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

Abstract

AbstractThe 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.