Silver nanowires with low load osmotic conductivity and silver nanowire conductive polymer composites coated with noble metals

Abstract

Composite materials in which silver nanowires coated with a noble metal are supported in a polymer are described. The composites may have a resistivity of no more than about 100 ohm-cm, or from about 100 ohm-cm to about 1 * 1011 ohm-cm, depending on the amount of noble metal coated silver nanowires supported in the polymer. The silver nanowire coated with the noble metal may be a silver nanowire coated with platinum. Metal particulates, such as silver flakes or silver particles, may be added to the composite material to achieve desired properties. Composite precursor compositions and methods of making composite materials are described.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 414,143 filed on October 7, 2022 by Virkar et al. and entitled “Silver Nanowires and Silver Nanowire Conductive Polymer Composites Coated with Precious Metals Having Low Loading Percolation Conductivity”, which is incorporated herein by reference. Technical Field

[0003] The present invention relates to composite materials of silver nanowires coated with a noble metal loaded in a polymer, in which relatively low resistivity values ​​can be achieved. The present invention further relates to composite precursor compositions having a relatively moderate loading of silver nanowires coated with a noble metal in composition and methods of forming the composite precursor compositions, the composite precursor compositions being cured to form composites. Background Art

[0004] The development of silver nanowires for forming transparent conductive films has attracted great attention. The one-dimensional nature of metal nanowires can be used to form conductive networks with sparse metal loading. For the formation of conductive composites, higher particle loadings can be used because transparency is generally not a concern, especially if transparency is not a concern. The establishment of conductive networks presents different challenges in thicker structures with three-dimensional configurations. Generally speaking, conductive composites are formed using silver particles or carbon conductors as, for example, antistatic materials or other similar uses to provide mechanical strength and conductivity. Summary of the invention

[0005] In a first embodiment, the present invention relates to a composite material comprising silver nanowires coated with a precious metal and a polymer matrix combined to form the composite material. The composite material may have a resistivity of no more than about 100 ohm-cm, or no more than about 1 ohm-cm. The composite material may include about 0.01 wt % to about 40 wt %, or about 0.1 wt % to about 20 wt % of the silver nanowires coated with the precious metal. In some embodiments, the silver nanowires coated with the precious metal may include silver nanowires coated with platinum. In some embodiments, the composite material may include at least about 90 wt % of the polymer matrix. Other metal particles may be added to the composite material, for example, in an amount not exceeding about the weight of the silver nanowires coated with the precious metal. The composite material may be configured as a heater in which the composite material is in contact with two bus bars of opposite polarity so that current flows between the bus bars when a voltage is applied.

[0006] In another embodiment, the present invention relates to a composite material comprising silver nanowires coated with a noble metal and a polymer matrix combined to form a composite material having a relative humidity of about 100 ohm-cm to about 1×10 11 The composite material may contain no more than about 10.0 wt %, in some embodiments no more than about 2.0 wt %, or no more than about 0.1 wt % of the silver nanowires coated with the precious metal. In some embodiments, the silver nanowires coated with the precious metal may include silver nanowires coated with platinum. In some embodiments, the composite material may contain at least about 90 wt % of the polymer matrix. Other metal particles may be added to the composite material in an amount not exceeding about the weight of the silver nanowires coated with the precious metal.

[0007] In another embodiment, the present invention relates to a composite precursor composition that can be used to form a composite material. In some embodiments, the composite precursor composition can be cured to form a composite material having a resistivity of no more than about 100 ohm-cm, or no more than about 1 ohm-cm. The composite precursor composition comprises silver nanowires coated with a noble metal, which may account for about 0.01% to about 40% by weight, or about 0.1% to about 20% by weight of the solid content of the composite precursor composition. In some embodiments, the silver nanowires coated with a noble metal may include silver nanowires coated with platinum. The composite precursor composition also comprises a polymer precursor composition, which may be a monomer, an oligomer, a solid polymer, or a combination thereof dissolved in a solvent. The solid content of the composite precursor composition may constitute at least about 90% by weight of the polymer precursor composition. Other metal particles may be added to the composite precursor composition in an amount not exceeding about the weight of the silver nanowires coated with the noble metal. The composite precursor composition may be cured to form a solid material by heating, exposure to radiation, chemical treatment, exposure to water or oxygen, or a combination thereof.

[0008] In another embodiment, the present invention relates to a composite precursor composition that can be used to form a composite precursor composition having a relative humidity of about 100 ohm-cm to about 1×10 11The composite material of the resistivity of ohm-cm. The composite precursor composition comprises silver nanowires coated with a noble metal, which may account for no more than about 2.0% by weight of the solid content of the composite precursor composition, or no more than about 0.1% by weight of the solid content of the composite precursor composition. In some embodiments, the silver nanowires coated with a noble metal may include silver nanowires coated with platinum. The composite precursor composition also comprises a polymer precursor composition, which may be a monomer, an oligomer, a solid polymer, or a combination thereof dissolved in a solvent. The solid content of the composite precursor composition may constitute at least about 90% by weight of the polymer precursor composition. Other metal particles may be added to the composite precursor composition in an amount not exceeding about the weight of the silver nanowires coated with the noble metal. The composite precursor composition may be cured to form a solid material by heating, exposure to radiation, chemical treatment, exposure to water or oxygen, or a combination thereof.

[0009] In another embodiment, the present invention relates to a method for forming a composite precursor composition, the method comprising blending a dispersion of nanowires coated with a precious metal with a polymer precursor composition to form a well-mixed blend. The method can be used to form the above-mentioned composite precursor composition. In some embodiments, the composite precursor composition can be cured to form a composite material having a resistivity of no more than about 100 ohm-cm, or no more than about 1 ohm-cm. In some embodiments, the composite precursor composition can be cured to form a composite material having a resistivity of about 100 ohm-cm to about 1×10 11 Ohm-cm resistivity of composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1A Image of ActiveGrid® ink GEN5 silver nanowires obtained after heating at 200°C for about 16 hours.

[0011] Figure 1B Image of ActiveGrid® ink GEN7 silver nanowires obtained after heating at 200°C for about 16 hours.

[0012] Figure 1C Image of ActiveGrid® ink GEN8 silver nanowires obtained after heating at 200°C for about 16 hours.

