Blended graphene dispersion

Abstract

Disclosed is a dispersion of graphene carbon nanoparticles, comprising: a solvent; greater than 1% by weight of graphene carbon nanoparticles, based on the total weight of the dispersion, the graphene carbon nanoparticles comprising thermally generated graphene carbon nanoparticles and base graphene particles; and a polymer resin dispersant. The weight ratio of the graphene carbon nanoparticles to the dispersant may be greater than 5:1, and the dispersion may have an instability index of less than 0.7. Also disclosed is a method for dispersing the graphene carbon nanoparticles in a solvent. The polymer resin dispersant is mixed into the solvent, and the graphene carbon nanoparticles comprising the thermally generated graphene carbon nanoparticles and base graphene particles are dispersed into the solvent.

Description

[0001] government contracts

[0002] This invention was made with government support under Government Contract No. NCMS FY2017 awarded by the United States Army Ground Vehicle Systems Center. The U.S. Government has certain rights in this invention.

[0003] Cross-application of related applications

[0004] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 174,799, filed on April 14, 2021, which is incorporated herein by reference. Technical Field

[0005] The present invention relates to a dispersion of graphene comprising thermally generated graphene carbon nanoparticles and at least one other type of graphene and / or graphite particles. Background Art

[0006] Graphene dispersions typically lack stability, even at low solids loadings (e.g., 1%), and typically require redispersion within hours. This makes it difficult to incorporate graphene sources into coatings or other materials to achieve their desired conductivity or mechanical properties. Summary of the Invention

[0007] Disclosed herein is a dispersion of graphene carbon nanoparticles, comprising: a solvent; greater than 1% by weight of graphene carbon nanoparticles, based on the total weight of the dispersion, the graphene carbon nanoparticles comprising thermally generated graphene carbon nanoparticles and base graphene particles; and a polymer resin dispersant. The weight ratio of the graphene carbon nanoparticles to the dispersant is greater than 5:1, and the dispersion has an instability index of less than 0.7.

[0008] Also disclosed herein is a method for dispersing graphene carbon particles in a solvent, the method comprising mixing a polymer resin dispersant into the solvent, and dispersing greater than 1% by weight of graphene carbon nanoparticles in the solvent, based on the total weight of the dispersion, the graphene carbon nanoparticles comprising thermally generated graphene carbon nanoparticles TG and base graphene particles BG. The weight ratio of the graphene carbon nanoparticles TG and BG to the dispersant is greater than 5:1, and the dispersion has an instability index of less than 0.7. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a plot of viscosity versus shear rate for various aqueous graphene dispersions.

[0010] Figure 2 is a graph showing the viscosity of various aqueous graphene dispersions.

[0011] Figure 3 is a plot of the instability index versus time for various aqueous graphene dispersions.

[0012] Figure 4 is a plot of storage and loss versus angular frequency for various aqueous graphene dispersions.

[0013] Figure 5 is an SEM image of a dried dispersion of thermally generated graphene carbon nanoparticles TG.

[0014] Figure 6 is an SEM image of a dried dispersion of a blend of thermally generated graphene carbon particles TG and base graphene carbon particles BG.

[0015] Figure 7 is an SEM image of a dried dispersion of basic graphene carbon particles BG. DETAILED DESCRIPTION

[0016] The present invention provides dispersions of thermally generated graphene carbon nanoparticles and other types of graphene or graphite particles. The thermally generated graphene carbon nanoparticles are used to achieve high stability in aqueous dispersions and solvent dispersions, for example, to achieve a loading of more than 2 wt % or 3 wt % with a small amount of dispersant. The high dispersion stability of the thermally generated graphene carbon nanoparticles, together with the interaction with other graphene sources in the solution, can stabilize other forms of graphene, thereby allowing it to be better integrated into coatings or other materials. The synergistic effect between the thermally generated graphene carbon nanoparticles and other graphene and / or graphite sources can help enable graphene / graphitic carbon to be used as nanoparticles with high electrical conductivity and high mechanical strength, to improve properties such as electrical conductivity, corrosion resistance, tensile strength, hydrogen impermeability that reduces hydrogen embrittlement, and other properties.

[0017] Introducing thermally generated graphene carbon nanoparticles into dispersions containing other graphene or graphite sources can improve slurry rheology, stability, and connectivity, thereby producing better results using the graphene sources intended to provide theoretical benefits, such as conductivity, mechanical strength, corrosion protection, etc. Compared to coatings that do not use thermally generated graphene carbon nanoparticles or use thermally generated graphene carbon nanoparticles alone, blended graphene dispersions using a combination of thermally generated graphene carbon nanoparticles and other graphene sources can improve desired performance metrics in a synergistic manner between the blended graphene sources.

[0018] The present invention provides a dispersion of two or more types of graphene carbon nanoparticles that are stable during storage and use. At least one of the nanoparticle types includes thermally generated graphene carbon nanoparticles, as described more fully below. The stable dispersion can be used in many different applications, including conductive inks, battery anode and / or cathode coatings, supercapacitors, EMI shielding, RFI shielding, thermally conductive coatings, conductive coatings, corrosion-resistant coatings, lubricants, coolants, composite materials, additive manufacturing products, etc. Conductive inks can include silver inks, medical electrode inks, silver mixtures, carbon inks, dielectric inks, zinc electrode battery inks, manganese battery inks, thermosetting carbon battery inks, IR transparent security inks, and low-resistance UV inks. Applications for conductive inks include smartphones, tablets, interactive and electrochromic displays, biomedical sensors, printed keyboards, industrial membrane switch controls, RFID tags, and other products with printed circuit systems.

