 wt% metal and at least about 10 wt% matrix polymer, but the composite materials may contain additional organic components as described above with respect to the dispersion. In some embodiments, the composite materials contain about 25 wt% to about 90 wt% metal, in further embodiments about 35 wt% to about 87.5 wt% metal, in other embodiments about 40 wt% to about 86 wt% metal, and in additional embodiments about 50 wt% to about 85 wt% metal. Furthermore, the composite material may comprise about 10% to about 75% by weight of a matrix polymer, in a further embodiment about 12.5% ​​to about 65% by weight of a matrix polymer, in another embodiment about 14% to about 60% by weight of a matrix polymer, and in an additional embodiment about 15% to about 50% by weight of a matrix polymer. The matrix polymer is generally a chemically or physically crosslinked polymer that is resistant to dissolution in all or most non-destructive solvents. Those skilled in the art will recognize that an additional range of composite material components within the express range described above is contemplated and falls within the scope of this disclosure.

[0105] The high-load dispersions described herein are generally intended for the formation of opaque materials and structures. While it is reasonable that some light transmittance can be achieved when applied to sufficiently thin deposits, due to the properties of the dispersions, forming thin deposits without diluting at least the silver nanowire dispersions can be difficult. Forming high-load dispersions and subsequently diluting them may seem like a considerable waste of effort, but this can be advantageous for transport purposes. Depending on the balance of efficiency, this can be a useful method for product distribution. Starting with a concentrated dispersion, customers can perform dilution to the degree desired for their use. From this perspective, the ability to form high-load dispersions suitable for subsequent dilution to well-dispersed dilute dispersions is advantageous for applications ranging from transparent to opaque.

[0106] Regardless of specific processing, dispersions are generally used to form conductive materials. Due to the commonality of mechanisms, good conductors are generally also good thermal conductors, but the correlation should not be expected to be perfect, and many systems are thought to follow the well-known Wiedemann-Franz law. For example, it is not established whether reduced silver salts improve thermal conductivity in addition to electrical conductivity. Naturally, the range of conductivity can be adjusted for applications and selections of other material properties. As found herein, the use of reduced silver salts may be effective in reducing the resistivity of the material for a given amount of silver nanowires and achieving the lowest achievable resistance value.

[0107] Processing for forming hardened products The term "cured" can have distinct meanings in different fields, but as used herein, cured broadly refers to the processing required to form a dry material from a dispersion, even if the dispersion is similar to a solid. In addition to or instead of removing the solvent, curing may, in relevant embodiments, involve polymerization of monomers or oligomers, crosslinking of polymers, reduction of silver salts, or a combination thereof. Curing may involve evaporation, application of heat for a selected period at a specified temperature, delivery of radiation, or simple aging under conditions that allow a combination thereof. The final material depends on both the composition used to form the deposits processed into the material and the processing used.

[0108] To use a concentrated dispersion, a certain amount of the dispersion is deposited to form a corresponding deposit. The deposition technique generally correlates with the dispersion properties. For example, paste-like materials can be deposited by extrusion, calendering, or screen printing. Flowable materials can be deposited using the methods described for pastes, but can also be deposited using injection molding, printing, slot coating, etc. The dimensions of the deposit are generally not limited, however pastes and highly viscous concentrated dispersions may be difficult to form into very thin deposits that can be easily formed with dilute dispersions. Surface dimensions generally correspond to dimensions suitable for the application. The higher the concentration of the dispersion, the smaller the shrinkage resulting from drying is compared to the shrinkage observed when drying dilute dispersions, and the wet dimensions can be selected accordingly to achieve the desired dry dimensions.

[0109] As described in detail above, the concentrated dispersion may have a higher boiling point solvent or a non-volatile solvent. To simply remove the higher boiling point, an inert solvent may be used, with or without heat, and reduced pressure may be used as needed to promote evaporation. Blowing air or other gases across the deposit with or without heat may also be used to accelerate evaporation. As described above, the solvent and / or other dispersion components may include precursors for the polymer matrix. The polymer matrix may be a chemically crosslinked, physically crosslinked, or solidified solid polymer. The formation of physical crosslinks may occur spontaneously from solvent removal by precipitation of the dissolved polymer and / or as a result of polymerization for chain elongation. Chemical crosslinking may generally involve addition reactions to the polymer side chains. The crosslinking reaction may be a free radical reaction, an electrophilic nucleophilic reaction, a redox reaction, or any other suitable reaction.

[0110] For embodiments based on polymer polymerization and / or crosslinking, since UV radiation or other suitable radiation generally does not penetrate particularly well, thermal reactions may be the most favorable, and therefore radiation curing may only be effective for very thin deposits. Regarding the reduction of silver ions in these high-density silver nanowire deposits, it was found that longer times and higher heat were required to reduce silver ions than observed in transparent conductive films. As can be seen in the examples, the reduction of silver ions is observed to significantly reduce resistivity. The physical effects of silver deposition are still under investigation. To achieve silver ion reduction and / or polymer curing, the deposited sample may be heated to a temperature of at least about 120°C, about 130°C to about 300°C in some embodiments, about 140°C to about 275°C in further embodiments and about 150°C to about 250°C in additional embodiments. Heating may be carried out for at least about 3 minutes, about 5 minutes to about 3 hours in further embodiments and about 8 minutes to about 2 hours in other embodiments. After this processing, the solvent does not need to be completely removed, and if additional solvent is present, a further drying step may be performed. In the case of deposits containing silver salts, gentler heating may be performed to “melt” the deposit, which may be used to facilitate the rearrangement of the deposit as needed. After melting, processing to harden the deposit may be continued. Those skilled in the art will recognize that additional ranges of temperature and time beyond the express range described above are intended and within the scope of this disclosure.

[0111] Uses of concentrated dispersions Based on the novelty of the concentrated dispersion, the exploration of suitable applications is an initial step. Applications are discussed above in relation to the investigation of material properties. For example, as stated therein, the concentrated dispersion may be in a form favorable for distributing silver nanowires, which can then be diluted and dispersed to form the desired silver nanowire dispersion concentration for use. Conductive pastes offer the possibility of directly using conductive pastes as electrical and thermal conductors in suitable applications. For these pastes, non-volatile solvents can be used, or the material can be placed in an environment that limits solvent evaporation.

[0112] With respect to concentrated fluid dispersions, these materials significantly improve the potential for blending with resins to form silver nanowire-loaded polymer composites. Lower solvent levels can facilitate the formation of higher loading amounts with less process effort. Highly conductive materials with high silver content provided by silver nanowires can achieve low resistivity values. These opaque materials can function as solder substitutes, printable conductive wires / conductors, conductive traces, or other desired highly conductive structures, which can be performed at lower temperatures than metal deposition while offering relatively low resistivity. [Examples]

[0113] General methods and materials Viscosity measurement Measurements were performed using two different rotary rheometers. The first rheometer was a Brookfield Model DV-III+ programmable rheometer, which was limited to lower viscosity values. For higher viscosity measurements, a TA Instrument ARES-G2 rheometer fitted with a 25 mm plate spindle was used. Viscosity was obtained at a single shear rate or as a function of shear rate. Storage modulus and loss modulus as functions of angular frequency were also measured for selected dispersions. Measurements were performed at 25°C unless otherwise specified.

[0114] Resistivity measurement The dispersion was formed into a cylindrical shape using a thin tube as needed, or into a rectangular composite material. The resistance was then measured for conduction from one end to the other of the tube or rectangular structure using a two-point probe equipped with a multimeter. The resistivity was then calculated from the shape of the sample, and the resistance was measured.