[0013] Figure 1D An image of GEN5 silver nanowires coated with platinum obtained after heating at 200°C for about 16 hours. DETAILED DESCRIPTION

[0014] Composites with silver nanowires coated with precious metals (particularly platinum-coated nanowires) in polymer matrices have been formed that provide surprising multiple desired properties. Polymer composites based on silver nanowires coated with precious metals are described herein, which reach electron percolation thresholds to provide good conductivity at low metal loading levels. It was surprisingly found that nanowires coated with precious metals (particularly platinum) can have significantly improved conductivity compared to uncoated nanowires for equivalent metal loadings. Although the applicant does not wish to be limited by theory, the basis for the increased conductivity of nanowires coated with platinum is unclear, but may be related to the surface of the nanowires and specific interactions with organic components in the composite. Therefore, at surprisingly low metal loadings, reasonable conductivity can be achieved, so that the mechanical properties of the composite can be substantially similar to the polymer matrix itself. Silver nanowires coated with precious metals have the additional advantage of being more stable in terms of thermal treatment even at relatively moderate (precious metal) coating levels. These unexpected advantages point to the potential expanded use of silver nanowires coated with precious metals in a range of applications that may be less desirable or impractical with uncoated silver nanowires or silver nanowires with other silver particles (e.g., silver flakes or silver particles). In addition, the precious metal coatings can provide improved chemical resistance against oxidation and corrosion. In situations where low to moderate conductivity is desired but the properties of composites with high metal loadings are not applicable, these loaded polymer composites provide the desired materials as enhanced conductive adhesives and polymer composites. The conductive composites can also effectively transfer or dissipate heat.

[0015] In the structures described herein, the material forms a three-dimensional structure. In other words, the material is formed into a structure with significant thickness. Depending on the polymer, the resulting composite may be transparent or opaque, because low metal loading may not qualitatively change the properties of the polymer. As further described below, silver nanowires have important uses in forming thin transparent conductive films. In order to form a highly transparent film, the metal nanowires are sparse so that they do not cover most of the surface. For highly transparent films, the polymer binder basically provides a consistent coating and stability for processing, so the volume percentage of the nanowires is high, but the coating maintains excellent optical properties because its thickness is generally in the nanometer range. Highly transparent conductive films with a transmittance value of at least about 90% of the conductive layer generally have a polymer overcoat so that the conductive film processing once completed stabilizes the structure. In thicker films, the metal nanowires are dispersed throughout the thicker polymer layer, so that the volume percentage of the metal is lower (possibly much lower) than in a sparse transparent film, but depending on the thickness, the total amount of the metal may be comparable or higher relative to the material area on the surface. In these three-dimensional systems, the factors that drive the percolation threshold to achieve lower resistance values ​​appear to be different from the generally two-dimensional structures of highly transparent films. In this context, percolation refers to the establishment of a suitable electrical conduction path, which involves different conductive elements that form the structure. In some embodiments, it may be desirable to use lower loading levels to provide lower resistivity values ​​while providing stability of the noble metal coating. An intermediate system with lower transmittance values ​​between 70% and 80% is described in U.S. Patent 10,487,222 to de Zeeuw et al. and entitled "Conductive Transparent Coating for Rigid and Flexible Substrates," which is incorporated herein by reference. The conductive coating in the '222 patent has more than 60% by weight of metal particles.

[0016] Polymers with relatively large loadings of metallic particles can be used to make conductive adhesives for polymer films and fillers. Conductive adhesives with high loading levels of metal particles, typically greater than 75% by weight, are presented in U.S. Pat. No. 9,589,693 to Dreezen et al. and entitled "Electrically Conductive Adhesives," which is incorporated herein by reference. Generally speaking, in order to achieve conductivity in a composite or adhesive using silver or carbon particles, the loading needs to be quite large, >30% by weight. Metal loading also helps to improve thermal conductivity. Table 1 shows a comparison of the general characteristics of different conductive fillers.

[0017] Table 1

[0018]

[0019] Silver nanowires have been successfully produced into transparent conductive coatings of high optical quality, which have desirable mechanical properties, such as stretchability and stability against repeated folding and unfolding, while maintaining electrical conductivity. With regard to transparent coatings, the use of nanowires to form transparent conductive coatings can have important applications in devices with displays and touch sensors. As the metal loading becomes higher, it is found that the resistance decreases while the transmittance of visible light decreases. In some embodiments, a metal-based transparent conductive component (e.g., a coating) includes a sparse metal conductive layer. The conductive layer is typically sparse to provide the desired amount of optical transparency through the conductive structure rather than around the conductive structure, so the metal coverage is typically on the layer of the conductive element with numerous but tiny gaps. For example, a transparent conductive coating may include metal nanowires deposited along a layer, in which sufficient contact can be provided for electron percolation to provide a suitable conduction path. The one-dimensional morphology of the nanowires helps to form a sparse metal conductive layer. In the embodiment of the transparent conductive layer, the transparent conductive coating may include a molten metal nanostructured network, which has been found to exhibit desirable electrical properties, optical properties, and mechanical properties. In a molten structure, unlike the corresponding non-molten structure, electrons can be conducted through the network rather than jumping between separate nanowires (percolation). Unless otherwise specifically stated, conductivity referred to herein refers to electrical conductivity.

[0020] The application of the applicant's melting process can be controlled to selectively deposit metal at the junctions between metal nanowires, or to form a fused mass of a less conductive structure regardless of the nanoparticles. In order to form a molten metal nanostructured network, the melting process can be controlled to deposit a desired amount of silver associated with the junction. The system can be prepared to provide thermodynamically driven melting to occur primarily at the junctions between adjacent metal nanowires, which are components that form the molten metal nanostructured network. A single solution method for forming a molten metal nanostructured layer is further described in U.S. Patent 9,183,968 B1 (hereinafter referred to as the '968 patent), issued to Li et al. and entitled "Metal Nanowire Inks for the Formation of Transparent Conductive Films with Fused Networks", which is incorporated by reference in this case. The processing described herein does not involve nanowire melting.

[0021] The synthesis of thin silver nanowires is described in U.S. Patent No. 10,714,230 B2, issued to Hu et al. and entitled "Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed From the Nanowires," which is incorporated herein by reference. High-quality silver nanowire products with small and uniform diameters and high purity are desirable for some applications in displays, but for applications with less optical requirements, lower-grade silver nanowires may be sufficient. For opaque composites, as described herein, nanowires with slightly larger diameters and lower production costs can provide desirable results, although thinner nanowires can provide a more dispersed system throughout the composite and may be desirable from a processing perspective, depending on length, stiffness, and other factors.

[0022] Applicants have previously described the synthesis of silver nanowires coated with precious metals suitable for large-scale production. See U.S. Patent No. 9,530,534 to Hu et al., entitled "Transparent Conductive Film" (hereinafter referred to as the '534 patent), which is incorporated herein by reference. For example, as shown in Figures 16 and 17 of the '534 patent, the nanowires coated with precious metals are shown to have improved stability in a transparent conductive film under accelerated wear conditions in the presence of heat and humidity.

