WO2019136517A1 - Viscoelastic fluid comprising non-ionic surfactant - Google Patents

Abstract

The invention provides a viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic surfactant comprises surfactant molecules having the formula: X–L–R, wherein: each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group, wherein a sufficient fraction of the surfactant molecules have R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5; and wherein a sufficient proportion of the surfactant molecules have R groups configured to solubilise the non-ionic surfactant in the viscoelastic fluid.

Description

Viscoelastic fluid comprising non-ionic surfactant

Technical Field

[1 ] The invention relates to viscoelastic fluids comprising non-ionic surfactant, and to non-ionic surfactant molecules. In particular, the viscoelastic fluids comprise non-ionic surfactant molecules having the formula X-L-R, where each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group. A sufficient fraction of the surfactant molecules are configured to confer viscoelastic properties to aggregates of the surfactant in the fluid, while a sufficient proportion of the surfactant molecules are configured to solubilise the surfactant in the fluid.

Background of Invention

[2] Surfactant-based viscoelastic fluids are of interest in a wide variety of applications, including as breakable viscosifers in oil field treatment fluids, as thickeners in home and personal care products, and as atomisation modulators in sprayable formulations for agriculture. An aqueous fluid comprising surfactant is thought to exhibit viscoelastic properties via self-assembly of the surfactant into elongated “worm-like” micelles of sufficient length and concentration to form an entangled network, similar to a polymer melt or solution. Unlike entangled polymers, however, the micelles can dynamically break and re-form in response to shear forces, and can advantageously be dissipated via a change in composition of the fluid.

[3] Surfactants with relatively larger hydrophilic head groups compared with the lipophilic tail are generally more soluble in aqueous formulations, according to the hydrophilic-lipophilic balance. However, the geometrical asymmetry of such surfactants often favours curved micellar interfaces, and hence tends towards spherical micelles. On the other hand, reducing the relative size of the head group to favour less curved micellar interfaces is known to produce elongated micellar structures. However, reducing the head group size in simple single-surfactant systems typically results in insolubility of the surfactant before the micellar elongation is sufficient to provide viscoelastic entanglement. Thus, many surfactant molecules with small hydrophilic head groups exhibit Krafft behaviour at room temperature, which limits their effectiveness as viscoelastic fluids for many potential applications. Therefore, previous strategies to develop viscoelastic surfactant systems have focused on deploying various additives to reduce the effective average cross- sectional head group area of strongly hydrophilic, water-soluble surfactants.

[4] Long chain cationic surfactant-based viscoelastic systems have thus been widely reported for a number of applications. Although highly soluble, cationic systems generally require charge-shielding additives, such as salts comprising salicylate or bromide counterions, to reduce the average effective cross-sectional area of the cationic surfactant head group. As a result, the rheological properties of these systems are highly susceptible to variations in the salinity of the fluid, limiting their utility in a number of applications. Moreover, cationic surfactants are considered undesirable for many applications due to toxicity and biodegradability concerns.

[5] Viscoelastic fluid systems with non-ionic surfactants have also been reported. In such systems, a ternary mixture of water, a highly hydrophilic base surfactant and a lipophilic co-surfactant (typically of a different surfactant class to the base surfactant) is generally required to provide an appropriate balance of properties. Such systems require careful formulation, as viscoelastic properties are only available over a very narrow range of surfactant mixing fractions. Outside of this window, non entangling spherical micelles are formed (insufficient lipophilic co-surfactant), or phase-separation occurs (excess lipophilic co-surfactant). Furthermore, high total surfactant concentrations (such as 10-20 weight %) are commonly required to obtain viscoelastic properties.

[6] Non-ionic surfactants with carbohydrate head groups are considered particularly advantageous for many applications, as their molecular constituents can be obtained from abundant renewable resources, and the surfactant molecules themselves are generally biocompatible, biodegradable and readily functionalized. Carbohydrate-based surfactants may, for example, be prepared by the esterification of oligo-saccharides with fatty acids of varying hydrocarbyl chain length.

[7] It has been reported that such carbohydrate-based surfactants, in common with other non-ionic surfactants, exhibit strong surface activity in water and typically form spherical micelles. At higher surfactant concentrations, and particularly when using longer hydrocarbyl chain length surfactants, micellar deformation produces elongated cylindrical micellar configurations. Thus, rheological studies have shown fluid viscosity increasing together with surfactant content in binary carbohydrate- based surfactant-water systems, the effect being attributable to steric hindrance of rod-like micelles. However, in order to provide worm-like micelles with sufficient elongation and entanglement to produce truly gel-like viscoelastic fluids, it has previously been considered necessary to add a lipophilic co -surfactant, as with other mixed hydrophilic-hydrophobic surfactant systems. Thus, a 20 weight % surfactant solution comprising sucrose-hexadecanoate required approximately 0.05 weight fraction of a lipophilic co-surfactant to provide significant micellar entanglement (Kunieda et al, Journal of Dispersion Science and Technology 27 (2006) 61 1 -616).

[8] There is therefore an ongoing need for new viscoelastic fluid compositions comprising non-ionic surfactant, and for new non-ionic surfactant molecules suitable for providing such compositions, which at least partially address one or more of the above-mentioned short-comings, or provide a useful alternative.

[9] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Summary of Invention

[10] In accordance with a first aspect the invention provides a viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic surfactant comprises surfactant molecules having the formula: X-L-R, wherein: each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group, wherein a sufficient fraction of the surfactant molecules have R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5; and wherein a sufficient proportion of the surfactant molecules have R groups configured to solubilise the non ionic surfactant in the viscoelastic fluid. [1 1 ] The“sufficient fraction” of the surfactant molecules, i.e. those molecules having R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5, is sufficient to impart viscoelastic properties to the fluid. Without wishing to be bound by any theory, the inventors consider that the viscoelasticity is caused by elongation of micelles containing the non-ionic surfactant micelles to the extent that they become entangled. It should be appreciated that the “sufficient fraction” and the“sufficient proportion” of the surfactant molecules, as used herein, both represent percentages of the surfactant molecules, which are not mutually exclusive. Suitably configured surfactant molecules may thus form part of both the sufficient fraction” and the“sufficient proportion” of the surfactant molecules, and in some embodiments each of the sufficient fraction” and the “sufficient proportion” may be up to 100%.

[12] In some embodiments, the sufficient fraction of the surfactant molecules is at least 20 mol%, such as at least 40 mol%.

[13] In some embodiments, the sufficient fraction of the surfactant molecules have R groups with from 16 to 22 carbon atoms.

[14] In some embodiments, the sufficient fraction of the surfactant molecules has a hydrophilic-lipophilic balance (HLB) of less than about 12, or less than about 1 1.5. In these or other embodiments, the sufficient fraction of the surfactant molecules has a hydrophilic-lipophilic balance (HLB) of greater than about 10, or greater than about 10.5.

[15] In some embodiments, substantially all of the surfactant molecules have the same X groups.

[16] In some embodiments, the non-ionic surfactant is present in an amount of less than about 100 mmol/litre, such as less than about 60 mmol/litre. In some embodiments, the non-ionic surfactant is present in an amount of greater than about 10 mmol/litre.

[17] In some embodiments, each R group has from 12 to 22 carbon atoms, such as from 12 to 20 carbon atoms or from 14 to 22 carbon atoms. [18] In some embodiments, the sufficient proportion of the surfactant molecules is sufficient to solubilise the non-ionic surfactant in the viscoelastic fluid at 25°C, such that the non-ionic surfactant is soluble in the viscoelastic fluid at 25°C.

[19] In some embodiments, all of the surfactant molecules have a hydrophilic- lipophilic balance (HLB) of greater than 10, or greater than 10.5. In some embodiments, all of the surfactant molecules have a hydrophilic-lipophilic balance (HLB) of less than 12.5, or less than 12.

[20] In some embodiments, the R groups configured to solubilise the non-ionic surfactant are ethylenically unsaturated. In some such embodiments, the sufficient proportion of the surfactant molecules, which solubilise the non-ionic surfactant, is at least 40 mol%, such as at least 80 mol%. In some such embodiments, the sufficient proportion of the surfactant molecules is substantially 100 mol%. The ethylenically unsaturated R groups may have at least 16 carbon atoms, and may be C-is to C₂₂ hydrocarbyl groups (i.e. have from 18 to 22 carbon atoms).

[21 ] In some embodiments, the R groups configured to solubilise the non-ionic surfactant are ethylenically mono-unsaturated. The ethylenically mono-unsaturated R groups may be C₁₆ to C₂₂ groups, or C-is to C₂₂ groups such as oleyl or erucyl groups.

[22] In some embodiments, the R groups configured to solubilise the non-ionic surfactant have from 12 to 14 carbon atoms. In some such embodiments, the sufficient proportion of the surfactant molecules, which solubilise the non-ionic surfactant, is at least 50 mol%. The R groups configured to solubilise the non-ionic surfactant may be saturated.

[23] In some embodiments, the surfactant molecules have the formula: X-(CH₂CH₂0)_n-(C=0)_p-R, wherein X and R are as defined herein, each n is independently an integer and the average value for n in the surfactant molecules is from above 2 to 6, and p is independently selected from 0 or 1 for each of the surfactant molecules. In some such embodiments, p is 0 for each of the surfactant molecules. The average value for n in the surfactant molecules may be from about 3 to about 4, and/or n may be independently selected from 3 or 4 for each of the surfactant molecules. In some embodiments, n is the same for each of the surfactant molecules. [24] In some embodiments, the carbohydrate is a monosaccharide or a disaccharide, and preferably a monosaccharide. The monosaccharide may be selected from the group consisting of glucose and galactose. In some embodiments, the carbohydrate is covalently bonded to the L group via a glycosidic bond in each of the surfactant molecules. In some embodiments, the carbohydrate is a beta- anomeric carbohydrate.

[25] In some embodiments, the viscoelastic fluid is substantially free of co surfactants which lack a head group comprising a carbohydrate. In some embodiments, the viscoelastic fluid is substantially free of ionic co-surfactants. In some embodiments, the non-ionic surfactant present in the viscoelastic fluid consists of the surfactant molecules having the formula X-L-R as defined herein.

[26] In some embodiments, the viscoelastic fluid comprises water. The water may be present in an amount of at least 75 weight %, such as at least 90 weight %, for example at least 95 weight %.