[0115] H-nanowire Silver nanowires called H-nanonowires (H-NWs) were synthesized in a closed reactor system. A heated reaction solution of ethylene glycol (EG), polyvinylpyrrolidone (PVP K30 from BASF), and NH4Cl was prepared, followed by the addition of AgNO3 while continuously stirring at approximately 160°C for several hours. After the synthesis was complete, the silver nanowires were purified by acetone precipitation and redispersion in water or other solvents. The purified silver nanowires were removed from the dispersion, dried, and characterized by electron microscopy, for example, as described in U.S. Patent No. 10,714,230 to Hu et al. H-nanonowires were prepared with a diameter of approximately 60 nm (H-60). The nanowires had an average length of approximately 6 microns.

[0116] N-nano Silver nanowires, called N-nanowires (N-NWs), were obtained from the applicant C3Nano, Inc. using the synthesis procedure described in U.S. Patent No. 10,714,230 to Hu et al. The N-nanowires had an average diameter of approximately 20–22 nm and a length of approximately 20 microns.

[0117] solvent The following solvents were used in the examples: Benzyl alcohol (BnOH), Butoxytriglycol (BTG), Butylcarbitol (BC), 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIPF6), Cyclohexanol (CH), Deionized H2O (DIW), Diethyl glycol (DEG), Bifunctional alicyclic diepoxide, Celloxide 2021P, manufactured by Daicel USA, Inc. (Cello) Dimethylacetamide (DMAc), Dimethyl sulfoxide (DMSO), Ethanol (EtOH), Ethoxytriglycol (ETG), Ethyl lactate (ELA), 2-Ethyl-4-methylimidazolium tetrafluoroborate (EMIBF4), Ethylene glycol butyl ether (EGBE), 1-Hexyl-3-methylimidazolium hexafluorophosphate (HMIPF6), Hydrogenated bisphenol A type epoxy resin, YX8000D manufactured by Mitsubishi Chemical (YX), N-hydroxyethylacrylamide (HEAA), 2-hydroxyethyl methacrylate (HEMA), i-propanol (IPA), N-methyl-2-pyrrolidone (NMP), Radiation-curing optical adhesive, NOA85 manufactured by Norland Optical Adhesives (NOA), Propylene glycol (PG), and Triethylene glycol (TEG).

[0118] salt The following salts were used in the examples: Silver acetate (AgAc), Silver fluoride (AgF), Silver heptafluorobutyrate C3F7CO2Ag (AgHFB), Perchloric acid (AgClO4), and Silver trifluoroacetate (AgTFA).

[0119] Summary of Examples 1 and 2 Examples 1A-1H target H-NW and N-NW silver nanowire dispersions in propylene glycol (PG) solvent. Examples 2A-11B target H-NW and N-NW dispersions in various other solvents such as ethyl lactate (ELA), ethanol (EtOH), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and others. The dispersions were evaluated for their rheological and conductivity properties. The effects of dilution and redispersibility from the dried film formed from the dispersions were evaluated using UV-Vis spectroscopy. The effects of adding different amounts of PVP to the dispersions before incorporation into the solvent were also evaluated. Qualitative evaluation of the regimes of the dispersions was also performed.

[0120] Example 1A: H-nanowires in PG H-nanohms were first dispersed in EtOH to obtain dilute dispersions with a concentration of approximately 8 wt%. Dispersions of H-NW at various concentrations were prepared directly by adding PG to the slurry and then removing EtOH using rotational evaporation at a bath temperature of approximately 60°C. Although not reported in this example, residual EtOH was retained in the material after the removal process, which is reported below. Viscosity and resistivity values ​​were obtained, and the results are shown in Table 1 and Figures 5A and 5B. Selected dispersions were diluted with IPA to form dispersions with a solid content concentration of 0.001 wt%. Figure 6 shows the normalized UV-Vis absorption spectra for H20-PG, H30-PG, H40-PG, H60-PGa, and H70-PG. The spectra suggest that good dispersion of H-NW was obtained with loading amounts ranging from 20 wt% to 70 wt% in PG.

[0121] [Table 1]

[0122] Viscosity as a function of shear rate was measured for the selected dispersions, and the results are shown in Figure 7. The data points inside the circle indicate the decrease in high shear rate due to material rotation from the gap observed after the experiment. The storage modulus and loss modulus as functions of angular frequency were measured for the selected dispersions, and the results are shown in Figure 8.

[0123] Example 1B: Rheology of serial dilution of H70-PG H-nanoblades were dispersed in EtOH to obtain dilute dispersions with a concentration of approximately 2-8% by weight. An initial dispersion of H-NW (H70-PG) at 70% by weight in PG was directly prepared by adding PG to a slurry and then removing EtOH, as described in Example 1A. Subsequently, six diluted samples were prepared by sequential dilution of H70-PG to obtain diluted dispersions of H60-PG-dil to H10-PG-dil.

[0124] Rheological tests were conducted, and data for H10-PG-dil to H40-PG-dil are shown in Tables 2 to 5, respectively. Data for H50-PG-dil, H60-PG-dil, and H70-PG could not be obtained because the sample was too thick to be measured with a specific rheometer.

[0125] [Table 2]

[0126] [Table 3]

[0127] [Table 4]

[0128] [Table 5]

[0129] Another set of samples was prepared by directly selecting the desired PG concentration using solvent exchange from EtOH. The initial dilute dispersion of H-nanowires in EtOH was serially diluted with PG and subjected to a rotary evaporator to remove EtOH at the compositions shown in Table 6. For each concentration, the dilution was calculated from an initial load of 70 wt% and then normalized to 100 g. Recovery rate is a measure of the actual weight relative to the expected weight after removal of EtOH by rotary evaporation (water bath 60°C). Values ​​exceeding 100 wt% can be explained by the retention of ethanol after the rotary evaporation process. The retained ethanol was independent of the amount of PG.

[0130] [Table 6]

[0131] Example 1C Comparison of viscosity and resistivity of sequentially diluted and directly prepared dispersions of H-NW in PG Viscosity and resistivity were measured for both the serially diluted samples and the "directly prepared" samples, and the results are reported in Tables 7 and 8, respectively. The corresponding plots are shown in Figures 9A and 9B. Resistivity was measured at 2 cm. 2 The calculation was performed using the cross-sectional area and a length of 12-14 cm.

[0132] [Table 7]

[0133] [Table 8]

[0134] Example 1D: Further characterization of serial dilutions of H-NW in PG The sequentially diluted dispersions were placed on a glass slide at an angle of approximately 60 degrees, and the slide was held in this angled position for several minutes. Images of the samples H10-PG-dil, H20-PG-dil, H30-PG-dil, H40-PG-dil, and H50-PG-dil are shown from left to right in Figure 10.

[0135] For each serially diluted sample, droplets were injected between two glass substrates to determine the approximate film thickness. Images were obtained at 10x magnification using optical microscopy, and selected images for H70-PG, H30-PG-dil, H20-PG-dil, and H10-PG-dil are shown in Figures 11A to 11D, respectively. The regimes and approximate film thicknesses are summarized in Table 9.

[0136] [Table 9]

[0137] Example 1E: N-nanowires in PG N-nanowires were dispersed in EtOH to obtain a slurry at a concentration of approximately 2-4% by weight. Dispersions of N-NW at concentrations ranging from 3% to 10% by weight in PG were prepared as described for Example 1A. The viscosity was determined, and the results are shown in Table 10.

[0138] [Table 10]

[0139] Viscosity was measured as a function of shear rate, and the results are shown in Figures 12a and 12b. Storage modulus and loss modulus as functions of angular frequency were measured for selected dispersions, and the results are shown in Figure 13. For silver nanowires with higher aspect ratios (N-wire vs. H-wire), viscosity increased at relatively low concentration levels. Non-Newtonian rheology was observed at all concentration levels tested.