[0023] Preferred methods for forming metal coatings on silver nanowires may involve modified galvanic replacement or direct deposition of the coating metal. In controlled galvanic replacement, gold, platinum or other noble metal ions, usually provided as metal ion complexes in solution, oxidize the silver in the wire at high temperature while being reduced to elemental noble metal. In direct deposition, a reaction solution having a dispersion of silver nanowires is formed, and a coating solution having noble metal ions is gradually added to the reaction solution. The reaction solution is maintained under reducing conditions. Hydrazine is a convenient reducing agent because its byproducts are nitrogen and water, but other reducing agents may also be used. In order to obtain a uniform coating, the coating process may be appropriately controlled. In addition to the possible use of a strong coordinating ligand and / or a polymer capping agent, control of the reaction may also involve gradually adding a metal ion complex of the coating metal to the reaction solution as a metal ion source solution. These reactions may be conveniently carried out in an aqueous solution optionally containing some alcohol or other co-solvent. The coordinating ligand may be included in a solution with the metal ion. The metal ion may be in the form of a suitable complex (e.g., PtCl6 -2 As used herein, a noble metal refers to a metal having a standard reduction potential greater than that of silver, and thus these metals include gold, platinum, iridium, rhodium, palladium, and osmium, with gold and platinum being of particular interest. The thickness of the noble metal coating can generally be adjusted during the deposition process. In order to achieve the remarkable conductivity results observed herein and the stability against various forms of degradation, the noble metal coating can be extremely thin, for example, a monolayer or a few atomic layers thick.

[0024] In general, it is desirable that the metal nanowires have an average diameter of no more than about 500 nanometers, no more than about 100 nanometers in some embodiments, no more than about 50 nanometers in some other embodiments, and no more than about 30 nanometers in other embodiments. In terms of average length, nanowires with longer lengths are expected to provide better conductivity in the network. In general, metal nanowires may have an average length of at least one micron, at least 2.5 microns in further embodiments, and about 5 microns to about 100 microns in other embodiments, but synthetic techniques developed in the future may be able to produce longer nanowires. The size of the nanowires can be reasonably controlled by adjusting the synthetic parameters. If necessary, the silver nanowires can be ultrasonically treated to break the nanowires into smaller lengths, and if necessary, this treatment can be performed before applying the precious metal coating to avoid damage to the coating. The aspect ratio can be defined as the ratio of the average length divided by the average diameter, and in some embodiments, the nanowires can have an aspect ratio of at least about 25, about 50 to about 5000 in some other embodiments, and about 100 to about 2000 in additional embodiments. One of ordinary skill in the art will recognize that other nanowire size ranges within the explicit ranges above are contemplated and fall within the scope of the present disclosure. Application of a noble metal coating does not qualitatively alter the nanowire size ranges described above.

[0025] By using a direct deposition method, a greater amount of precious metal can be deposited in a smooth coating and a stable silver metal core than can be obtained by electroplating exchange. Generally speaking, the precious metal coating may not exceed about 55% by weight, in further embodiments about 0.03% by weight to about 40% by weight, and in additional embodiments about 0.9% by weight to about 25% by weight relative to the amount of silver. As a component of the total coated nanowires, the amount of coating metal is typically about 0.02 atomic percent (atomic %) to about 35 atomic %, in further embodiments about 0.1% by weight to about 25 atomic %, and in additional embodiments about 0.5% by weight to about 20 atomic %. Assuming that the coating is uniform and has a bulk material density, the coating thickness can be roughly estimated from the weight of the coating and the average parameters of the initial nanowires. Those of ordinary skill in the art will recognize that other coating amount ranges within the above explicit ranges will be contemplated and fall within the scope of the present disclosure.

[0026] The conductive composites described herein provide another family of materials for use in devices using conductive polymer-based materials. Because the composites can exhibit good conductivity at relatively low metal loadings, the composites can have substantially similar properties to unloaded polymers. Because the composites can be formed using a wide range of polymers, the composites can similarly provide a correspondingly wide range of mechanical properties. This flexibility in composite composition design provides the ability to form a variety of desirable composite compositions.

[0027] Although silver nanowires coated with noble metals can provide significantly reduced resistance at low to moderate loadings, in embodiments where low conductivity is desired, it can be desirable to take advantage of the corrosion resistance and resistance to other attenuation pathways due to the coating. In these embodiments, the concentration of silver nanowires coated with noble metals can be reduced, nanowire morphologies with reduced conductivity can be used, and / or the polymer matrix can be selected to favor higher resistance due to inherent insulating properties and / or the nature of the interaction with the metal nanowires. These materials can be used for electrostatic discharge, grounding, or other suitable purposes.

[0028] These composite materials are suitable for forming resistive heaters. The amount of metal can be adjusted to balance the amount of current for a specific heating level. Nanowires coated with platinum can provide the advantage of being more heat resistant, so higher temperatures can be achieved with the heater without damaging the heater. Since silver nanowires coated with precious metals do not significantly change the properties of the polymer relative to the composite at lower loadings, transparent polymers can be used to form transparent heater components. For the heating component, the resistance does not need to be too low. The conductive composite is suitable for a wide range of other applications related to the use of conductive adhesives, etc.

[0029] Composite compositions and precursor compositions

[0030] The precursor composition is a depositable material that solidifies into a conductive composite loaded with silver nanowires coated with a precious metal in a polymer matrix. Curing refers broadly to the process of converting the precursor composition into a solid material of a conductive composite. Curing may refer to polymer cross-linking reactions, polymerization and / or solvent removal. After curing, the product is a conductive composite material that has significant conductivity at relatively low metal loadings in some embodiments. The polymer can be formed from a wide range of suitable polymers that may or may not be cross-linked after curing. Suitable process aids may be included in the precursor composition, for example to facilitate the deposition and / or curing process.

[0031] The precursor composition may be a liquid / ink or paste that can be appropriately deposited for a suitable application. The curing process converts the precursor composition into a solid substance. The precursor composition has the common feature of being depositable as a coating, a dispensable composition, a printed structure, an extrudable material, a spreadable paste or the like, and the rheology of the composition is selected depending on the deposition method. The precursor composition typically comprises nanowires coated with platinum and organic components, which optionally have volatile components. The organic component may comprise a monomer, an oligomer, a polymer, a dissolved polymer binder, a volatile solvent, a combination thereof, and the like.

[0032] The choice of polymer generally depends on the use of the composite. The choice of polymer is generally not limited as long as a dispersed and relatively uniform composite can be formed. Examples are described based on both hydrophilic polymers and hydrophobic polymers. The use of composites loaded with silver nanowires for forming adhesives is described in U.S. Patent Application Publication No. 2016 / 0177146A to Mun et al. and entitled "Adhesive Film and Display Member Including the Same" (hereinafter referred to as the '146 application), which is incorporated by reference in this case. The '146 application describes the use of polyacrylates, polymethacrylates, or copolymers thereof formed with each other or with different monomers. Other suitable thermoplastic polymers include, for example, polyamides, polyesters, polyethers, polyacetals, block polyester ether copolymers, acrylonitrile butadiene styrene copolymers, polyacrylates, polybutylene terephthalate, polyolefins (e.g., polyethylene and / or polypropylene (co)polymers), polyimides, polyarylene ethers, polyalkylene oxides, polystyrenes, polyether sulfones, polyurethanes, epoxy resins, and mixtures, copolymers, or blends thereof. The formation of silver nanowire composites for non-adhesive coatings is described in Cortes et al., "High-performance thermoplastic composites poly(ether ketone ketone) / silvernanowires: Morphological, mechanical and electrical properties," Journal of Non-crystal Solids, 2014, Vol. 391, pp. 106-111, which is incorporated herein by reference.