[27] In some embodiments, the viscoelastic fluid has a zero-shear viscosity of greater than 100 mPa.s at 25°C, or greater than 1000 mPa.s at 25°C.

[28] In accordance with a second aspect the invention provides a viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic surfactant comprises surfactant molecules having the formula: X-L-R, wherein: each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; each R group is independently a linear hydrocarbyl tail group having at least 16 carbon atoms, wherein the surfactant molecules have a hydrophilic-lipophilic balance (HLB) of less than 12.5, and wherein a proportion of the surfactant molecules sufficient to solubilise the non-ionic surfactant in the viscoelastic fluid have ethylenically un saturated R groups.

[29] In some embodiments of the second aspect, the carbohydrate is a monosaccharide or a disaccharide, and preferably a monosaccharide. The monosaccharide may be selected from the group consisting of glucose and galactose. In some embodiments, the carbohydrate is covalently bonded to the L group via a glycosidic bond in each of the surfactant molecules. In some embodiments, the carbohydrate is a beta-anomeric carbohydrate.

[30] In some embodiments of the second aspect, L has the formula -(CH₂CH₂0)_n-, wherein each n is independently an integer and the average value for n in the surfactant molecules is from above 2 to 6. The average value for n in the surfactant molecules may be from about 3 to about 4, and/or n may be independently selected from 3 or 4 for each of the surfactant molecules. In some embodiments, n is the same for each of the surfactant molecules.

[31 ] In some embodiments of the second aspect, each R is an ethylenically unsaturated group; i.e. the sufficient proportion of the surfactant molecules, which solubilise the non-ionic surfactant, is substantially 100 mol%. In some embodiments, each R is an ethylenically mono-unsaturated group. The ethylenically mono- unsaturated R groups may be Ci₆ to C₂₂ groups, or C-is to C₂₂ groups such as oleyl or erucyl groups.

[32] In some embodiments of the second aspect, the surfactant molecules have a hydrophilic-lipophilic balance (HLB) of less than 12, or less than 1 1.5. In some embodiments, the surfactant molecules have a hydrophilic-lipophilic balance (HLB) of greater than 10, or greater than 10.5.

[33] In some embodiments of the second aspect, the non-ionic surfactant is present in an amount of less than about 100 mmol/litre, such as less than about 60 mmol/litre. In some embodiments, the non-ionic surfactant is present in an amount of greater than about 10 mmol/litre.

[34] In some embodiments of the second aspect, the viscoelastic fluid is substantially free of co-surfactants which lack a head group comprising a carbohydrate. In some embodiments, the viscoelastic fluid is substantially free of ionic co-surfactants. In some embodiments, the non-ionic surfactant present in the viscoelastic fluid consists of the surfactant molecules having the formula X-L-R as defined herein. [35] In some embodiments of the second aspect, the viscoelastic fluid comprises water. The water may be present in an amount of at least 75 weight %, such as at least 90 weight %, for example at least 95 weight %.

[36] In some embodiments of the second aspect, the viscoelastic fluid has a zero-shear viscosity of greater than 100 mPa.s at 25°C.

[37] In accordance with a third aspect the invention provides a viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic surfactant comprises surfactant molecules having the formula: X-L-R, wherein: each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group, wherein a sufficient fraction of the surfactant molecules have R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5; and wherein a proportion of the surfactant molecules sufficient to solubilise the non-ionic surfactant in the viscoelastic fluid have R groups having from 12 to 14 carbon atoms.

[38] In accordance with a fourth aspect the invention provides a non-ionic surfactant molecule having the formula: X-L-R, wherein: X is a head group comprising a carbohydrate; L is a linking group comprising a plurality of alkylene glycol units; and R is a linear, ethylenically mono-unsaturated hydrocarbyl tail group having at least 16 carbon atoms, wherein the surfactant molecule has a hydrophilic- lipophilic balance (HLB) of less than 12.5.

[39] In some embodiments of the fourth aspect, the carbohydrate is a monosaccharide or a disaccharide, and preferably a monosaccharide. The monosaccharide may be selected from the group consisting of glucose and galactose. In some embodiments, the carbohydrate is covalently bonded to the L group via a glycosidic bond. In some embodiments, the carbohydrate is a beta-anomeric carbohydrate.

[40] In some embodiments of the fourth aspect, L has the formula -(CH₂CH₂0)_n-, where n is an integer of from 3 to 6. In some such embodiments, n is 3 or 4. [41 ] In some embodiments of the fourth aspect, R is a mono-unsaturated Ci₆ to C₂2 group, such as an oleyl or erucyl group.

[42] In some embodiments of the fourth aspect, the hydrophilic-lipophilic balance (HLB) is less than 12, or less than 11.5. In some embodiments, the hydrophilic-lipophilic balance (HLB) is greater than 10, or greater than 10.5.

[43] In some embodiments of the fourth aspect, the non-ionic surfactant molecule has the formula X¹-(CH₂CH₂0)_ni-R¹, wherein X¹ is a beta-anomeric monosaccharide head group; n¹ is an integer of from 3 to 6 and R¹ is selected from the group consisting of oleyl and erucyl groups, with the proviso that n¹ is 3 or 4 when R¹ is an oleyl group and n¹ is 4, 5 or 6 when R¹ is an erucyl group.

[44] In some embodiments of the fourth aspect, the non-ionic surfactant molecule is soluble in water to form a viscoelastic fluid. The non-ionic surfactant molecule may be soluble in water to form a viscoelastic fluid at a concentration of less than about 100 mmol/litre, such as less than about 60 mmol/litre. In some embodiments, the non-ionic surfactant molecule is soluble in water to form a viscoelastic fluid at a concentration of greater than about 10 mmol/litre. The viscoelastic fluid formed may have a zero-shear viscosity of greater than 100 mPa.s at 25°C.

[45] In accordance with a fifth aspect, the invention provides a viscoelastic fluid, comprising water and one or more non-ionic surfactant molecules according to any embodiment of the fourth aspect disclosed herein.

[46] Where the terms“comprise”,“comprises” and“comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[47] Further aspects of the invention appear below in the detailed description of the invention. Brief Description of Drawings

[48] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[49] Figures 1 A-1 F depict small-angle neutron scattering (SANS) spectra where scattering intensity I is a function of scattering variable q for surfactant molecules 1 to 6 (prepared in Example 1 ) at various concentrations in D₂0, including model best fits for spherical, cylindrical or flexible cylindrical micelles.

[50] Figures 2A-2F depict small-angle neutron scattering (SANS) spectra where scattering intensity I is a function of scattering variable q for surfactant molecules 7, 9, 10, 12, 13 and 14 (prepared in Example 1 ) at various concentrations in D₂0, including best fits for the modelled geometry.

[51 ] Figures 3A-3C depict small-angle neutron scattering (SANS) spectra where scattering intensity I is a function of scattering variable q for surfactant molecules 15, 16 and 18 (prepared in Example 1 ) at various concentrations in D₂0, including best fits for the modelled geometry.

[52] Figure 4 is a plot depicting the micellar geometry (obtained from fitted SANS spectra) of mixtures of surfactant molecules 5 and 7 (prepared in Example 1 ) in D₂0, as a function of the concentrations of 5 and 7.

[53] Figure 5 is a plot depicting the micellar geometry (obtained from fitted SANS spectra) of mixtures of surfactant molecules 5 and 2 (prepared in Example 1 ) in D₂0, as a function of the concentrations of 5 and 2.

[54] Figure 6 is a plot depicting the micellar geometry (obtained from fitted SANS spectra) of mixtures of surfactant molecules 5 and 4 (prepared in Example 1 ) in D₂0, as a function of the concentrations of 5 and 4.

[55] Figure 7 is a plot depicting the micellar geometry (obtained from fitted SANS spectra) of mixtures of surfactant molecules 6 and 4 (prepared in Example 1 ) in D₂0, as a function of the concentrations of 6 and 4. [56] Figures 8A-8E depict viscosity h plotted as a function of shear rate g for aqueous solutions of molecule 7, 9, 13, 15 and 16 (prepared in Example 1 ) at different concentrations, as determined via steady shear viscosity rheological measurements.

[57] Figure 9 depicts zero-shear viscosities (h₀) as a function of concentration for aqueous solutions of molecule 7, 9, 13, 15 and 16, calculated from the data depicted in Figures 8A-8E.

[58] Figures 10A-10 depict the storage modulus G’ and the loss modulus G” plotted as a function of radial frequency w for aqueous solutions of molecules 7, 9, 13, 15 and 16 (prepared in Example 1 ) at different concentrations, as determined via frequency sweep rheological measurements (10% strain amplitude).

Detailed Description

[59] The present invention relates to a viscoelastic fluid comprising non-ionic surfactant. In its most general form, the viscoelastic fluid comprises non-ionic surfactant molecules having the formula: X-L-R, where each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group. A sufficient fraction of the surfactant molecules have R groups with at least 16 carbon atoms and a hydrophilic- lipophilic balance (FILB) of less than 12.5. This fraction should be sufficient to confer viscoelastic properties to the fluid, a result which the inventors attribute to elongation of the non-ionic surfactant micelles. Moreover, a sufficient proportion of the surfactant molecules have R groups configured to solubilise the non-ionic surfactant in the viscoelastic fluid. This proportion should generally be sufficient to solubilise the surfactant in the fluid at the required temperature, such that the non-ionic surfactant may aggregate into micelles.

[60] The inventors have found that non-ionic surfactant molecules having the formula X-L-R as defined represent a class of surfactant with functionality that may be tailored, according to the principles disclosed herein, to provide viscoelastic properties in aqueous fluids. These properties may be provided even when the surfactant is present in low concentrations (such as below 5 weight %), and generally without the requirement for additives from other surfactant classes. The hydrophilic portion of the molecules combines a strongly hydrophilic yet compact carbohydrate- based head group and a less hydrophilic alkylene glycol-based linking group, while the lipophilic portion is a linear hydrocarbyl group. Without wishing to be bound by any theory, it is believed that the flexible alkylene glycol linker increases the surfactant solubility and modulates the spatial separation between the polar carbohydrate and hydrophobic tail, thereby contributing to the surfactant aggregation behaviour responsible for the fluid’s viscoelastic properties.

