Alkaline suspension system constructed from a hydrotrope and an amine

Abstract

A non-settling aqueous pourable alkaline suspension can be produced from a mixture of at least one water-soluble amphiphilic substance and at least one oil-soluble amphiphilic substance, the amphiphilic substances having 6 to 11 carbon atoms in the hydrophobic part of the amphiphilic substance. The water-soluble amphiphilic substance is classified as a hydrotrope and the oil-soluble amphiphilic component contains at least one amine group.

Description

Technical Field

[0001] The present invention relates to an alkaline structured low-foaming amphiphilic suspension system for producing suspensions of water-insoluble (or slightly water-soluble) solid particles or liquids. The present invention further relates to a composition comprising the suspension system.

Background Art

[0002] In a recent patent application, US Provisional Patent Application No. 63 / 308452, a novel structured low-foaming composition is claimed that uses a blend of short-chain (i.e., 7 to 11 carbon atoms) amphiphilic substances in water to suspend immiscible solid or liquid particles in a highly cost-effective manner without sedimentation. This system comprises a mixture of at least one water-soluble amphiphilic substance and at least one water-insoluble amphiphilic substance, wherein at least one water-soluble amphiphilic substance is a hydrotrope. The hydrotrope is a high HLB hydrotrope having an HLB value of 10 or more, and at least one water-insoluble amphiphilic substance is a low HLB amphiphilic substance having an HLB value of less than 10 and containing at least one hydroxyl group.

[0003] Without being bound by theory, it is thought that the hydroxyl group provides hydrogen bonding, which "hardens" the amphiphilic substances together into regular nano-sized droplets of a lamellar liquid crystal. The regularly sized nano-droplets have a positively charged surface (although the droplets are electrically neutral as a whole), and this unequal charge distribution at the droplets causes the droplets to always repel each other, resulting in a 3D structure with a yield point that can suspend solids, liquids, or gases. This system has high optical transparency and a large yield point as evidenced by the fact that it can suspend air bubbles.

Summary of the Invention

[0004] Here, it has been found that a structured suspension system can be constructed from a mixture of a short-chain (i.e., C7 - C11 carbon atoms) hydrotrope and an amine-containing amphiphilic substance. Surprisingly, such a suspension system is shear-thickening, which is opposite to the shear-thinning behavior of a suspension system formed from a hydroxyl-containing water-insoluble amphiphilic substance and a hydrotrope.

[0005] According to a first aspect of the present invention, there is provided an alkaline structured aqueous system having a yield point and capable of suspending solid, liquid, or gas particles, the system comprising a mixture of at least one water-soluble amphiphilic substance and at least one water-insoluble amphiphilic substance. The at least one water-soluble amphiphilic substance is a hydrotrope, and the at least one water-insoluble amphiphilic substance contains at least one amine group. In a further aspect, the hydrotrope has at least one polar head group and a lipophilic moiety having less than 12 carbon atoms per polar head group. It has been the most unexpected and surprising discovery that a low-foaming shear-thickening structured lamellar suspension system containing a high proportion of hydrotrope can be favorably formulated. This system can have high optical transparency and can have a large yield point as evidenced by the fact that it can suspend air bubbles.

[0006] Structured suspensions can be used for suspending water-insoluble materials for industrial applications such as graphene or diamond powder, where highly foaming surfactants are not suitable. Thus, a further aspect of the present invention is a composition comprising an alkaline structured system, wherein the alkaline structured system is (a) a mixture of at least one water-soluble amphiphilic substance and at least one water-insoluble amphiphilic substance, based on the weight of the structured aqueous system, from 2 wt% to 50 wt%, wherein at least one water-soluble amphiphilic substance is a hydrotrope comprising at least one polar head group and a lipophilic tail group having 6 to 11 carbon atoms per polar head group, and at least one water-insoluble amphiphilic substance comprises at least one amine group; (b) at least one of solid, liquid, or gaseous particles suspended in the alkaline structured system, and (c) water up to 100% of the composition. In some embodiments, the solid particles constitute from about 0.5 wt% to about 25 wt% of the composition. In some embodiments, the solid particles are graphene particles.