[0033] In some embodiments, the polymer precursor of the precursor composition can serve as a non-volatile solvent. Typically, the precursor composition may include no more than about 40% by weight of a volatile solvent as needed. Correspondingly, the precursor composition may include about 60% to 100% by weight of a non-volatile organic component based on the organic portion of the precursor composition. Suitable solvents should be compatible with the dissolution of the components of the polymer precursor and the dispersion of the nanowires coated with precious metals. Some monomers or oligomers may be suitable as non-volatile solvents. Volatile solvents may have a low boiling point or a high boiling point. Compared to high boiling point solvents (e.g., ethylene glycol or other polyols), low boiling point solvents (e.g., ethanol, isopropanol, etc.) can consume less energy to eventually remove the solvent. The amount of the volatile solvent can be selected based on the characteristics of the polymer precursor, for example, to provide solubility for the polymer precursor, and to be compatible with the desired processing method, for example, to adjust viscosity or other related properties. Because the silver nanowires coated with noble metals are compatible with a variety of polymers, and because the nanowires coated with noble metals are typically included at a relatively low volume percent, the precursor composition can generally be processed after forming the precursor composition similar to the unfilled polymer, as is well known in the art.

[0034] The loading of metal nanowires (silver nanowires coated with precious metals) can be driven by various parameters such as target conductivity, mechanical properties, cost and processability. At sufficient loading levels, metal nanowires cross the so-called percolation threshold, at which time the conductivity increases sharply and the resistance decreases accordingly. After the conductivity increases sharply over a certain range, the increase in conductivity with increasing load may show a relatively small slope. It may be desirable or undesirable that the metal nanowire loading is higher than the percolation threshold. In general, for the embodiments of interest herein, the metal loading in the polymer composite may not exceed about 40% by weight, in some embodiments, about 0.001% by weight (wt%) to about 30% by weight, in further embodiments, about 0.01% by weight to about 20% by weight, in some embodiments, about 0.0025% by weight to about 15% by weight, and in other embodiments, about 0.1% by weight to about 10% by weight. It should be understood that the upper and lower limits of these ranges are interchangeable, for example, about 0.01% by weight to about 10% by weight. If the conductive precursor composition has volatile components or releases other volatile byproducts during curing, the precursor composition has a correspondingly lower concentration of metal nanowires relative to the concentration of metal nanowires in the cured composite based on the corresponding organic contribution ratio (scaling). Equivalent loadings can also be provided in terms of volume percentage (based on the density of the nanowires and the resin / polymer system). In general, the metal loading in the polymer composite may not exceed about 10 volume percent, in some embodiments, from about 0.0001 volume percent (volume %) to about 10 volume percent, in further embodiments, from about 0.001 volume % to about 5 volume %, and in other embodiments, from about 0.01 volume % to about 2 volume %. As described below, for some applications, it is desirable that the conductive composite has a higher resistivity value. For these embodiments, the silver nanowires coated with the precious metal may be present in the composite at a concentration of not more than about 10 weight percent, in some embodiments, not more than about 2 weight percent, in other embodiments, not more than about 0.1 weight percent, and in further embodiments, not more than about 0.025 weight percent, and in other embodiments, not more than about 0.01 weight %, while achieving not more than about 1×10 11 Resistivity values ​​in Ohm-cm. One of ordinary skill in the art will recognize that other nanowire loading ranges within the explicit ranges above are contemplated and fall within the scope of the present disclosure.

[0035] Metal nanowires (including silver nanowires coated with precious metals) should generally be kept wet to avoid forming a state where the nanowires cannot be dispersed again. Due to the relative fragility of metal nanowires, ultrasonic treatment cannot generally be used to disperse agglomerated metal nanowires because the nanowires may break into fragments, so metal nanowires are generally processed from a dispersed state to form a well-mixed material. As described above, ultrasonic treatment can be selectively used to form shorter nanowires by fragmentation. The illustrated processing involves dispersed metal nanowires introduced at a dilute concentration. Applicants have recently discovered a processing method to form a metal nanowire dispersion at a significantly higher concentration depending on the size of the metal nanowires. See co-pending U.S. Provisional Patent Application No. 63 / 459,495 to Virkar et al., entitled "High Loadings of Silver Nanowires: Dispersions and Conductive Pastes; And Corresponding Methods" (hereinafter referred to as the '495 application), which is incorporated by reference herein. Using a higher concentration of a dispersion of the precious metal-coated nanowires may introduce some processing flexibility, but using a lower concentration of the nanowire dispersion may be suitable for forming a comparable composite with appropriate removal of the solvent at a convenient time in the process. However, in general, the dispersion of the precious metal-coated silver nanowires is admixed with the organic component and mixed thoroughly to form a precursor composition. Depending on the scale of the process, commercial mixers of appropriate size are commercially available.

[0036] The results presented herein are based on loading metal nanowires in a polymer matrix. Other metallic materials, carbon-based materials, or other filler materials and particles (non-wires) can be added with silver nanowires coated with precious metals to provide increased conductivity (electrical conductivity and / or thermal conductivity) and possible desired mechanical properties to the final composite. In some embodiments, the composite material is substantially free of other conductive metal particles and / or other carbon-based conductive particles, but there is usually a certain amount of metal particle contamination in the metal nanowires. Other particles can be other metal particles, such as metal nanoparticles other than metal nanowires, or carbon particles, such as graphite particles, carbon black, graphene sheets, fullerenes, carbon nanotubes, carbon nanofibers, etc. Suitable conductive additives include, for example, silver nanoparticles and / or silver flakes. The amount of other conductive additives is not particularly limited, but in terms of weight percentage, it is generally not more than about 5 times that of the nanowires, and in other embodiments not more than about 2 times, in further embodiments not more than about the weight percentage of the metal nanowires, and in some embodiments not more than about 0.5 times the weight percentage of the nanowires. One of ordinary skill in the art will recognize that other ranges of added conductive particles within the explicit ranges above are contemplated and fall within the scope of the present disclosure.

[0037] As mentioned above, the precursor composition may contain additional components or additives, which may be referred to as processing aids, and it should be understood that this can broadly cover various compositions covering corresponding various functions. In some embodiments, the precursor composition may generally contain up to about 10% by weight of processing aids, such as crosslinking agents, viscosity modifiers, plasticizers, hardeners (copolymer constituents), surfactants, etc. The crosslinking agent may be a thermal or UV initiator, a crosslinking reactant, etc. The choice of processing aids is generally strongly influenced by the choice of polymer and the corresponding deposition method to be used.