[61 ] The inventors have also recognised that the length of the hydrocarbyl chain R is an important determinant of the viscoelastic properties of the surfactant. Increasing the number of carbon atoms in the hydrocarbyl chain results in elongation of the surfactant micelles in aqueous fluids. Surfactant molecules of the formula X-L- R as defined having R groups with at least 16 carbon atoms and a hydrophilic- lipophilic balance (HLB) of less than 12.5 are believed to have a suitable molecular structure such that flexible cylindrical (“worm-like”) micelles, capable of viscoelastic entanglement above a critical overlapping micellar concentration, are provided. Accordingly, at least a fraction (and in some cases up to 100%) of the total non-ionic surfactant molecules, sufficient to confer viscoelasticity to the fluid, should have these features.

[62] The inventors have recognised, however, that surfactant molecules of the formula X-L-R as defined become increasing insoluble as the length of the hydrocarbyl chain R increases, particularly when R is a saturated hydrocarbyl group. A tension therefore exists between the imperative to increase the R chain length for micellar elongation, while providing a surfactant system that is sufficiently soluble to dissolve and form micelles, particularly at lower temperatures such as room temperature. Accordingly, a sufficient proportion of the surfactant molecules should have R groups configured to solubilise the non-ionic surfactant in the viscoelastic fluid. R groups suitably configured to solubilise the non-ionic surfactant may, for example, be ethylenically unsaturated hydrocarbyl groups and/or have between 12 and 14 carbon atoms in the linear chain.

[63] The hydrophilic-lipophilic balance (HLB) is a parameter commonly used in the art of surfactants to classify surfactant molecules according to their relative hydrophilicity / hydrophobicity, with more hydrophilic molecules having higher HLB values. As used herein, HLB is calculated according to Griffin’s method, as shown in Formula 1 :

HLB = 20 x M_h / M (Formula 1 ) where M_h is the molecular mass of the hydrophilic portion of the molecule; and M is the molecular mass of the whole molecule.

Viscoelastic fluids comprising non-ionic surfactant

[64] As used herein, a viscoelastic fluid exhibits both viscous and elastic characteristics when deformed, i.e. it elastically recovers (elastic) and dissipates energy via stress relaxation (viscous) when a deformation is applied. In the case of a surfactant-based viscoelastic fluid, the viscoelasticity is believed to be provided by internal structure in the solution, i.e. formation of elongated micelles. Viscoelastic behaviour is characterised, via standard rheological measurements, by a viscosity plateau at low shear rates followed by a shear-thinning region at higher shear rates. The zero-shear viscosity for such materials is determined by taking the average viscosity in the plateau region. As a guide, an internally structured surfactant-based viscoelastic fluid may have a zero-shear viscosity of at least 100 mPa.s. Viscoelastic gels, being highly structured viscoelastic fluids, which are visually thickened gels and exhibit a correspondingly strong rheological response, may have a zero-shear viscosity of greater than 1000 mPa.s.

[65] The viscoelastic fluid of the invention comprises non-ionic surfactant, and in at least some embodiments is substantially free of ionic co-surfactants, including anionic, cationic and zwitterionic surfactants. The non-ionic surfactant comprises non-ionic surfactant molecules having the formula: X-L-R, where each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group. The R groups in particular are selected, according to the principles disclosed hereafter, to provide the right balance of properties for solubility and viscoelasticity. [66] In some embodiments, the non-ionic surfactant is substantially free of surfactant molecules which lack a head group comprising a carbohydrate. In some embodiments, the non-ionic surfactant consists of the non-ionic surfactant molecules having the formula X-L-R as defined. In some embodiments, substantially all of the non-ionic surfactant molecules have a hydrophilic-lipophilic balance (HLB) of less than 12.5.

[67] Typically, the viscoelastic fluid is an aqueous fluid, i.e. it has water as the base fluid. In some embodiments, the viscoelastic fluid comprises water in an amount of at least 75 weight %, preferably at least 90 weight %, such as at least 95 weight %. In some embodiments, the non-ionic surfactant is present in an amount of less than 100 mmol/litre, such as less than 80 mmol/litre. However, the non-ionic surfactant should be present in an amount sufficient to produce viscoelasticity, i.e. in an amount greater than a critical overlapping micellar concentration where the elongated micelles entangle. In some embodiments, therefore, the non-ionic surfactant is present in an amount greater than about 10 mmol/litre. Suitable concentrations of non-ionic surfactant include concentrations between about 15 mmol/litre and about 80 mmol/litre, such as between about 20 mmol/litre and about 60 mmol/litre.

[68] It will be appreciated that the viscoelastic fluid may further comprise, or carry, various soluble or insoluble additives. A wide variety of such additives, including suspended particulate solids and dissolved actives, may be present as required for the intended application of the viscoelastic fluid, provided that viscoelastic properties of the fluid are retained in their presence.

Head groups

[69] The non-ionic surfactant molecules have the formula: X-L-R, where each X group is independently a head group comprising a carbohydrate; each L group is independently a linking group comprising a plurality of alkylene glycol units; and each R group is independently a linear hydrocarbyl tail group. In some embodiments, each X group is independently a head group comprising a saccharide, preferably selected from a monosaccharide and a disaccharide. In some embodiments, the saccharides are cyclic pyranose forms of hexose saccharides. In some preferred embodiments, each head group is a monosaccharide. Suitable monosaccharides include glucose and galactose.

[70] In some embodiments, each head group is a monosaccharide or disaccharide which is unsubstituted, apart from the bond connecting the carbohydrate head group to the linking group. Unsubstituted mono- and disaccharides are believed to provide suitably polar head groups of relatively compact size, thereby affording solubility in aqueous fluids while promoting micellar elongation when combined with suitable L and R groups. Furthermore, the carbohydrate head group may be a beta- anomeric carbohydrate. Certain beta-anomeric carbohydrates, such as the monosaccharides b-glucose and b-galactose and the disaccharide b-maltose, are believed to be more hydrophobic, and thus confer greater solubility, than otherwise similar carbohydrates in the alpha-anomeric form. Without wishing to be bound by any theory, the inventors also believe that the molecular packing of beta-anomeric carbohydrates in the micelles may be particularly advantageous, as the equatorial configuration places the hydrophobic tail “in-line” with the carbohydrate. The carbohydrate-containing head group may generally be covalently bonded to the linking group at any suitable position, however in exemplary embodiments the carbohydrate is covalently bonded to the linking group via a glycosidic bond. In some embodiments, the X groups of substantially all of the non-ionic surfactant molecules are the same.

Linking groups

[71 ] Each L group of the non-ionic surfactant molecules of formula X-L-R is independently a linking group comprising a plurality of alkylene glycol units. As used herein, an alkylene glycol unit refers to a divalent monomeric unit having the formula -CH₂CH(R’)0-, where R’ is selected from -H or hydrocarbyl. Alkylene glycol units are thus the residues of a polymerised alkylene oxide; a plurality of alkylene glycol units is obtained when dimerising, oligomerising or polymerising alkylene oxides such as ethylene oxide, propylene oxide or butylene oxide. In some preferred embodiments, the alkylene glycol units are ethylene glycol units, i.e. -CH₂CH₂0-

[72] In some embodiments, the L groups comprise from two to six alkylene glycol units, for example three or four alkylene glycol units. In some embodiments, the non-ionic surfactant molecules all have the same number of alkylene glycol units, for example three or four. However, it will be appreciated that oligomerisation of alkylene oxides generally produces oligo(alkylene glycol) chains with the number of alkylene glycol units in statistical distribution, the average number being susceptible to manipulation. In some embodiments, therefore, the non-ionic surfactant molecules have differing numbers of alkylene glycol units, but the average number of alkylene glycol units is from above two to about six, and is preferably from about three to about four.

[73] In some embodiments, the L groups of the non-ionic surfactant molecules have the formula -(CH₂CH(R’)0)_n-(C=0)_p-, where R’ is selected from -H and hydrocarbyl (preferably -H), n is an integer of two or greater (preferably three or greater) and p is selected from 0 or 1 (preferably 0). It will be appreciated that the value of p may depend on the synthetic methodology for preparing the surfactant molecules, as will be described in greater detail hereafter.

Tail groups

[74] Each R group of the non-ionic surfactant molecules of formula X-L-R is independently a linear hydrocarbyl tail group. As will be appreciated, a linear hydrocarbyl tail group is a hydrocarbyl group comprising an unbranched carbon chain. In some embodiments, each R group independently has from 12 to 22 carbon atoms. In some embodiments, each R group is independently either saturated or mono- un saturated.

“Viscoelasticity-conferring” fraction of non-ionic surfactant molecules

[75] At least a fraction of the non-ionic surfactant molecules of formula X-L-R as defined have R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5. As discussed herein, this fraction should generally be sufficient to confer viscoelastic properties to the fluid as a result of elongation of the non-ionic surfactant micelles. In some embodiments, the sufficient fraction is at least 20 mol%, such as at least 40 mol%. In embodiments where the R groups of the non-ionic surfactant are unsaturated and thus configured to solubilise the non-ionic surfactant in the viscoelastic fluid, the fraction of surfactant molecules having R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5 may be up to 100%, as will be described in greater detail hereafter.

[76] In some embodiments, the sufficient fraction of the surfactant molecules has from 16 to 22 carbon atoms. In some embodiments, the surfactant molecules of the sufficient fraction have an HLB of less than 12, or less than 11.5. However, the non-ionic surfactant molecules should remain sufficiently hydrophilic for acceptable water solubility. Accordingly, in some embodiments the surfactant molecules of the sufficient fraction have an HLB of greater than 10, such as greater than 10.5. The inventors have found that the surfactant molecules with the best capacity to provide viscoelasticity in solution have an HLB between 10.7 and 1 1.8.

“Solubility-conferring” proportion of non-ionic surfactant molecules

[77] A sufficient proportion of the non-ionic surfactant molecules have R groups configured to solubilise the non-ionic surfactant in the viscoelastic fluid. The proportion of the surfactant molecules with the solubilising R groups is preferably sufficient to solubilise the non-ionic surfactant in the viscoelastic fluid at 25°C, since many applications of viscoelastic fluids must operate at ambient conditions.

