General Patterns of the Phase Behavior of Mixtures of H₂O, Alkanes, Alkyl Glucosides, and Cosurfactants

We demonstrate how rather hydrophilic surfactants can be used for solubilizing simultaneously water and alkane. The required hydrophilic−lipophilic balance can be achieved by the addition of a medium-chain alcohol, that is, a hydrophobic cosurfactant. Specifically, the phase behavior of the quaternary water− n -octane− n -octyl β- d -glucopyranoside (C 8 G 1 )− n -octanol (C 8 E 0 ) system has been investigated. Sugar surfactants, in general, are hydrophilic and, because of the comparatively large number of hydroxyl groups, much less temperature-sensitive than the well-known alkylpolyglycolether (C i E j ) surfactants. Therefore, one has to resort to tuning the phase behavior by mixing with a hydrophobic cosurfactant. Once this is done, the phase behavior mimics that of water−alkane−C i E j microemulsions. To show this, the trajectory of the middle-phase is determined as the phase inversion is passed. A scaling of the trajectory onto the trajectories of conventional temperature-sensitive ternary microemulsions is possible after the composition (i.e. the fraction of n -octanol) of the mixed amphiphilic film is determined from phase behavior and density measurements.