[0140] UV-Vis absorption spectrum of Example 1F N15-PG As shown in Tables 11A and 11B, dispersions of N-NW in PG were prepared by diluting N15-PG (15% by weight silver) to target silver weight percentage values ​​in the range of 10% by weight to 3% by weight. The initial dilute dispersions of N-NW in EtOH were sequentially diluted with PG and subjected to a rotary evaporator to remove EtOH. For each concentration, the dilution was calculated from the initial load of 15% by weight. Recovery rate is a measure of the actual weight relative to the predicted weight after EtOH removal. Values ​​exceeding 100% by weight can be explained by the retention of ethanol after the rotary evaporation process. The concentrations of all components listed in Tables 11A and 11B are summarized in Table 12.

[0141] Next, to obtain optical measurements, the dispersion was diluted with IPA as shown in Table 13. The corresponding UV-Vis absorption spectra are shown in Figure 14.

[0142] [Table 11]

[0143] [Table 12]

[0144] [Table 13]

[0145] [Table 14]

[0146] Example 1: Effect of PVP level on N-NW in GPG Samples of N-nanowires (N15-PG) at 15% by weight in PG were prepared using the method described above. The effect of adding an additional amount of PVP on the concentrated dispersion was investigated. The weight ratio of organic matter to silver (O / Ag) was formed as a solid for three samples: O / Ag = 0.13 for dispersion N15-PG-PVP-Ag, O / Ag = 0.26 for dispersion N15-PG-PVP-Ag + 1PVP, and O / Ag = 0.39 for dispersion N15-PG-PVP-Ag + 2PVP. The compositions are shown in Tables 14A-14B and 15A-15B. The effect on retained ethanol as recovery rate and the obtained resistivity are included in Table 15B.

[0147] The UV-Vis absorption spectra for the dispersions N15-PG-PVP-Ag, N15-PG-PVP-Ag+1PVP, and N15-PG-PVP-Ag+2PVP are shown in Figure 15. The plot of O / Ag as a function of recovery is shown in Figure 16. The samples of the three dispersions were placed on a glass slide at an angle of approximately 60 degrees, and the slide was held in that angled position for several minutes. Images of the samples N15-PG-PVP-Ag, N15-PG-PVP-Ag+1PVP, and N15-PG-PVP-Ag+2PVP are shown from left to right in Figure 17.

[0148] [Table 15]

[0149] [Table 16]

[0150] [Table 17]

[0151] [Table 18]

[0152] The results suggest that increasing the amount of PVP made the removal of EtOH more difficult, as evidenced by the change in recovery rate. The UV-Vis absorption spectrum suggests that the wet dispersion can be adequately redispersed in IPA. In general, increasing the amount of PVP leads to improved coating quality and increased resistivity.

[0153] Table 16 shows the effect on the conductivity of coatings prepared from dispersions N15-PG-PVP-Ag, N15-PG-PVP-Ag+1PVP, and N15-PG-PVP-Ag+2PVP, dried under different conditions. Certain amounts of these dispersions were dried either in an oven or using high-intensity pulsed light (IPL) provided by a system from XENON Corp. The redispersibility of these dispersions is further described in Example 4A. Increasing the PVP level resulted in increased resistivity.

[0154] [Table 19]

[0155] Example 1: Effect of PVP level on H-NW in HPG Samples of N-nanowires (H50-PG) at 50 wt% in PG were prepared using the method described above. The effect of adding an additional amount of PVP on the concentrated dispersion was investigated. The organic-to-silver (O / Ag) ratio was formed in solid form for the three samples: O / Ag = 0.25 for dispersion H50-PG-1AP, O / Ag = 0.50 for dispersion H50-PG-1AP + PVP, and O / Ag = 0.25 for dispersion H50-PG-3AP + PVP. For H50-PG-1AP and H50-PG-1AP + PVP, the PVP was from the original batch. For H50-PG-3AP + PVP, it was from the H-NW batch that was initially processed to obtain O / Ag = 0.137. For these samples, the synthesized H-silver nanowires were further purified by one or three additional acetone precipitation and rinsing steps to remove additional PVP (1AP or 3AP). In some samples, additional PVP was added back afterward (+PVP). The compositions are summarized in Tables 17 and 18A-18B.

[0156] The effect on retained ethanol as a recovery rate is shown in Tables 18A-18B. The target recovery rate is 118%. For H50-PG-1AP and H50-PG-1AP+PVP, approximately the same time / conditions are required to reach 118%. However, for H50-PG-3AP+PVP, removing the solvent appears to be very easy. The added free PVP does not appear to promote solvent retention.

[0157] [Table 20]

[0158] Table 19 shows the form, wet resistance, and conditions for rotational evaporation (for removing EtOH).

[0159] [Table 21]

[0160] [Table 22]

[0161] [Table 23]

[0162] Table 20 shows the effect on the conductivity of dispersions H50-PG-1AP, H50-PG-1AP+PVP, and H50-PG-3AP+PVP dried under various conditions. These large quantities of dispersions were dried either in an oven or using an IPL (Intense Pulsed Light).

[0163] [Table 24]

[0164] The original H-NW dispersion H50-PG-Ace1, which had an Org / Ag ratio of 0.245, was further processed to reduce the Org / Ag ratio: for dispersion H50-PG-Ace2, Org / Ag = 0.211, and for dispersion H50-PG-Ace3, Org / Ag = 0.137. The effect on the conductivity of these dispersions dried under various conditions is shown in Table 21. These large quantities of dispersions were dried either in an oven or using IPL. Resistivity did not decrease even as the Org / Ag ratio decreased. The resistivity of the wet dispersions is shown in Table 22.

[0165] [Table 25]

[0166] [Table 26]

[0167] Example 2A: H-nanowires in ethyl lactate H-nanoblades were dispersed in EtOH to obtain slurries with concentrations of approximately 2–8 wt%. Dispersions of H-NW in ELA at concentrations ranging from 30–70 wt% were prepared directly by adding ELA to the slurry and then removing EtOH using rotational evaporation at a bath temperature of approximately 60°C. The compositions are shown in Table 23. The UV-Vis absorption spectra of the ELA dispersions are shown in Figure 18, suggesting a decrease in dispersion quality in samples with loadings of 60% and 70% wt%. Resistivity values ​​were obtained and the results are shown in Table 24. Visual evaluation of regium is also shown in Table 24. Images obtained by optical microscopy at 10x magnification are shown in Figures 19A–19C.

[0168] [Table 27]

[0169] [Table 28]

[0170] Example 2B: N-nanowires in ELA N-nanowires were dispersed in EtOH to obtain a slurry with a concentration of approximately 2 wt%. Dispersions of N-NW at concentrations ranging from 3 wt% to 10 wt% in ELA were prepared directly by adding ELA to the slurry and then removing the EtOH using rotary evaporation at a bath temperature of approximately 60°C. The composition is shown in Table 25. Viscosity and resistivity values ​​were obtained, and the results are shown in Table 26. Visual evaluation of regium is also shown in Table 26.

[0171] [Table 29]

[0172] [Table 30]

[0173] Example 3: N-nanowires and H-nanowires in EtOH A dispersion of N-NW was prepared at a loading volume of 7 wt%, and its viscosity was measured at three different shear rates. The results are shown in Table 27. Subsequently, the UV-Vis absorbance spectrum of the starting dispersion of 1.9 wt% N-NW in EtOH concentrated to 12 wt% showed little change, suggesting that the dispersion quality remained good at higher concentrations of N-NW. The 12 wt% dispersion was redispersed, and excellent redispersibility was obtained.