[0038] In general, any processing method that allows the polymer and nanowires to form a good blend may be appropriate. Metal nanowires are usually kept dispersed in the liquid used for processing to avoid agglomeration. Metal nanowires are usually dispersed in polar solvents such as alcohol or water, but are not limited by theory. Depending on the properties of the surfactant, dispersant and other components, they may also be dispersed in other solvents. If a suitable solvent is available for the polymer or polymer precursor and the dispersion of the nanowires, solution processing is usually a convenient method. In general, for nanowire suspensions, suitable solvents include, for example, water, alcohols, ketones, esters, ethers (e.g., ethylene glycol ethers), aromatic compounds, alkanes, etc. and mixtures thereof. Specific solvents include, for example, water, ethanol, isopropanol, isobutanol, tert-butanol, ethylene glycol, triethylene glycol, methyl ethyl ketone, glycol ethers, butyl carbitol (diethylene glycol butyl ether), methyl isobutyl ketone, toluene, hexane, ethyl acetate, butyl acetate, ethyl lactate, PGMEA (2-methoxy-1-methylethyl acetate), mixtures thereof, etc. Additionally, a mixture of solvent, polymer or monomer, and nanowires can be prepared, and the solvent can be removed to form a nanowire-resin system that can be further processed.

[0039] To form a conductive composite composition, a precursor composition (nanowire-polymer precursor blend) may be deposited and then cured to generate a conductive composite. Various coating methods may be suitable, such as slit coating. Spraying with a larger orifice nozzle may be suitable, considering the length of the nanowires. The paste precursor composition may be appropriately placed and spread for application, such as by extrusion. The concentration of volatile solvents and other processing aids may be appropriately adjusted to facilitate deposition while achieving the target conductive composite composition. If at least some solvent evaporation is desired during deposition, a solvent with a lower boiling point temperature may be used, while if most of the solvent removal occurs during curing, a solvent with a higher boiling point temperature may be used.

[0040] Curing can be achieved in a variety of ways, including but not limited to by heating, radiation, chemical methods, exposure to water or oxygen (which may be ambient air), or a combination thereof. Various commercial polymers crosslink in response to ultraviolet (UV) radiation. UV radiation may be applied accordingly during the curing step. The solvent may also be removed after the deposition step (e.g., by heating, reducing pressure and / or blowing). The appropriate temperature may depend on the polymer and is typically less than 250°C, and the heating time may depend on whether the polymer is thermally crosslinked and how much solvent removal occurs. In some embodiments, the polymer matrix is ​​formed by a binder polymer that is dissolved by a solvent during deposition and forms a solid polymer matrix after the solvent is removed. The polymer concentration may be selected to obtain the desired metal nanowire loading. In other embodiments, the polymer (e.g., a thermoplastic polymer) may be processed as a melt, and the metal nanowires are blended with the molten polymer. Solvents associated with a dispersion of silver nanowires coated with a precious metal may evaporate during blending with the melt. The temperature of the metal should be below the temperature at which the metal nanowires are damaged. The blended polymer melt may be extruded, cast or molded to form the resulting composite after cooling.

[0041] Conductive composite compositions, properties and applications

[0042] After curing, a conductive composite composition is formed at the location where the precursor was deposited. The overall organic composition of the conductive composite may change based on the loss of volatile components of the precursor and any reactions that occur during curing. For example, the polymerization reaction and / or the curing reaction may involve the production of gaseous or volatile byproducts based on specific chemical reactions. After curing, the silver nanowires coated with the precious metal become embedded in a solid polymer matrix. The resulting properties of the composite result from the composite composition.

[0043] Under appropriate curing conditions, silver nanowires coated with precious metals generally do not change significantly during curing, but surface interactions with various polymer components (e.g., dispersants) may or may not change. The mechanical properties of the composite can be affected to varying degrees depending on the metal loading level. At low loading levels, the mechanical properties are dominated by the polymer matrix. At higher loading levels within the ranges shown herein, the mechanical properties change to reflect the presence of the metal, depending on the polymer-metal interactions. At higher metal loadings, the thermal conductivity of the composite should be significantly higher than that reflected by the polymer matrix alone.

[0044] The weight percentage and volume percentage ranges of silver nanowires coated with precious metals in the conductive composite composition are presented above. The remaining weight and volume of the composite can be organic and optionally other modified inorganics. For example, inorganic particles such as silica, alumina or carbon fibers can be added to increase the mechanical strength of the composite. Other inorganic or organic compositions can be added to change the color. Typically, other property enhancing additives can constitute up to about 10% by volume, and in some other specific embodiments, larger amounts can be used. The polymer matrix comprises the remainder of the composite structure. The polymer matrix can include one or more chemically cross-linked polymers and can include uncross-linked polymer binders having entangled polymer chains that effectively form reversible physical crosslinks that are stable as long as the polymer is not dissolved or melted.

[0045] As shown in the following examples, silver nanowires coated with precious metals exhibit significant conductivity at low concentrations. Although silver nanowires themselves can provide excellent conductivity, at low concentrations, silver nanowires coated with precious metals exhibit conductivity that is several orders of magnitude greater than the corresponding system loaded with silver nanowires. Since the bulk conductivity is actually equal, this significant increase in conductivity at lower concentrations can provide a large number of material design options for low and medium conductivity applications. Due to the ability to introduce low concentrations of conductive fillers, the mechanical properties of the composite can be significantly closer to the mechanical properties of the unfilled polymer matrix, such as adhesion, cohesion, mechanical strength, elongation, modulus, etc. Since a wide range of polymer matrix materials are suitable, the conductive composite composition can provide desirable conductive properties over a wide range of mechanical properties.

[0046] Resistivity is also known as volume resistivity and is equal to RA / L, where R is the resistance in ohms, A is the area of ​​the conductive material, and L is the electrical conduction length along the conductive element. If A and L are in centimeters, then the resistivity p is in ohm-centimeter. The bulk resistivity of silver is reported to be 1.59×10 -6 Ohm-cm, while the bulk resistivity of platinum is about 1.09×10 -5Ohm-cm. Since the bulk resistivity of platinum is greater than that of silver, the most conductive metal, the effect of the precious metal coating is independent of the bulk resistivity property. As the metal loading increases, the increased conductivity, decreased resistivity, and ultimately irrelevant relationship of the silver nanowires coated with the precious metal for the atomic percent of the precious metal coating loading decreases, or conversely, the conductivity relative to the silver nanowires decreases if the atomic percent of the precious metal coating is large. At lower nanowire loadings, the resistivity of the composite with the precious metal-coated silver nanowires may be at least about 100 times lower, in yet other embodiments at least about 1000 times lower, and in additional embodiments at least about 1×10 4 times, and in some embodiments at least about 1×10 5 times, and in other embodiments at least about 1×10 6 The resistivity values ​​are times greater than 100%, in other words, this is the ratio of the resistivity of the composite with silver nanowires divided by the resistivity of the composite loaded with silver nanowires coated with a noble metal. At larger ratios, the electrical properties become difficult to measure, so the ultimate boundary cannot be precisely determined. As described above, these examples are consistent in that the reduction in the resistance of the silver nanowires coated with a noble metal relative to the resistance of the silver nanowires becomes increasingly significant as the metal loading decreases.