[78] In some embodiments, the R groups configured to solubilise the non-ionic surfactant are ethylenically unsaturated, preferably ethylenically mono-unsaturated groups. As used herein, an ethylenically unsaturated linear hydrocarbyl group is a linear hydrocarbyl group with a carbon-carbon double bond in the chain, while an ethylenically mono-unsaturated linear hydrocarbyl group is a linear hydrocarbyl group with only one carbon-carbon double bond in the chain, and which is otherwise saturated. The carbon-carbon double bond may be located towards the middle of the linear chain (for example, in a position other than the first, second, second-last or last in the chain), and preferably has a c/s-configuration. In some embodiments, the ethylenically unsaturated R groups have at least 16 carbon atoms, and may be unsaturated, preferably mono-unsaturated, C-i₈ to C₂2 hydrocarbyl groups, such as oleyl groups or erucyl groups. The inventors have found, for example, that a surfactant molecule having the formula X-L-R as defined where R is an unsaturated C-_I8 group (oleyl) is notably more water soluble in comparison with the equivalent molecule having a saturated C-is group (octadecyl). The c/s-mono-unsaturation present in the middle of the chain in the oleyl (and erucyl) group is believed to disrupt the crystalline packing of the hydrocarbyl tails and thus facilitate solubility. Despite the increase in solubility, the molecule retains an excellent ability to form elongated micelles suitable for viscoelastic entanglement above the critical overlapping micelle concentration.

[79] In some preferred embodiments, therefore, the same non-ionic surfactant molecules having unsaturated solubilising R groups also have at least 16 carbon atoms in the R groups and a hydrophilic-lipophilic balance (HLB) of less than 12.5. In such embodiments, the proportion of the non-ionic surfactant molecules having R groups configured to solubilise the non-ionic surfactant may be up to 100%. In some such embodiments, the non-ionic surfactant in the viscoelastic fluid comprises, or indeed consists of, surfactant molecules selected from the group consisting of:

wherein n² is 3 or 4, n³ is 4, 5 or 6, Cis:1 is an oleyl group and C22-1 is an erucyl group.

[80] In other embodiments, the non-ionic surfactant molecules having unsaturated solubilising R groups are used in combination with other non-ionic surfactant molecules of the same class (i.e. with the formula X-L-R as most broadly defined), but which are differently configured for their micellar elongation capabilities. Thus, a viscoelastic fluid according to the invention may comprise both molecules of the formula X-L-R having unsaturated R groups, and molecules of the formula X-L- R having saturated R groups with at least 16 carbon atoms and an HLB of less than 12.5. In such embodiments, the proportion of non-ionic surfactant molecules having the solubilising unsaturated R groups may be at least 40 mol%, such as at least 80 mol%.

[81 ] As an example, the inventors have found that a non-ionic surfactant molecule of formula X-L-R as defined, where R is an unsaturated Ci₈ group (oleyl), may be used in combination with a molecule of the formula X-L-R as defined, where R is a saturated Ci₆ group and the HLB is less than 12.5. Provided that the molecule with oleyl tail is present in a sufficient proportion to solubilise the otherwise insoluble molecule with saturated C-i₆ tail, the mixed non-ionic surfactant aggregates in solution at 25°C to provide highly elongated micelles, and thus imparts viscoelasticity to the solution.

[82] In some embodiments, the R groups configured to solubilise the non-ionic surfactant have from 12 to 14 carbon atoms, and may optionally be saturated. The inventors have found, for example, that non-ionic surfactant with the formula X-L-R as defined, and comprising a combination of saturated C-_|4 and Ci₆ tail groups, can form elongated micelles in an room temperature aqueous fluid with a geometry believed to be suitable for entanglement when mixed in the appropriate ratio. Thus, viscoelastic properties were conferred to the solution. By contrast, the individual homologues were found unable to provide this result: a molecule X-L-R with saturated C tail group was soluble but did not form sufficiently elongated micelles, whereas a molecule X-L-R with saturated Ci₆ tail group was insoluble at 25°C.

[83] In embodiments where X-L-R surfactant molecules having R groups with from 12 to 14 carbon atoms are used to solubilise X-L-R surfactant molecules having at least 16 carbon atoms and a HLB of less than 12.5, the sufficient proportion of the molecules with the solubilising C-_|2 to C-_|4 R groups may be at least 50 mol%.

Non-ionic surfactant molecules

[84] The present invention also relates to non-ionic surfactant molecules. The non-ionic surfactant molecules have the formula: X-L-R, where X is a head group comprising a carbohydrate; L is a linking group comprising a plurality of alkylene glycol units; and R is a linear, ethylenically mono-unsaturated hydrocarbyl tail group having at least 16 carbon atoms. The surfactant molecules have a hydrophilic- lipophilic balance (HLB) of less than 12.5.

[85] The inventors have found that non-ionic surfactant molecules of this type provide particularly useful viscoelastic properties when dissolved and aggregated in aqueous fluids. Such molecules combine good solubility with a propensity to form elongated micelles capable of viscoelastic entanglement. Thus, viscoelastic fluids may be formed at one or more of low temperatures (such as 25°C), low surfactant concentrations (such as below 5 weight %) and without the requirement for a co surfactant.

[86] In some embodiments, the head group X comprises a saccharide, preferably selected from a monosaccharide and a disaccharide. In some embodiments, the saccharides are cyclic pyranose forms of hexose saccharides. The carbohydrate may be a beta-anomeric carbohydrate. In preferred embodiments, the head group is a monosaccharide, such as glucose and galactose and in particular b- glucose and b-galactose. In some embodiments, the head group is a monosaccharide or disaccharide which is unsubstituted, apart from the bond connecting the head group to the linking group. In some embodiments, the saccharide is covalently bonded to the linking group L via a glycosidic bond.

[87] In some embodiments, the linking group L has the formula -(CH₂CH(R’)0)_n-(C=0)_p- where R’ is selected from -H and hydrocarbyl (preferably -H), n is an integer of two or greater (preferably three or greater) and p is selected from 0 or 1 (preferably 0). In some embodiments, the alkylene glycol units of the linking group L are ethylene glycol units, i.e. -CH₂CH₂0-. In some embodiments, the linking group L comprises from two to six alkylene glycol units, preferably three or four alkylene glycol units. In some embodiments, the linking group L has the formula -(CH₂CH₂0)_n- where n is 3 or 4.

[88] In some embodiments, the tail group R is a mono-unsaturated Ci₆ to C₂₂ group, such as an oleyl group (i.e. cis- 9-octadecenyl) or an erucyl group (i.e. c/s-13- docosenyl). [89] In some embodiments, the non-ionic surfactant molecules have an HLB of less than less than 12, or less than 11.5. In some embodiments, the non-ionic surfactant molecules have an an HLB of greater than 10, such as greater than 10.5.

[90] In some embodiments, the non-ionic surfactant molecules having the formula X-L-R have the formula X¹-(CH₂CH₂0)_ni-R¹, where X¹ is a beta-anomeric monosaccharide head group; n¹ is an integer of from 3 to 6 and R¹ is selected from the group consisting of oleyl and erucyl groups, with the proviso that n¹ is 3 or 4 when R¹ is oleyl and n¹ is 4, 5 or 6 when R¹ is erucyl.

[91 ] In some embodiments, the non-ionic surfactant molecules having the formula X-L-R are selected from the group consisting of:

wherein n² is 3 or 4, n³ is 4, 5 or 6, Ci₈:1 is an oleyl group and C₂₂:1 is an erucyl group.

Synthesis of non-ionic surfactant molecules

[92] Any suitable means may be used to prepare the non-ionic surfactant molecules of formula X-L-R as defined, and the invention is not generally considered to be limited by the synthetic methodology. However, by way of non-limiting example, the surfactant molecules may be derived by a multi-step process that includes reaction of an oligo(alkylene glycol) (such as a polyethylene glycol) with either a hydrocarbyl halide (such as R-Br; via a Williamson ether synthesis) or a fatty acid (RCOOH; via an esterification condensation reaction), as depicted in Scheme 1 (a) and (b) respectively. Alternatively, the process may include a direct alkoxylation of either a fatty alcohol (ROH) or a fatty acid (RCOOH) with an alkylene oxide (such as ethylene oxide), as depicted in Scheme 1 (c) and (d) respectively.

R' = H or hydrocarbyl

R = linear hydrocarbyl

n is 2 or greater

Scheme 1

[93] Therefore, in at least some embodiments where a fatty alcohol or hydrocarbyl halide precursor is used, the L linking groups of the non-ionic surfactant molecules will have the formula -(CH₂CH(R’)0)_n- (i.e. p = 0). In at least some embodiments where a fatty acid precursor is used, the L groups of the non-ionic surfactant molecules will have the formula -(CH₂CH(R’)0)_n-(C=0)- (i.e. p = 1 ).

[94] The surfactant molecules may be derived by a process that includes a glycosylation reaction between a saccharide and a precursor alcohol of the form H0-(CH₂CH(R’)0)_n-(C=0)_p-R, where R’ is selected from -H and hydrocarbyl (preferably -H), n is an integer of two or greater and p is selected from 0 or 1 (preferably 0). Optionally, the saccharide may be in a protected form prior to the glycosylation reaction, and surfactant molecules having an unsubstituted carbohydrate head group are then prepared by a sugar deprotection reaction. A non limiting example of a suitable reaction sequence for preparing non-ionic surfactant molecules of the form Fl-L-X as defined is thus shown in Scheme 2.

p

or

Scheme 2

EXAMPLES

[95] The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.

Materials and experimental procedures

[96] 1 -Bromooctane, 1 -bromodecane, 1 -bromododecane, 1 -bromotetradecane, 1 -bromohexadecane, 1 -bromooctadecane, oleic alcohol, linoleic acid, erucyl acid, diethylene glycol, tri-ethylene glycol, tetra-ethylene glycol, hexaethylene glycol, b-D- glucose pentaacetate, b-D-galactose pentaacetate, a-D-mannose pentacetate, b-D- maltose octaacetate and other synthetic reagents and solvents were purchased from Sigma-Aldrich, Alfa Aesar, Chem Supply, and Merck and used as received.

[97] Analytical thin layer chromatography (TLC) was performed on commercially prepared silica gel plates (Merck Kieselgel 60 0.25 mm F254). Flash column chromatography was performed on silica gel (Merck Kieselgel 60 230-400 mesh), eluting with solvents as described.