[0174] A dispersion of H-NW was prepared with a loading volume of 70% by weight. Viscosity could not be measured, as shown in Table 27, because the instrument stopped after two measurements due to excessive viscosity.

[0175] [Table 31]

[0176] Example 4A Effect of PVP level on N-NW, EtOH, IPA in PG and redispersion in PG N-NW dispersions with nearly zero solvent were prepared, and the redispersibility of these dispersions in different solvents was investigated. Dispersions N15-PG-PVP-Ag, N15-PG-PVP-Ag+1PVP, and N15-PG-PVP-Ag+2PVP were dried under different conditions as described in Example 1G and Table 16. The UV-Vis absorption spectra of the samples redispersed in IPA are shown in Figure 20, suggesting that the dried samples did not redisperse into good dispersions. More PVP may help reduce some of the aggregation after the sample reaches nearly zero solvent. Dispersion N15-PG-PVP-Ag+2PVP redispersed in EtOH appears more turbid compared to the others.

[0177] Example 4B: Effect of PVP level on H-NW, EtOH, IPA in PG and redispersion in PG H-NW dispersions with nearly zero solvent were prepared, and the redispersibility of these dispersions in different solvents was investigated. Dispersions H50-PG-Ace1, H50-PG-Ace2, and H50-PG-Ace3 were dried under different conditions as described in Example 1H and Table 21. A dispersion containing H-NW at 50% by weight in PG was also prepared and dried so that the nanowires would not undergo the acetone precipitation step (H50-PG-Ace0). The UV-Vis absorption spectra of the samples redispersed in IPA are shown in Figure 21, suggesting that the dried samples could not be redispersed into good dispersions. Here again, additional PVP is helpful to a detectable degree.

[0178] Example 5: H-nanowires in TEG, EGBE, and PG, redispersed in IPA Dispersions of H-NW were prepared directly by adding TEG or EGBE (2–8 wt%) to a slurry, followed by removal of EtOH using rotational evaporation at a bath temperature of approximately 60°F. The resulting concentrated dispersion was redispersed in IPA. UV-Vis absorption spectra suggested somewhat reduced dispersion quality at high loadings in both solvents.

[0179] Using an H-NW dispersion containing 5.247 wt% Ag and an O / Ag weight ratio of 0.2528, 90 wt% dispersions in PG and EGBE, H90-PG and H90-EGBE, were prepared, respectively. The composition and recovery rates are shown in Table 28. The data suggest that PG has stronger ethanol retention / affinity compared to EGBE. Dispersions prepared with EGBE dried faster than those prepared with PG. EtOH removal was more difficult at high target loads. Aggregation was observed, but most of the fraction could still be redispersed. When dispersions diluted with IPA were prepared, the UV-Vis absorption spectra showed somewhat reduced dispersion quality for H80-EGBE. Figures 22A and 22B are images showing the precipitation observed for IPA-diluted dispersions H90-PG and H90-EGBE, respectively. Wetting resistivity for H90-PG and H90-EGBE was determined, and the results are shown in Table 28.

[0180] [Table 32]

[0181] Example 6A: H-nanowires in HEAA, HEMA, and EGBE H-nanoblades were dispersed in EtOH to obtain slurries with concentrations of approximately 2–8% by weight. Dispersions of H-NW at various concentrations were prepared directly by adding a solvent to the slurry and then removing the EtOH using rotational evaporation at a bath temperature of approximately 60°F. The following solvents were used: HEAA, HEMA, EGBE, and CH. Viscosity was obtained, and the results are shown in Table 29.

[0182] [Table 33]

[0183] Example 6B: N-nanowires in HEAA, HEMA, and other media. N-nanowires were dispersed in EtOH to obtain a dilute dispersion with a concentration of approximately 2 wt%. Dispersions of various concentrations of H-NW were prepared directly by adding a solvent to a slurry and then removing the EtOH using rotational evaporation at a bath temperature of approximately 60°C. The following solvents were used: HEAA, HEMA, Celloxide 2021P, a bifunctional alicyclic diepoxide from Daicel USA, Inc. (Cello); YX8000D, a hydrogenated biphenol A type epoxy resin from Mitsubishi Chemical Group (YX); and NOA 85, a radiation-curable optical adhesive from Norland Optical Adhesives (NOA). Viscosity was obtained, and the results are shown in Table 30. The samples exhibited strong shear reduction and non-Newtonian behavior. Viscosity as a function of shear rate was measured for 3.5 wt% N-NW in HEMA, and the results are shown in Figure 23.

[0184] [Table 34]

[0185] Example 7: H-nanowires in CH Dispersions of H-NW at 10% and 20% by weight in cyclohexanol (CH) were prepared directly by adding CH to a slurry of H-NW in EtOH, followed by removal of EtOH using a rotary evaporator. The dispersions were observed and imaged at time intervals up to 30 hours. In the case of H-NW at a 10% by weight load, sedimentation began after 5 hours and increased as a function of time. After 24 hours, a considerable amount of H-NW had precipitated and settled at the bottom of the glass cylinder. In the case of H-NW at a 20% by weight load, no significant visual changes or precipitation were observed after at least 27 hours.

[0186] Example 8A: H-nanowires in NMP and DMSO Dispersions of H-NW in solvents NMP and DMSO at 60% by weight were prepared directly by adding the solvent to a slurry of H-NW in EtOH (at 5.724% by weight) and then removing the EtOH using rotational evaporation at a bath temperature of approximately 60°C. The composition and regime are reported in Table 31. Overall, the dispersion quality appeared to be good. Images at 10x magnification were obtained by optical microscopy, and selected images are shown in Figure 24A for NMP and Figure 24B for DMSO. The images suggest a mixture of solid and liquid.

[0187] [Table 35]

[0188] Example 8B: N-nanowires in NMP, DMSO, and PG Dispersions of N-NW at 15% by weight in solvents NMP, DMSO, and PG were prepared directly by adding the solvent to an N-NW slurry in EtOH, followed by removal of EtOH using rotary evaporation at a bath temperature of approximately 60°C. The composition and regime for N15-NMP and N15-DMSO are reported in Table 32. Overall, the dispersion quality appeared to be good.

[0189]

Table 36

[0190] Example 9A H-Nanowires in H2O Dispersions of H-NWs at 80 wt%, 70 wt%, and 60 wt% in H2O were prepared directly by adding H2O to a slurry of H-NWs in EtOH (at 9.49 wt%) and then removing the EtOH using rotary evaporation at a bath temperature of about 60 °C. The compositions and regimes are reported in Table 33. The weight percentages and volume percentages for the dispersions are shown in Tables 34 - 36.

[0191]

Table 37

[0192]

Table 38

[0193]

Table 39

[0194]

Table 40

[0195] Example 9B N-Nanowires in DIW Dispersions of N-NW at 15% and 20% by weight in DIW were prepared directly by adding H2O to a slurry of N-NW in EtOH (at 1.997% by weight) and then removing the EtOH using rotary evaporation at a bath temperature of approximately 60°C. During rotary evaporation, the N-NW dried on the sidewall of the flask, forming a silver mirror. All water was removed from the dispersion by a water-ethanol azeotrope mixture formed at approximately 91% by weight (approximately 96% by volume) of EtOH molecules. The 15% by weight dispersion of N-NW contained approximately 35 g of EtOH, which may result in the removal of approximately 3.2 g of H2O. The 20% by weight dispersion of N-NW contained approximately 45 g of EtOH, which may result in the removal of approximately 4 g of H2O, the amount present in the dispersion. The 20% by weight dispersion of N-NW in DIW was prepared as described above. During rotational evaporation, a silver mirror formed on the side wall of the flask, with a recovery rate of approximately 100%. The near-100% recovery rate suggests that water is effective in replacing ethanol, which is easily trapped within the material. Approximately 3.4 g of concentrate (from a 5 g batch) was recovered from the center of the bottom of the flask, and the actual concentration of the recovered sample may be less than 20%. The composition and results are reported in Table 37. The UV-Vis absorption spectrum suggested good dispersion quality. Viscosity was measured as a function of shear rate, and the results are shown in Table 38.

