Suspension systems constructed from hydrotropes

Abstract

Non-settling aqueous pourable suspensions can be produced from mixtures of water-soluble amphiphiles with 6-11 carbon atoms in the hydrophobic portion of the amphiphile and oil-soluble amphiphiles. The water-soluble amphiphiles are classified as hydrotropes. This system is low foaming and is particularly useful for suspending problematic materials such as graphene and diamond powders.

Description

[Technical field]

[0001]

[0001] The present invention relates to a structured, low foaming, amphiphilic suspending system for suspending water-insoluble or slightly water-soluble solid particles or liquids. The present invention further relates to compositions comprising the suspending system. [Background technology]

[0002]

[0002] Formulating suspensions of water-insoluble or slightly water-soluble solids or liquids in industrial compositions such as lapping fluids, pigment suspensions, or pesticide dispersions has been a long-standing challenge. Formulators need to suspend a wide variety of raw ingredients such as diamond powder or iron oxide, and pesticide formulators in particular have a pressing need to suspend active agents such as bifenthrin. More recently, the discovery of carbon nanotubes and graphene has posed major problems for formulators, such as how to prepare them as stable dispersions in aqueous media.

[0003]

[0003] The present inventors have discovered a novel, structured, low foaming composition that is extremely cost effective and capable of suspending particles of immiscible solids or liquids without settling, by using a blend of short chain amphiphiles in water.

[0004]

[0004] As used herein, the term "structured system" is intended to mean a pourable composition comprising water, an amphiphile, and optionally other dissolved substances which together form a mesophase or mesophase dispersion in a continuous medium, which has the ability to immobilize non-colloidal water-insoluble particles while the system is at rest, thereby forming a stable pourable suspension. The amphiphile and water interact to form what are commonly referred to as "liquid crystal phases", or alternatively "mesostatic phases" or "mesophases".

[0005]

[0005] The term "pourable" is used herein to mean a pseudoplastic fluid having a viscosity of around 2000 cps (at a shear rate of 21 cps) at room temperature.

[0006] Known structured surfactants generally contain an L-alpha phase, where the surfactant bilayer is arranged with the hydrophobic portion of the surfactant on the inside of the bilayer and the hydrophilic portion on the outside of the bilayer, and the bilayer is usually present in a parallel or concentric arrangement, alternating with layers of the aqueous medium.

[0007] Other conventional structured suspension systems may include a spherulitic phase. The spherulitic phase contains spheres, commonly referred to in the art as spherulites, with an onion-like structure containing concentric shells of surfactant. The spherulites usually have diameters in the range of 0.1 to 15 microns and are dispersed in the aqueous phase as in classical emulsions, but interact to form a structured system. Spherulitic systems are described in more detail in EP 0 151 884.

[0008]

[0008] Most structured surfactant systems require the presence of not only a surfactant and water, but also a structurant to form a system capable of suspending solids. The term "structurant" is used to describe any non-surfactant that, when dissolved in water, can interact with the surfactant to form a structured system. It is typically a desolubilizer for the surfactant, e.g., an electrolyte. The term "electrolyte" refers to an ionic compound that at least partially dissociates in aqueous solution to provide ions.

[0009] The main problem with lamellar structured surfactant suspensions is that they are most easily formed by high foaming mixtures of detergents (surfactants) plus electrolytes. Such high foaming mixtures are undesirable for industrial low foaming applications. Low foaming amphiphiles, classified as hydrotropes, are very soluble in water and actually tend to disrupt rather than aid in the formation of lamellar bilayers. Thus, previous attempts to formulate industrial low foaming suspensions have used detergents, and as a result, these systems have required the use of high concentrations of undesirable electrolytes and antifoam agents to minimize foaming from the detergent surfactants.

[0010]

[0010] Both electrolytes and antifoaming agents are non-essential ingredients in that they are added at extra cost to induce lamellar structure and suppress foaming. Therefore, there is a need for industrial compounders to be able to formulate low foaming suspensions without resorting to the addition of non-essential ingredients such as electrolytes and antifoaming agents.