[0019] Dispersion of the present invention can comprise aqueous solvent and / or organic solvent, and the graphene particles of selected amount are dispersed in described aqueous solvent and / or organic solvent.As used herein, term " dispersion " refers to that the combination of thermally generated graphene carbon nanoparticles and at least one other type of graphene particles is dispersed in medium (as solvent containing polymer dispersant), to form the substantially uniform dispersion of the graphene carbon nanoparticles of combination in whole medium, and particles are not reunited basically.As described more comprehensively below, the uniformity of dispersion can be measured by " instability index ".The existence of reunion can be determined by standard methods such as visual analysis of TEM micrographs. Reunion can also be detected by the measurement of the conductivity of the material containing graphene carbon particles by standard particle size measurement technology and the measurement of optical properties (as color, haze, blackness, reflectivity and transmittance properties).

[0020] The dispersion of the present invention comprises thermally generated graphene carbon particles (TG) and base graphene particles (BG). It has been found that the thermally generated graphene carbon particles TG facilitate dispersion and allow for a greater total loading of at least one additional type of base graphene or graphite particles BG, as described more fully below.

[0021] Based on the weight percentage of the dispersion, the total amount of graphene particles TG and BG can be at least 1 weight %, or at least 1.2 weight %, or at least 1.5 weight %, or at least 2 weight %, or at least 3 weight %, or at least 4 weight %, or at least 5 weight %, or at least 6 weight %, or at least 7 weight %, or at least 8 weight %, or more. For example, the total weight % of the graphene carbon particles can be 0.1 weight % to 15 weight %, or 0.5 weight % to 12 weight %, or 1 weight % to 10 weight %, or 2 weight % to 9 weight %, or 3 weight % to 8 weight %. In some cases, the total % of the graphene carbon particles can be 2 weight % to 9 weight %, or 3 weight % to 8 weight %, or 3 weight % to 6 weight %.

[0022] The weight ratio of thermally generated graphene carbon particles to base graphene particles TG:BG can be selected as needed to provide sufficient stability and total particle loading in the dispersion. For example, the weight ratio of TG:BG can generally be greater than 0.1:1, or greater than 0.2:1, or greater than 0.5:1, or greater than 0.8:1, or greater than 0.9:1, or greater than 1:1, or greater than 1.2:1, or greater than 1.5:1. The weight ratio of TG:BG can generally be less than 100:1, or less than 50:1, or less than 20:1, or less than 10:1, or less than 5:1, or less than 3:1, or less than 2:1, or less than 1.5:1, or less than 1.2:1. The weight ratio of TG:BG may generally range from 0.1:1 to 20:1, or 0.8:1 to 10:1, or 0.9:1 to 5:1, or 1:1 to 3:1, or 1.2:1 to 2:1.

[0023] The base graphene particles BG may include graphene particles and / or graphite particles, such as graphene produced by exfoliated graphite. Examples of commercially available exfoliated graphite graphene include XG Sciences grades M, C, R and H, such as M5, M15 and M25. Exfoliated graphite graphene is also commercially available from Global Graphene Group / Angstron Materials, First Graphene and NanoXplore under the names N002-PDRAM, N002-PDEAM, N006-P, N008-N, N008-P-10, N008-P-10, N008-P-40, N002-PS, Gi-PW-B056, PureGRAPH and GrapheneBlack. Other types of base graphene particles BG include reduced graphene oxide, graphene oxide, amine-functionalized reduced graphene oxide, amine-functionalized graphene oxide, nitrogen-doped graphene, graphene carbon black, graphene nanoribbons, single-walled carbon nanotubes, multi-walled carbon nanotubes, fullerenes, and the like.

[0024] When the base graphene carbon particles BG are in the form of nanotubes, the outer diameter of the base graphene carbon particles BG can be in the range of 0.3 nm to 100 nm, or 0.4 nm to 40 nm, the length is in the range of 0.3 nm to 50 cm, or 500 nm to 500 μm, and the length:diameter aspect ratio is in the range of 1:1 to 100,000,000:1, or 10:1 to 10,000:1.

[0025] The dispersion can be prepared by adding two types of graphene TG and BG together to water or an organic solvent, followed by mixing and optionally grinding. Alternatively, different graphene TG and BG can be added to water or an organic solvent separately and mixed separately, and then the mixture is combined together. The mixture can be optionally ground before the mixture is combined, or it can be ground after the mixture is combined.

[0026] In addition to the graphene carbon particles TG and BG of the above amounts, aqueous solvent dispersions or organic solvent dispersions can include at least one dispersant, such as the polymeric dispersants described more comprehensively below. Based on the gross weight of the dispersion, the weight % of dispersant can generally be less than 10 weight %, or less than 5 weight %, or less than 2 weight %, or less than 1 weight %, or less than 0.5 weight %. When present, the weight % of dispersant can generally be greater than 0.005 weight %, or greater than 0.01 weight %, or greater than 0.05 weight %, or greater than 0.1 weight %. The weight % of dispersant can generally be in the range of 0.01 weight % to 10 weight %, or 0.05 weight % to 5 weight %, or 0.1 weight % to 1 weight %.

[0027] The weight ratio of the combined graphene carbon nanoparticles TG and BG to the total weight of the resin dispersant can generally be greater than 4:1, or greater than 5:1, or greater than 6:1, or greater than 8:1, or greater than 10:1, or greater than 12:1, such as 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1 or higher. For example, the weight ratio of TG and BG to the resin dispersant can be at most 100:1, or at most 50:1, or at most 25:1, or at most 20:1, or at most 15:1. The weight ratio of TG and BG to the resin dispersant can generally be in the range of 5:1 to 50:1, or 8:1 to 25:1, or 10:1 to 20:1, or 12:1 to 16:1.

[0028] The thermally generated graphene carbon particles TG used in the present invention can be obtained from commercial sources. For example, they are available from Raymor Corporation (Raymor) under the name PureWave Graphene. As discussed in detail below, the thermally generated graphene carbon particles TG can be produced according to the methods and apparatus described in U.S. Patents Nos. 8,486,363, 8,486,364, and 9,221,688, which are incorporated herein by reference.

