Dispersion

Abstract

A method for forming a liquid dispersion of 2D material / graphite nanoplatelets in an aqueous solution is disclosed. The method includes: (1) creating a dispersion medium; (2) mixing the 2D material / graphite nanoplatelets into the dispersion medium; and (3) subjecting the 2D material / graphite nanoplatelets to sufficient shear and / or crushing forces using mechanical means to reduce the particle size of the 2D material / graphite nanoplatelets. The liquid dispersion includes the 2D material / graphite nanoplatelets, at least one grinding medium, water, and at least one wetting agent, wherein the at least one grinding medium is water soluble or functionalized to be water soluble.

Description

Technical Field

[0001] The present invention relates to dispersions, and more particularly to aqueous dispersions containing two-dimensional (2D) materials and methods for preparing such dispersions.

Background Art

[0002] The 2D materials referred to herein include one or more known 2D materials, and / or graphite flakes having at least one nanoscale dimension, or mixtures thereof. These 2D materials are collectively referred to herein as "2D material / graphite nanoplatelets" or "2D material / graphite nanoplate".

[0003] 2D materials (sometimes referred to as monolayer materials) are crystalline materials consisting of a single layer or up to a few layers of atoms. Stacked 2D materials consist of 2D layers that are weakly stacked or bonded to form a three-dimensional structure. The nanoplatelets of 2D materials have a thickness below the nanoscale, and the other two dimensions are generally on a scale larger than the nanoscale.

[0004] Known 2D nanomaterials include graphene (C), graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulfide (MoS 2 2), tungsten diselenide (WSe 2 2), silicene (Si), germanene (Ge), graphyne (C), borophene (B), phosphorene (P), or 2D vertical or in-plane heterostructures of two of the aforementioned materials, but are not limited thereto.

[0005] Graphite flakes having at least one nanoscale dimension contain 10 to 40 layers of carbon atoms and have lateral dimensions in the range of about 100 nm to 100 μm.

[0006] 2D materials / graphite nanoplatelets, and in particular graphene and hexagonal boron nitride, have many interesting properties in the physical world and many more are being discovered. A major challenge for the exploitation of such materials and their properties is to produce compositions in which these materials are dispersed that can be made by commercial processes and are commercially attractive. In particular, such compositions need to have a sufficient shelf life / lifetime for the material to be sold, stored within a known period and then used. Further, such compositions must not be harmful to the user and / or the environment, or at least any harmfulness must be within acceptable limits.

[0007] Specific problems faced in relation to 2D materials / graphite nanoplatelets are their very low dispersibility in water and aqueous solutions and, once dispersed, the low stability of such dispersions. For example, graphene nanoplatelets and / or graphite nanoplatelets having one nanoscale dimension face this problem in water and aqueous solutions. Hexagonal boron nitride nanoplatelets also face the same problem.

[0008] For 2D materials / graphite nanoplatelets known or suspected to be harmful, especially when not encapsulated in other materials, the stability of those 2D materials / graphite nanoplatelets in the dispersion is particularly important. This is because when they separate and dry out of the dispersion when not bound or encapsulated in non-aerosolized materials, they easily become aerosolized. Aerosolized graphene nanoplatelets and / or graphite nanoplatelets having at least one nanoscale dimension are thought to be able to damage the health of humans and animals if inhaled into the lungs. The harmfulness of other 2D materials / graphite nanoplatelets is still being evaluated, but it is considered prudent to assume that other 2D materials / graphite plateletlets will exhibit similar harmfulness.

[0009] 2D materials / graphene nanoplatelets have a large surface area and low functionality, and historically it has been proven that they are very difficult to wet and / or disperse in water or aqueous solutions. Furthermore, it is known that it is very difficult to prevent aggregation of the once-dispersed 2D materials / graphene nanoplatelets.

[0010] For example, the improvement of methods for achieving wetting and dispersion stability in non-aqueous solutions such as organic solvents and aqueous solutions has been an active research topic since the discovery of 2D materials / graphene nanoplatelets and their properties.

[0011] The parameters for making good dispersions are well established in the field of colloid science, and the free energy of any colloidal system is determined by both the interfacial area and the interfacial tension. The theoretically calculated surface area of a single layer of graphene is about 2590 m 2 g -1 2, and as a result, the range of conditions under which it can be dispersed is limited, and usually these conditions included sonication and the use of polar aprotic solvents.

[0012] In order to maintain the stability of graphene / graphene nanoplatelets (where graphene nanoplatelets are graphene nanoplatelets having nanoscale dimensions, 10 - 20 layers, and lateral dimensions in the range of about 100 nm - 100 μm) in the dispersion when they are dispersed, the generation of an energy barrier to prevent aggregation of these nanoplatelets is necessary. This can be achieved by either electrostatic or steric repulsive forces. If the energy barrier is high enough, Brownian motion will maintain the dispersion. This has been achieved by using one or more approaches characterized as follows. a. Solvent selection, b. Chemical (covalent) modification of graphene / graphene nanoplatelets, and c. Non-covalent modification of graphene / graphene nanoplatelets.