[0011]

[0011] A further concern is that the lamellar bilayers formed in detergent plus electrolyte mixtures tend to be present in large vesicles containing many (e.g., 100-150) bilayers. The large vesicles dissolve slowly on dilution in water. Attempts to use systems containing large vesicles, for example in personal care formulations, have been largely unsuccessful, generally resulting in poor "flash foam" because it takes a significant amount of time to dissolve the vesicles in water. Thus, much smaller vesicles with only a few bilayers are preferred.

[0012]

[0012] Recently, it has been found that clear, electrolyte-free lamellar suspension systems can be formulated by preparing aqueous blends of (for example) glyceryl fatty acid esters with surfactants having high hydrophilic-lipophilic balance (HLB) values ​​("high HLB surfactants") (WO 2013 / 119908 A1). Such systems generate large amounts of foam when stirred with water, making them particularly suitable for personal care compositions, but not for low foaming industrial applications.

[0013]

[0013] A further consideration is cost. The suspending systems described in WO 2013 / 119908 A1 contain a high proportion of expensive ingredients, for example glyceryl caprylate / caprate. For personal care, where the cost of the individual ingredients is a small fraction of the selling price, this may not be as big an issue, but for industrial applications it is a huge concern.

[0014]

[0014] The low-cost amphiphiles of choice are usually hydrotropes, which have not been used in lamellar suspension systems so far because of their tendency to interact with and destroy liquid crystals. Indeed, one of the main applications of hydrotropes is in concentrated detergent systems, where they interact to prevent the formation of a liquid crystalline gel phase, for example in dispenser nozzles. Summary of the Invention

[0015] It is an object of embodiments of the present invention to provide a pourable, low foaming aqueous suspension system capable of suspending water-insoluble particles or liquids. It is also an object of embodiments of the present invention to overcome or mitigate at least one problem of the prior art, whether or not expressly disclosed herein.

[0016] According to a first aspect of the present invention, there is provided a structured aqueous system having a yield point and capable of suspending solid, liquid or gas particles, the structured aqueous system comprising a mixture of at least one water-soluble amphiphile and at least one water-insoluble amphiphile, the at least one water-soluble amphiphile being a hydrotrope. 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 a most unexpected and surprising discovery to find that it is possible to successfully formulate a low foaming structured lamellar suspension system containing a high proportion of hydrotrope. The system can have high optical clarity and a large yield point as evidenced by the fact that it is capable of suspending gas bubbles.

[0017] The hydrotrope may be a high HLB hydrotrope, having an HLB value of 10 or greater.

[0018] At least one water-insoluble amphiphile may be a low HLB amphiphile having an HLB value of less than 10.

[0019]

[0019] The low foaming structured aqueous system can be used to suspend problematic water-insoluble materials such as graphene and diamond powder for use in industrial applications where high foaming surfactants are not suitable. Thus, a further aspect of the invention is a composition comprising: (a) a structured aqueous system comprising water and 2% to 50% by weight, based on the weight of the structured aqueous system, of a mixture of at least one water-soluble amphiphile and at least one water-insoluble amphiphile, the at least one water-soluble amphiphile 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; and (b) at least one of solid, liquid, or gas particles suspended in the structured aqueous system. In some embodiments, the solid particles comprise about 0.5% to about 60% by weight of the composition. In some embodiments, the solid particles are graphene particles.

[0020] Another aspect of the invention is a method for making a stable graphene dispersion, comprising: (a) forming a structured aqueous system, the structured aqueous system comprising water and 2% to 50% by weight, based on the weight of the structured aqueous system, of a mixture of at least one water soluble amphiphile and at least one water insoluble amphiphile, where the at least one water soluble amphiphile is a hydrotrope comprising at least one polar head group and a lipophilic tail group having from 6 to 11 carbon atoms per polar head group; and (b) suspending graphene particles in the structured aqueous system to form a stable graphene dispersion. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows the chemical structures of exemplary low HLB amphiphiles and high HLB hydrotropes that can be used in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022]