[0029] As used herein, the terms "thermally generated graphene carbon particles" and "TG" refer to particles having a carbon structure comprising one or more layers of sp 2Carbon nanoparticles having a structure of single-atom-thick planar sheets of bonded carbon atoms, the carbon atoms being tightly packed in a honeycomb lattice. The average number of stacked layers may be less than 100, for example, less than 50. In certain embodiments, the average number of stacked layers is 30 or less, such as 20 or less, 10 or less, or in some cases 5 or less. The average number of stacked layers may be greater than 2, for example, greater than 3 or greater than 4. At least a portion of the thermally generated graphene carbon particles TG may be in a sheet form that is substantially bent, curled, wrinkled, creased or buckled. The thermally generated graphene carbon nanoparticles may be turbostatic, that is, adjacent stacked atomic layers do not exhibit the ordered AB Bernal stacking associated with conventional exfoliated graphene, but exhibit disordered or non-ABABAB stacking.

[0030] The graphene carbon nanoparticles TG of heat generation can be no more than 10 nanometers, no more than 5 nanometers in the thickness measured in the direction perpendicular to the carbon atom layer, or in certain embodiments, no more than 4 nanometers, or 3 nanometers, or 2 nanometers, or 1 nanometer, as being no more than 3.6 nanometers.Graphene carbon nanoparticles TG can be 1 atomic layer to 3, 6, 9, 12, 20 or 30 atomic layers thick or thicker.The width and length that the graphene carbon particles present in the composition of the present invention are measured in the direction parallel to the carbon atom layer are at least 50 nanometers, as being greater than 100 nanometers, in some cases greater than 100 nanometers to 500 nanometers or greater than 100 nanometers to 200 nanometers.Graphene carbon nanoparticles can provide with the form of ultrathin slice, flake or sheet with relatively high aspect ratio (aspect ratio is defined as the ratio of the longest dimension of particle to the shortest dimension of particle), and described aspect ratio is greater than 3:1, as being greater than 10:1.

[0031] The graphene carbon nanoparticles TG produced by heat can have relatively low oxygen content. For example, the graphene carbon particles can have an oxygen content of no more than 2 atomic weight % even when the thickness is no more than 5 nanometers or no more than 2 nanometers, such as no more than 1.5 atomic weight % or 1 atomic weight % or no more than 0.6 atomic weight %, such as about 0.5 atomic weight %. The oxygen content of the graphene carbon particles TG produced by heat can be determined using X-ray photoelectron spectroscopy, as described in the following document: DRDreyer et al., Chem.Soc.Rev. 39, 228-240 (2010).

[0032] The BET specific surface area of ​​the thermally generated graphene carbon nanoparticles TG can be at least 50 square meters / gram, such as 70 square meters / gram to 1000 square meters / gram, or in some cases, 200 square meters / gram to 1000 square meters / gram or 200 square meters / gram to 400 square meters / gram. As used herein, the term "BET specific surface area" refers to the specific surface area determined by nitrogen adsorption according to the Brunauer-Emmett-Teller method (Brunauer-Emmett-Teller method) described in ASTM D 3663-78 standard, "Journal of the American Chemical Society", 60,309 (1938).

[0033] The Raman spectrum 2D / G peak ratio of the thermally generated graphene carbon nanoparticles TG can be at least 0.7:1, or at least 0.8:1, or at least 0.9:1, or at least 0.95:1, or at least 1:1, for example, at least 1.1:1 or at least 1.2:1. As used herein, the term "2D / G peak ratio" refers to the peak at 2692 cm -1 The 2D peak intensity at 1,580 cm -1 Such a 2D / G peak ratio may exist in graphene carbon nanoparticles having an average number of stacked layers greater than 2 (such as 3 or more stacked layers).

[0034] The thermally generated graphene carbon nanoparticles TG may have a relatively low bulk density. For example, the thermally generated graphene carbon particles TG used in certain embodiments of the present invention are characterized by having a bulk density of less than 0.2 g / cm 3 , if not exceeding 0.1g / cm 3 The bulk density (tapped density) of the graphene carbon particles is determined by placing 0.4 grams of graphene carbon particles in a glass graduated cylinder with a readable scale. The graduated cylinder is raised by about one inch and the graduated cylinder is tapped 100 times by hitting the bottom of the graduated cylinder onto a hard surface to allow the graphene carbon particles to settle in the graduated cylinder. The volume of the particles is then measured, and the bulk density is calculated by dividing 0.4 grams by the measured volume, where the bulk density is expressed in g / cm 3 express.

[0035] The compression density and densification percentage of thermally generated graphene carbon nanoparticles TG can be less than the compression density and densification percentage of graphite powder and certain types of substantially flat graphene carbon particles. Compared to graphene carbon particles that exhibit a higher compression density and a higher densification percentage, it is currently believed that lower compression density and lower densification percentage each contribute to better dispersion and / or rheological properties. In certain embodiments, the compression density of the graphene carbon particles is 0.9 or less, such as less than 0.8, less than 0.7, such as 0.6 to 0.7. In certain embodiments, the densification percentage of the graphene carbon particles is less than 40%, such as less than 30%, such as 25% to 30%.

[0036] For the purposes of the present invention, the compression density of the graphene carbon particles is calculated from the measured thickness of a given mass of particles after compression. Specifically, the measured thickness is determined by subjecting 0.1 grams of the graphene carbon particles to a cold press at 15,000 pounds of force for 45 minutes in a 1.3 cm mold, with a contact pressure of 500 MPa. The compression density of the graphene carbon particles is then calculated from this measured thickness according to the following equation:

[0037]

[0038] Then, the calculated compressed density of the graphene carbon particles determined above was compared with the density of graphite 2.2 g / cm 3 The densification percentage of graphene carbon particles is determined in the form of a ratio of .