[0013] a. Selection of solvent Several solvents, especially N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and dimethylformamide (DMF), have been identified as being particularly good for the dispersion of graphene / graphite nanoplatelets. These solvents have health and safety issues and it is desirable not to use them.

[0014] The interaction of solvents has been reasonably explained by both the use of surface energy and Hansen solubility parameters. By using Hansen solubility parameters, several solvents have been identified as potential carrier media, but their effectiveness depends on the functionality of the graphene / graphite nanoplatelets, the mode of dispersion, the time from dispersion, and / or the temperature of the dispersion.

[0015] However, water is not a solvent that interacts well with graphene / graphite nanoplatelets. Water is a solvent with a high level of polarity, while graphene / nanoplatelets have a high degree of hydrophobicity. For this reason, water and graphene / graphite nanoplatelets repel each other, so the graphene / graphite nanoplatelets aggregate, coagulate and do not disperse.

[0016] b. Chemical (covalent) modification of graphene / graphite nanoplatelets The functionalization of graphene / graphite nanoplatelets depends significantly on the level of availability of functional groups. When oxygen is present (such as in reduced graphene oxide), one of the most common routes is to introduce functionality using diazonium salts.

[0017] Alternatively, when the functionality is absent (pure graphene or graphite) or very low, plasma modification may be used to introduce functionality. These graphene / graphite nanoplatelets may then be further processed to generate new functional species. The most important processing parameter for plasma treatment is the process gas. This is because the process gas defines the chemical groups being introduced, while the process time and power used affect the concentration of the functional groups being introduced.

[0018] The dispersibility of graphene / graphite nanoplatelets can be improved by their chemical functionalization, but it has been observed that such chemical functionalization also increases the level of defects within the graphene sp2 structure, which can have an adverse effect on properties such as conductivity. This is clearly an undesirable result.

[0019] c. Non-covalent modification of graphene / graphite nanoplatelets Non-covalent modification of graphene / graphite nanoplatelets has several advantages over covalent modification in that it does not involve additional chemical steps and damage to the sp2 domains within the nanoplatelets is avoided. A variety of interactions are possible and the principles are π-π, cation-π, and the use of surfactants.

[0020] The π-π bond may be achieved through either dispersive or electrostatic interactions. For example, a wide range of aromatic-based systems such as polyaromatic hydrocarbons (PAHs), pyrene, and polyacrylonitrile (PAN) have been shown to interact with graphene.

[0021] The cation-π bond may use either a metal or an organic cation. Generally, organic cations are preferred, and imidazolium cations are preferred because of their planar aromatic structure.

[0022] Since a variety of surfactants are commercially available, surfactants are widely used. Usually, the surfactant is first adsorbed on the basal edge of the nanoplate and then on the surface. Adsorption is promoted when there is the ability of π-π interaction and a planar tail that can be solvated. Based on the functionality of the basal edge and surface of graphene / graphite nanoplatelets and the medium in which the graphene / graphite nanoplatelets are dispersed, both nonionic and ionic surfactants have been shown to be effective.

[0023] Summarizing the above considerations, highly specific additives are required to wet, disperse, and stabilize the dry powder of graphene / graphite nanoplatelets for use in liquid formulations using organic solvents. It is understood that the same applies to other 2D materials / graphite nanoplatelets.

[0024] The use of organic solvents in the environment is a matter of increasing concern, and it is generally desirable to reduce or remove organic solvents in the environment if possible.

Summary of the Invention

Means for Solving the Problems

[0025] According to a first aspect of the present invention, there is provided a method for forming a liquid dispersion of 2D materials / graphite nanoplatelets in water or an aqueous solution, the method comprising: (1) a step of preparing a dispersion medium; (2) a step of mixing 2D materials / graphite nanoplatelets into the dispersion medium; (3) a step of subjecting the 2D materials / graphite nanoplatelets to a shear force and / or a crushing force sufficient to reduce the particle size of the 2D materials / graphite nanoplatelets using mechanical means. The mixture of this 2D material / graphene nanoplatelet and the dispersion medium includes a 2D material / graphene nanoplatelet, at least one grinding medium, water, and at least one wetting agent, and this at least one grinding medium is characterized in that it is water-soluble or is functionalized to be water-soluble.

[0026] Step (2) of the first aspect of the present invention is performed to achieve initial wetting of the 2D material / graphene platelet before step (3).

[0027] According to a second aspect of the present invention, a dispersion is provided that includes a 2D material / graphene nanoplatelet, at least one grinding medium, water, and at least one wetting agent, where the at least one grinding medium is water-soluble or is functionalized to be water-soluble.

[0028] According to a third aspect of the present invention, a liquid coating system is provided that includes the dispersion according to the second aspect of the present invention.

[0029] In some embodiments of the first aspect of the present invention, the 2D material / graphene nanoplatelet includes one or more graphene or graphene nanoplatelets, where the graphene nanoplatelet includes graphene nanoplate, reduced graphene oxide nanoplate, bilayer graphene nanoplate, bilayer reduced graphene oxide nanoplate, trilayer graphene nanoplate, trilayer reduced graphene oxide nanoplate, few-layer graphene nanoplate, few-layer reduced graphene oxide nanoplate, and one or more of graphene nanoplate with 6 to 10 layers of carbon atoms, and the graphene platelet includes graphene nanoplate having at least 10 layers of carbon atoms.