[0007] Another aspect of the present invention is a method for producing a stable graphene dispersion, which comprises (a) forming an alkaline structured aqueous system, wherein the alkaline structured aqueous system comprises water and a mixture of at least one water-soluble amphiphilic substance and at least one water-insoluble amphiphilic substance, based on the weight of the structured aqueous system, from 2 wt% to 50 wt%, wherein at least one water-soluble amphiphilic substance is a hydrotrope comprising at least one polar head group and a lipophilic tail group having 6 to 11 carbon atoms per polar head group, and at least one water-insoluble amphiphilic substance comprises at least one amine group; and (b) suspending graphene particles in the structured aqueous system to form a stable graphene dispersion. BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention relates to an alkaline suspension system based on a lamellar mesophase constructed from amphiphilic molecules. It has high optical transparency, low foaming properties, and may have extremely low electrolytes. A system with high optical transparency typically has a light transmittance of more than about 50 percent using a 1-centimeter cuvette at a wavelength of 570 nanometers when the composition is measured at 25 °C in the absence of dyes and opacifiers. "Low foaming properties" means that any foam generated during the process for forming the suspension system is transient and collapses within a few seconds. A system with extremely low electrolytes is a system in which the electrolyte is less than 2% by weight, preferably less than 1% by weight. For example, the structured suspension system may not contain an electrolyte. The alkaline suspension system of the technology of the present invention is also shear-thickening and exhibits an increase in viscosity when shaken or sheared over time. When the shear is stopped, the alkaline suspension system returns to its initial viscosity over time, usually within 24 hours. The suspension system has a wide range of applications as a suspension medium for payloads such as pesticides, pigments, graphene, oils, etc.

[0010] The amphiphilic molecules used in the production of the suspension system include at least one water-insoluble amphiphilic substance containing an amino group and at least one water-soluble amphiphilic substance that is a hydrotrope. A hydrotrope is a molecule having a hydrophilic or polar head group and a hydrophobic (lipophilic) tail group, but the tail group is generally too small to cause spontaneous self-association or aggregation in an aqueous solution. A specific combination of the water-insoluble amine-containing amphiphilic substance and the hydrotrope has a yield point and can form a shear-thickening structured system capable of suspending solid particles, droplets, and bubbles.

[0011] The amphiphilic substances for use in the production of the structured suspension should include at least one amphiphilic substance with a low hydrophilic-lipophilic balance (HLB), e.g., less than 10, and at least one amphiphilic substance with a high HLB, e.g., 10 or more. The HLB of the mixture as a whole should be in the range where a liquid crystal is formed, which can be approximately 11 - 13, preferably about 12 HLB units.

[0012] The low HLB amphiphilic substance contains a lipophilic tail group with less than 12 carbon atoms and at least one amine group. In some embodiments, the low HLB amphiphilic substance can include at least one lipophilic tail containing 4 - 11 carbon atoms, alternatively 5 - 11 carbon atoms, alternatively 6 - 11 carbon atoms, alternatively 7 - 11 carbon atoms. The lipophilic tail group can be linear or branched.

[0013] In some embodiments, the low HLB amphiphilic substance can include at least one linear tail having a carbon chain containing 4, 5, 6, 7, 8, 9, or 10 carbon atoms. In other embodiments, the low HLB amphiphilic substance can have a branched or cyclic (including aromatic) tail having 6, 7, 8, 9, or 10 carbon atoms. Without being bound by theory, the amine group of the low HLB amphiphilic substance is thought to exchange protons with the head group of the hydrotrope. This is considered to be the driving force for nano-droplet formation and the "cement" that holds the droplets together. Examples of water-insoluble amphiphilic substances suitable for forming the suspension include, but are not limited to, octylamine, para-ethylaniline, para-toluidine, and 4-isopropylaniline.

[0014] It is also possible to prepare mixed hydrogen bond (amino + hydroxyl) systems. Such mixed systems may in fact be preferred in some applications, since the amino hydrogen bond alone has been found to impart shear thickening behavior to the structured system. This is believed to be due to the amino group imparting droplet-to-droplet hydrogen bonding, and it is this associated cluster of droplets that causes the thickening upon application of shear.

[0015] A high HLB amphiphile or hydrotrope comprises at least one polar head group and at least one lipophilic tail. The lipophilic tail may be aliphatic or aromatic. The hydrotrope may have a lipophilic tail containing at least 5, alternatively about 6, about 7, about 8, about 9, about 10, or about 11 carbon atoms. In some embodiments, the lipophilic tail is a linear lipophilic tail. In embodiments containing a linear lipophilic tail, the carbon chain may contain 5, alternatively about 6, about 7, about 8, about 9, about 10, or about 11 carbon atoms. In some embodiments, the lipophilic tail is a cyclic or branched tail. For a cyclic (including aromatic) tail with 6 carbon atoms, the tail should have at least one pendant methyl group. Alkylbenzene sulfonates containing 6 or more carbon atoms in the alkyl portion are not considered hydrotropes as defined herein. The polar groups may include sulfate, sulfonate, carboxylate, or phosphate groups. The counter ion of the polar head group may be sodium, potassium, lithium, monoethanolamine, diethanolamine, or triethanolamine.