[0039] The thermally generated graphene carbon nanoparticles TG can have a measured bulk liquid conductivity of at least 100 microSiemens, such as at least 120 microSiemens, such as at least 140 microSiemens immediately after mixing and at a later time point (such as at 10 minutes, or 20 minutes, or 30 minutes, or 40 minutes). For the purposes of the present invention, the bulk liquid conductivity of the graphene carbon particles is determined as follows. First, a sample comprising a 0.5% solution of graphene carbon particles in butyl cellosolve is sonicated for 30 minutes using a bath sonicator. Immediately after sonication, the sample is placed in a standard calibrated electrolytic conductivity cell (K=1). A Fisher Scientific AB 30 conductivity meter is introduced into the sample to measure the conductivity of the sample. The conductivity is plotted over the course of approximately 40 minutes.

[0040] The thermally produced graphene carbon nanoparticles TG can be substantially free of unwanted or harmful materials. For example, the graphene carbon particles can contain zero or only trace amounts of polycyclic aromatic hydrocarbons (PAHs), such as less than 2 wt% PAH, less than 1 wt% PAH, or zero PAH.

[0041] According to an embodiment of the present invention, thermally generated graphene carbon particles TG are made from a carbon-containing precursor material that is heated to a high temperature in a hot zone, such as a plasma. A carbon-containing precursor (such as a hydrocarbon provided in a gaseous or liquid form) is heated in the hot zone to produce graphene carbon particles in or downstream of the hot zone. For example, thermally generated graphene carbon particles can be prepared using the systems and methods disclosed in U.S. Patents Nos. 8,486,363, 8,486,364, and 9,221,688.

[0042] Thermally generated graphene carbon particles TG can be prepared using the apparatus and method described in U.S. Patent No. 8,486,363, wherein (i) one or more hydrocarbon precursor materials capable of forming dicarbon fragment species (e.g., n-propanol, ethane, ethylene, acetylene, vinyl chloride, 1,2-dichloroethane, allyl alcohol, propionaldehyde, and / or vinyl bromide) are introduced into a hot zone (e.g., a plasma); and (ii) the hydrocarbon is heated in the hot zone to a temperature of at least 1,000° C. to form graphene carbon particles. Thermally generated graphene carbon particles TG can be prepared using the apparatus and method described in U.S. Patent No. 8,486,364, wherein (i) a methane precursor material (e.g., a material comprising at least 50% methane, or, in some cases, gaseous or liquid methane having a purity of at least 95% or 99% or more) is introduced into a hot zone (e.g., a plasma); and (ii) the methane precursor is heated in the hot zone to form graphene carbon particles. Such methods can produce graphene carbon particles having at least some, and in some cases all, of the properties described above.

[0043] During the production of graphene carbon particles by the above-mentioned thermal production method, a carbon-containing precursor is provided as a feed material that can be contacted with an inert carrier gas. The carbon-containing precursor material can be heated in a hot zone, for example by a plasma system, such as a DC plasma, an RF plasma, a microwave plasma, etc. In certain embodiments, the precursor material is heated to a temperature in the range of greater than 2,000°C to 20,000°C or higher, such as 3,000°C to 15,000°C. For example, the temperature of the hot zone can be in the range of 3,500°C to 12,000°C, such as 4,000°C to 10,000°C. Although the hot zone can be generated by a plasma system, it should be understood that any other suitable heating system can be used to generate the hot zone, such as various types of furnaces, including electrically heated tubular furnaces, etc.

[0044] The gaseous stream may be contacted with one or more quench streams injected into the plasma chamber through at least one quench stream injection port. The quench stream may cool the gaseous stream to promote the formation of graphene carbon particles or control the particle size or morphology of the graphene carbon particles. In certain embodiments of the present invention, after the gaseous product stream is contacted with the quench stream, the ultrafine particles may pass through a converging member. After the graphene carbon particles leave the plasma system, the graphene carbon particles may be collected. Any suitable method may be used to separate the graphene carbon particles from the gas stream, such as a bag filter, a cyclone separator, or deposition on a substrate.

[0045] Without being bound by any theory, it is believed at present that the method for above-mentioned heat manufacturing graphene carbon nanoparticles TG is particularly suitable for producing the graphene carbon nanoparticles of the combination with relatively low thickness and relatively high aspect ratio and relatively low oxygen content as described above.In addition, it is believed at present that such method produces a large amount of graphene carbon nanoparticles with substantially bending, curling, crease or buckling morphology (referred to herein as " 3D " morphology), rather than mainly producing the particle with substantially two-dimensional (or flat) morphology.This characteristic is considered to be reflected in the compression density characteristic described previously and is considered to be beneficial in the present invention, because it is currently believed that, when the significant part of graphene carbon particle has 3D morphology, " edge to edge " and " edge to face " contact between the graphene carbon particle in composition can be promoted.Think this is because compared to the particle with two-dimensional morphology, the particle with 3D morphology is unlikely to agglomerate (due to lower van der Waals force) in composition. Furthermore, it is currently believed that even in the case of "face-to-face" contact between particles with 3D morphology, since a particle can have more than one face plane, the entire particle surface is not involved in a single "face-to-face" interaction with another single particle, but can instead participate in interactions with other particles, including other "face-to-face" interactions in other planes. Therefore, graphene carbon particles with 3D morphology can provide good electrical and / or thermal conductive pathways in dispersions and can be used to achieve electrical and / or thermal conductive properties. Furthermore, the 3D morphology can provide superlubricity in certain formulations.

[0046] Graphene carbon nanoparticles TG and / or BG can be ground to improve their dispersibility and / or stability in the composition. Various different types of grinding techniques can be used, such as solid state grinding, ball milling, dry ball milling, Eiger milling, LAU milling, Cowles blade milling, etc.