[0022] The present invention relates to a suspension system based on a lamellar mesophase constructed from certain amphiphilic molecules. It may have high optical clarity, low foaming, and very low electrolytes. A system with high optical clarity typically has a light transmittance of greater than about 50 percent using a one 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" means that any bubbles that develop during processing to form the suspension are transient and collapse within a few seconds. A very low electrolyte system is one that has less than 2% by weight electrolyte, preferably less than 1% by weight electrolyte. For example, the structured aqueous system may be electrolyte-free. It has a wide range of applications as a suspension medium for payloads such as pesticides, pigments, graphene, oils, and the like. It is also believed to be useful in decommissioning nuclear power plants to wash, flush, and suspend radioactive particles, and to suspend high concentrations of (for example) lead to serve as a liquid radiation shield. It is believed that they may also find application in the emerging field of oil-free lubricants.

[0023]

[0023] Analysis of the suspension by small angle X-rays indicates that the units of the lamellar structure are microvesicles of regular size containing 3-6 concentric shells with bilayer spacings of 30-40 angstroms. The microvesicles are believed to be arranged in a regular lattice structure. This particular structure was identified in WO 2013 / 119908 A1, although the structured system in WO 2013 / 119908 is formed from a mixture of high foaming surfactants.

[0024]

[0024] Although microvesicles are electrically neutral overall, the surface of each microvesicle (when viewed from adjacent microvesicles) carries a net positive charge. Like positive charges repel each other, and as a result, each microvesicle is held in a high energy lattice. This lattice energy provides a yield point that allows the particles to be suspended indefinitely. A suspension system with a yield point is one that has an initial resistance to applied shear, which can be measured using a cone and plate viscometer.

[0025] The amphiphilic molecules used to prepare the suspension system include at least one water-insoluble amphiphile and at least one water-soluble amphiphile that is a hydrotrope. A hydrotrope is a molecule that has a hydrophilic or polar head group and a hydrophobic (lipophilic) portion or tail group, but the hydrophobic portion or tail group is generally too small to cause spontaneous self-association or aggregation in aqueous solution. Hydrotropes are usually not surface active and typically do not form micelles or lamellar vesicles. Surprisingly, it has now been found that certain combinations of water-insoluble amphiphiles and hydrotropes are capable of forming structured systems that have a yield point and can suspend solid particles, liquid droplets, or gas bubbles.

[0026]

[0026] Amphiphiles for use in preparing structured systems should include at least one amphiphile with a low hydrophilic-lipophilic balance (HLB), e.g., less than 10, and at least one amphiphile with a high HLB, e.g., greater than or equal to 10. The overall HLB of the mixture should be in the range in which liquid crystals are formed, which may be about 11 to 13, preferably about 12 HLB units.

[0027]

[0027] The low HLB amphiphile has a polar head group containing a terminal OH group, which may be hydroxyl or carboxyl, and contains a lipophilic (hydrophobic) tail group. It has been found that low HLB amphiphiles that do not contain at least one hydroxyl or carboxyl in the polar head group may not induce the formation of a structured aqueous system. In some embodiments, the low HLB amphiphile may contain at least one lipophilic tail containing at least about 4 carbon atoms, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, or at least about 14 carbon atoms. The lipophilic tail may be linear or branched.

[0028] In some embodiments, the low HLB amphiphile may include at least one linear tail having a carbon chain containing at least about 4, about 5, about 6, about 7, about 8, about 9, or about 10 carbon atoms. In some embodiments, the low HLB amphiphile may include at least one hydroxyl group in addition to the terminal OH group. Without being bound by theory, it is believed that the hydroxyl groups of the low HLB amphiphile exchange protons with the sulfate / carboxyl anions of the hydrotrope, and the entire surface of the vesicle is in a state of flux or resonance. This is believed to be the driving force for vesicle formation and the "cement" that holds the vesicles together. Examples of water-insoluble amphiphiles suitable for forming suspension systems include 1,2-octanediol, ethylhexylglycerin, octanol, octanoic acid, and glyceryl caprate / caprylate.