[98] Proton and carbon nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectra were recorded using a Bruker Avance III 400 NMR spectrometer at frequencies of 400 MHz and 100 MHz respectively, using deuterated solvents as described. Chemical shift is reported as parts per million (ppm) downfield shift relative to the TMS internal standard. The data are reported as chemical shift (d), multiplicity, relative integral, coupling constant (J = Hz) and assignment where possible.

[99] Surface tension values for surfactant-water solutions were measured at 25°C using the maximum bubble pressure tensiometry method with a Kruss BP100 bubble pressure tensiometer. The Critical Micelle Concentration (CMC) was determined by plotting the equilibrium surface tension over a range of surfactant concentrations and finding the concentration (determined via the intersection of two extrapolated straight lines) at which the minimum surface tension is first reached. In other cases, the Critical aggregation concentration (CAC) was determined via Nile red encapsulation assay. A Nile red stock solution (1 mg/ml_) was prepared in DCM and surfactant solutions were prepared in ultra-pure water at given concentrations. Samples were made by adding 10 microlitres of Nile red stock solution and allowing the DCM to evaporate, then adding 4 ml_ of surfactant solution. The fluorescence emission spectra were measured on an Agilent Technologies Cary Eclipse Fluorescence Spectrophotometer using an excitation wavelength of 550 nm with signals recorded over 570-700 nm range with a 5 nm excitation/emission slit. The CAC was determined (using a similar method as CMC) by plotting the wavelength at maximum fluorescence emission intensity over a range of surfactant concentrations and finding the concentration at which the minimum wavelength is first reached, at the intersection of two extrapolated lines.

[100] Small-angle neutron scattering (SANS) measurements were obtained using the Quokka and Bilby beamlines at the Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights NSW, Australia. Samples of surfactant-water mixtures above the critical micelle concentration were prepared in D₂0. The samples were loaded into 2 mm thick Hellma quartz cells and placed into a thermostatically-controlled automatic sample changer which maintained the desired temperature of either 25 or 50°C (± 0.05°C) using a recirculating water bath. For the Quokka beamline, an incident neutron wavelength of 5 A was used and raw scattering counts were collected on a 128x128 element area detector with sample-detector distances of 2 and 14 m, giving an effective q range of 0.004-0.4 A^-1. Data were converted from raw counts into 1 D scattering spectra by first subtracting the scattering from an empty cell and then radially averaging the resulting spectrum under the assumption of isotropic scattering, normalising for the measured sample transmission. The 1 D data are thus indicative of scattering from the sample on an absolute intensity scale.

[101] SANS data were fit to models using SasView software. Scattering from spherical and cylindrical micelles was modelled using the respective analytical functions derived by Guinier (Guinier, A.; Fournet, G. Small-Angle Scattering of X- Rays. John Wiley and Sons: New York, 1955). Scattering from worm-like micelles was modelled using the flexible cylinder functions developed by Pedersen and Schurtenburger (Pedersen, J. S.; Schurtenberger, P. Scattering Functions of Semiflexible Polymers with and without Excluded Volume Effects. Macromolecules 1996, 29, 7602-7612).

[102] Rheological measurements were performed on an Anton-Paar MCR302 strain controlled rheometer using a double gap measuring system with a sample volume of 3 ml_. The measuring system was equipped with a Peltier plate temperature unit with counter cooling, allowing accurate temperature control (± 0.05°C). Samples were prepared at given concentrations and allowed to equilibrate for at least 24 hours before being loaded into the measuring system using a syringe, where they were allowed to reach the desired testing temperature. Steady shear viscosity measurements were conducted at shear rates from 0.01 -100 s ¹ with six data points per decade. Oscillatory shear amplitude sweep measurements were conducted at a constant angular frequency of 10 rad-s ¹ at shear strains from 0.01 -10 (1-1000%) with six data points per decade. Oscillatory shear frequency sweep measurements were conducted at a constant shear strain of 10%, as informed from the linear viscoelastic region (LVER) observed in the amplitude sweep measurements, at angular frequencies from 0.1 -100 rad-s ¹ with six data points per decade. Each rheology measurement was repeated three times on the same sample to ensure good reproducibility and was shown to have minimal variation.

Example 1

General procedure: synthesis of fatty alcohols from fatty acids

[103] To a stirred solution of LiAIH₄ (0.6 equiv.) in anhydrous THF (0.25 M), fatty acid (1.0 equiv.) dissolved in anhydrous THF (3.5 M) was added drop-wise at 0°C. The reaction was then allowed to reach room temperature and stirred for 4 h under nitrogen. The reaction was cooled to 0°C, then quenched with a 70:3 mixture of diethyl ether / water followed by aqueous NaOH (15 wt%) to precipitate white solid which was filtered. The filtrate was extracted with diethyl ether, and the combined organic layers were washed with saturated aqueous NaCI, dried over anhydrous Na₂S04, filtered, and concentrated. The crude product was purified by flash column chromatography (1 :9 ethyl acetate:petroleum ether) to yield the pure product (approx. 60% yield). Linoleic alcohol and erucyl alcohol were prepared in this manner, starting with linoleic acid and erucyl acid as the fatty acid respectively.

General procedure: synthesis of fatty bromides from fatty alcohols

[104] Oleic alcohol (c/s- 9-octadecen-1 -ol) (1.0 equiv.) was added to a stirred flask containing dichloromethane (DCM) to produce a 0.2 mmol/litre solution. CBr₄ (1.3 equiv.) and PPh₃ (1.7 equiv.) were added in portions at 0°C and the mixture was stirred for 10 minutes. The reaction mixture was diluted with petroleum ether to precipitate excess PPh₃ and filtered through celite. The product was recovered from the filtrate by removing the volatiles. The product was again dissolved in DCM, petroleum ether added to precipitate PPh₃, filtered and concentrated, and this process was repeated until no more precipitate formed to yield the pure product 1 -bromo -cis- 9-octadecene (approx. 99% yield).

[105] Linoleic alcohol and erucyl alcohol, prepared as described above, were converted to their respective bromides by a similar synthetic methodology.

General procedure: synthesis of R-(Q-CH?- n-OH (R = hvdrocarbyl, n = 2, 3, 4, 6) [106] Oligo(ethylene glycol) (i.e. di-, tri-, tetra- or hexa-ethylene glycol) (2.0 equiv.) was added to a stirred flask containing anhydrous dimethylformamide (DMF) to produce a 1.0 mmol/litre solution under nitrogen. NaH (2.1 equiv.) was slowly added and the mixture was stirred for 30 minutes. The reaction mixture was cooled to 0°C and a solution of the appropriate hydrocarbyl bromide (R-Br) (1.0 equiv.) dissolved in anhydrous DMF to a concentration of 1.0 mmol/litre was added dropwise. The reaction mixture was allowed to reach room temperature then stirred for 12 hours. The reaction mixture was quenched with saturated aqueous NH₄CI and extracted with ethyl acetate. The combined organic layers were washed with saturated aqueous NaCI, dried over anhydrous Na₂S0₄ and filtered. The crude product was recovered by removing the volatiles and purified by flash column chromatography (ethyl acetate / petroleum ether) to yield the pure product R-(0-CFl2-CFl2)n-OFI (R = hydrocarbyl, n = 2, 3, 4 or 6) (approx. 40% yield).

General procedure: synthesis of R-(Q-CFI?- n-Y (Y = per-acetylated saccharide.

R = hydrocarbyl, n = 2, 3, 4, 6)

[107] The R-(0-CFl2-CFl2)n-OFI (R = hydrocarbyl, n = 2, 3, 4 or 6) product thus prepared (1.0 equiv.) and per-acetylated saccharide (glucose-pentaacetate, galactose pentaacetate, mannose pentacetate or maltose octaacetate) (1.0 equiv.) were added to a stirred flask containing anhydrous DCM to form a 0.1 mmol/litre solution under nitrogen. The solution was cooled to 0°C then BF₃ Et₂0 (5.0 equiv.) was added dropwise. After 1 hour the reaction mixture was allowed to reach room temperature then stirred for a further 14 hours. The reaction mixture was quenched by the dropwise addition of N,N-diisopropylethylamine (DIPEA) (5.0 equiv.), diluted with saturated aqueous NaFICOa, and extracted with DCM. The combined organic layers were washed with saturated aqueous NaCI, dried over anhydrous Na₂S0₄ and filtered. The crude product was recovered by removing the volatiles and purified by flash column chromatography (ethyl acetate / petroleum ether) to yield the pure product R-(0-CFl2-CFl2)n-Y (Y = per-acetylated saccharide, R = hydrocarbyl, n = 2, 3, 4 or 6) (approx. 50% yield). General procedure: synthesis of R-(Q-CHp-CHp)_n-X (X = saccharide. R = hvdrocarbyl,

[108] The R-(0-CH₂-CH₂)_n-Y (Y = per-acetylated saccharide, R = hydrocarbyl, n = 2, 3, 4 or 6) product thus prepared (1 .0 equiv.) was added to a stirred flask containing anhydrous methanol to form a 0.1 mmol solution under nitrogen. NaOCH₃ (0.1 equiv.) was added and the mixture was stirred for 1 hour. The reaction mixture was neutralized by adding Amberlite IR-120 resin, filtered, and the volatiles were removed to yield the pure product R-(0-CH₂-CH₂)_n-X (X = glucose, galactose, mannose or maltose, R = hydrocarbyl, n = 2, 3, 4 or 6) (approx. 99% yield).

[109] Surfactant molecules 1 - 18, depicted in Formula 2 and Table 1 below, were prepared via the above procedures and characterized by ¹ H-NMR and ¹³C-NMR spectroscopy (selected data shown below).

X = maltose

Formula 2 Table 1. Surfactant molecules prepared with a structure according to Formula 2.