[0047] At higher metal loadings, the bulk metal conductivity is the limit to the conductivity that can be achieved, and typically the conductivity can be a reasonable multiple smaller than the bulk conductivity value. As the loading level decreases, the resistivity of the composite with the silver nanowires coated with the precious metal decreases significantly more slowly than the conductivity of the composite with the silver nanowires decreases with loading level. This difference becomes particularly evident at loading levels below about 10 wt %. This can be considered in terms of the parameters described in the previous paragraph involving the ratio of two resistivities. For example, if the resistivity value is about 10 2 Up to 10 -3 If the amount of silver nanowires coated with precious metals is of the order of magnitude 2, then relatively low loading levels can be used with appropriate processing and polymer selection.

[0048] For heater applications, the heat generated can be described in terms of surface power density, which can be evaluated as: P d =V 2 / (R · A), where V is the voltage, R is the resistance, and A is the area of ​​the heater. If V is in volts and R is in ohms, then P dThe units are Watts divided by A. Applicants have previously described the use of thin molten metal nanostructured networks based on silver nanowires coated with precious metals to form transparent heaters. See co-pending provisional patent application 63 / 441,656 to Chen et al., entitled "Stable Thin Film Heaters Based on Noble Metal Coated Silver Nanowires and Applications Thereof," which is incorporated herein by reference. As previously shown, silver nanowires coated with precious metals can exhibit greater than about 0.5 Watts per square centimeter (W / cm 2 ) (2000 W / cm2), in some embodiments greater than about 0.6 W / cm2, and in some embodiments at least about 1 W / cm2. Using the composite materials described herein, similar resistance times area values ​​can be achieved to provide comparable surface power densities to stable thicker structures. These heater assemblies can be used for transparent or opaque heaters. These structures can provide alternatives to thin transparent heaters using molten metal nanostructure networks, where each alternative can provide advantages in different scenarios.

[0049] In some embodiments, for certain applications, it is desirable to have a lower conductivity. Specifically, for electrostatic discharge, antistatic or grounding purposes, a suitable resistivity may be about 10 2 Ohm-cm to 10 11 Ohm-cm, and less than 10 2 The value of ohm-cm can be considered as conductive. Depending on the specific use of the material, the resistivity can be selected accordingly. Thus, in some applications, the resistivity can be between 100 ohm-cm and 10 8 Ohm-cm, while in other applications the desired resistivity may be about 10 6 Ohm-cm to about 10 11Ohm-cm. One of ordinary skill in the art will recognize that other ranges within these defined resistivity ranges are contemplated and fall within the scope of the present disclosure. The concentration of the silver nanowires coated with the precious metal can be reduced until the desired resistivity range is reached. In addition, other features of the composite can be selected to contribute to the low conductivity of the composite. For example, an electrically insulating adhesive can be used for the polymer matrix. For example, electrically insulating epoxies, silicones, polyurethanes, polysulfides, cyanoacrylates can be obtained from Masterbond® and DuPont. Since the slope of the resistivity change with nanowire concentration decreases over a wider concentration range, the composite composition can be effectively used to obtain higher resistance values ​​within the target range. The specific loading level can depend on the polymer and may depend on the presence of any additives.

[0050] Experiments have been conducted to form polymer composites with silver nanowires with or without platinum coating. The results are shown in the Examples. These results show that the conductivity and thermal stability of silver nanowires with platinum coating are increased.

[0051] Example

[0052] General Materials and Methods

[0053] Silver nanowires (Ag NWs) used in the following examples are available from applicant C3Nano, Inc. as a component in ActiveGrid® inks. ActiveGrid® inks include GEN5 silver nanowires having an average diameter of about 20 nm to 22 nm, GEN7 silver nanowires having an average diameter of about 18 nm, and GEN8 ActiveGrid® inks having silver nanowires having an average diameter of <16 nm. The preparation of these nanowires is described in the '230 patent cited above. Silver nanowires coated with platinum (Ag@Pt NWs) were prepared using GEN5 silver nanowires, which were coated with platinum using a direct deposition method as described in U.S. Pat. No. 9,530,534 B2 to Hu et al. and U.S. Pat. No. 10,714,230 B2 to Hu et al. The platinum coating may include about one or several monolayers of platinum on the silver nanowires.

[0054] The diluted good nanowire dispersion is blended with a monomer or polymer to form a composite. For some embodiments, the nanowires are blended with ethoxylated (20 mol %) trimethylolpropane triacrylate monomer (AM1). A blend of 3 UV photoinitiators (PI) is used to initiate polymerization of AM1, and this PI blend is called MP8. For some embodiments, the nanowires are blended with a polymer such as polylactic acid (PLA). When blending the nanowires with the polymer, the polymer is dissolved in a suitable solvent and mixed with the nanowire dispersion, and the solvent is removed by heating and / or under vacuum. For example, for nanowires blended in PLA, chloroform is used as a solvent for the polymer. The nanowires can be dispersed in alcohol or an alcohol-water solution for processing.

[0055] A composite comprising nanowires blended with monomer and photoinitiator was prepared by wetting a glass slide with the blend and then placing a second glass slide on top so that a wet film formed between the two slides. The nanowires were prepared by three passes each delivering 1.8 J / cm 2 The samples were subjected to UV light using a fusion UV system with an energy density of 100 Å / min. After the composite was cured, the sample could be removed from the glass slide. For the nanowire-PLA composite, a thin film was formed by placing a dispersion of nanowire-PLA-solvent in a flat-bottomed glass container and removing the solvent by evaporation under ambient conditions. The film could be peeled off the glass surface for evaluation.

[0056] The composites were evaluated by measuring the resistance using a two-point probe method using a silver conductor paste (DuPont TM PE828) as a trace electrode for electrical connection; the length of the silver paste is about 1 cm to 3 cm, and the width of the channel length is about 0.2 cm to 1.0 cm. Copper foil tape (3M TM Copper foil shielding tape (1182) was applied to the surface of the sample to help provide a guide and template for the silver paste. The sample was then heated at 80°C for 40 minutes to cure the paste. The resistance of each composite was measured using an electronic multimeter equipped with a pair of probes.

[0057] Example 1 - Thermal Behavior

[0058] Thermal behavior of Ag NW and Ag@Pt NW was studied. A dilute solution of the nanowires was prepared and dropped onto a glass slide. The samples were heated and images were taken at hour intervals using a magnification of 1000x and an exposure setting of 150 ms to 160 ms. The results for samples heated at 150°C are summarized in Table 2. The results for samples heated at 200°C are summarized in Table 3. Figures 1A to 1C The images of GEN5 silver nanowires, GEN7 silver nanowires and GEN8 silver nanowires obtained after heating at 200° C. for about 16 hours are shown respectively, and Figure 1D Images obtained for GEN5 silver nanowires coated with platinum are shown. Although the term melting is used in Table 3, some combination of melting, fragmentation, and oxidation was observed.