[0029]

[0029] High HLB amphiphiles (hydrotropes) contain 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 of 6 carbons, the tail should have at least one pendant methyl group. Alkylbenzenesulfonates 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 counterion of the polar head group may be, for example, sodium, potassium, lithium, monoethanolamine, diethanolamine, or triethanolamine.

[0030] 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 molecules in the mixture being sulfonated at the double bond to make them short-tailed double-headed hydrotropes. These molecules are believed to fold together in the vesicle such that as many as 10 carbon atoms are incorporated into the lipophilic portion of the bilayer. Di(C4-C18) alkyl phosphate esters may also function as hydrotropes in structured aqueous systems.

[0031] In some embodiments, the hydrotrope can be a salt of a C6-C10 carboxylic acid, such as, for example, morpholine octanoate. In other embodiments, the hydrotrope can be a cationic protonated amine oxide, such as, for example, dimethyloctylamine oxide, that is protonated with an acid.

[0032] For hydrotropes with a single cyclic tail, the total number of carbon atoms in the tail can be from 7 to 11. It is believed that tails containing 7 to 11 carbon atoms provide sufficient lipophilicity to allow the tail to associate in liquid crystal bilayers. For hydrotropes with bipolar or dipolar head groups, the number of carbon atoms can be from 7 to 11 carbon atoms per polar head group. Examples of hydrotropes that can be used in the present invention are triethanolamine octanoate, morpholine octanoate, sodium octyl sulfate, sodium cumene sulfonate, sodium xylene sulfonate, sodium toluene sulfonate, and sulfonated oleic acid.

[0033] Experiments indicate that for linear tails, a minimum chain length of around 7-8 carbon atoms is preferred to form liquid crystals. Amphiphiles with shorter chain lengths may be too soluble. The preferred short chain length of the lipophilic tails of amphiphiles, i.e. around 7-10 carbon atoms, is believed to form very flexible narrow bilayers, which flexibility allows them to be packed into microvesicles containing only a few concentric shells (e.g. 5). These microvesicles are believed to be nanodroplets of lamellar phase that are electrically neutral overall but have a positively charged surface. Without wishing to be bound by theory, it is believed that the uneven charge distribution in the droplets causes them to constantly repel each other, resulting in a 3D structure with a yield point in which solids, liquids or gases can be suspended.

[0034]

[0034] Linear amphiphiles with longer chains, i.e., 12 or more carbon atoms, can result in thicker bilayers, which tend to be more rigid and packed into multilamellar large vesicles with tens of concentric shells. The large vesicles are sized to reflect light rather than transmit it, and as a result, these particular systems are opaque. However, it may be possible to include amphiphiles with linear tails of 12 or more carbon atoms, so long as at least the majority of the lipophilic tails in the overall blend of low and high HLB amphiphiles have less than 12 carbon atoms.

[0035]

[0035] Figure 1 shows examples of low HLB and high HLB amphiphiles of the present invention that have been found to be effective. Any combination of the low HLB amphiphiles of Figure 1 may be blended together with any combination of the high HLB amphiphiles (hydrotropes) of Figure 1 to produce highly transparent, structured aqueous systems capable of suspending solids. However, the examples of Figure 1 are not intended to be an exhaustive list of examples of the present invention.

[0036]

[0036] At least one water-soluble amphiphile (hydrotrope) and at least one water-insoluble amphiphile 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 amphiphile) can 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.

[0037]

[0037] The hydrotrope and at least one water-insoluble amphiphile 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.

[0038] The hydrotrope and at least one water-insoluble amphiphile may be present in a total amount of about 2 wt / wt% or less, about 4 wt / wt% or less, about 6 wt / wt% or less, about 8 wt / wt% or less, about 10 wt / wt% or less, about 12 wt / wt% or less, about 14 wt / wt% or less, about 16 wt / wt% or less, about 18 wt / wt% or less, about 20 wt / wt% or less, about 22 wt / wt% or less, about 24 wt / wt% or less, about 26 wt / wt% or less, about 28 wt / wt% or less, about 30 wt / wt% or less, about 35 wt / wt% or less, about 40 wt / wt% or less, about 45 wt / wt% or less, or about 50 wt / wt% or less, based on the total weight of the structured aqueous system.