[0030] In some embodiments of the present invention, one or both of the graphene nanoplatelet and the graphene nanoplatelet have a lateral dimension in the range of about 100 nm to 100 μm.

[0031] In some embodiments of the first aspect of the present invention, the 2D material / graphene nanoplatelet includes one or more graphene nanoplatelets, where the graphene nanoplatelets are graphene nanoplatelets having 10 to 20 layers of carbon atoms, graphene nanoplatelets having 10 to 14 layers of carbon atoms, graphene nanoplatelets having 10 to 35 layers of carbon atoms, graphene nanoplatelets having 10 to 40 layers of carbon atoms, graphene nanoplatelets having 25 to 30 layers of carbon atoms, graphene nanoplatelets having 25 to 35 layers of carbon atoms, graphene nanoplatelets having 20 to 35 layers of carbon atoms, or graphene nanoplatelets having 20 to 40 layers of carbon atoms.

[0032] In some embodiments of the first aspect of the present invention, the 2D material / graphene nanoplatelet includes one or more 2D material nanoplatelets, where the 2D material platelet includes hexagonal boron nitride (hBN), molybdenum disulfide (MoS 2 ), tungsten diselenide (WSe 2 ), silicene (Si), germanene (Ge), graphene (C), borophene (B), phosphorene (P), or one or more of two or more 2D in-plane or vertical heterostructures of the aforementioned materials.

[0033] Few-layer graphene / reduced graphene oxide nanoplatelets have 4 to 10 layers of carbon atoms, where a single layer has a thickness of 0.035 nm and a typical interlayer distance of 0.14 nm.

[0034] In some embodiments of the first aspect of the present invention, the 2D material / graphene nanoplatelet includes a graphene / graphene platelet and at least one 1D material. In some embodiments, the 1D material includes carbon nanotubes.

[0035] In some embodiments of the first aspect of the present invention, the grinding medium is a polymer modified with strong anchor groups, a grinding resin, an aqueous solution of a modified aldehyde resin having at least one amine group, a low molecular weight styrene / maleic anhydride copolymer, or a mixture of these media.

[0036] In some preferred embodiments, the grinding media for the dispersion of the 2D material / graphene nanoplatelets is Laropal™ LR 9008, a water-soluble modified aldehyde resin commercially available from BASF, Dispersions & Resins Division, North America; ADDITOL™ XL 6515, a modified alkyd polymer; ADDITOL XW 6528, a polyester-modified acrylic polymer; ADDITOL XW 6535, a highly polymerized self-emulsifying pigment grinding media; ADDITOL XW 6565, a highly polymerized self-emulsifying pigment grinding media; ADDITOL XW 6591, a polyester-modified acrylic polymer. The ADDITOL products are commercially available from the group of Allnex.

[0037] In some embodiments of the first aspect of the present invention, the dispersion medium comprises a mixture of at least one grinding medium and water, and the step of preparing the dispersion medium comprises (i) mixing at least one grinding medium with water until substantially homogeneous.

[0038] In some embodiments of the first aspect of the present invention, at least one grinding medium is a liquid, and the dispersion medium comprises 50 wt% to 90 wt% of at least one grinding medium and 10 wt% to 50 wt% of water, 60 wt% to 80 wt% of at least one grinding medium and 20 wt% to 40 wt% of water, 65 wt% to 75 wt% of at least one grinding medium and 25 wt% to 35 wt% of water, or about 70 wt% of at least one grinding medium and about 30 wt% of water.

[0039] In some embodiments of the first aspect of the present invention, the method comprises (ii) after completion of step (i), adding the 2D material / graphene nanoplatelets to the mixture of at least one grinding medium and water; and (iii) further including the step of mechanically mixing the 2D material / graphite nanoplatelets with at least one grinding medium and a mixture of water until the 2D material / graphite nanoplatelets are substantially dispersed in the grinding medium solution.

[0040] In some embodiments of the first aspect of the present invention, the dispersion medium further includes at least one wetting agent, which is stored as a liquid, and the step of preparing the dispersion medium (i) includes the step of mixing at least one grinding medium, water, and the wetting agent until the mixture of the grinding medium, water, and the wetting agent becomes substantially homogeneous.

[0041] In some embodiments of the first aspect of the present invention, the dispersion medium further includes at least one wetting agent, which is stored as a solid (including powder), and the step of preparing the dispersion medium (i) includes the step of mixing at least one grinding medium, water, and the wetting agent until the wetting agent is dissolved and the mixture of the grinding medium, water, and the wetting agent becomes substantially homogeneous.

[0042] In some embodiments of the first aspect of the present invention, at least one wetting agent is added to the dispersion medium substantially simultaneously with the 2D material / graphite nanoplatelets.