[0196] [Table 41]

[0197] [Table 42]

[0198] Example 10: H-nanowires and N-nanowires in DMAc A dispersion of H-NW at 60 wt% in DMAc was prepared directly by adding 2 g of DMAc to a 3 g slurry of H-NW in EtOH (9.81 wt% and O / Ag = 0.1862), followed by removing EtOH using rotary evaporation at a bath temperature of about 60 °C. A dispersion of N-NW at 15 wt% in DMAc was prepared directly by adding 4.25 g of DMAc to a 0.75 g slurry of N-NW in EtOH (1.997 wt%), followed by removing EtOH using rotary evaporation at a bath temperature of about 60 °C. The UV-Vis absorption spectra for the diluted samples of H60-DMAc and N15-DMAc are shown in Figure 25. For H60-DMAc, some precipitation was observed upon dilution, and it was found to be readily redispersible. For N15-DMAc, severe precipitation was observed upon dilution with IPA, indicating poor dispersibility. The dispersions were very thick. The selected data are shown in Table 39.

[0199]

Table 43

[0200] Example 11A H-Nanowires in EGBE Dispersions of H-NW at concentrations in the range of 80 - 20 wt% in EGBE were prepared directly by adding EGBE to a slurry of H-NW in EtOH, followed by removing EtOH using rotary evaporation at a bath temperature of about 60 °C. The UV-Vis absorption spectra for the diluted samples of H80-, H70-, H60-, H50-, H40- and H30-EGBE are shown in Figure 26. The selected data are shown in Tables 40 and 41. A plot of resistivity as a function of the wt% of H-NW is shown in Figure 27. Viscosity as a function of shear rate was obtained for H20-, H30-, H40- and H50-EGBE, and the results are shown in Tables 42 - 45 respectively. Shear stress and torque % are conventional parameters measured using a rheometer, and shear stress is the force per unit area.

[0201]

Table 44

[0202] [Table 45]

[0203] [Table 46]

[0204] [Table 47]

[0205] [Table 48]

[0206] [Table 49]

[0207] Example 11B: N-nanowires in EGBE Dispersions of N-NW in EGBE at concentrations of 15%, 10%, and 7% by weight were prepared directly by adding EGBE to an N-NW slurry in EtOH, followed by removal of EtOH using rotary evaporation at a bath temperature of approximately 60°C. The compositions are shown in Table 46. The UV-Vis absorption spectra for diluted samples of N15-, N10-, and N7-EGBE are shown in Figure 28. Selected data are shown in Tables 47 and 48. Viscosity as a function of shear rate was obtained for N15-, N10-, and N7-EGBE, and the results are shown in Tables 49-51, respectively.

[0208] [Table 50]

[0209] [Table 51]

[0210] [Table 52]

[0211] [Table 53]

[0212] [Table 54]

[0213] [Table 55]

[0214] Example 12A: H-nanowires and N-nanowires in PG and silver salt As shown in Table 52, H-NW dispersions at a concentration of 55 wt% in PG were prepared without silver salts, and also with silver salts AgHFB and AgF. The morphology, resistivity, and redispersibility in IPA are summarized in Table 53. Figure 29 is an image showing the dispersions H55-PG, H55-PG-AgHFB, and H55-PG-AgF from left to right.

[0215] [Table 56]

[0216] [Table 57]

[0217] As shown in Table 54, dispersions of N-NW at a concentration of 10% by weight in PG were prepared with and without silver salt AgF. The samples prepared with silver salt showed significant aggregation in a semi-solid state, as shown in Table 54.

[0218] [Table 58]

[0219] Example 12B: H-nanowires without silver salts in an imidazolium-based solvent As shown in Table 55, dispersions of H-NW were prepared in solvents BMIBF4, BMIPF6, HMIPF6, and EMIPF4 at concentrations of approximately 50% and 70% by weight, respectively. Coatings were prepared from the dispersions, and their resistivity was measured. The results are shown in Table 55. Coatings prepared with BMIBF4 and BMIPF6 without nanowires were also fabricated, and their resistivity is included.

[0220] [Table 59]

[0221] Example 13: H-nanowires and Ag salts in various solvents As shown in Table 56, H-NW dispersions at a concentration of approximately 50% by weight in various solvents were prepared both with and without silver salts.

[0222] [Table 60]

[0223] The UV-Vis absorption spectra for the selected diluted samples are shown in Figure 30. The two spectra labeled "TEG, unheated" correspond to the unheated H50-TEG-AgTFA repeat, and the spectrum labeled "TEG, heated" corresponds to one of the heated samples. The other spectra are labeled as follows: "DEG" = H50-DEG-AgTFA, "DMAc" = H50-DMAc-AgTFA, "BnOH" = H50-BnOH-AgTFA, and "TEG, AgClO4" = H50-TEG-AgClO4.

[0224] Figures 31A and 31B show images of H50-BTG-AgTFA at 50x magnification, obtained by optical microscopy, before and after heating in an oven at 150°C for 5 minutes.

[0225] The effect of drying coatings under various conditions on their conductivity was investigated. Dispersions shown in Table 57 were prepared and dried using IPL or in an oven at 200°C for 30 minutes. The resistivity of each coating was measured before and after treatment, and the results are shown in Table 58.

[0226] [Table 61]

[0227] [Table 62]

[0228] Example 14: H5 nanowires and H2 nanowires in BC and ETG, and AgTFA H5 nanowires were fabricated with an average diameter of approximately 60 nm and an average length of approximately 5 microns. H2 nanowires with an average length of approximately 2 microns were fabricated by sonication of H5 nanowires. As shown in Table 59, dispersions of H2 nanowires at a concentration of approximately 60% by weight in BC and ETG were prepared with and without AgTFA. Dispersions of H5 nanowires at a concentration of approximately 30% by weight were also prepared as shown in Table 59.

[0229] [Table 63]

[0230] The effect of drying coatings at various temperatures on their conductivity was investigated. Dispersions shown in Table 59 were prepared and dried in an oven at 150°C, 200°C, and 250°C for 30 minutes. The resistivity is shown in Table 60. The resistivity for H2 nanowire and H5 nanowire dispersions is plotted in Figures 32 and 33, respectively. A combined plot showing the resistivity for both H2 nanowire and H5 nanowire dispersions is shown in Figure 34.

[0231] [Table 64]

[0232] As shown in Table 61, dispersions of H2 nanowires at a concentration of approximately 60% by weight in BC were prepared with and without AgTFA. The coatings were dried at a temperature of 150°C for 30 minutes. The resistivity is shown in Table 61. Images obtained by optical microscopy of H260-BC and H260-BC-AgTFA (from 1% AgTFA to Ag) at a magnification of 25,000x are shown in Figures 35A and 35B, respectively. The dotted circles in Figure 35A indicate examples of nanowire aggregation that occurs to a greater extent when the dispersion and coating are formed without the use of silver salts.