[0039] In some embodiments, the concentration of the amphiphile may need to be 10% by weight or more to "fill" the available volume and provide a yield point. However, by adding ingredients to the structured aqueous system that can increase the repulsion of the nanodroplets, it may be possible to provide a yield point at active agent concentrations less than 10%. Potential ingredients that can increase the repulsion between the nanodroplets include morpholine soaps, C8 / C10 alkylamine oxides, 1,4-thiazine, thiomorpholine, and thiomorpholine 1,1 dioxide.

[0040] The ratio of hydrotrope to water-insoluble amphiphile is determined, at least in part, by the particular hydrotrope and water-insoluble amphiphile that form the structured system. Suitable suspending systems containing high and low HLB amphiphiles, and the optimal ratio of the particular components, can be determined by experimentation. Various ratios of hydrotrope and water-insoluble amphiphile are pre-blended together, then diluted with water to a total active concentration of about 15% by weight, and mixed (low shear manual mixing). The composition thickens upon mixing and remains substantially transparent, and then aerated by shaking. Isotropic (to visible light) compositions that suspend air bubbles are identified and rated as "strong" or "weak" (high or low yield point) depending on whether the system suspends large or small air bubbles. In various samples prepared with different ratios of high HLB amphiphile to low HLB amphiphile, some samples usually exhibit suspending properties. Samples in the middle of the range tend to exhibit the highest yield points, i.e., suspend the largest air bubbles, and therefore the center of the middle range is identified as the optimal ratio for microbubble formation. In general, a suitable weight ratio of water-insoluble amphiphile to hydrotrope can be in the range of 1:1 to about 4:1.

[0041]

[0041] The structured aqueous system is produced by low shear mixing of the components together at room temperature or at a temperature higher than room temperature, for example, about 27°C, about 28°C, about 29°C, about 30°C, about 32°C, about 34°C, or about 35°C. Mixing is applied until the blend thickens and reaches its yield point, which is the point at which the blend is capable of suspending insoluble (solid, liquid, or gas) particles. The amphiphiles are usually (but not necessarily) pre-blended together before dispersing in water. This has the advantage of preventing unwanted emulsification from occurring. Pre-blending the amphiphiles also has the added benefit of producing a commercial concentrate for sale to customers who prefer to make "in-house" finished structured liquid formulations. It has been found that the high surfactant concentrate is pourable and disperses easily in water with low shear mixing at room temperature to form a structured aqueous system. The resulting structured aqueous system is flowable and achieves good suspending capabilities without the addition of electrolytes, i.e., it can be electrolyte-free, hi some embodiments, the structured aqueous system is clear or slightly hazy.

[0042]

[0042] The structured aqueous system may be stable within a temperature range of 0-60°C, with some systems being stable even at lower or higher temperatures. The structured aqueous system is a low foaming system that can be used to suspend a variety of solid, liquid, or gas particles, and is particularly useful in applications where foaming is not desired or where surfactant systems cannot be used due to interactions with the dispersant. 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 total amount of particulate solids that can be suspended in the structured aqueous system may be in the range of about 0.5% to about 60% by weight of the structured aqueous system. The structured aqueous system may be used in many different applications, such as the manufacture of graphene dispersions, diamond suspensions (lapping fluids), oil-free lubricants, cutting fluids, agricultural compositions such as insecticide, herbicide, and / or fertilizer suspensions, pigment suspensions, adhesive suspensions, 3D printing media, and ink suspensions.

