Characterization of Microemulsion Systems Formed by a Mixed 1,3-Dioxolane Ethoxylate/Octyl Glucoside Surfactant System

The phase behavior of microemulsion systems containing water (or 1.0 wt% NaClaq), isooctane, and the binary surfactant system consisting of n-octyl-β-D-glucopyranoside, C8βG1, and the acid-cleavable alkyl ethoxylate, 4-CH3O (CH2CH2O)7.2, 2-(CH2)12CH3, 2-(CH2)CH3, 1,3-dioxolane, or 'cyclic ketal' ('CK-2,13'), was determined. Large temperature-insensitive one, two, and three-phase microemulsion-phase regions were obtained when equal masses of the two surfactants were employed, suggesting that C8βG1 reduces the temperature sensitivity of CK-2,13's ethoxylate group. Addition of C8βG1 to CK-2,13 greatly improves the latter's low efficiency, evidenced by the formation of a three-phase microemulsion system for surfactant concentrations at low fractions of total surfactants for systems with equal mass ratios of water to oil and CK-2,13 to C8βG1. Analysis of the phase diagrams also suggests that CK-2,13 and C8βG1 impart hydrophobic and hydrophilic character, respectively, to the surfactant mixture, and that addition of salt further increases the hydrophilicity of C8βG1, presumably because of the salting-in of the latter. Analysis of small-angle neutron scattering data revealed that the mixed surfactant system formed spherical oil-in-water microemulsions, and that increasing the CK-2,13 fraction among the surfactants reduced the critical microemulsion concentration but slightly increased the nanodroplet size.