[0043] The single or plural wetting agents of the present invention may be one of a polymeric wetting agent, an ionic wetting agent, a polymeric non-ionic dispersion and wetting agent, a cationic wetting agent, an amphoteric wetting agent, a Gemini wetting agent, a polymer resin-like wetting and dispersing agent, or a mixture of two or more of these wetting agents. A Gemini wetting agent has two polar centers or heads connected by a spacer segment in a polyether segment.

[0044] Preferred wetting agents for dispersions of 2D materials / graphite nanoplatelets include, but are not limited to, ADDITOL™ VXW 6208 / 60, a modified acrylic copolymer which is a polymeric nonionic dispersing and wetting additive commercially available from Allnex Belgium SA / NV; DISPERBYK™ - 2150, a block copolymer having basic pigment affinity groups commercially available from BYK-Chemie GmbH; and Surfynol™ 104, a gemini wetting agent and molecular defoamer commercially available from Evonik Nutrition & Care GmbH.

[0045] Dry 2D materials / graphite nanoplatelets, such as graphene / graphite nanoplatelets, are typically made up of primary particles or aggregates or agglomerates of nanoplatelets. During the dispersion process, those aggregates or agglomerates need to be broken down as much as possible into primary particles or nanoplatelets of a suitable size for the intended application of the 2D material / graphite nanoplatelets. The breaking down of aggregates or agglomerates of primary particles or nanoplatelets is thought to involve a process of exfoliation.

[0046] In some embodiments of the present invention, the dispersing means is a means suitable for applying both a crushing action and a mechanical shear force to the 2D material / graphite platelet while it is being mixed with the dispersion medium. Suitable devices for achieving this are known grinding or milling devices such as, for example, dissolvers, bead mills, or three-roll mills.

[0047] In some embodiments of the present invention, it is preferred that the aggregates or agglomerates are broken down into particles or nanoplatelets of a particle size such that they cannot be broken down any further. This is beneficial because the manufacture and storage of 2D materials / graphite nanoplatelets prior to use are often carried out in a form of larger particles than is desired for the 2D material / graphite nanoplatelet dispersion.

[0048] When the aggregates or agglomerates of 2D materials / graphite nanoplatelets are reduced to smaller particles or nanoplatelets, it helps to prevent the re-aggregation or re-agglomeration of those particles or nanoplatelets by rapidly stabilizing the newly formed surface resulting from the size reduction of the aggregates or agglomerates.

[0049] For example, the higher the interfacial tension between a dispersion medium such as a dispersion medium containing water and 2D materials / graphite nanoplatelets, the stronger the force to reduce the interfacial area is found. Therefore, the method of the present invention is particularly beneficial. In other words, the force to re-aggregate or re-agglomerate the 2D materials / graphite nanoplatelets or to form aggregates becomes stronger. Since the interfacial tension between the wetting agent in the dispersion medium and 2D materials / graphite nanoplatelets is lower than the interfacial tension between water and 2D nanomaterials, the wetting agent helps to stabilize the newly formed surface and prevent the aggregation, agglomeration, and / or coagulation of 2D materials / graphite nanoplatelets.

[0050] The action of the wetting agent to stabilize the newly formed surface and prevent the aggregation, agglomeration, and / or coagulation of 2D materials / graphite nanoplatelets is beneficial, but it has been found not to provide sufficient benefits to enable the formation of an improved stable dispersion. The reason is that the wetting agent suspends 2D nanomaterials in an aqueous dispersion medium, but the 2D materials / graphite nanoplatelets are characterized by having a large surface area compared to other compounds. Water with high polarity may be replaced by the wetting agent.

[0051] Increasing the proportion of the wetting agent in the dispersion medium may ultimately result in a dispersion in which all components remain suspended. However, this approach to forming a dispersion has the problem that the coating formed from this dispersion will have a high degree of water solubility. This is highly undesirable because it leads to rapid damage of the coating.

[0052] According to the present invention, an improved dispersion is provided by applying a crushing action and mechanical shear force to a dispersion containing a mixture of 2D materials / graphene nanoplatelets in a mixture of a grinding medium, water, and a wetting agent.

[0053] This is thought to be because a proportion of the 2D materials / graphene nanoplatelets are at least partially encapsulated within the coating of the grinding medium, so that in addition to the wetting agent, the grinding medium also stabilizes the newly formed surfaces of the 2D materials / graphene plateletlets. The wetting agent then binds to the combined grinding medium / 2D materials / graphene nanoplatelet particles, enabling the grinding medium / 2D materials / graphene nanoplatelet particles to be suspended in the dispersion. Since the grinding medium requires less wetting agent than the 2D materials / graphene nanoplatelets to enable suspension in the dispersion, the problem of increased solubility of any coating formed from the dispersion due to the need for an excess of wetting agent is avoided.

[0054] This is thought to be because water as a solvent has a high level of polarity, while graphene / graphene nanoplatelets having a high carbon / oxygen ratio have low polarity and a high degree of hydrophobicity, so that these two repel each other. For this reason, the graphene / graphene nanoplatelets aggregate, coagulate, and do not disperse. In some embodiments of the present invention where the 2D materials / graphene plateletlets are graphene / graphene nanoplatelets, the carbon / oxygen ratio of the graphene / graphene nanoplatelets is 15 or more.