[0043]

[0043] In some embodiments, the structured aqueous system can be used to suspend graphene particles. Thus, one aspect of the present technology is a method for making a stable graphene dispersion. The graphene dispersion can be made by forming a structured aqueous system, the structured aqueous system comprising water and 2% to 50% by weight, based on the weight of the structured aqueous system, of a mixture of at least one water-soluble amphiphile and at least one hydroxyl-terminated water-insoluble amphiphile, the at least one water-soluble amphiphile 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; and suspending graphene particles in the structured aqueous system to form a stable graphene dispersion. In some embodiments, the graphene particles can be mixed with the hydrotrope and water to form a homogenous mixture, followed by adding a low HLB amphiphile to the mixture to form a structured aqueous system in which the graphene particles are stably dispersed in the structured aqueous system. Alternatively, the low HLB amphiphile and hydrotrope may be mixed together to form a structured aqueous system, and the graphene particles may be mixed with the structured aqueous system to form a stable graphene dispersion. In some embodiments, the low HLB amphiphile and hydrotrope may be pre-blended to form a concentrate, which is then diluted to form the structured aqueous system. The graphene particles may be mixed with the concentrate prior to dilution. EXAMPLES

[0044] The following examples describe some of the preferred embodiments of the present technology, without limiting the technology. Other embodiments include, but are not limited to, those described in the textual description above, including additional or alternative ingredients, alternative concentrations, and additional or alternative properties and uses.

[0045] Example 1

[0045] The optimum ratio of high HLB amphiphile to low HLB amphiphile was identified for several binary blends by the method described in paragraph

[0040] above. All blends had strong yield points, i.e., they suspended large bubbles at room temperature without degassing. The blends are listed in Table 1 below.

[0046] [Table 1]

[0047] The structures of samples 1, 3, 4, 6, 8, and 9 listed in Table 1 were analyzed by small angle X-ray scattering. The scattering patterns of the samples all exhibited weak scattering and showed symmetrical lumps with peaks around 30-40 angstroms. Further evidence from electron micrographs suggests that these systems contain regularly sized microvesicles with around 3-6 concentric shells.

[0048] Example 2

[0047] The optimum ratios of high HLB amphiphile to low HLB amphiphile were identified for sodium xylene sulfonate, sodium toluene sulfonate, and sodium cumene sulfonate in combination with glyceryl caprylate / caprate by the method described in paragraph

[0040] above. In this series, the total actives concentration was fixed at 25% w / w. The ratios are shown in Table 2.

[0049] [Table 2]

[0050] The strongest suspending system was obtained with sodium cumene sulfonate and the weakest with sodium toluene sulfonate. Sodium xylene sulfonate was intermediate between the two. These results indicate that the yield point of the system increases with increasing amount of alkyl substitution on the benzene ring and that the microbubbles contain as many as three molecules of low HLB amphiphile per two molecules of hydrotrope.

[0051] Example 3 Various ratios of glyceryl oleate to sodium cumene sulfonate were investigated at 15% total active by the method described in paragraph

[0040] above. An opaque structured system was obtained with 2:1 (w / w) oleate:sulfonate. This confirms that higher amounts of longer linear tails (>C10) produce larger vesicles that scatter light and give opaque suspension systems.

[0052] Example 4 Sodium cyclamate (a sweetener, hydrotrope) was unable to induce the formation of a structured system when combined with either Lactem or oleic acid (low HLB emulsifiers), fully confirming that at least one pendant methyl group must be present for hydrotropes containing a C6 ring to function as co-structurants.

[0053] Example 5 Pure (99%) lauric acid was partially neutralized with triethanolamine in hot water (60°C) to obtain a 15% w / w blend of lauric acid (low HLB component) and lauric acid soap (high HLB component). Ratios of 1.5:1, 1:1, and 1.0:1.5 (w / w) lauric acid:TEA soap were prepared. Pourable, cloudy liquids with strong yield points were obtained. However, the samples had a "lumpy" heterogeneous appearance (like chunks of dispersed gel), unlike the clear, isotropic systems obtained with C7-C10 chains. These results indicate that the lipophilic tail should have an alkyl chain length of less than 12 carbon atoms.

[0054] Example 6

[0052] When a blend of octanoic acid:morpholine octanoate 1:1.4 (w / w) with a total active concentration of 10 wt% is prepared in water, a structured system with good suspending power is formed. This may be due to charge repulsion from the unshared electron pair on the oxygen in morpholine imparting additional energy to the lattice. This particular system has texture when viewed between polarizing filters, indicating that the system is anisotropic.

