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% NaCl_aq), isooctane, and the binary surfactant system consisting of n-octyl-β-d-glucopyranoside, C₈βG₁, and the acid-cleavable alkyl ethoxylate, 4-CH₃O (CH₂CH ₂O)_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 C₈βG ₁ 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 C₈β G₁, 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.