[0055] A further advantage of the method of the present invention is that the milling performance of the dispersing means when acting on the 2D material / graphene nanoplatelets is further improved by the presence of the grinding medium in the mixture to be milled. The improvements are higher speed milling, reduced heat generation in the milling process, more uniform particle size in the dispersion, smaller D50 particle size in the dispersion, reduced viscosity of the dispersion, higher storage stability compared to dispersions with a known short shelf life, and the ability to redisperse any combination of grinding medium / 2D material / graphene nanoplatelet particles that had sedimented from the dispersion by simple stirring of the dispersion.

[0056] The use of the grinding medium allows the use of less wetting agent in the preparation of the dispersion than would be expected, thus minimizing solubility problems with coatings formed from coating systems incorporating the dispersion prepared according to the present invention.

[0057] According to a second aspect of the present invention, there is provided a liquid dispersion comprising a 2D material / graphene nanoplatelet, at least one grinding medium, water, and at least one wetting agent.

[0058] In some embodiments of the second aspect of the present invention, the 2D material / graphite nanoplatelets include one or more of graphene nanoplatelets, graphite nanoplatelets, and 2D material nanoplatelets. The graphene nanoplatelets include one or more of graphene nanoplates, reduced graphene oxide nanoplates, bilayer graphene nanoplates, bilayer reduced graphene oxide nanoplates, trilayer graphene nanoplates, trilayer reduced graphene oxide nanoplates, few-layer graphene nanoplates, few-layer reduced graphene oxide nanoplates, and graphene nanoplates with 6 to 10 layers of carbon atoms. The graphite nanoplatelets include graphite nanoplates having at least 10 layers of carbon atoms. The graphite nanoplatelets include one or more of graphite nanoplates having 10 to 20 layers of carbon atoms, graphite nanoplates having 10 to 14 layers of carbon atoms, graphite nanoplates having 10 to 35 layers of carbon atoms, graphite nanoplates having 10 to 40 layers of carbon atoms, graphite nanoplates having 25 to 30 layers of carbon atoms, graphite nanoplates having 25 to 35 layers of carbon atoms, graphite nanoplates having 20 to 35 layers of carbon atoms, or graphite nanoplates having 20 to 40 layers of carbon atoms. The 2D material nanoplatelets include hexagonal boron nitride (hBN), molybdenum disulfide (MoS 2 ), tungsten diselenide (WSe 2 ), silicene (Si), germanene (Ge), graphyne (C), borophene (B), phosphorene (P), or one or more of 2D in-plane or vertical heterostructures of two or more of the aforementioned materials.

[0059] In some embodiments of the second aspect of the present invention, the 2D material / graphite nanoplatelets include at least one 1D material.

[0060] In some embodiments of the second aspect of the present invention, at least one grinding medium is a polymer modified with strong anchor groups, an aqueous solution of a modified aldehyde resin having at least one amine group, or a low molecular weight styrene / maleic anhydride copolymer.

[0061] In some preferred embodiments, the grinding media for the dispersion of the 2D material / graphene platelet is Laropal™ LR 9008, a water-soluble modified aldehyde resin commercially available from BASF, Dispersions & Resins Division, North America; ADDITOL™ XL 6515, a modified alkyd polymer; ADDITOL XW 6528, a polyester-modified acrylic polymer; ADDITOL XW 6535, a highly polymerized self-emulsifying pigment grinding media; ADDITOL XW 6565, a highly polymerized self-emulsifying pigment grinding media; ADDITOL XW 6591, a polyester-modified acrylic polymer. The ADDITOL products are commercially available from the group of Allnex.

[0062] In some embodiments of the second aspect of the present invention, the wetting agent includes one of a polymeric wetting agent, an ionic wetting agent, a polymeric non-ionic dispersing and wetting agent, a cationic wetting agent, an amphoteric wetting agent, a gemini wetting agent, a polymeric resin-like wetting and dispersing agent, or a mixture of two or more of these wetting agents.

[0063] Preferred wetting agents include, but are not limited to, ADDITOL™ VXW 6208 / 60, a modified acrylic copolymer which is a polymeric non-ionic dispersing and wetting additive commercially available from Allnex Belgium SA / NV; DISPERBYK-2150™, a block copolymer having a basic pigment affinity group commercially available from BYK-Chemie GmbH; and Surfynol™ 104, a combination of a gemini wetting agent and a molecular defoaming agent commercially available from Evonik Nutrition & Care.

[0064] In some embodiments of the second aspect of the present invention, the liquid dispersion is produced using the method according to the first aspect of the present invention.

Mode for Carrying Out the Invention

[0065] For a better understanding of the various examples useful for understanding the detailed description, the following will be referred to here as examples. [Examples]

[0066] The following Tables 1 and 2 show typical formulations of the dispersions according to the present invention.

[0067] All dispersions were produced in an Eiger Torrance 250 horizontal bead mill. The dispersions were milled for 15 minutes in the maximum speed recirculation mode.