[0055] Example 7 A 0.5% w / w graphene dispersion was prepared using a structured aqueous system in which the low HLB amphiphile was octanoic acid and the hydrotrope was triethanolamine octanoate. The ratio of octanoic acid to triethanolamine octanoate was 1.25 parts by weight octanoic acid to 1.0 part by weight triethanolamine octanoate, resulting in a total actives concentration of 17.5% by weight based on the total weight of the structured aqueous system. After storage at room temperature for 3 weeks, the graphene dispersion had no visible precipitation of graphene.

[0056] Example 8 A 2% w / w graphene oxide dispersion was prepared using the same structured aqueous system as in Example 7, except the total active concentration was 15% w / w instead of 17.5% w / w. The dispersion had a viscosity of about 1000 cps at room temperature, was pourable, and did not settle for over 3 weeks.

[0057] Example 9 A 40 g sample of "puregraph 50" (100% graphene) was mixed with 12 g sulfonated oleic acid (50% solids) and 150 g DI water and homogenized at room temperature for 45 minutes using a Silverson mixer. The pH of the homogenized mixture was 5.5. 7.6 g of caprylic / capric glyceryl (StepanMild® GCC, available from Stepan Company, Northfield, Illinois) was then added by hand with a spatula to the 86.1 g mixture with gentle stirring. The graphene composition contained 18.2 wt / wt% graphene, 10.8% surfactant caprylic / capric glyceryl:sulfonated oleic acid in a 3:1 (wt / wt) ratio. The composition was homogenous, stable, easily pourable (approximately 900 cps at room temperature) and showed no precipitation / separation after 4 days at room temperature.

[0058] Example 10 Combinations of N,N-dimethyl-N-octylhydroxylamine (ColaLux C-8 from Colonial) and glyceryl caprylate / caprate (StepanMild® GCC) were prepared in different ratios (15% w / w total active). Samples ranged from 3:1 to 10:1 (w / w) GCC:amine oxide and were prepared by hand mixing at room temperature. Only the 4:1 (w / w) GCC:amine oxide sample appeared to have very weak structure. However, adding a small amount of HCL to the 4:1 (w / w) GCC:amine oxide with 15% active immediately gave a clear, strongly structured system. Without being bound by theory, it is believed that under acidic conditions, the NO amino group is protonated to produce cationic hydroxylamine as shown in the reaction scheme below, and this species is believed to facilitate nanodroplet formation.

[0059] [ka]

[0060] These results indicate that it may be possible to form a structured system after formation of a solid dispersion. For example, solid particles can be dispersed in a neutral aqueous mixture of StepanMild® GCC and an amine oxide, any entrained air can be removed, and the dispersion is subsequently acidified with an acid to form a structured system.

[0061]

[0058] The present invention is now described in such full, clear and concise terms as to enable any person skilled in the art to which the present invention pertains to practice the present invention. It is to be understood that the foregoing describes preferred embodiments of the present invention, and that modifications may be made therein without departing from the spirit or scope of the present invention as set forth in the appended claims. Moreover, the examples are not exhaustive, but are provided to illustrate some embodiments falling within the scope of the claims.

Claims

1. 1. A structured aqueous system having a yield point and capable of suspending solid, liquid, or gas particles, said structured aqueous system comprising: (a) from 2% to 50% by weight, based on the weight of the structured aqueous system, of a mixture of at least one water-soluble amphiphile and at least one water-insoluble hydroxy-terminated amphiphile, wherein the at least one water-soluble amphiphile is a hydrotrope comprising at least one polar head group and a lipophilic tail group having from 6 to 11 carbon atoms per polar head group; and (b) water in amounts that together make 100% of the structural aqueous system; A structured aqueous system comprising:

2. 10. The structured aqueous system of claim 1, wherein the at least one water-soluble amphiphile and the at least one water-insoluble amphiphile are present in a combined amount of 10% to 30% by weight of the structured aqueous system.

3. 3. The structured aqueous system of claim 1 or 2, wherein the water-insoluble amphiphile has a hydrophobic tail containing from 6 to 11 carbon atoms.