[0059] Table 2

[0060]

[0061] Table 3

[0062]

[0063] Example 2 - AgNW and Ag@Pt NW composites prepared using hydrophilic triacrylate monomer AM1

[0064] Formulations comprising GEN5 silver nanowires and GEN5 silver nanowires coated with platinum were prepared by combining 0.2 grams or 0.35 grams of each nanowire with 10 grams of triacrylate monomer AM1 and 20 milligrams of photoinitiator blend MP8. After UV curing, the top glass slide was removed and the composite structure was released from the bottom glass slide. The color of the resulting composite was reddish brown, with the composite prepared with the nanowires coated with platinum being darker than the composite prepared with the uncoated nanowires. The thickness of the composite structure was about 110 microns to about 120 microns. The resistance of each composite was measured and the results are shown in Table 4.

[0065] The results shown in Table 4 show that the conductivity of silver nanowires coated with platinum is better than that of uncoated silver nanowires. When using nanowires coated with platinum, composites prepared with 2.0 wt% NW loading can achieve resistances below 10 ohms compared to MOhms for uncoated silver nanowires.

[0066] Table 4

[0067]

[0068] 1. Unstable megaohm readings

[0069] Example 3 - AgNW and Ag@Pt NW composites prepared using PLA

[0070] As shown in Table 5, composites C1, C2, X1 and X2 (comprising GEN5 silver nanowires and GEN5 silver nanowires coated with platinum) were prepared by combining 10 grams of PLA with 0.2 grams of each nanowire. The weight percentage of nanowires in the composite was about 2% by weight. The composite was cut into different sizes and the thickness was measured. For each sample, the resistance was measured at the initial time (R0), and then measured every other day for three days (R1, R2 and R3). The samples were kept at 85°C and 85% relative humidity. Therefore, this embodiment also tests the stability of the composite under accelerated wear test conditions. Commercial testing equipment that provides heat and humidity control includes, for example, an ESPEC model BTL-433 environmental chamber (ESPEC North America, Hudsonville, Michigan, USA) or a Thermotron SM-3.5-3800 benchtop environmental chamber (Thermotron Inc., Holland, Michigan, USA). The results are shown in Table 5.

[0071] PLA / Ag samples C1 and C2 gave extremely high resistance, while PLA / Ag@Pt samples (X1 and X2) showed high conductivity when using about 2 wt% nanowire loading. It can also be noted that the PLA / Ag@PtNW composite film samples gained conductivity after treatment at 85°C and 85% relative humidity. This may be due to the percolation network undergoing some polymer reorganization and enhanced wire-to-wire contact under high humidity-high temperature conditions.

[0072] Table 5

[0073]

[0074] 1.OL = open loop, the value is too large to be measured by the instrument.

[0075] As shown in Table 6, composites M1, M2, N1 and N2 (comprising GEN5 silver nanowires and GEN5 silver nanowires coated with platinum) were prepared by combining 0.2 grams of each nanowire with 10 grams of PLA. The weight percentage of nanowires in the composite was about 2 weight %. The composite was cut into different sizes and the thickness was measured. The resistance was measured at the initial time (R0) and after one day (R1). The samples were kept at 150°C and dry conditions. The results are shown in Table 6. The results show that the composite film is stable to high temperature treatment.

[0076] Table 6

[0077]

[0078] 1.OL = Open Loop, the value is too large to be measured by the instrument.

[0079] Example 4 - AgNW and Ag@Pt NW composites prepared using AM1 and PLA

[0080] As shown in Table 7, composites including GEN5 silver nanowires and GEN5 silver nanowires coated with platinum were prepared by combining the nanowires with AM1 or PLA. The composites prepared using AM1 were UV cured as described above. The resistance of each of the coatings was measured and the results are shown in Table 7.

[0081] Table 7

[0082]

[0083] Example 5 - Ag@Pt NW composite prepared using AM1

[0084] Composite 5a was prepared by combining Ag@Pt NW with AM1 so that the normalized loading was 1.5x. Composite 5a was used to form a coating with a thickness of about 200 microns. The resistivity was measured and the results are shown in Table 8.

[0085] Table 8

[0086]

[0087] Example 6 - Effect of Silver Paste and Copper Strip on Electrical Conductivity

[0088] As shown in Table 9, composites 6 and composites 7a to 7c were prepared by combining GEN5 silver nanowires and GEN5 silver nanowires coated with platinum with AM1. The coatings of the composites were prepared as described above and maintained at _°C and _% relative humidity. For each sample, the resistance was measured at the initial time (R0), and then measured every other day for two days (R1 and R2). The coating was then configured using copper foil tape and / or silver paste to provide electrical connections. The resistance of each configuration was measured, and the results are shown in Table 9.

[0089] Table 9

[0090]

[0091] Example 7 - Applying voltage to heat

[0092] The coating of composite 7c was prepared and configured with either copper foil tape only or a combination of silver paste and copper foil tape to provide electrical connection. The coating was heated in a voltage range of 1 volt to 4 volts with the amperage set to 2. No temperature change was observed for the coating configured with copper foil tape only. A temperature change of about 10°C was observed for the coating configured with a combination of silver paste and copper foil tape. The initial resistance (at 1 volt) was about 14.5 ohms, and the final resistance (at 4 volts) was about 17.7 ohms.

[0093] The above embodiments are intended to be exemplary and not restrictive. Other embodiments also fall within the scope of the patent application. In addition, although the present invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present invention. Any of the above-mentioned documents incorporated by reference are limited so that they will not be incorporated into the target object that violates the explicit disclosure herein. In terms of describing specific structures, compositions and / or processes in this article with components, elements, ingredients or other divisions, it should be understood that the disclosure herein covers these specific embodiments; embodiments including these specific components, elements, ingredients, other divisions or combinations thereof; and embodiments consisting essentially of these specific components, ingredients, other divisions or combinations thereof and may include additional features that do not change the basic properties of the target object, as described in the discussion, unless otherwise specifically stated. The term "approximately" used in this article refers to what a person of ordinary skill in the art understands in a specific context, unless otherwise explicitly stated, otherwise it may involve measurement errors and / or reporting accuracy as understood by a person of ordinary skill in the art in the context of a specific parameter.

Claims

1. A composite material comprising silver nanowires coated with a noble metal and a polymer matrix combined to form the composite material, the composite material having a molecular weight of no more than about 1×10 11 Resistivity in ohm-cm.

2. The composite material of claim 1, having a resistivity of no more than about 100 ohm-cm.

3. The composite material of claim 2, having from about 0.01 wt% to about 40 wt% of the silver nanowires coated with a noble metal.

4. The composite material of claim 2, having from about 0.1 wt% to about 20 wt% of the silver nanowires coated with a noble metal.