[0016] In some embodiments, the high HLB amphiphile may have a double polar or dipolar head group. For example, it is believed that sulfonated oleic acid may function as a high HLB component in structured aqueous systems. Without being bound by theory, this may be due to the molecules in the mixture being sulfonated at the double bond, making them short-tailed double-headed hydrotropes. These molecules are believed to fold together in the vesicle, with around 10 carbon atoms incorporated into the lipophilic portion of the bilayer.

[0017] Di-(C4-C18)-alkyl phosphates can also function as hydrotropes in structured aqueous systems. In the case of hydrotropes having a single cyclic tail, the total number of carbon atoms can be 7 to 11. The tail containing 7 to 11 carbon atoms is considered to produce sufficient lipophilicity for the tail to associate in the liquid crystal bilayer. In the case of hydrotropes having a bipolar head group, the number of carbon atoms can be 7 to 11 carbon atoms per polar head group. Examples of hydrotropes that can be used in the present invention are triethanolamine octanoate, ethanolamine octanoate, sodium octyl sulfate, sodium cumenesulfonate, sodium xylenesulfonate, sodium toluenesulfonate, sulfonated oleic acid, ammonium octyl sulfate, triethanolamine octyl sulfate, and octylamine hydrochloride.

[0018] Experiments show that in the case of a linear tail, a minimum chain length of about 7 to 8 carbon atoms is preferred for forming a liquid crystal. Amphiphilic substances with shorter chain lengths may be too soluble. The preferred short chain length of the lipophilic tail of the amphiphilic substance, that is, about 7 to 10 carbon atoms, is considered to form a very flexible narrow bilayer, and this flexibility allows them to be filled into microvesicles containing only a few concentric shells (e.g., 5). These microvesicles are considered to be lamellar phase nanodroplets that are electrically neutral as a whole but have a positively charged surface. Without being bound by theory, an unequal charge distribution in the droplets is considered to always repel the droplets from each other, resulting in a 3D structure with a yield point that can suspend solids, liquids, or gases.

[0019] Linear amphiphilic substances having longer chains, i.e., 12 or more carbon atoms, can result in thicker bilayers, which are more rigid and tend to be filled in multilayered membrane macrovesicles having dozens of concentric shells. The macrovesicles are sized to reflect light rather than transmit it, and as a result, these particular systems are opaque.

[0020] Figure 1 shows an example of the low HLB (water-insoluble) amphiphilic substance of the present invention that has been found to be effective in the formation of a structured alkaline suspension system. Figure 2 shows an example of the high HLB (water-soluble) amphiphilic substance of the present invention that has been found to be effective in the formation of a structured alkaline system. To produce an alkaline structured aqueous system, any combination of the low HLB amphiphilic substances in Figure 1 may be blended together with any combination of the high HLB amphiphilic substances (hydrotropes) in Figure 2, as long as the combination of low HLB amphiphilic substances includes at least one amphiphilic substance containing an amine group. The alkaline structured aqueous system formed from the combination of the low HLB amphiphilic substance and the high HLB amphiphilic substance has high transparency and can suspend solids. However, the amphiphilic substances shown in Figures 1 and 2 are not intended to be an exhaustive list of examples of the present invention.

[0021] At least one water-soluble amphiphilic substance and at least one water-insoluble amphiphilic substance are mixed together in water to obtain a structured aqueous system. The active ingredients of the suspension system (i.e., the hydrotrope and at least one water-insoluble amphiphilic substance) may be present in a total amount of about 2 to about 50 wt / wt%, about 4 to about 45 wt / wt%, about 6 to about 40 wt / wt%, about 8 to about 35 wt / wt%, about 10 to about 30 wt / wt%, or about 15 to about 25 wt / wt% based on the total weight of the structured aqueous system.