[0233] [Table 65]

[0234] The embodiments described above are intended to be illustrative and not limiting. Additional embodiments are within the claims. In addition, while the invention has been described with reference to specific embodiments, those skilled in the art will recognize that modifications to form and detail may be made without departing from the spirit and scope of the invention. Any incorporation by reference to the above documents is limited so as not to incorporate subject matter contrary to the express disclosure herein. Unless otherwise indicated, as suggested in the discussion, the disclosure herein should be understood to include embodiments that consist of specific components, elements, components, or other sections, insofar as specific structures, compositions and / or processes are described herein using components, elements, components, or other sections, and may include additional features that do not alter the fundamental nature of the subject matter. The use of the term “about” herein refers to the expected uncertainty in the relevant values, which will be understood by those skilled in the art in a particular context.

Claims

1. A fluid concentrated dispersion comprising a polar solvent, at least about 8 wt% of silver nanowires, and about 0.1 wt% to about 60 wt% of a soluble polymer dispersant relative to the silver concentration, wherein the silver nanowires have an average aspect ratio of at least about 25, the dispersion has a non-Newtonian viscosity, the dispersion does not show visible sedimentation over a week, and dilution of the dispersion to a concentration of 0.1 wt% with isopropyl alcohol results in a stable dispersion.

2. The fluid concentrated dispersion according to claim 1, wherein the polar solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

3. The fluid concentrated dispersion according to claim 1, wherein the polar solvent comprises water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof.

4. The fluid concentrated dispersion according to claim 1, wherein the polar solvent comprises a monomer or oligomer that can be polymerized and / or crosslinked.

5. The fluid concentrated dispersion according to claim 1, wherein the polar solvent comprises an acrylate monomer.

6. A fluid concentrated dispersion according to any one of claims 1 to 5, comprising at least about 15% by weight of silver nanowires.

7. A fluid concentrated dispersion according to any one of claims 1 to 5, comprising at least about 20% by weight of silver nanowires.

8. The fluid concentrated dispersion according to any one of claims 1 to 7, wherein the silver nanowires have an average aspect ratio of about 50 to about 500.

9. A fluid concentrated dispersion according to any one of claims 1 to 8, comprising approximately 0.1% by weight of a polymer dispersant to approximately 20% by weight of a polymer dispersant, wherein the polymer dispersant comprises polyvinylpyrrolidone.

10. 0.1s －１ The fluid concentrated dispersion according to any one of claims 1 to 9, wherein the viscosity at the shear rate is at least about 100 cP.

11. A fluid concentrated dispersion according to any one of claims 1 to 10, further comprising a silver salt that provides up to about 50% by weight of silver ions relative to the weight of silver nanowires.

12. The fluid concentrated dispersion according to claim 11, further comprising a reducing agent additive having a concentration of approximately 0.001 mM to approximately 1000 mM.

13. The fluidity-concentrated dispersion according to any one of claims 1 to 12, wherein the non-Newtonian behavior is observed to be shear viscosity reduction.

14. The fluid concentrated dispersion according to any one of claims 1 to 13, wherein the silver nanowires have an average diameter of about 35 nm to about 80 nm.

15. The fluidity of the fluidity-concentrated dispersion according to any one of claims 1 to 14, wherein the fluidity is observed when a certain amount of the fluidity-concentrated dispersion is placed on a surface at an angle of 60 degrees from the horizontal.

16. A fluid concentrated dispersion useful for forming conductive composite materials and adhesives, comprising at least about 8 weight percent of silver nanowires, a soluble polymer dispersant, and a polar solvent containing a liquid polymer precursor having functional groups suitable for polymerization and / or crosslinking, wherein the silver nanowires are substantially non-aggregating and uniformly distributed, and the dispersion has a temperature of 0.1 s. －１ A fluid concentrated dispersion exhibiting a viscosity of at least about 100 cPs when subjected to a shear rate.

17. The fluid concentrated dispersion according to claim 16, wherein the liquid polymer precursor comprises a monomer or oligomer that can be polymerized and / or crosslinked.

18. The fluid concentrated dispersion according to claim 16, wherein the liquid polymer precursor comprises an acrylate monomer.

19. The fluid concentrated dispersion according to any one of claims 16 to 18, wherein the polar solvent further comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

20. The fluid concentrated dispersion according to any one of claims 16 to 18, wherein the polar solvent further comprises water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof.

21. A fluid concentrated dispersion according to any one of claims 16 to 20, comprising at least about 15% by weight of silver nanowires.

22. A fluid concentrated dispersion according to any one of claims 16 to 20, comprising at least about 20% by weight of silver nanowires.

23. The fluid concentrated dispersion according to any one of claims 16 to 22, wherein the silver nanowires have an average aspect ratio of about 50 to about 500.

24. A fluid concentrated dispersion according to any one of claims 16 to 23, comprising about 0.25% by weight of a polymer dispersant to about 20% by weight of a polymer dispersant relative to the weight of silver nanowires, wherein the polymer dispersant comprises polyvinylpyrrolidone or a copolymer thereof.

25. 0.1s －１ The fluid concentrated dispersion according to any one of claims 16 to 24, wherein the viscosity at the shear rate is about 500 cP to about 5000 cP.

26. A fluid concentrated dispersion according to any one of claims 16 to 25, further comprising a salt that provides up to about 50% by weight of silver ions relative to the weight of silver nanowires.

27. The fluid concentrated dispersion according to claim 26, further comprising a reducing agent additive at a concentration of approximately 0.001 mM to approximately 1000 mM.

28. A fluid concentrated dispersion according to any one of claims 16 to 27, which is observed to exhibit shear viscosity reduction.

29. The fluid concentrated dispersion according to any one of claims 16 to 28, wherein the silver nanowires have an average diameter of about 35 nm to about 80 nm.

30. The fluidity of the fluidity-concentrated dispersion according to any one of claims 16 to 29, wherein the fluidity is observed when a certain amount of the fluidity-concentrated dispersion is placed on a surface at an angle of 60 degrees from the horizontal.

31. A solid material containing a fluid concentrated dispersion according to any one of claims 16 to 30 after curing.

32. A fluid dispersion of silver nanowires comprising a polar solvent, at least about 5% by weight of silver nanowires, a polymer dispersant, and at least about 1% by weight of a silver salt of the weight of the silver nanowires, wherein the silver nanowires have an average aspect ratio of about 30 to about 1000, and the dispersion is 0.1 s －１ A fluid dispersion of silver nanowires having non-Newtonian viscosity at a shear rate.

33. The fluid dispersion of silver nanowires according to claim 32, which does not show visible sedimentation over a week, and dilution of the dispersion with isopropyl alcohol to a concentration of 0.1% by weight results in a stable dispersion.

34. A fluid dispersion of silver nanowires according to claim 32 or 33, comprising at least about 8% by weight of silver nanowires and about 5% to about 50% by weight of silver ions relative to the weight of the silver nanowires.

35. The fluid dispersion according to any one of claims 32 to 34, wherein the polar solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

36. The fluid dispersion according to any one of claims 32 to 34, wherein the polar solvent comprises water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof.

37. The fluid dispersion according to any one of claims 32 to 34, wherein the polar solvent comprises a monomer or oligomer that can be polymerized and / or crosslinked.

38. The fluid dispersion according to any one of claims 32 to 34, wherein the polar solvent comprises an acrylate monomer.

39. A fluid dispersion according to any one of claims 32 to 38, comprising at least about 15% by weight of silver nanowires.

40. A fluid dispersion according to any one of claims 32 to 38, comprising at least about 20% by weight of silver nanowires.

41. The fluid dispersion according to any one of claims 32 to 40, wherein the silver nanowires have an average aspect ratio of about 50 to about 500.

42. A fluid dispersion according to any one of claims 32 to 41, further comprising about 0.1% by weight of a polymer dispersant to about 5% by weight of a polymer dispersant, wherein the polymer dispersant comprises polyvinylpyrrolidone or a copolymer thereof.