5. The composite material of claim 4, having a resistivity of no more than about 1 ohm-cm.

6. The composite material of any one of claims 2 to 5, wherein the silver nanowires coated with a noble metal comprise silver nanowires coated with platinum, and the composite material comprises from about 0.5 wt % to about 10 wt % of the silver nanowires coated with platinum.

7. The composite material according to any one of claims 2 to 6, wherein the silver nanowires coated with a noble metal have an average diameter of 100 nm or less.

8. The composite material of claim 7, wherein the silver nanowires coated with a precious metal comprise no more than about 2.5 volume % of the composite material.

9. The composite material of any one of claims 2 to 8, wherein the polymer matrix constitutes at least about 90% by weight of the composite material.

10. The composite material of any one of claims 2 to 9, wherein the composite material further comprises other metal particles, the amount of the other metal particles not exceeding about the weight of the silver nanowires coated with the precious metal.

11. A heater comprising two bus bars having opposite polarities and the composite material of any one of claims 2 to 10, wherein the composite material is in contact with the bus bars so that current flows between the bus bars when a voltage is applied.

12. The composite material of claim 1, wherein the composite material has a relative humidity of about 100 ohm-cm to about 1×10 11 Resistivity in ohm-cm.

13. The composite material of claim 12, wherein the concentration of the silver nanowires coated with the noble metal does not exceed about 10.0 wt%.

14. The composite material of claim 12, wherein the concentration of the silver nanowires coated with the noble metal does not exceed about 2.0 wt%.

15. The composite material of claim 12, wherein the concentration of the silver nanowires coated with the noble metal does not exceed about 0.1 wt%.

16. The composite material of any one of claims 12 to 15, wherein the precious metal-coated silver nanowires comprise platinum-coated silver nanowires, and the composite material contains no more than about 2.0 wt. % of the platinum-coated nanowires.

17. The composite material according to any one of claims 12 to 16, wherein the silver nanowires coated with a noble metal have an average diameter of 100 nm or less.

18. The composite material of any one of claims 12 to 17, wherein the silver nanowires coated with a precious metal comprise no more than about 2.5 volume % of the composite material.

19. The composite material of any one of claims 12 to 18, wherein the polymer matrix comprises at least about 90% by weight of the composite material.

20. The composite material of any one of claims 12 to 19, wherein the composite material comprises other metal particles in an amount not exceeding about the weight of the precious metal-coated silver nanowires.

21. A composite precursor composition comprising silver nanowires coated with a noble metal and a polymer precursor composition, wherein the polymer precursor composition is a monomer, an oligomer, a solid polymer or a combination thereof dissolved in a solvent, wherein the solid content of the composite precursor composition comprises about 0.01 wt % to about 40 wt % of the silver nanowires coated with a noble metal.

22. The composite precursor composition of claim 21, wherein the solids content of the composite precursor composition comprises from about 0.1 wt% to about 20 wt% of the silver nanowires coated with a noble metal.

23. The composite precursor composition of claim 21 or claim 22, wherein the silver nanowires coated with a noble metal comprise silver nanowires coated with platinum, and the solids content of the composite precursor composition comprises from about 0.5 wt % to about 10 wt % of the platinum-coated nanowires.

24. The composite precursor composition of any one of claims 21 to 23, wherein the silver nanowires coated with a noble metal have an average diameter of 100 nm or less.

25. The composite precursor composition of any one of claims 21 to 24, wherein the solids content of the composite precursor composition constitutes at least about 90% by weight of the polymer precursor composition.

26. The composite precursor composition of any one of claims 21 to 25, further comprising a volatile solvent.

27. The composite precursor composition of any one of claims 21 to 26, wherein the composite precursor composition is capable of being cured to form a composite material having a resistivity of no more than about 100 ohm-cm.

28. The composite precursor composition of any one of claims 21 to 27, wherein the composite precursor composition is capable of being cured to form a composite material having a resistivity of no more than about 1 ohm-cm.

29. The composite precursor composition of any one of claims 21 to 28, wherein the composite precursor composition further comprises other metal particles, the amount of the other metal particles not exceeding about the weight of the precious metal-coated silver nanowires.

30. The composite precursor composition of any one of claims 21 to 29, wherein the composite precursor composition can be cured to form a solid material by heating, exposure to radiation, chemical treatment, exposure to water or oxygen, or a combination thereof.

31. The composite precursor composition of any one of claims 21 to 30, wherein the solids content of the composite precursor composition comprises no more than about 2.0 wt% of the precious metal-coated silver nanowires.

32. The composite precursor composition of any one of claims 21 to 31, wherein the solids content of the composite precursor composition comprises no more than about 0.1 wt% of the silver nanowires coated with a noble metal.

33. The composite precursor composition of any one of claims 21 to 32, wherein the silver nanowires coated with a noble metal comprise silver nanowires coated with platinum.

34. The composite precursor composition of any one of claims 21 to 33, wherein the silver nanowires coated with a noble metal have an average diameter of 100 nm or less.

35. The composite precursor composition of any one of claims 21 to 34, wherein the solids content of the composite precursor composition constitutes at least about 90% by weight of the polymer precursor composition.

36. The composite precursor composition of any one of claims 21 to 35, wherein the composite material comprises other metal particles in an amount not exceeding about the weight of the precious metal-coated silver nanowires.

37. The composite precursor composition of any one of claims 21 to 36, wherein the composite precursor composition can be cured to form a composite precursor having a relative humidity of about 100 ohm-cm to about 1×10 11 Ohm-cm resistivity of composite materials.

38. The composite precursor composition of any one of claims 21 to 37, wherein the composite precursor composition is capable of being cured to form a solid material by heating, exposure to radiation, chemical treatment, exposure to water or oxygen, or a combination thereof.

39. A method for forming a composite precursor composition, the method comprising blending a dispersion of nanowires coated with a noble metal and a polymer precursor composition to form a well-mixed blend, the polymer precursor composition being a monomer, oligomer, polymer, or combination thereof dissolved in a solvent, wherein the solids content of the composite precursor composition comprises from about 0.01 wt % to about 40 wt % of silver nanowires coated with a noble metal.

40. The method of claim 39, wherein the well-mixed admixture comprises a volatile solvent, and the method further comprises removing at least a portion of the volatile solvent to obtain a desired solids content of the composite precursor composition.

41. The method of claim 39 or claim 40, wherein the composite precursor composition is capable of being cured to form a composite material having a resistivity of no more than about 100 ohm-cm.

42. The method of claim 39 or claim 40, wherein the composite precursor composition is capable of being cured to form a composite material having a resistivity of no more than about 1 ohm-cm.

43. The method of any one of claims 39 to 42, wherein the solids content of the composite precursor composition comprises no more than about 2.0 wt% of the precious metal-coated silver nanowires.

44. The method of any one of claims 39 to 43, wherein the composite precursor composition can be cured to form a film having a thermal conductivity of about 100 ohm-cm to about 1×10 11 Ohm-cm resistivity of composite materials.

45. The method of claim 39, wherein the composite precursor composition is the composite precursor composition of any one of claims 21 to 38.

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