[110] Nuclear magnetic resonance (NMR) data for compound 7: ¹H NMR (400 MHz, CD₃OD) d 5.42-5.34 (m, 2H, 2xC H), 4.33 (d, J= 7.76 Hz, 1H, C H), 4.07-4.02 (m, 1 H, C H), 3.89 (dd, J= 11.89, 1.68 Hz, 1H, C H), 3.79-3.65 (m, 10H, 5xC H₂), 3.62-3.59 (m, 2H, C H₂), 3.50 (t, J= 6.62 Hz, 2H, C H₂), 3.41-3.36 (m, 1H, C H), 3.31- 3.29 (m, 2H, 2xC H), 3.23 (dd, J= 9.05, 7.80 Hz, 1H, C H), 2.09-1.99 (m, 4H, 2xC H₂), 1.60 (quin, J = 6.92 Hz, 2H, C H₂), 1.40-1.31 (m, 22H, 11 xCH₂), 0.93 (t, J = 6.79 Hz, 3H, CH₃); ¹³C NMR (100 MHz, CD₃OD) d 131.0, 130.9, 104.6, 78.1, 78.0, 75.2, 72.5, 71.7, 71.6, 71.6, 71.3, 69.8, 62.9, 33.7, 33.2, 30.9, 30.9, 30.8, 30.7, 30.7, 30.5, 30.4, 30.4, 28.2, 27.3, 23.8, 14.6.

[1 1 1] Nuclear magnetic resonance (NMR) data for compound 9: ¹H NMR (400 MHz, CD₃OD) d 5.45-5.37 (m, 2H, 2xC H), 4.36 (d, J = 7.77 Hz, 1 H, C H), 4.09-4.05 (m, 1 H, C H), 3.92 (dd, J = 1 1.92, 1.70 Hz, 1 H, C H), 3.82-3.67 (m, 14H, 7xCH₂), 3.65-3.62 (m, 2H, C Hz), 3.53 (t, J = 6.60 Hz, 2H, C Hz), 3.44-3.40 (m, 1 H, C H), 3.35- 3.33 (m, 2H, 2xC H), 3.26 (dd, J = 9.01 , 7.81 Hz, 1 H, C H), 2.12-2.02 (m, 4H, 2xC H₂), 1.63 (quin, J = 6.88 Hz, 2H, C H₂), 1.45-1.32 (m, 22H, 11 xC Hz), 0.96 (t, J = 6.63 Hz, 3H, CH₃); ¹³C NMR (100 MHz, CD₃OD) d 131.0, 130.9, 104.5, 78.0, 78.0, 75.2, 72.5, 71.7, 71.6, 71.6, 71.2, 69.8, 62.9, 33.7, 33.1 , 30.9, 30.8, 30.8, 30.7, 30.7, 30.5, 30.4, 30.4, 28.2, 27.3, 23.8, 14.6.

[1 12] Nuclear magnetic resonance (NMR) data for compound 13: ¹H NMR (400 MHz, CD3OD) d 5.44-5.36 (m, 2H, 2xC H), 4.35 (d, J = 7.77 Hz, 1 H, CH), 4.09^.04 (m, 1 H, CH), 3.92 (dd, J = 1 1.89, 1.65 Hz, 1 H, CH), 3.82-3.67 (m, 14H, 7xCH₂), 3.64-3.61 (m, 2H, CH2), 3.52 (t, J = 6.64 Hz, 2H, CH₂), 3.43-3.39 (m, 1 H, CH), 3.34- 3.32 (m, 2H, 2xC H), 3.25 (dd, J = 9.05, 7.81 Hz, 1 H, CH), 2.13-2.01 (m, 4H, 2xC H_z), 1.62 (quin, J = 7.02 Hz, 2H, C Hz), 1.45-1.30 (m, 30H, 15xCH2), 0.96 (t, J = 6.87 Hz, 3H, C H₃); ¹³C NMR (100 MHz, CD₃OD) d 131.0, 104.6, 78.1 , 75.2, 72.5, 71.8, 71.7,

71.6, 71.3, 69.8, 33.2, 30.9, 30.9, 30.8, 30.7, 30.5, 30.4, 28.2, 27.3, 23.8, 14.6.

[1 13] Nuclear magnetic resonance (NMR) data for compound 15: ¹H NMR (400 MHz, CD3OD) d 5.43-5.33 (m, 2H, 2xC H), 4.28 (d, J = 7.43 Hz, 1 H, CH), 4.06-4.00 (m, 1 H, CH), 3.86-3.84 (m, 1 H, CH), 3.81-3.65 (m, 12H, 6xCH₂), 3.62-3.48 (m, 6H, CH₂ and 4xC H), 2.08-1.98 (m, 4H, 2xC H₂), 1.60 (quin, J = 6.39 Hz, 2H, C H₂), 1.41- 1.30 (m, 22H, 1 1 xC H₂), 0.93 (t, J = 5.89 Hz, 3H, C H₃); ¹³C NMR (100 MHz, CD₃OD) d

131.6, 131.0, 105.2, 76.8, 75.0, 72.6, 72.5, 71.6, 71.6, 71.3, 70.4, 69.7, 62.6, 33.7, 33.2, 30.9, 30.9, 30.8, 30.7, 30.6, 30.4, 30.4, 30.3, 30.2, 28.2, 27.3, 23.8, 14.6.

[1 14] Nuclear magnetic resonance (NMR) data for compound 16: ¹H NMR (400 MHz, CD3OD) d 5.45-5.36 (m, 2H, 2xCH), 4.31 (d, J = 7.44 Hz, 1 H, CH), 4.09^.04 (m, 1 H, CH), 3.88-3.87 (m, 1 H, CH), 3.83-3.74 (m, 5H, 2xC H₂ CH), 3.73-3.67 (m, 10H, 5xC H₂), 3.64-3.61 (m, 2H, C H₂), 3.59-3.56 (m, 2H, 2xC H), 3.54-3.50 (m, 3H, CH₂ CH), 2.1 1-2.01 (m, 4H, 2xC H_z), 1.62 (quin, J = 6.88 Hz, 2H, CH₂), 1.45-1.29 (m, 22H, 11XCH₂), 0.96 (t, J= 6.63 Hz, 3H, CH₃); ¹³C NMR (100 MHz, CD₃OD) d 131.0, 130.9, 105.2, 76.8, 75.0, 72.6, 72.5, 71.7, 71.6, 71.3, 70.4, 69.7, 62.6, 33.2, 30.9,

30.8, 30.7, 30.7, 30.5, 30.4, 30.4, 28.2, 27.3, 23.8, 14.5.

[115] Nuclear magnetic resonance (NMR) data for compound 18: ¹H NMR (400 MHz, CD₃OD) d 5.45-5.36 (m, 2H, 2xC H), 5.21 (d, J= 3.80 Hz, 1 H, C H), 4.37 (m, 1 H, C H), 4.09-4.04 (m, 1H, C H), 3.96-3.48 (m, 22H, 8xC H₂6xC H), 3.45-3.40 (m, 1H, C H), 3.35-3.29 (m, 2H, 2xC H), 2.11-2.01 (m, 4H, 2xC H_z), 1.62 (quin, J= 6.87 Hz, 2H, C Hz), 1.44-1.33 (m, 22H, 11xCH₂), 0.96 (t, J=6.61 Hz, 3H, C H₃); ¹³C NMR (100 MHz, CD₃OD) d 131.6, 131.0, 130.9, 104.5, 103.0, 81.4, 78.1, 77.8, 76.7, 75.2, 74.9,

74.8, 74.3, 72.5, 71.6, 71.6, 71.6, 71.2, 69.8, 62.8, 62.3, 33.7, 33.2, 30.9, 30.8, 30.8, 30.7, 30.7, 30.5, 30.4, 30.4, 30.3, 28.2, 27.3, 23.8,14.6.

Example 2

[116] The solubility and aggregation behaviour of binary mixtures of glucoside surfactant molecules 1 6 in water was investigated across a range of concentrations and temperatures by maximum bubble pressure tensiometry and SANS measurements, as shown in Table 2 below.

Table 2. Solubility parameters for surfactant molecules 1 -6

[1 17] Molecules 1 - 4 (n-C₈ - n-C tails) were all soluble in water, with no upper limit on the soluble surfactant fraction. The critical micelle concentration decreased with increasing tail length. Molecules 5 and 6 (n-Ci₆ and n-C-is tails) were insoluble at room temperature, i.e. the Krafft temperature of these molecules is greater than 25°C. At 50°C, 5 and 6 were found to be soluble (and above the CMC) between 0.8 and 12.8 mmol/litre, but further surfactant could not be dissolved to produce solutions above this concentration range (i.e. above about 0.7 weight %). The Krafft temperatures of the surfactants were determined to be 7°C for 4, 43 °C for 5 and 48°C for 6.

[1 18] In order to determine the geometry and size of the micelles formed in the soluble regions, SANS measurements were performed in D₂0 for a range of fixed concentrations above the CMC, as shown in Table 2 and depicted in Figures 1 A-1 F.

[1 19] Spherical micellar geometries were modelled for molecules 1 , 2, and 3, with larger micelles for the longer alkyl tail groups (average fitted radii of 17, 22, and 24 A respectively). Further lengthening of the alkyl tail results in the elongation of the aggregate geometry from spheres to cylinders (molecule 4) to flexible cylinders (molecules 5 and 6 at 50°C) with average fitted radii of 22, 24, and 25 A respectively. For all the molecules, higher surfactant concentration increased the scattering intensity, but was found to have little effect on the fitted micellar dimensions.

[120] Without wishing to be bound by any theory, it is believed that flexible cylinders (“worm-like” micelles) having the geometries of the molecule 5 and 6 micelles are sufficiently elongated to provide viscoelastic entanglement above a critical overlapping micellar concentration. Flowever, 5 and 6 are insoluble at room temperature and only soluble up to approximately 13 mmol/litre at 50°C, thus limiting the degree of entanglement between the micelles.

Example 3

[121] In an effort to produce a more soluble non-ionic surfactant molecule, while retaining the structural motifs of molecules 5 and 6 which conferred worm-like micellar geometries, glucoside surfactant molecules 7, 11 and 12, having unsaturated hydrocarbyl tails (oleyl = Ci_8:i, linoleyl = Ci_8:2 and erucyl = C_22:i respectively), were prepared. Molecules 8, 9, and 10, similar to 7 but with two, four and six ethylene glycol units in the linking group respectively (instead of 3) were also prepared to investigate the effect of polyethylene glycol) linker length. Molecule 13 and 14, respectively with four and six ethylene glycol units in the linking group and a C22.1 unsaturated hydrocarbyl tail, was prepared in the same series.

[122] The solubility and aggregation behaviour of binary mixtures of these surfactant molecules in water was investigated across a range of concentrations at room temperatures by Nile red encapsulation assay and SANS measurements, as shown in Table 3 below.