[0068] Characterization of the Dispersions The particle size was measured in a Mastersizer 3000 to determine the effectiveness of the grinding resin and the dispersant for deagglomeration and particle size reduction.

[0069] To assist in understanding the rheological properties of the dispersions, the viscosity was measured. This was done using a Kinexus Rheometer.

[0070] The storage stability was determined by using a Turbiscan Stability Analyser. The Turbiscan Stability Index (TSI) is a relative measure of stability that enables comparison of multiple samples. It enables a quantifiable evaluation of the formulation that is closely related as a relative measure.

[0071] The stability tests were carried out at ambient temperature and elevated temperature (40°C).

[0072] [Table 1]

[0073]

Table 2

[0074] The graphite material A-GNP10 is commercially available from Applied Graphene Materials UK Limited, UK and contains graphite nanoplatelets with a thickness of 25 - 35 atomic layers. The graphite nanoplatelets are supplied as a powder and are generally aggregated into lumps of nanoplatelets.

[0075] The graphene / graphite material A-GNP35 is commercially available from Applied Graphene Materials UK Limited, UK and contains graphene / graphite nanoplatelets with a thickness of 5 - 15 atomic layers. The graphite nanoplatelets are supplied as a powder and are generally aggregated into lumps of nanoplatelets.

[0076] Each dispersion was prepared using the following steps. 1 Surfynol 104 and Laropal LR9008 were added to water. This was stirred until the mixture became substantially homogeneous. 2 A-GNP-10 or A-GNP-35 was added to the mixture and stirred until the powder was uniformly dispersed in the mixture. 3 The mixture was bead milled by recirculation in a bead mill for 15 minutes using beads.

[0077] Discussion Graphene dispersed in water only (A-GNP10) A-GNP10 was dispersed in water at four different concentrations of 0.1, 1, 5, and 10%. The samples were stored for 4 weeks under ambient conditions.

[0078] The 5% and 10% samples deposited within 2 - 3 days from manufacture.

[0079] For the 0.1% and 1% samples, there was no visible deposition even after 4 weeks of production.

[0080] Due to the severe deposition observed at 5% and 10% weight addition of graphene (A - GNP10), there was a need to identify suitable pigment dispersion resins (i.e., grinding media) and / or surfactants (i.e., wetting agents) to improve the shelf life and storage stability of the product.

[0081] Graphene dispersed in water containing a dispersion resin (i.e., grinding medium) (A-GNP10) Tested dispersions 10% A - GNP10 was dispersed in various media with an increasing amount of the grinding media Laropal LR9008. 1. Water only 2. 10% Laropal 90% water mixture 3. 20% Laropal 80% water mixture 4. 30% Laropal 70% water mixture 5. 40% Laropal 60% water mixture 6. 50% Laropal 50% water mixture

[0082] Viscosity of the aqueous dispersion of A - GNP10 As shown in Table 3 below, all the dispersions had a very low viscosity (less than 1 PaS). Overall, there was no significant change in the rheology profile of these dispersions. However, the dispersion of 10% Laropal LR9008 and 90% water showed a particularly high viscosity.

[0083]

Table 3

[0084] Particle size distribution of the aqueous dispersion of A - GNP10 The particle size distribution for all samples was monitored and the results are shown in Table 4 below. Except for the dispersion with 10% amount of Laropal, all the dispersions showed a D90 in the range of 15 - 25 microns.

[0085]

Table 4

[0086] Storage Stability of Aqueous Dispersion of A-GNP10 Samples were tested at ambient temperature and elevated temperature (40 °C). Generally, the addition of Laropal LR 9008 improved the stability against sedimentation overall.

[0087] Turbiscan Measurement - Multiple Light Scattering Static multiple light scattering was performed on the samples, and the results are shown in Table 5 below. Static multiple light scattering is an optical method used to characterize concentrated liquid dispersions. When light is transmitted through the sample, it is backscattered or transmitted by the dispersion depending on the concentration and the dominant particle size. The TSI number is used to indicate the degree of change within the sample, and a large number indicates a large degree of change within the sample, i.e., instability.

[0088]

Table 5

[0089] Comment For the aqueous dispersion of A-GNP10, the presence of Laropal showed an improvement in stability as tested by Turbiscan, with the only exception being the dispersion with 10% Laropal LR9008. Without Laropal LR9008, sedimentation of the dispersion was observed after the first 2 - 3 days of storage. By using the dispersion resin, the stability against sedimentation increased to 6 weeks.

[0090] Graphene dispersed in water containing a dispersion resin (i.e., grinding medium) (A-GNP35) Dispersion Tested 0.5% of A-GNP35 was dispersed in water / solvent and subjected to bead milling with recirculation for 15 minutes.

[0091] 0.5% of A-GNP35 was dispersed as follows · Only water · 10% Laropal and 90% water · 20% Laropal and 80% water · 30% Laropal and 70% water · 40% Laropal and 60% water · 50% Laropal and 50% water

[0092] Viscosity of the aqueous dispersion of A - GNP35 As shown in Table 6 below, the aqueous dispersion of A - GNP35 tends to show only very high viscosity. For all the systems tested, the viscosity decreased with the addition of Laropal LR9008. The lowest viscosity was achieved with 20% amount of Laropal.