43. 0.1s －１ The fluid dispersion according to any one of claims 32 to 42, wherein the viscosity at the shear rate is at least 100 cP.

44. A fluid dispersion according to any one of claims 32 to 43, further comprising a salt that provides up to about 50% by weight of silver ions relative to the weight of silver nanowires.

45. The fluid dispersion according to any one of claims 32 to 44, wherein the non-Newtonian behavior is observed to be shear viscosity reduction.

46. The fluid dispersion according to any one of claims 32 to 45, wherein the silver nanowires have an average diameter of about 35 nm to about 80 nm.

47. The fluidity of the fluidity-concentrated dispersion according to any one of claims 32 to 46, wherein the fluidity is observed when a certain amount of the fluidity-concentrated dispersion is placed on a surface at an angle of 60 degrees from the horizontal.

48. A fluid dispersion according to any one of claims 32 to 47, further comprising a reducing agent additive at a concentration of approximately 0.001 mM to approximately 1000 mM.

49. A conductive material comprising at least about 95% by weight of silver, wherein the silver has a structure formed by the reduction of a silver salt in the presence of a silver nanowire deposit comprising at least about 50% by weight of the silver, which is derived from silver nanowires having an aspect ratio of at least about 30.

50. The conductive material according to claim 49, wherein the silver is formed from a reduced silver salt and at least about 75% by weight of silver nanowires having an aspect ratio of at least about 50.

51. The conductive material according to claim 49 or 50, comprising approximately 0.1% to approximately 5% by weight of a polymer dispersant.

52. The conductive material according to any one of claims 49 to 51, wherein the silver is formed from at least about 90% by weight of silver nanowires.

53. The conductive material according to any one of claims 49 to 52, wherein the amount of silver from silver ions reduced in situ is about 5% to about 30% by weight relative to the weight of the silver nanowire.

54. Approximately 1×10 ４ A conductive material according to any one of claims 49 to 53, having a resistivity of ohms-cm or less.

55. Approximately 5×10 －５ Ohm - cm ~ approximately 4 x 10 －６ A conductive material according to any one of claims 49 to 53, having a resistivity of ohms-cm.

56. A silver paste comprising a uniform distribution of silver nanowires and optionally additional silver nanostructures, a polymer dispersant, a salt optionally providing up to about 50% by weight of metal ions relative to the weight of the silver nanowires, and a polar solvent, wherein the silver paste is stable with respect to phase separation and does not flow under zero shear, and dilution and harmless mixing of the conductive dispersion with isopropyl alcohol to a metal concentration of 0.1% by weight results in a well-dispersed solution.

57. The silver paste according to claim 56, wherein the silver nanowires have an average aspect ratio of at least about 250, and the total metal concentration is at least about 12% by weight, with at least about 80% by weight of the metal being silver nanowires.

58. The silver paste according to claim 56, wherein the silver nanowires have an average aspect ratio of about 15 to about 250, and the total metal concentration is at least about 25% by weight, with at least about 80% by weight of the metal being silver nanowires.

59. The silver paste according to claim 56, wherein the total metal concentration is at least about 40% by weight.

60. A silver paste according to any one of claims 56 to 59, comprising a polymer dispersant in an amount of approximately 20% by weight or less.

61. The silver paste according to any one of claims 56 to 60, wherein the polymer dispersant comprises polyvinylpyrrolidone or a copolymer thereof.

62. The silver paste according to any one of claims 56 to 61, further comprising a salt that provides up to about 50% by weight of silver ions relative to the weight of silver nanowires.

63. A silver paste according to any one of claims 56 to 62, which can be spread by the application of shear and does not flow on a surface inclined at 60 degrees from the horizontal.

64. The silver paste according to any one of claims 56 to 63, wherein the polar solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

65. The silver paste according to any one of claims 56 to 63, wherein the polar solvent comprises water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof.

66. The silver paste according to any one of claims 56 to 63, wherein the polar solvent comprises a monomer or oligomer that can be polymerized and / or crosslinked.

67. The silver paste according to any one of claims 56 to 63, wherein the polar solvent comprises an acrylate monomer.

68. About 5×10 －２ The silver paste according to any one of claims 56 to 67, having a resistivity of 0.0000009 ohm-cm or less.

69. A method for forming a concentrated silver nanowire dispersion, comprising evaporating a low-boiling point solvent component of a silver nanowire dispersion containing a polar solvent, wherein the low-boiling point solvent component has a boiling point of about 125°C or less at atmospheric pressure, and the removal of the low-boiling point solvent results in the formation of a well-dispersed concentrated silver nanowire dispersion having a solid concentration of at least about 5% by weight, wherein before the evaporation of the low-boiling point solvent component, the silver nanowire dispersion is a stable dispersion containing about 10% by weight or less of silver nanowires.

70. The method according to claim 69, wherein the silver salt is added to the silver nanowire dispersion having the low-boiling solvent in an amount of about 1% by weight of silver ions to about 50% by weight of silver ions relative to the weight of the silver nanowires.

71. The method according to claim 69 or 70, wherein the low-boiling point solvent is replaced with a higher-boiling point solvent, and the low-boiling point solvent includes an alcohol.

72. The method according to claim 71, wherein the alcohol is ethanol or isopropanol.

73. The method according to claim 71 or 72, wherein the solvent with a higher boiling point than described above includes water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

74. The method according to claim 71 or 72, wherein the solvent with a higher boiling point than those mentioned above includes water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof.

75. The method according to claim 71 or 72, wherein the amount of the higher boiling point solvent is selected to yield a desired silver concentration after substantial removal of the lower boiling point solvent.

76. The method according to claim 71 or 72, wherein the solvent with a higher boiling point comprises a monomer or oligomer that can be polymerized and / or crosslinked.

77. The aforementioned silver salt is silver acetate (Ag(O) ２ CCH ３ )), silver trifluoroacetate (Ag(O ２ CCF ３ )), heptafluorobutyrate silver (Ag(O ２ CC ３ F ７ )), silver lactate (Ag(O ２ CCH(OH)CH ３ )), Silver hexafluoroantimonate (AgSbF ６ ), silver fluoride (AgF), silver tetrafluoroborate (AgBF) ４ ), silver nitrate (AgNO) ３ ), silver perchlorate (AgClO ４ The method according to any one of claims 70 to 76, comprising ) or a mixture thereof.

78. The method according to any one of claims 69 to 77, wherein, after removal of low-boiling point solvent components, the concentrated silver nanowire dispersion contains about 10% by weight of silver nanowires to about 70% by weight of silver nanowires.

79. The method according to claim 78, wherein the concentrated silver nanowire dispersion contains about 2.5% to about 40% by weight of silver ions relative to the weight of the silver nanowires.

80. The method according to any one of claims 69 to 79, wherein the concentrated silver nanowire dispersion is fluid.

81. The method according to claim 80, wherein the concentrated silver nanowire dispersion exhibits non-Newtonian behavior.

82. The method according to any one of claims 69 to 81, wherein the concentrated silver nanowire dispersion is a paste.

83. A method for forming a conductive silver-based material, Forming a concentrated silver nanowire dispersion according to the method described in any one of claims 69 to 82, The concentrated silver nanowire dispersion is cured to form the conductive silver-based material. A method that includes this.

84. A method for forming a conductive solid structure containing silver, comprising heating a three-dimensional deposit containing silver nanowires and a silver salt at a temperature of at least about 120°C for at least about 5 minutes to reduce the silver salt and form the conductive solid structure, wherein the deposit before curing has at least about 25% by weight of silver nanowires and at least about 1% by weight of silver ions relative to the weight of the silver nanowires.