Table 3. Solubility parameters for surfactant molecules 6, 7, 11 , 12, 8, 9, 10, 13 and

14 at 25°C

[123] Unlike molecule 6, molecules 7 and 12 with mono-unsaturated tails were soluble in water at room temperature, with no apparent upper limit on the soluble surfactant fraction. The CAC was below the concentration ranges tested by SANS measurements. Thus the CAC of 7 was below 0.8 mmol/litre (0.05 weight %). It is apparent that the unsaturation in the hydrocarbyl tail chain increased the surfactant solubility relative to the equivalent saturated hydrocarbyl tail chain, to the extent that solubility even with the C22 tail was achieved. The c/s-mono-unsaturation is believed to disrupt the crystalline packing of the hydrocarbyl tails and thus facilitate solubility. However, in the case of molecule 11 with a linoleyl di-unsatu rated hydrocarbyl tail, the surfactant was soluble but the solution was unstable and phase-separated over time.

[124] Molecule 8, with only two ethylene glycol units and thus a low HLB value of only 10.3, was insoluble, but molecules 9 and 13 with four ethylene glycol units (and oleyl and erucyl tails respectively) and 10 with six ethylene glycol units (and oleyl tail) were soluble without limit.

[125] In order to determine the geometry and size of the micelles in solutions of each soluble surfactant, SANS measurements were performed in D₂0 for a range of fixed concentrations at room temperature (25°C), as shown in Table 3 and depicted in Figures 2A-2F.

[126] Flexible cylindrical (“worm-like”) micellar geometries were modelled for molecules 7, 9 and 13, with an average fitted radius of c.a. 23 to 28 A. The length of the micelles was greater than 120 nm, i.e. the maximum measurable length. The fitted micellar dimensions were relatively consistent across a wide concentration range, i.e. from 0.8 mmol/litre to 51.2 mmol/litre (0.05 - 2.9 weight %). Molecules 7, 9 and 13 have an HLB of below 12.5 (but above 10.5), and the formation of worm-like micelles is consistent with the relatively low head size relative to tail size for these molecules.

[127] Molecule 12, with three ethylene glycol units and a C22 erucyl tail and thus an HLB of only 10.1 , did not form worm-like micelles but was best modelled as a bilayer vesicle type structure. By contrast, molecule 13 with four ethylene glycol units and the erucyl tail had a higher HLB of 10.7, and was able to form worm-like micelles.

[128] Molecule 10, with six ethylene glycol units and a Ci₈ oleyl tail and thus an HLB of 12.8, produced spherical micelles with a fitted radius of about 30 A. The large hydrophilic portion of this molecule relative to the tail is believed to be responsible for a preference for curved micellar walls, and thus the spherical geometry. Substantial elongation of the micelles (modelled as ellipsoids, but sufficiently elongated to enhance viscosity by a degree of entanglement) was achieved with molecule 14 by switching to the longer erucyl chain, and thus reducing the HLB to 1 1.8. Consistent with this observation, the higher concentration solutions of 14 were visibly viscous when manipulated. [129] The geometry and size of the micelles in solutions of selected surfactants was then similarly investigated by SANS at elevated temperature (50°C). At this temperature, molecules 10 and 14 modelled as worm-like micelles, with average fitted radius of c.a. 24 and 27 A respectively. Without wishing to be bound by theory, it is believed that the oligo(ethylene glycol) linker dehydrates at elevated temperature, such that the effective size of the hydrophobic portion of the molecule increases relative to the hydrophilic head. Thus, the micellar interface becomes less curved, favouring micellar elongation.

Example 4

[130] The effect of different carbohydrate head groups on solution properties was then investigated. Thus, oleyl-tailed, oligo(ethylene glycol)-linked surfactant molecules with galactose (15 and 16), mannose (17) and maltose (18) head groups were prepared. These molecules (having three or four ethylene glycol units) were all found to be soluble in water.

[131] The solubility and aggregation behaviour of binary mixtures of these surfactant molecules in water was investigated across a range of concentrations at room temperatures by Nile red encapsulation assay and SANS measurements, as shown with comparison against glucose equivalents 7 and 9 in Table 4 below.

Table 4. Solubility parameters for surfactant molecules 7, 9, 15, 16, 17 and 18 at

25°C

[132] Galactose-based molecules 15 and 16 and maltose-based molecule 18 were similarly soluble as their glucose-based counterparts, with no upper limit on the soluble surfactant fraction. However, in the case of mannose-based molecule 17, phase separation appeared to occur at concentrations above about 6 mmol/litre. Without wishing to be bound by theory, it is believed that the axial hydroxyl at the C2 ring position and the alpha-anomeric form of mannose renders this head-group significantly less hydrophilic than glucose, galactose and maltose, which are all in the beta-anomeric form.

[133] The geometry and size of the micelles in solutions of each soluble surfactant was then investigated by SANS measurements in D₂0 for a range of fixed concentrations at room temperature (25°C), as shown in Table 4 and depicted in Figures 3A-3C.

[134] Flexible cylindrical (“worm-like”) micellar geometries were modelled for galactose-based molecules 15 and 16, with an average fitted radius of c.a. 23 and 24 A respectively. These molecules have an HLB below 12.5 (but above 10.5), and the formation of worm-like micelles is consistent with the relatively low head size relative to the tail size for these molecules.

[135] Molecule 18, with the disaccharide maltose head group and consequently a higher HLB of 13.1 , produced elongated ellipsoidal, but not worm-like, micelles at 25°C. The large head group relative to tail size, as reflected in the HLB value, is believed to be responsible for the preference for curved micellar walls, and thus the ellipsoidal geometry. Nevertheless, the inventors consider that related surfactant molecules with disaccharide (such as maltose) head groups but HLB values below 12.5, for example by virtue of an erucyl tail group, will produce sufficient micellar elongation for viscoelastic entanglement at room temperature.

[136] At 50°C, solutions of molecule 18 form true worm-like micelles. Without wishing to be bound by theory, it is again believed that the polyethylene glycol) linker dehydrates at elevated temperature, such that the effective size of the hydrophobic portion of the molecule increases relative to the hydrophilic head. Thus, the micellar interface becomes less curved, favouring further micellar elongation. Example 5

[137] The solubility and aggregation behaviour of ternary mixtures of surfactant molecules 5 and 7 in water was investigated across a range of concentrations and mixing fractions by SANS measurements at 25°C and 50°C. The micellar geometry of the SANS spectra were modelled in the soluble regions, and the results are depicted in Figure 4.

[138] It is evident that mixtures of molecules 5 and 7 with a 7:5 molar ratio of about 1 :1 or lower were insoluble at room temperature. At high molar ratios (e.g. 7:5 above about 3:1 ), the unsaturated tail was present in a sufficient proportion to solubilise the surfactant system, and worm-like micelles were thus formed at room temperature and 50°C.

Example 6

[139] In another effort to produce a soluble non-ionic surfactant system with worm-like micelles of suitable geometry for viscoelastic entanglement, mixtures combining one of molecules 5 and 6 with one of the molecules 1 to 4 were prepared. It was hypothesized that the soluble, short hydrocarbyl chain surfactant molecules would solubilise the overall surfactant system while retaining the“worm-like” micellar geometry conferred by the insoluble, long hydrocarbyl chain surfactant molecules.

[140] The solubility and aggregation behaviour of these ternary mixtures in water was thus investigated across a range of concentrations and mixing fractions by SANS measurements at 25°C and 50°C. The micellar geometry of the SANS spectra were modelled in the soluble regions, and the results are depicted in Figure 5 (mixtures of 5 and 2), Figure 6 (mixtures of 5 and 4) and Figure 7 (mixtures of 6 and 4).

[141] It is evident from Figure 5 that the micellar geometry of the mixed 5 + 2 system is dominated by the shorter (n-Cio) hydrocarbyl chains of molecule 2. Spherical micelles were formed in all mixtures in the soluble region.

[142] By contrast, Figure 6 shows that combinations of soluble molecule 4 (n-C-i₄ tail) and worm-forming molecule 5 (n-C-i₆ tail) produced worm-like micelles at room temperature across a wide range of total surfactant concentrations (c.a. 3.2 mmol/litre to 22.4 mmol/litre). The viscous properties of the mixed solution were visually apparent when agitating the solutions, by contrast against the low viscosity solutions of molecule 4 alone. The worm-like micellar systems generally had a molecule 5 : molecule 4 molar ratio of between about 1 :3 and about 1 :1. Above this ratio range, the surfactant system was insoluble, while below this ratio range, the micelles were not sufficiently elongated for entanglement.

[143] Figure 7 depicts equivalent results for soluble molecule 4 (n-C-i₄ tail) and worm-forming molecule 6 (n-C-is tail). Due to the greater insolubility of the C18 hydrocarbyl chain, a higher proportion of molecule 4 is required to solubilise the mixed surfactant system. Nevertheless, worm-like micelles are formed at room temperature with some of the mixtures, for example mixtures with a molecule 6 : molecule 4 molar ratio of about 1 :4.

Example 7

[144] Binary mixtures of each of molecules 7, 9, 13, 15 and 16 in water were subjected to rheological analysis at a range of concentrations from 6.4 mmol/litre to 51.2 mmol/litre. Converted to weight % values, these equate to concentrations between approximately 0.35 and 3 wt % (with specific wt % values at each concentration depending on the molecular weight of the surfactant). Solutions of molecules 14 and 18 were also evaluated at 50°C. Initial visual observations confirmed that these surfactant solutions were viscoelastic above a minimum surfactant-specific concentration, with molecules 13 and 15 providing particularly high viscosities.

[145] The solution viscosity as a function of applied shear stress, in steady shear viscosity measurement mode, for 25°C solutions of each of the molecules is depicted in Figures 8A-8E. Molecules 13 and 15 could not be evaluated above about 20-25 mmol/litre as the viscosities were too high for the instrument to process. The viscosity data shows shear-thinning (non-Newtonian) behaviour characteristic of an entangled network of elongated worm-like micelles for each of molecules 7, 9, 13, 15 and 16. Similar shear-thinning behaviour was observed for molecules 14 and 18 at 50°C. As the concentration increases in each case, the viscosity increases and the response transitions from single yielding to a low-shear plateau. This indicates an increase in the internal structure and networking from the entangled worm-like micelles. The “peaks” in the viscosity curves measured for solutions of 13 and 15 are consistent with other reports of highly viscous colloidal systems, where the shear response has been described in three regimes: (1 ) post-yield, there is an initial shear-thinning region due to the flow-induced alignment of the worm-like micelles, followed by (2) a shear-thickening transition region which occurs at a critical shear rate (or equivalently shear stress) due to the formation of a ^'shear-induced structure' (SIS) consisting of transient “hydro-clusters”, and finally (3) a second shear-thinning region due to destabilization and break-down of the hydro-clusters.