[0093]

Table 6

[0094] Particle size distribution of the aqueous dispersion of A - GNP35 The particle size distribution for all samples was evaluated and the results are shown in Table 7 below. It was shown that the particle size was significantly reduced by the use of Laropal LR9008. For the systems containing Laropal, the dispersion with 10% amount of Laropal showed the least reduction in particle size distribution. There was no significant variation in the particle size distribution between 20 - 50% amounts of Laropal. The D90 for these systems was half of that obtained without using a dispersion resin (i.e., grinding medium).

[0095]

Table 7

[0096] Storage stability The samples were tested at ambient temperature and elevated temperature. The aqueous dispersions of A-GNP35 usually have a high viscosity with the consistency of a thick paste. For this reason, these dispersions tend to be more stable than the equivalent dispersions of A-GNP10. After a one-week test, there were no visible differences in the stability of the samples, whether stored at ambient temperature or elevated temperature (40 °C).

[0097] The Turbiscan evaluations of the samples as shown in Table 8 below showed no significant differences in the stability index of the samples, whether at ambient temperature or elevated temperature. The Turbiscan Stability Index (TSI) is a relative measure of stability that enables comparison of multiple samples. It enables a quantifiable evaluation of the formulation that is closely related as a relative measure.

[0098]

Table 8

[0099] Comment For the aqueous dispersions of A-GNP35, the presence of Laropal significantly reduced the viscosity of the dispersion, making the dispersion easier to use and handle. By including Laropal, a higher degree of particle size reduction was also achieved.

[0100] Graphene dispersed in water containing a dispersion resin (i.e., grinding medium) and a wetting agent (Surfynol) (A-GNP35) The stability of the dispersions in Table 1 was monitored over a four-month period. Changes in particle size and the degree of sedimentation were monitored. Four batches of the stabilized formulation were tested. Surfynol (wetting agent) was introduced to further improve pigment wetting and act as an anti-foaming agent. The stabilized formulation is as shown in Table 1 above.

[0101] Turbiscan - Multiple Light Scattering Static multiple light scattering is an optical method used to characterize concentrated liquid dispersions. When light is transmitted through the sample, it is either backscattered or transmitted by the dispersion depending on the concentration and dominant particle size. Any destabilization phenomena occurring in a given sample during the aging process will affect the backscattering and / or transmission signal intensity. Formulations with large intensity fluctuations have changed significantly and can be considered unstable.

[0102] To understand the stability of this dispersion, four batches of the dispersion in Table 1 were tested. After 46 days of storage, there was development of surface separation, which was evidenced by the appearance of a (transparent) layer that transmitted near the surface. Just below the developed transparent layer, there was a slightly denser layer where backscattering increased.

[0103] Monitoring of particle size changes The particle size distribution for the dispersion in Table 1 was evaluated, and the results are shown in Table 9 below.

[0104] Changes in particle size can indicate aggregation, agglomeration, or coagulation.

[0105]

Table 9

[0106] A slight decrease in the initial D90 was recorded after 4 months. The increase from 16.2 to 17.7 initially is considered within the range of measurement error.

[0107] Degree of sedimentation The degree of sedimentation is shown in Table 10 below.

[0108]

Table 10

[0109] Recommendation for shelf life The dispersion of Table 1 should be stored for a period of 3 months at ambient temperature (15 - 25 °C). Some separation may occur, which can be mixed back to a homogeneous dispersion by gentle mechanical stirring.

Claims

1. A method for forming a liquid dispersion of 2D materials / graphite nanoplatelets in water or an aqueous solution, the method comprising: (1) preparing a dispersion medium by mixing at least one grinding medium, water, and at least one wetting agent until the mixture of the grinding medium, the water, and the wetting agent becomes substantially homogeneous, wherein the at least one grinding medium is water-soluble or functionalized to be water-soluble and comprises an aqueous solution of a modified aldehyde resin having at least one amine group, and wherein the dispersion medium comprises at least 20% of the grinding medium; (2) mixing the 2D materials / graphite nanoplatelets into the dispersion medium; and (3) subjecting the 2D materials / graphite nanoplatelets to shear force and / or crushing force sufficient to reduce the particle size of the 2D materials / graphite nanoplatelets using mechanical means. The liquid dispersion is characterized by comprising the 2D materials / graphite nanoplatelets, the at least one grinding medium, the water, and the at least one wetting agent. The 2D materials / graphite nanoplatelets comprise one or more of graphene nanoplatelets, graphite nanoplatelets, and 2D material nanoplatelets. The graphene nanoplatelet includes one or more of graphene nanoplate, reduced graphene oxide nanoplate, bilayer graphene nanoplate, bilayer reduced graphene oxide nanoplate, trilayer graphene nanoplate, trilayer reduced graphene oxide nanoplate, few-layer graphene nanoplate, few-layer reduced graphene oxide nanoplate, and graphene nanoplate with 6 to 10 layers of carbon atoms. The graphite nanoplatelet includes one or more of graphite nanoplate having at least 10 layers of carbon atoms, graphite nanoplate having 10 to 20 layers of carbon atoms, graphite nanoplate having 10 to 14 layers of carbon atoms, graphite nanoplate having 10 to 35 layers of carbon atoms, graphite nanoplate having 10 to 40 layers of carbon atoms, graphite nanoplate having 25 to 30 layers of carbon atoms, graphite nanoplate having 25 to 35 layers of carbon atoms, graphite nanoplate having 20 to 35 layers of carbon atoms, or graphite nanoplate having 20 to 40 layers of carbon atoms. The 2D material nanoplatelet includes one or more of hexagonal boron nitride (hBN), molybdenum disulfide (MoS ２ ), tungsten diselenide (WSe ２ ), silicene (Si), germanene (Ge), graphene (C), borophene (B), phosphorene (P), or one or more of in-plane or vertical heterostructures of two or more of these 2D materials.