[0047] In addition to graphene carbon nanoparticles TG and BG, dispersion can also include various types of resin dispersants. Resin can improve the dispersibility and / or stability of graphene carbon nanoparticles in dispersion. For example, resin dispersants can include addition polymers comprising the residue of vinyl pyrrolidone, such as polyvinyl pyrrolidone (PVP). The weight-average molecular weight of PVP can be at least 1,000 g / mol, such as at least 3,000 g / mol, such as at least 5,000 g / mol. The weight-average molecular weight of PVP can be no more than 5,000,000 g / mol, such as no more than 4,000,000 g / mol, such as no more than 3,000,000 g / mol, such as no more than 2,000,000 g / mol. The weight average molecular weight of PVP may be 1,000 g / mol to 5,000,000 g / mol, such as 1,000 g / mol to 4,000,000 g / mol, such as 1,000 g / mol to 3,000,000 g / mol, such as 1,000 g / mol to 2,000,000 g / mol.

[0048] For example, the resin dispersant can include a combination of lauryl methacrylate (LMA) and vinyl pyrrolidone (VP) resin. Conventional free radical polymerization chemistry can be used to synthesize LMA-VP copolymers. In such formulations, LMA can generally account for 10% to 90% by weight, and VP can generally account for 10% to 90% by weight. For example, LMA can be in the range of 40% or 50% to 85% by weight, and VP can be in the range of 15% to 50% or 60% by weight. In certain embodiments, LMA can account for about 75% by weight, and VP can account for about 25% by weight. The resin dispersant can promote dispersibility and stability in both ground and non-ground graphene carbon nanoparticle dispersions.

[0049] For example, the resin dispersant may comprise an addition copolymer comprising residues of stearyl acrylate (SA) and vinyl pyrrolidone (VP). Conventional free radical polymerization chemistry may be used to synthesize the SA-VP copolymer. In such formulations, SA may typically comprise 10% to 90% by weight, and VP may typically comprise 10% to 90% by weight. For example, SA may comprise 40% or 50% to 85% by weight, and VP may comprise 15% to 50% or 60% by weight. In certain embodiments, SA may comprise approximately 75% by weight, and VP may comprise approximately 25% by weight.

[0050] Dispersant resins enhance the dispersion stability of graphene carbon nanoparticles and can expand the use of such nanoparticles in applications such as conductive inks, battery manufacturing, thermally conductive coatings, conductive coatings, EMI and RFI shielding coatings, anti-corrosion coatings, lubricants, composites, 3-D printing, etc. Advantages of the dispersants of the present invention can include extended shelf life, high graphene carbon nanoparticle loading, and dispersions that remain stable at room and elevated temperatures.

[0051] Graphene carbon nanoparticles and resin dispersants can be added to various types of solvents to produce the dispersion of the present invention. Suitable solvents include aqueous solvents and organic solvents, such as N-methyl-2-pyrrolidone (NMP), oil, benzyl alcohol, diethylene glycol monoethyl ester (DE) acetate, butyl cellosolve, triethyl phosphate, etc.

[0052] Therefore, the graphene carbon nanoparticles TG and BG of the combination of the present invention can be dispersed in various types of aqueous solvents and organic solvents with relatively large amounts, to produce a dispersion of the graphene carbon particles TG and BG of the combination with relatively high loadings compared to the dispersion of conventional graphene carbon particles BG. For example, graphene carbon particles TG and BG can account for at least 1 weight % of the total combined weight of solvent and graphene carbon particles. For example, graphene carbon particles can account for at least 1.5 weight % or at least 2 weight % or at least 3 weight % or at least 6 weight % of dispersion. For example, in a water-based solvent dispersion, graphene carbon particles TG and BG can be dispersed with up to 8 weight % or up to 10 weight %, up to 12 weight % or higher. In organic solvent dispersions such as NMP, graphene carbon particles TG and BG can be present with up to 8 weight % or up to 10 weight % or up to 12 weight % or higher.

[0053] Instability index analysis can be used for the accelerated assessment of long-term stability, which measures dispersion sedimentation at a specified centrifugal speed and temperature. Unless otherwise specified in this specification or claims, "instability index" is measured as follows: a dispersion sample is loaded into a centrifuge, and a pulsed near-IR light at 865 nm is transmitted through the sample. During centrifugation, the near-IR light transmitted through the sample is measured using a dispersion analyzer sold by LuM GmbH under the name LUMiSizer Model 611. During centrifugation for approximately 20 minutes to 35 minutes, at a relative centrifugal acceleration (RCA) of 2202, measurements are made at 25 ° C and a centrifugal speed of 4000 rpm. The transmission level at the beginning of centrifugation is compared with the transmission level at the end of the 20-minute period, and the instability index is calculated by normalizing the change in the transmission level recorded. The reported instability index is a dimensionless number between 0 and 1, where "0" refers to that the particle concentration does not change, and "1" refers to that the dispersion has completely separated. Relatively unstable dispersions exhibit higher transmittance increases due to significant phase separation of graphene carbon nanoparticles and solvent, while relatively stable dispersions exhibit lower transmittance increases due to less phase separation. The software tool calculates the instability index. The article entitled "Instability Index" (T. Detloff, T. Sobisch, D. Lerche, "Instability Index, Dispersion Letters Technical", T4 (2013) 1-4, updated 2014) provides A description of how the software tool determines the instability index is provided herein, which is incorporated herein by reference. The instability index of an aqueous dispersion of graphene carbon nanoparticles can typically be less than 0.7, such as less than 0.6, or less than 0.5, or less than 0.4, or less than 0.3, or less than 0.1. The instability index of a dispersion of graphene carbon nanoparticles in an oil solvent can typically be less than 0.5, such as less than 0.4, or less than 0.3, or less than 0.2, or less than 0.1.