85. The method according to claim 84, wherein the three-dimensional deposit comprises a concentrated silver nanowire dispersion containing a polar solvent, and the method further comprises removing the polar solvent by blowing a gas over the three-dimensional deposit.

86. The method according to claim 85, wherein the polar solvent includes water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

87. The method according to claim 85 or 86, wherein the concentrated silver nanowire dispersion comprises monomers or oligomers that can be polymerized and / or crosslinked.

88. The method according to claim 87, wherein the monomer or oligomer is thermally polymerized and / or crosslinked.

89. The method according to any one of claims 85 to 88, wherein dilution of the concentrated silver nanowire dispersion with isopropyl alcohol to a concentration of 0.1% by weight results in a stable dispersion.

90. The method according to any one of claims 85 to 89, wherein the concentrated silver nanowire dispersion has non-Newtonian rheology.

91. The method according to any one of claims 85 to 90, wherein the heating is performed to a temperature of at least about 150°C for at least about 30 minutes.

92. The method according to any one of claims 85 to 91, wherein spraying is provided to facilitate solvent removal.

93. The method according to any one of claims 85 to 92, wherein reduced pressure is applied to facilitate solvent removal.

94. The method according to any one of claims 85 to 93, wherein the heating yields a cured material containing at least about 25% by weight of silver that forms the conductive solid structure.

95. The method according to claim 94, wherein the curing material comprises a polymer matrix and about 5% to about 75% by weight of an organic composition.

96. The method according to claim 94, wherein the curing material contains at least about 95% by weight of silver.

97. The method according to claim 94, wherein the curing material comprises at least about 75% by weight of silver and at least about 5% by weight of an organic composition.

98. The conductive solid structure is approximately 1 × 10 ４ The method according to any one of claims 85 to 97, having a resistivity of ohms-cm or less.

99. The conductive solid structure is approximately 5 × 10 －５ Ohm - cm ~ approximately 4 x 10 －６ The method according to any one of claims 85 to 97, having a resistivity of ohms-cm.

100. The method according to any one of claims 85 to 99, wherein the conductive solid structure is opaque and has an average thickness of at least about 2 microns.

101. A composite material having an opaque structure comprising at least about 5 wt% of a polymer matrix and at least about 25 wt% of silver, wherein the silver is formed in the form of a mass of three-dimensional silver nanowires, through which the silver salt is reduced to silver metal and contributes to a conductive composite material.

102. The composite material according to claim 101, wherein the polymer matrix is ​​thermally crosslinked.

103. The composite material according to claim 101 or 102, comprising at least about 50% by weight of silver.

104. The composite material according to claim 101 or 102, comprising approximately 75% by weight of silver to approximately 90% by weight of silver.

105. The composite material according to any one of claims 101 to 104, wherein the amount of silver derived from reduced silver is about 2% by weight to about 40% by weight relative to the silver nanowire.

106. The composite material according to any one of claims 101 to 104, wherein the amount of silver derived from reduced silver is about 2.5% to about 40% by weight relative to the silver nanowire.

107. The composite material according to any one of claims 101 to 106, wherein the silver nanowire has an aspect ratio of at least about 75.

108. The composite material according to any one of claims 101 to 107, wherein the silver nanowire has an average diameter of about 35 nm to about 80 nm.

109. The composite material according to any one of claims 101 to 108, wherein the matrix polymer is polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyamide, polyimide, polysulfone, polysiloxane, polyester, epoxy, polyurethane, polyvinyl alcohol, polyvinyl acetate, copolymers thereof, or blends thereof.

110. The composite material according to any one of claims 101 to 109, further comprising approximately 0.1% to 5% by weight of a polymer dispersant.

111. Approximately 1×10 －３ A composite material according to any one of claims 101 to 110, having a resistivity of ohms-cm or less.

112. Approximately 5×10 －５ Ohm - cm ~ approximately 4 x 10 －６ A composite material according to any one of claims 101 to 110, having a resistivity of ohms-cm.

113. A dispersion of silver nanowires, comprising essentially at least about 8 wt% silver nanowires, a uniform distribution of optionally additional silver nanostructures, a polymer dispersant, an optionally silver salt providing at least about 0.5 wt% silver ions relative to the weight of the silver nanowires, and a polar solvent, wherein the dispersion is stable with respect to phase separation, and dilution and harmless mixing of the conductive dispersion with isopropyl alcohol to a metal concentration of 1 wt%, results in a well-dispersed solution.

114. The silver nanowire dispersion according to claim 113, wherein the silver nanowire has an average aspect ratio of at least about 250, and the total metal concentration is at least about 12 weight percent.

115. The silver nanowire dispersion according to claim 113, wherein the silver nanowire has an average aspect ratio of about 15 to about 250, and the total metal concentration is at least about 25 weight percent.

116. The dispersion of silver nanowires according to any one of claims 113 to 115, wherein the total metal concentration is at least about 40 weight percent.

117. A dispersion of silver nanowires according to any one of claims 113 to 116, comprising a polymer dispersant of approximately 20 weight percent or less.

118. The dispersion of silver nanowires according to any one of claims 113 to 117, wherein the polymer dispersant comprises polyvinylpyrrolidone or its copolymer, and the silver dispersion has about 0.1% to about 5% by weight of polyvinylpyrrolidone and / or its copolymer relative to the weight of silver.

119. A dispersion of silver nanowires according to any one of claims 113 to 118, which is fluid.

120. A dispersion of silver nanowires according to any one of claims 113 to 118, which is a non-flowing paste.

121. A dispersion of silver nanowires according to any one of claims 113 to 120, wherein the dispersion does not show visible sedimentation over a week, and dilution of the dispersion with isopropyl alcohol to a concentration of 0.1% by weight results in a stable dispersion.

122. A dispersion of silver nanowires according to any one of claims 113 to 121, comprising at least about 8 weights of silver nanowires and about 5% to about 50% by weight of silver ions relative to the weight of the silver nanowires.

123. The dispersion of silver nanowires according to any one of claims 113 to 122, wherein the polar solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

124. The dispersion of silver nanowires according to any one of claims 113 to 122, wherein the polar solvent comprises water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol, butyl cellosolve, butyl carbitol, dimethylacetamide, dimethylformamide, acetonitrile, and mixtures thereof.

125. The dispersion of silver nanowires according to any one of claims 113 to 122, wherein the polar solvent comprises a monomer or oligomer that can be polymerized and / or crosslinked.

126. A dispersion of silver nanowires according to any one of claims 113 to 125, comprising at least about 15% by weight of silver nanowires.

127. A dispersion of silver nanowires according to any one of claims 113 to 125, comprising at least about 20% by weight of silver nanowires.

128. The silver nanowire dispersion according to any one of claims 113 to 127, wherein the silver nanowire has an average aspect ratio of about 40 to about 500.

129. 0.1s －１ A dispersion of silver nanowires according to any one of claims 113 to 128, wherein the viscosity at the shear rate is at least 100 cP.

130. A dispersion of silver nanowires according to any one of claims 113 to 129, further comprising a salt that provides up to about 50% by weight of silver ions relative to the weight of the silver nanowires.

131. A dispersion of silver nanowires according to any one of claims 113 to 130, wherein the non-Newtonian behavior is observed to be shear reduction.

132. The silver nanowire dispersion according to any one of claims 113 to 131, wherein the silver nanowire has an average diameter of about 35 nm to about 80 nm.

133. The dispersion of silver nanowires according to any one of claims 113 to 132, wherein the flow is observed when a certain amount of the fluid concentrated dispersion is placed on a surface at an angle of 60 degrees from the horizontal.

Images