[0022] The hydrotrope and at least one water-insoluble amphiphilic substance may be present in a total amount of at least about 2 wt / wt%, about 4 wt / wt%, about 6 wt / wt%, about 8 wt / wt%, about 10 wt / wt%, about 12 wt / wt%, about 14 wt / wt%, about 16 wt / wt%, about 18 wt / wt%, about 20 wt / wt%, about 22 wt / wt%, about 24 wt / wt%, about 26 wt / wt%, about 28 wt / wt%, about 30 wt / wt%, about 35 wt / wt%, about 40 wt / wt%, about 45 wt / wt%, or at least about 50 wt / wt% based on the total weight of the structured aqueous system.

[0023] In some embodiments, the concentration of the amphiphilic substance may need to be 10 wt% or more in order to "fill" the available volume and provide a yield point. However, by adding components to the structured aqueous system that can increase the repulsive force of the nanodroplets, it may be possible to provide a yield point at an activator concentration of less than 10%. Components that may be able to increase the repulsive force between the nanodroplets include morpholine soaps, C8 / C10 alkylamine oxides, 1,4-thiazine, thiomorpholine, and thiomorpholine 1,1-dioxide.

[0024] The ratio of the hydrotrope to the water-insoluble amphiphilic substance is determined, at least in part, by the specific hydrotrope and water-insoluble amphiphilic substance that form the structured system. Suitable suspension systems containing high HLB and low HLB amphiphilic substances, and the optimal ratio of the specific components, can be determined experimentally. Hydrotropes and water-insoluble amphiphilic substances in various ratios are pre-blended together and subsequently diluted with water to a total surfactant concentration of about 15 wt% and mixed (low shear mixing by hand). Compositions that thicken upon mixing and remain substantially transparent are subsequently shaken to introduce air. Identify isotropic compositions that suspend bubbles and subsequently evaluate as "strong" or "weak" (high or low yield point) depending on whether the system suspends large or small bubbles. In various samples prepared at different ratios of high HLB amphiphilic substance to low HLB amphiphilic substance, usually some samples exhibit suspension characteristics. Samples in the intermediate range within a certain range exhibit the highest yield point, i.e., tend to suspend the largest bubbles, so the center of the intermediate range is identified as the optimal ratio for microvesicle formation. Generally, the appropriate weight ratio of water-insoluble amphiphilic substance to hydrotrope can be in the range of 1:1 to about 4:1.

[0025] The structured aqueous system is produced by low-shear mixing the respective components together at room temperature or a temperature higher than room temperature, such as about 27 °C, about 28 °C, about 29 °C, about 30 °C, about 32 °C, about 34 °C, or about 35 °C. The mixing is applied until the blend thickens and reaches the yield point, which is the point at which the blend is able to suspend insoluble (solid, liquid, or gas) particles. The amphiphilic substances are usually (but not necessarily) pre-blended together before being dispersed in water. This has the advantage of preventing the occurrence of unwanted emulsification. There is also the added benefit of producing a commercially available concentrate for sale to customers who prefer to "make it themselves" the finished structured liquid formulation in the pre-blending of the amphiphilic substances. The highly active agent concentrate can still be poured and is easily dispersed by low-shear mixing at room temperature to form a structured aqueous system. Although shear-thickening, the resulting structured aqueous system has a viscosity low enough to be flowable and achieves good suspension ability without the addition of electrolytes, i.e., it can be electrolyte-free. In some embodiments, the structured aqueous system is transparent or slightly turbid.

[0026] The structured aqueous system can be stable within a temperature range of 0 to 60 °C, and depending on the system, it can also be stable at lower or higher temperatures than this. The structured aqueous system is a low-foaming system that can be used to suspend various solid, liquid, or gas particles and is particularly useful in applications where foaming is not desired or where a surfactant system cannot be used due to interactions with the dispersant. Since the structured system is alkaline, it can be beneficial for suspending acidic substances, or it can be used in applications where an acidic system is not suitable or where pH control is required. The shear-thickening behavior of the structured alkaline system can make such a system useful for preventing the suspended solids from settling during transportation, etc. Substances suspended in a shear-thinning system can tend to settle during transportation due to movement. The structured alkaline system of the technology of the present invention may be able to better maintain substances in a suspended state due to the shear-thickening behavior of the alkaline structured system.

[0027] Examples of particulate solids that can be suspended in the structured aqueous system of the present invention include, but are not limited to, graphene, diamond powder, insecticides and herbicides, and pigments. The amount of particulate solid that can be suspended in the structured aqueous system of the present invention can be in the range of about 0.5 wt% to about 25 wt% of the structured aqueous system. The structured aqueous system can be used in many different applications, such as the production of graphene dispersions, diamond suspensions (lapping fluids), oil-free lubricants, cutting fluids, insecticides, herbicides, and / or agricultural compositions such as fertilizer suspensions, pigment suspensions, suspensions of adhesives, media for 3D printing, and ink suspensions.