[146] The zero-shear viscosities (h₀), depicted in Figure 9, were calculated by averaging the values across the low-shear plateau for each sample, allowing direct comparison between the different concentrations and surfactants. It is evident that each surfactant provides a zero-shear viscosity of greater than 100 mPa.s at a concentration of 40 mmol/litre in water. The relative zero-shear viscosities (averaged across all concentrations), relative to molecule 7 set at an arbitrary value of 1 , are given in Table 5 below.

Table 5. Relative zero-shear viscosity of solutions of selected surfactant molecules

[147] The solutions of 7, 9, 13, 15 and 16 were also subjected to frequency sweep rheological experiments at 10% strain amplitude, with the results for different concentrations depicted in Figures 10A-10E. [148] The rheological characterization of worm-like micellar systems is most usefully performed with oscillatory shear frequency sweep measurements, which are performed to observe how the viscoelastic material reacts to probing at different time- scales. Specifically, this time-scale probing reveals the stress relaxation time of the entangled network of worm-like micelles, the result of a dynamic equilibrium between (1 ) reptation, which involves the combined effects of contour length, flexibility (i.e. Kuhn length), and intermicellar interactions, and (2) breaking and recombination of the micelles. When the rate of breaking and recombination is much greater than reptation, the measured elastic modulus will plateau across a range of frequencies, a property consistent with Maxwell fluids.

[149] The frequency sweep responses shown in Figure 10 generally reveal the evolution from a simple surfactant solution at low concentrations to the typical response for worm-like micellar systems at high concentrations: G’ increases with frequency until it crosses over G” and reaches a plateau; G” meanwhile reaches a maximum around the cross-over point then passes through a minimum before again increasing, potentially toward a second relaxation time outside of the measured frequency range.

[150] The 25.6 mmol/litre solutions of 7 maintained a predominantly viscous response throughout the frequency sweep, but at 51.2 mmol/litre it exhibits a stronger frequency response with the cross-over point shifting to lower frequencies. Solutions of 9 and 16 exhibit weaker viscoelastic responses compared to 7. Solutions of 13 and 15 show a strong viscoelastic response, characteristic of the single relaxation time Maxwellian nature of worm-like micelles in the case of 15. This behaviour of 15 is still apparent even at 12.8 mmol/litre concentration which, in addition to it exhibiting a cross-over point at much lower frequencies compared to 7, indicates its strong tendency to form entangled worm-like micelles. Molecule 13 exhibits very strong elastic behaviour with an elastic plateau across the full frequency range for the measured concentrations, indicating strong worm-like micelles.

[151] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

Claims

Claims

1. A viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic

surfactant comprises surfactant molecules having the formula:

X-L-R, wherein:

each X group is independently a head group comprising a carbohydrate;

each L group is independently a linking group comprising a plurality of alkylene glycol units; and

each R group is independently a linear hydrocarbyl tail group, wherein a sufficient fraction of the surfactant molecules have R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5; and

wherein a sufficient proportion of the surfactant molecules have R groups configured to solubilise the non-ionic surfactant in the viscoelastic fluid.

2. The viscoelastic fluid according to claim 1 , wherein the sufficient fraction of the surfactant molecules is at least 20 mol%.

3. The viscoelastic fluid according to claim 1 or claim 2, wherein the sufficient fraction of the surfactant molecules have R groups with from 16 to 22 carbon atoms.

4. The viscoelastic fluid according to any one of claims 1 to 3, wherein the sufficient fraction of the surfactant molecules have a hydrophilic-lipophilic balance (HLB) of less than 12.

5. The viscoelastic fluid according to any one of claims 1 to 4, wherein all of the

surfactant molecules have the same X groups.

6. The viscoelastic fluid according to any one of claims 1 to 5, wherein the non-ionic surfactant is present in an amount of less than 100 mmol/litre.

7. The viscoelastic fluid according to any one of claims 1 to 6, wherein each R group has from 12 to 22 carbon atoms.

8. The viscoelastic fluid according to any one of claims 1 to 7, wherein the non-ionic surfactant is soluble in the viscoelastic fluid at 25°C.

9. The viscoelastic fluid according to any one of claims 1 to 8, wherein all of the

surfactant molecules have a hydrophilic-lipophilic balance (HLB) of greater than 10.5.

10. The viscoelastic fluid according to any one of claims 1 to 9, wherein the R groups configured to solubilise the non-ionic surfactant are ethylenically unsaturated.

1 1.The viscoelastic fluid according to claim 10, wherein the sufficient proportion of the surfactant molecules is at least 40 mol%.

12. The viscoelastic fluid according to claim 10, wherein the sufficient proportion of the surfactant molecules is substantially 100 mol%.

13. The viscoelastic fluid according to any one of claims 10 to 12, wherein the

ethylenically unsaturated R groups have at least 16 carbon atoms.

14. The viscoelastic fluid according to any one of claims 10 to 13, wherein the R

groups configured to solubilise the non-ionic surfactant are ethylenically mono- un saturated.

15. The viscoelastic fluid according to claim 14, wherein the ethylenically mono- unsaturated R groups are C-i₆ to C₂2 groups.

16. The viscoelastic fluid according to any one of claims 1 to 9, wherein the R groups configured to solubilise the non-ionic surfactant have from 12 to 14 carbon atoms.

17. The viscoelastic fluid according to claim 16, wherein the sufficient proportion is at least 50 mol%.

18. The viscoelastic fluid according to claim 16 or claim 17, wherein the R groups configured to solubilise the non-ionic surfactant are saturated.

19. The viscoelastic fluid according to any one of claims 1 to 18, wherein the

surfactant molecules have the formula:

X-(CH₂CH₂0)_n-(C=0)_p-R,

wherein each n is independently an integer, and the average value for n in the surfactant molecules is from above 2 to 6, and

wherein p is independently selected from 0 or 1 for each of the surfactant molecules.

20. The viscoelastic fluid according to claim 19, wherein p is 0 and n is independently selected from 3 or 4 for each of the surfactant molecules.

21.The viscoelastic fluid according to any one of claims 1 to 20, wherein the

carbohydrate is a monosaccharide.

22. The viscoelastic fluid according to claim 21 , wherein the monosaccharide is

selected from the group consisting of glucose and galactose.

23. The viscoelastic fluid according to any one of claims 1 to 22, wherein the

carbohydrate is a beta-anomeric carbohydrate.

24. The viscoelastic fluid according to any one of claims 1 to 23, wherein the

viscoelastic fluid is substantially free of co-surfactants which lack a head group comprising a carbohydrate.

25. The viscoelastic fluid according to any one of claims 1 to 24, comprising water in an amount of at least 90 weight %.

26. The viscoelastic fluid according to any one of claims 1 to 25, having a zero-shear viscosity of greater than 100 mPa.s at 25°C.

27. A viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic surfactant comprises surfactant molecules having the formula:

X-L-R, wherein:

each X group is independently a head group comprising a carbohydrate;

each L group is independently a linking group comprising a plurality of alkylene glycol units;

each R group is independently a linear hydrocarbyl tail group having at least 16 carbon atoms; and

wherein the surfactant molecules have a hydrophilic-lipophilic balance (HLB) of less than 12.5, and

wherein a proportion of the surfactant molecules sufficient to solubilise the non-ionic surfactant in the viscoelastic fluid have ethylenically unsaturated R groups.

28. A viscoelastic fluid comprising non-ionic surfactant, wherein the non-ionic

surfactant comprises surfactant molecules having the formula:

X-L-R, wherein:

each X group is independently a head group comprising a carbohydrate;

each L group is independently a linking group comprising a plurality of alkylene glycol units; and

each R group is independently a linear hydrocarbyl tail group, wherein a sufficient fraction of the surfactant molecules have R groups with at least 16 carbon atoms and a hydrophilic-lipophilic balance (HLB) of less than 12.5; and

wherein a proportion of the surfactant molecules sufficient to solubilise the non-ionic surfactant in the viscoelastic fluid have R groups having from 12 to 14 carbon atoms.

29. A non-ionic surfactant molecule having the formula:

X-L-R, wherein:

X is a head group comprising a carbohydrate;

L is a linking group comprising a plurality of alkylene glycol units; and R is a linear, ethylenically mono-unsaturated hydrocarbyl tail group having at least 16 carbon atoms,

wherein the surfactant molecule has a hydrophilic-lipophilic balance (HLB) of less than 12.5.

30. A non-ionic surfactant molecule according to claim 29, wherein the carbohydrate is a monosaccharide.

31.A non-ionic surfactant molecule according to claim 29 or claim 30, wherein L has the formula -(CH₂CH₂0)_n-, wherein n is an integer of from 3 to 6.

32. A non-ionic surfactant molecule according to any one of claims 29 to 31 , wherein R is a mono-unsaturated Ci₆ to C₂₂ group.

33. A non-ionic surfactant molecule according to claim 32, wherein R is an oleyl or erucyl group.

34. A non-ionic surfactant molecule according to any one of claims 29 to 33, wherein the hydrophilic-lipophilic balance (HLB) is less than 12.

35. A non-ionic surfactant molecule according to any one of claims 29 to 33, having the formula X¹-(CH₂CH₂0)_ni-R¹, wherein X¹ is a beta-anomeric monosaccharide head group; n¹ is an integer of from 3 to 6 and R¹ is selected from the group consisting of oleyl and erucyl groups, with the proviso that n¹ is 3 or 4 when R¹ is an oleyl group and n¹ is 4, 5 or 6 when R¹ is an erucyl group.

36. A non-ionic surfactant molecule according to any one of claims 29 to 35, which is soluble in water to form a viscoelastic fluid.

37. A viscoelastic fluid, comprising water and one or more non-ionic surfactant

molecules according to any one of claims 29 to 36.