[0054] The instability index may be at least 10% lower, e.g., at least 50% lower, or at least 100% lower, or at least 300% lower, or at least 500% lower than a similar dispersion containing only basic graphene carbon particles BG.

[0055] Compared to a similar solvent mixture containing only basic graphene carbon nanoparticles BG, a solvent mixture containing a combination of thermally generated graphene carbon particles TG and basic graphene particles BG can have a lower viscosity. For example, at a total loading of 1% by weight of graphene carbon nanoparticles, the combined TB / BG particles can result in a solvent dispersion with a viscosity that is at least 10% or 20% lower than that of a similar solvent dispersion containing only BG particles. Viscosity can be measured by standard techniques using an Anton Paar MCR 302 and a CP50-1 TG measuring cone to collect rheological measurements. Viscosity measurements at a shear rate of 10 Hz can be used for comparison of dispersion rheology.

[0056] The graphene carbon nanoparticle dispersion can be added to various base formulations, for example, by stirring, shaking, grinding, milling, etc. As described above, the base formulation to which the graphene carbon nanoparticle dispersion can be added can include various types of inks, coatings, lubricants, etc.

[0057] The following examples illustrate the present invention, which, however, should not be considered as limiting the invention to its details. Unless otherwise indicated, all parts and percentages in the following examples and throughout the specification are by weight.

[0058] Examples

[0059] Using a pigment and dispersant weight ratio TG and BG: dispersant of 14: 1, an aqueous dispersion weighing 1500g was produced, comprising thermally generated graphene particles TG and / or base graphene particles BG, with a total solid loading between 3% and 6% by weight depending on the formulation. The graphene carbon source comprises thermally generated graphene carbon nanoparticles TG sold under the names Raymor PureWave graphene nanosheets and XG Sciences M25 exfoliated graphite graphene nanosheets BG. The dispersant is a polyvinyl pyrrolidone with a molecular weight close to 1.3MDa. Before being transferred to an Egger grinder with a 250mL grinding chamber volume, the dispersion was first mixed for approximately 60 minutes in a suitable amount of water at 500rpm and 1000rpm using a Cowles blade. The grinding media used during the grinding step was approximately 1.0mm (Zirmil Y) in size and was added to the grinding chamber to account for approximately 80% of the total volume. The dispersion was ground at 2000rpm for 15 minutes.

[0060] Table 1 lists the particle size distribution of the aqueous dispersion after milling in an Egger mill with a residence time of 15 minutes, showing that solutions containing M25 generally correspond to larger particle sizes. In Table 1, D10 indicates that 10% of the particles are less than or equal to the specified size, D50 indicates that 50% of the particles are less than or equal to the specified size, and D90 indicates that 90% of the particles are less than or equal to the specified size.

[0061] Table 1

[0062] Particle size distribution of different graphene dispersions in aqueous solution

[0063]

[0064] Particle sizes collected using a Mastersizer 2000 with a Hydro 2000S(A) accessory using the Universal (Spherical) analysis model.

[0065] Figure 1 Rheological properties are provided for 3 wt % aqueous graphene dispersions of (·) TG Raymor PureWave Graphene, (+) BG XG Sciences M25 exfoliated graphite graphene, (■) 1:1 TG:BG and (▲) 1:3 TG:BG weight ratios of TG Raymor PureWave Graphene and BG XG Sciences M25 exfoliated graphite graphene, and (◆) 1:3 TG:BG TG Raymor PureWave Graphene and BG XG Sciences M25 exfoliated graphite graphene. All dispersions contain a polyvinylpyrrolidone dispersant with a graphene / dispersant weight ratio of 14:1. The dispersions were prepared using an Egger mill at 2000 rpm with a 15 minute residence time.

[0066] Figure 2 Viscosity measurements of aqueous dispersions containing varying amounts of BG XGSciences M25 exfoliated graphite graphene carbon, TG Raymor PureWave graphene carbon, and dispersant are provided, with total TG and BG solids at 3 w% or 6 wt%. Figure 1 The rheological properties shown in Figure 2 The viscosity measurements shown in were measured by standard procedures using an Anton Paar MCR 302 and a CP50-1 TG measuring cone as described above.

[0067] like Figure 1 and Figure 2As shown, the 3wt% dispersion of BG XG Sciences M25 graphene produces extremely low viscosity. On the other hand, the similar wt% dispersion of TG Raymor Purewave graphene produces significantly higher viscosity. The viscosity of the 1:1 blend of two TG / BG graphene dispersions produces a lower but similar (order of magnitude) viscosity than the viscosity of 100% TG Raymor PureWave graphene dispersion, which shows that the dispersion rheology is dominated by that material, even if half of the TG Raymor PureWave graphene is present by weight. If no synergistic effect occurs, the viscosity of the blended graphene carbon dispersion will be expected to be approximately half between the viscosity of the dispersion containing only TG Raymor PureWave graphene and the viscosity of the dispersion containing only BG XG Sciences M25 graphene. This higher than expected viscosity of the blend of two TG and BG graphene carbon sources in different ratios demonstrates a significant interaction between the two graphene sources, which produces a much higher viscosity than the viscosity predicted with the graphene material (XG Sciences M25). In addition, increasing the total solids of the 1:3 blend of TG Raymor PureWave / BG XG Sciences M25 graphene from 3 wt% to 6 wt% returned the viscosity to that of the 1:1 TG Raymor PureWave / BG XG Sciences M25 graphene dispersion. In both cases, the total content of TG Raymor PureWave graphene was approximately 1.4 wt% to 1.5 wt%. This further supports the view that TG graphene has a strong impact on the overall viscosity of the dispersion. Although both the 3 wt% 1:1 blend and the 6 wt% 1:3 blend have close to the same concentration of TG Raymor PureWave graphene, both dispersions contain different amounts of other components, such as dispersant (0.2 wt% vs. 0.4 wt%, respectively) and BG XG Sciences M25 graphene (1.6 wt% and 4.2 wt%, respectively).