2. The method according to claim 1, wherein the 2D materials / graphite nanoplatelets comprise at least one 1D material.

3. The method according to claim 1 or 2, wherein the at least one wetting agent comprises one of a polymeric wetting agent, an ionic wetting agent, a polymeric non-ionic dispersion and wetting agent, a cationic wetting agent, an amphoteric wetting agent, a gemini wetting agent, a polymeric resin-like wetting and dispersing agent, or a mixture of two or more of these wetting agents.

4. The dispersion medium further comprises the at least one wetting agent stored in liquid form, and the step of preparing the dispersion medium comprises: (i) mixing the at least one grinding medium, the water, and the wetting agent until the mixture of the grinding medium, the water, and the wetting agent becomes substantially homogeneous, according to any one of claims 1 to 3.

5. The dispersion medium further comprises the at least one wetting agent, the wetting agent is stored as a solid, and the step of preparing the dispersion medium is: The method according to any one of claims 1 to 3, comprising the step of mixing the at least one grinding medium, the water, and the wetting agent until the wetting agent is dissolved and the mixture of the grinding medium, the water, and the wetting agent becomes substantially homogeneous.

6. The method according to any one of claims 1 to 3, wherein the at least one wetting agent is added to the dispersion medium substantially simultaneously with the 2D material / graphite nanoplatelet.

7. The step (3) of subjecting the 2D material / graphite nanoplatelet to shear force and / or crushing force sufficient to reduce the particle size of the 2D material / graphite nanoplatelet is performed using one or more of a dissolver, a bead mill, and a three-roll mill. The method according to any one of claims 1 to 6.

8. A liquid dispersion comprising the 2D material / graphite nanoplatelet, at least one grinding medium, water, and at least one wetting agent, wherein the at least one grinding medium is water-soluble or functionalized to be water-soluble, and comprising an aqueous solution of a modified aldehyde resin having at least one amine group, wherein the liquid dispersion comprises at least 20% of the grinding medium. The 2D material / graphite nanoplatelet comprises one or more of graphene nanoplatelets, graphite nanoplatelets, and 2D material nanoplatelets. The graphene nanoplatelet includes one or more of a graphene nanoplate, a reduced graphene oxide nanoplate, a bilayer graphene nanoplate, a bilayer reduced graphene oxide nanoplate, a trilayer graphene nanoplate, a trilayer reduced graphene oxide nanoplate, a few-layer graphene nanoplate, a few-layer reduced graphene oxide nanoplate, and a graphene nanoplate having 6 to 10 layers of carbon atoms. The graphite nanoplatelet includes one or more of a graphite nanoplate having at least 10 layers of carbon atoms, a graphite nanoplate having 10 to 20 layers of carbon atoms, a graphite nanoplate having 10 to 14 layers of carbon atoms, a graphite nanoplate having 10 to 35 layers of carbon atoms, a graphite nanoplate having 10 to 40 layers of carbon atoms, a graphite nanoplate having 25 to 30 layers of carbon atoms, a graphite nanoplate having 25 to 35 layers of carbon atoms, a graphite nanoplate having 20 to 35 layers of carbon atoms, or a graphite nanoplate having 20 to 40 layers of carbon atoms. The 2D material nanoplatelet includes one or more of hexagonal boron nitride (hBN), molybdenum disulfide (MoS ２ ), tungsten diselenide (WSe ２ ), silicene (Si), germanene (Ge), graphene (C), borophene (B), phosphorene (P), or one or more of in-plane or vertical heterostructures of two or more of these 2D materials, a liquid dispersion.

9. The liquid dispersion according to claim 8, wherein the 2D material / graphite nanoplatelet comprises at least one 1D material.

10. The wetting agent comprises one of a polymeric wetting agent, an ionic wetting agent, a polymeric non-ionic dispersant and wetting agent, a cationic wetting agent, an amphoteric wetting agent, a gemini wetting agent, a polymer resin-like wetting and dispersing agent, or a mixture of two or more of these wetting agents. The liquid dispersion according to claim 8 or 9.

11. A liquid coating composition comprising the liquid dispersion according to any one of claims 8 to 10.

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