[0028] In some embodiments, the structured alkaline aqueous system can be used to suspend graphene particles. Thus, one aspect of the technology of the present invention is a method for producing a stable graphene dispersion. The production of the graphene dispersion is by forming an alkaline structured aqueous system, the alkaline structured aqueous system comprising water and a mixture of at least one water-soluble amphiphilic substance and at least one water-insoluble amphiphilic substance containing at least one amine group, the at least one water-soluble amphiphilic substance being a hydrotrope comprising at least one polar head group and a lipophilic tail group having 6 to 11 carbon atoms per polar head group, in an amount of 2 wt% to 50 wt% based on the weight of the structured aqueous system; and suspending graphene particles in the structured aqueous system to form a stable graphene dispersion. In some embodiments, the graphene particles may be mixed with the hydrotrope and water to form a homogeneous mixture, and subsequently, a low HLB water-insoluble amphiphilic substance may be added to this mixture to form a structured aqueous system in which the graphene particles are stably dispersed in the structured aqueous system. As another option, the low HLB water-insoluble amphiphilic substance and the hydrotrope may be mixed together to form an alkaline structured aqueous system, and the graphene particles may be mixed with this structured aqueous system to form a stable graphene dispersion. In some embodiments, the low HLB amphiphilic substance and the hydrotrope may be pre-blended to form a concentrate, which is subsequently diluted to form the structured aqueous system. The graphene particles may be mixed with the concentrate before dilution.

[0029] Example In the following examples, some preferred embodiments of the technology of the present invention, which is not limited to the technology, are described. Other embodiments include, but are not limited to, those described in the above description including additional or alternative components, alternative concentrations, and additional or alternative properties and uses.

[0030] Example 1 A 3:1 weight / weight blend of octylamine:octylamine hydrochloride was prepared at a total surfactant amount of 11.0 wt% by adding octylamine to a hydrochloric acid solution at room temperature and gently stirring the mixture by hand. The resulting sample had slight turbidity and a viscosity of approximately 2000 cp at room temperature. It had a strong yield point (as indicated by the suspension of large bubbles) and was found to thicken upon stirring. When stirring was stopped, the viscosity was found to drop back to its original value.

[0031] Example 2 A 1:1.6 weight / weight blend of sulfonated oleic acid:octylamine was prepared at a total surfactant amount of 11.6 wt% by adding octylamine to a sulfonated oleic acid solution at room temperature and gently stirring the mixture by hand. The resulting sample had slight turbidity and a viscosity of approximately 1500 cp at room temperature. It had a strong yield point (as indicated by the suspension of large bubbles) and was found to thicken upon stirring. When stirring was stopped, the viscosity was found to drop back to its original value.

[0032] Example 3 Sodium cumenesulfonate:octylamine 1:1 weight / weight blend was prepared at 20.0 wt% activator by adding octylamine to a sodium cumenesulfonate solution at room temperature and gently stirring the mixture by hand. The resulting sample was turbid and had a viscosity of approximately 1500 cp at room temperature. It had a strong yield point (as indicated by the suspension of large bubbles) and was found to thicken upon stirring. When stirring was stopped, the viscosity was found to drop back to its original value.

[0033] Example 4 A structuring system for suspending graphene is prepared from a 3:1 weight / weight blend of octylamine:octylamine hydrochloride at a total activator amount of 4 wt%. This system can suspend 20 weight / weight% of 100% graphene powder (PUREGRAPH 50 from First Graphene) even with a total activator amount as low as 4%.

[0034] Here, the technology of the present invention is described in sufficient, clear, and concise terms so that those skilled in the art to which the present invention pertains can practice the technology of the present invention. It should be understood that the above description is of a preferred embodiment of the technology of the present invention and that modifications may be made thereto without departing from the spirit or scope of the technology of the present invention as set forth in the appended claims. Furthermore, the examples are not exhaustive and are provided to illustrate some of the embodiments included within the scope of the claims.