[0068] Figure 3Shown are the instability indices for 3 wt % aqueous graphene dispersions containing (·) TG Raymor PureWave graphene, (+) BG XG Sciences M25 graphene, (■) blends of TG Raymor PureWave graphene and BG XG Sciences M25 graphene in weight ratios of 1:1 and (▲), and (◆) a 6 wt % aqueous dispersion of 1:3 TG Raymor PureWave graphene and BG XG Sciences M25 graphene. All dispersions contained a polyvinylpyrrolidone dispersant with a graphene / dispersant ratio of 14 / 1. The dispersions were prepared by an Egger mill at 2000 rpm with a 15 minute residence time. The instability indices were measured at 4000 rpm over time at 25° C. Figure 3 The instability index values ​​shown are measured using the centrifuge and pulsed near-IR light procedure described above.

[0069] like Figure 3 As shown, the 1:1 TG PureWave / BG M25 blended graphene dispersion has a high stability over time similar to the stability of an equal weight % graphene dispersion containing only TG Raymor PureWave graphene. When the ratio of TG PureWave to BG M25 is reduced from 1:1 to 1:3, the stability decreases significantly at a constant total solid loading of 3 wt% in the dispersion, indicating that the stabilizing effect provided by TG Raymor PureWave graphene is limited to a ratio closer to 1:1. Increasing the weight % of total graphene in the unstable solution can still produce an unstable dispersion, as evidenced by the instability index of the 1:3 TG PureWave / BG M25 graphene dispersion at 6 wt% compared to the instability index of the 3 wt%. Reducing the P:B from 14 to 3 can further stabilize the 1:3 TG PureWave / BG M25 graphene dispersion. However, this example provides graphene dispersions containing other BG graphene sources for high P:B to highlight the stabilizing effect of TG PureWave graphene.

[0070] Figure 4Figure 2 is a graph of the storage (closed shape) and loss (open shape) moduli as a function of angular frequency for 3 wt% total solid loading of (■, □) TG PureWave thermally produced graphene, (▲, △) BG XG Sciences M25 exfoliated graphene, and (◆, ◇) 1: 1 w / w blend of TG PureWave and BG M25 graphene at a shear strain of 1%. Oscillatory rheology measurements were performed on TG and 1: 1 w / w blended graphene dispersions using an Anton Parr PP50 parallel plate spindle, while oscillatory rheology data were performed on M25 graphene dispersions using a PP25 parallel plate spindle. A list of all terms and vocabulary can be found in ISO 6721-10, and the method for data collection follows ASTM D7271-06 or ASTM D4440-15. Oscillatory measurements were performed by measuring the complex viscosity at different shear strain values ​​between 0.1% and 100%. The complex viscosity and torque felt by the spindle were plotted as a function of shear strain, and then a specific shear strain percentage was selected at the highest torque felt in the linear region of the complex viscosity. Within that shear strain (1%), the angular frequency was 0.1 rad s -1 With 100rad s -1 The values ​​were varied between , and the storage modulus and loss modulus measurements were collected.

[0071] The flat curves of G' versus ω for both TG PureWave and 1:1 TG PureWave / BG M25 graphene dispersions indicate the strong 3-D carbon network formed by the stabilizing effect of TG PureWave graphene. In contrast, the BG M25 graphene dispersion shows a high stability from 10 rad s -1 The initial slope increases rapidly, indicating carbon network breakdown and rheological properties dominated by the solvent and polymer matrix. No angular frequency values ​​were observed where the carbon network of TG PureWave or 1:1 TG PureWave / BGM25 was disrupted, highlighting the robust graphene dispersion capabilities of the TG PureWave formulations. Data collected for TG PureWave and 1:1 TG PureWave / BGM25 graphene dispersions at angular frequencies between 0.1 rad / s and 100 rad / s, combined with instability measurements of these dispersions and SEM images of dried powders of the dispersions described below, support the increased stability of these dispersions from a stronger particle network compared to the M25 dispersion.

[0072] Figure 5 is an SEM image of a dried dispersion of 3 wt% TG PureWave, showing a uniform, well-connected dispersion of small particles of thermally generated graphene TG.

[0073] Figure 6 is an SEM image of a dried dispersion of 3 wt% 1:1 TG PureWave / BG M25, showing a uniform, well-connected dispersion of small particles of thermally generated graphene with larger M25 exfoliated graphene particles.

[0074] Figure 7 is an SEM image of a dried dispersion of 3 wt% BG XG Sciences M25 exfoliated graphene, showing a poorly connected dispersion of larger graphene particles with a flaky appearance.

[0075] Will Figure 5-7 The SEM samples shown in the figure were dispersed, then cast and allowed to dry on aluminum stubs with carbon tape. The samples were then coated with Au / Pd for 20 seconds and analyzed in a Quanta 250 FEG SEM under high vacuum. The accelerating voltage was set to 10.00 kV and the spot size was 3.0.

[0076] Those skilled in the art will appreciate that, based on the foregoing disclosure, many modifications and variations are possible without departing from the broad inventive concepts described and exemplified herein. Therefore, it should be understood that the foregoing disclosure is merely illustrative of various exemplary aspects of the present application, and that those skilled in the art can readily make many modifications and variations within the spirit and scope of the present application and the appended claims.

[0077] For the purpose of detailed description, it should be understood that, unless clearly pointed out to the contrary, the present invention can take various alternative variations and step sequences. In addition, except in any operating examples or when indicated otherwise, all numerals such as those numerals of expression value, amount, percentage, scope, sub-range and fraction can be interpreted as starting with the word "about", even if the term does not clearly appear. Therefore, unless indicated to the contrary, the numerical parameters set forth in the following description and the appended claims are approximate values ​​that can be changed according to the desired properties obtained by the present invention. Minimally, and without attempting to limit the scope of the principle of equivalents applied to claims, each numerical parameter should at least be interpreted according to the number of reported significant digits and by applying general rounding technology. In the case of describing closed or open numerical ranges herein, all numerals, values, amounts, percentages, sub-ranges and fractions within or covered in the numerical range will be considered as specifically included in the original disclosure of the application and belong to the original disclosure, as if these numerals, values, amounts, percentages, sub-ranges and fractions have been clearly written out in their entirety.