4. 10. The structured aqueous system of claim 1, wherein the hydrotrope is selected from the group consisting of sodium toluene sulfonate, sodium xylene sulfonate, sodium cumene sulfonate, octyl sulfate, triethanolamine octanoate, morpholine octanoate, sulfonated oleic acid, and di(C4-C18) alkyl phosphate esters.

5. The structured aqueous system of claim 1 , wherein the water-insoluble amphiphile comprises at least one additional hydroxyl group.

6. 10. The structured aqueous system of claim 1, wherein the water-insoluble amphiphile is selected from the group consisting of 1-octanol, octanoic acid, 1,2 octanediol, ethylhexylglycerin, and glyceryl caprate / caprylate.

7. 10. The structured aqueous system of claim 1, wherein the weight ratio of water-insoluble amphiphile to hydrotrope is in the range of 1:1 to 4:

1.

8. 10. The structured aqueous system of claim 1 having an overall HLB value in the range of about 11 to about 13.

9. 10. The structured aqueous system of claim 1, further comprising solid particles, liquid droplets, or gas bubbles stably suspended in said structured aqueous system.

10. 10. The structured aqueous system of claim 9, wherein the solid particles are graphene.

11. 11. The structured aqueous system of claim 9 or 10, wherein the solid particles comprise up to 60% by weight of the structured aqueous system.

12. (a) a structured aqueous system comprising water and 2% to 50% by weight, based on the weight of the structured aqueous system, of a mixture of at least one water-soluble amphiphile and at least one hydroxy-terminated water-insoluble amphiphile, wherein the at least one water-soluble amphiphile is a hydrotrope comprising at least one polar head group and a lipophilic tail group having from 6 to 11 carbon atoms per polar head group; and (b) at least one of solid, liquid, or gas particles suspended in said structured aqueous system; A composition comprising:

13. 13. The composition of claim 12, wherein the at least one water-soluble amphiphile and the at least one water-insoluble amphiphile are present in a combined amount of from 10% to 30% by weight of the structured aqueous system.

14. 14. The composition of claim 12 or 13, wherein the water-insoluble amphiphile has a hydrophobic tail containing from 6 to 11 carbon atoms.

15. 13. The composition of claim 12, wherein the hydrotrope is selected from the group consisting of sodium toluene sulfonate, sodium xylene sulfonate, sodium cumene sulfonate, octyl sulfate, triethanolamine octanoate, morpholine octanoate, sulfonated oleic acid, and di(C4-C18) alkyl phosphate esters.

16. The composition of claim 12 , wherein the water-insoluble amphiphile comprises at least one additional hydroxyl group.

17. 13. The composition of claim 12, wherein the water-insoluble amphiphile is selected from the group consisting of 1-octanol, octanoic acid, 1,2 octanediol, ethylhexylglycerin, and glyceryl caprate / caprylate.

18. 13. The composition of claim 12, wherein the solid particles suspended in the structured aqueous system comprise from about 0.5% to about 60% by weight of the composition.

19. 13. The composition of claim 12, wherein the solid particles suspended in the structured aqueous system are graphene particles.

20. 1. A method for producing a stable graphene dispersion, comprising: (a) forming a structured aqueous system, the structured aqueous system comprising water and 2% to 50% by weight, based on the weight of the structured aqueous system, of a mixture of at least one water-soluble amphiphile and at least one hydroxyl-terminated water-insoluble amphiphile, the at least one water-soluble amphiphile 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; and (b) suspending the graphene particles in the structured aqueous system to form the stable graphene dispersion; A method comprising:

21. 21. The method of claim 20, wherein the graphene dispersion comprises up to 60% by weight of graphene.

22. 22. The method of claim 20 or 21, wherein the graphene particles are mixed with the hydrotrope and water to form a homogeneous mixture, and the water-insoluble amphiphile is added to the mixture to form the structured aqueous system.

23. 21. The method of claim 20, wherein the water-insoluble amphiphile and the hydrotrope are pre-blended to form a concentrate, and the concentrate is diluted with water to form the structured aqueous system.

24. 21. The method of claim 20, wherein the graphene in the graphene dispersion does not settle at room temperature for at least three weeks.

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