Alkyl polyglucoside microemulsion phase behavior

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We review several key elements of alkyl polyglucoside (C mG n) microemulsion phase behavior. The low solubility of C mG n surfactants in oils such as alkanes makes producing C mG n microemulsions and subsequent study of their phase behavior difficult. Increasing the solubility of C mG n in oil is therefore helpful for the systematic study of C mG n-based microemulsion formulations. To this end, the role of cosurfactants in producing microemulsions with water, alkanes, and n-alkyl β- d-glucopyranosides is first discussed. Adding C 10βG 1 to mixtures of water–alkane–ethoxylated alcohol surfactants (C iE j) produces a region of the three-phase body (a ‘chimney’) that is independent of temperature; thus C mβG 1 are not completely soluble in the co-oil formed of alkane and C iE j at higher temperatures. Then, through a novel approach using oxygenated ether oils (C kOC 2OC k), microemulsions are formed with water, C kOC 2OC k, and C mβG 1 and the phase behavior studied as a function of temperature and composition. Increased C mβG 1 solubility in the more hydrophilic ether oils produces patterns of phase behavior in water–C kOC 2OC k–C mβG 1 mixtures that are identical to those observed in water–alkane–C iE j mixtures. Using the water–ether oil–C mβG 1 mixtures as a base case, the role of C mG n surfactant structure in setting C mG n microemulsion phase behavior is explored. The solubility of the α- d anomer (n-alkyl α- d-glucopyranosides, C mαG 1) in water is much less than that of the β- d surfactant, and these solubility boundaries extend to high surfactant and oil concentrations in water–C kOC 2OC k–C mαG 1 mixtures. Adding C mG 2 compounds to water–C kOC 2OC k–C mβG 1 mixtures shifts the phase behavior to high temperatures, again demonstrating the extreme hydrophilic nature of the sugar headgroup. Finally, adding small amounts of ionic alkyl sulfate surfactants to water–C kOC 2OC k–C mβG 1 mixtures dramatically reduces the total amount of surfactant needed to form a single-phase microemulsion.