[0078] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0079] As used herein, unless otherwise specified, plural terms may encompass their singular counterparts, and vice versa, unless otherwise specified. Additionally, in this application, the use of "or" means "and / or" unless expressly specified otherwise, even though "and / or" may be explicitly used in certain contexts.

[0080] As used herein, "including," "containing," and similar terms are understood in the context of this application to be synonymous with "comprising" and are therefore open-ended and do not exclude the presence of additional, undescribed or unrecited elements, materials, ingredients, or method steps. As used herein, "consisting of" is understood in the context of this application to exclude the presence of any unspecified elements, ingredients, or method steps. As used herein, "consisting essentially of" is understood in the context of this application to include the specified elements, materials, ingredients, or method steps "and those elements, materials, ingredients, or method steps that do not materially affect the basic and novel characteristics of what is described."

[0081] While specific embodiments of the present invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that numerous changes in detail may be made without departing from the invention as defined in the appended claims.

Claims

1. A dispersion of graphene carbon nanoparticles, comprising: solvents; greater than 1 wt% of graphene carbon nanoparticles based on the total weight of the dispersion, the graphene carbon nanoparticles including thermally generated graphene carbon nanoparticles TG and base graphene particles BG; and A polymer resin dispersant, wherein the weight ratio of the graphene carbon nanoparticles TG and BG to the dispersant is greater than 5:1, and the instability index of the dispersion is less than 0.7; and The weight ratio of the thermally generated graphene carbon nanoparticles TG to the base graphene particles BG is greater than 1.2:

1. 2 . The dispersion according to claim 1 , wherein the thermally generated graphene carbon nanoparticles TG comprise more than 0.5 wt %, based on the total weight of the dispersion.

3. The dispersion according to claim 1, wherein the total amount of graphene carbon nanoparticles TG and BG is at least 3 wt%, based on the total weight of the dispersion, and the instability index is less than 0.

3.

4. The dispersion according to claim 1, wherein the weight ratio of the total graphene carbon nanoparticles TG and BG to the dispersant is greater than 10:

1.

5. The dispersion according to claim 1 , wherein the Raman 2D:G peak ratio of the thermally generated graphene carbon particles TG is at least 0.9:1, and the instability index of the dispersion is less than the instability index of the same dispersion consisting only of the base graphene particles BG, the amount of the base graphene particles BG being equal to the total weight of the thermally generated graphene carbon nanoparticles TG and the base graphene particles BG.

6. The dispersion according to claim 1, wherein the viscosity of the dispersion is greater than the viscosity of the same dispersion consisting only of the base graphene particles BG, the amount of the base graphene particles BG being equal to the total weight of the thermally generated graphene carbon nanoparticles TG and the base graphene particles BG. 7 . The dispersion according to claim 1 , wherein the base graphene particles BG comprise graphene oxide, reduced graphene oxide, functionalized graphene, graphenized carbon black, graphene nanoribbons, carbon nanotubes and / or fullerenes.

8. The dispersion of claim 1, wherein the thermally generated graphene carbon nanoparticles are generated at a temperature of at least 3500°C.

9. The dispersion of claim 1 , wherein the thermally produced graphene carbon particles are turbostratic and have a BET specific surface area of ​​at least 70 m 2 / g, an average aspect ratio greater than 3:1 and a Raman 2D:G peak ratio of at least 0.9:

1.

10. The dispersion according to claim 1, wherein the thermally generated graphene carbon nanoparticles TG and BG are milled.

11. The dispersion of claim 1 , wherein the dispersant comprises an addition polymer comprising the residue of vinyl pyrrolidone.

12. The dispersion of claim 11, wherein the vinyl pyrrolidone comprises polyvinyl pyrrolidone.

13. The dispersion of claim 1, wherein the solvent comprises water.

14. The dispersion of claim 1, wherein the solvent comprises an organic solvent.

15. A method for dispersing graphene carbon particles in a solvent, the method comprising: mixing a polymer resin dispersant into the solvent; as well as Based on the total weight of the dispersion, more than 1 wt% of graphene carbon nanoparticles are dispersed into the solvent, wherein the graphene carbon nanoparticles include thermally generated graphene carbon nanoparticles TG and base graphene particles BG, wherein The weight ratio of the graphene carbon nanoparticles TG and BG to the dispersant is greater than 5:1, and the instability index of the dispersion is less than 0.7, and the weight ratio of the thermally generated graphene carbon nanoparticles TG to the base graphene particles BG is greater than 1.2:

1. 16 . The method according to claim 15 , wherein the weight ratio of the total graphene carbon nanoparticles TG and BG to the dispersant is greater than 10:

1.

17. The method according to claim 15, wherein the Raman 2D:G peak ratio of the thermally generated graphene carbon particles TG is at least 0.9:1, and the instability index of the dispersion is less than the instability index of the same dispersion consisting only of the base graphene particles BG, the amount of the base graphene particles BG being equal to the total weight of the thermally generated graphene carbon nanoparticles TG and the base graphene particles BG.

18. The method according to claim 15, wherein the viscosity of the dispersion is greater than the viscosity of the same dispersion consisting only of the base graphene particles BG, the amount of the base graphene particles BG being equal to the total weight of the thermally generated graphene carbon nanoparticles TG and the base graphene particles BG.

19. The method of claim 15, wherein the thermally generated graphene carbon nanoparticles TG and BG are milled.

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