Claims

1. An alkaline structured aqueous system having a yield point and capable of suspending solid, liquid, or gaseous particles, wherein the structured aqueous system is (a) 2% to 50% by weight based on the weight of the structured aqueous system, (i) A water-soluble amphiphilic substance which is a hydrotrope comprising one or two polar head groups and lipophilic tail groups having 6 to 11 carbon atoms per polar head group, (ii) A water-insoluble amphiphilic substance having an amine group and a hydrophobic tail containing 6 to 11 carbon atoms, A mixture wherein the weight ratio of the water-insoluble amphiphilic substance to the hydrotrope is in the range of 1:1 to 4:1, and (b) Water up to 100% by weight of the structured aqueous system An alkaline structured aqueous system containing [the specified ingredient].

2. The alkaline structured aqueous system according to claim 1, wherein the water-soluble amphiphilic substance and the water-insoluble amphiphilic substance are present in a total amount of 10% to 30% by weight of the structured aqueous system.

3. The alkaline structured aqueous system according to claim 1, wherein the hydrotrope is selected from the group consisting of sodium toluenesulfonate, sodium xylenesulfonate, sodium cumenesulfonate, sodium octyl sulfate, triethanolamine octanoate, ethanolamine octanoate, sulfonated oleic acid, octylamine hydrochloride, ammonium octyl sulfate, and triethanolamine octyl sulfate.

4. The alkaline structured aqueous system according to claim 1 or 3, wherein the water-insoluble amphiphilic substance is selected from the group consisting of octylamine, p-ethylaniline, isopropylaniline, and p-toluidine.

5. The alkaline structured aqueous system according to claim 1, having an overall HLB value in the range of approximately 11 to approximately 13.

6. The alkaline structured aqueous system according to claim 1, further comprising solid particles, droplets, or bubbles stably suspended in the alkaline structured aqueous system.

7. The alkaline structured aqueous system according to claim 6, wherein the solid particles are graphene.

8. The alkaline structured aqueous system according to claim 6 or 7, wherein the solid particles constitute 0.5% to 25% by weight of the alkaline structured aqueous system.

9. A composition, (a) A structured aqueous system, wherein 2% to 50% by weight of the structured aqueous system, (i) A water-soluble amphiphilic substance which is a hydrotrope comprising one or two polar head groups and lipophilic tail groups having 6 to 11 carbon atoms per polar head group, (ii) A water-insoluble amphiphilic substance having an amine group and a hydrophobic tail containing 6 to 11 carbon atoms, A mixture wherein the weight ratio of the water-insoluble amphiphilic substance to the hydrotrope is in the range of 1:1 to 4:

1. (b) Solid particles, liquid particles, or gaseous particles suspended in the structured aqueous system, and (c) Water up to 100% by weight of the composition A composition containing the following:

10. The composition according to claim 9, wherein the water-soluble amphiphilic substance and the water-insoluble amphiphilic substance are present in a total amount of 10% to 30% by weight of the structured aqueous system.

11. The composition according to claim 9, wherein the hydrotrope is selected from the group consisting of sodium toluenesulfonate, sodium xylenesulfonate, sodium cumenesulfonate, sodium octyl sulfate, triethanolamine octanoate, ethanolamine octanoate, sulfonated oleic acid, octylamine hydrochloride, ammonium octyl sulfate, and triethanolamine octyl sulfate.

12. The composition according to claim 9 or 11, wherein the water-insoluble amphiphilic substance is selected from the group consisting of octylamine, p-ethylaniline, isopropylaniline, and p-toluidine.

13. The composition according to claim 9, wherein the solid particles suspended in the structured aqueous system constitute 0.5% to 25% by weight of the structured aqueous system.

14. The composition according to claim 13, wherein the solid particles suspended in the structured aqueous system are graphene particles.

15. A method for producing a stable graphene dispersion, (a) To form an alkaline structured aqueous system, Here, the alkaline structured aqueous system is water, and Based on the weight of the aforementioned structured aqueous system, 2% to 50% by weight, (i) A water-soluble amphiphilic substance which is a hydrotrope comprising one or two polar head groups and lipophilic tail groups having 6 to 11 carbon atoms per polar head group, (ii) A water-insoluble amphiphilic substance having an amine group and a hydrophobic tail containing 6 to 11 carbon atoms, A mixture comprising a mixture in which the weight ratio of the water-insoluble amphiphilic substance to the hydrotrope is in the range of 1:1 to 4:1, and (b) Suspending graphene particles in the alkaline structured aqueous system to form the stable graphene dispersion. Methods that include...

16. The method according to claim 15, wherein the graphene dispersion comprises 0.5% to 25% by weight of graphene particles.

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