General patterns of the phase behavior of mixtures of H2O, alkanes, alkyl glucosides, and cosurfactants
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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 beta-glucopyranoside (C(8)G(1))-n-octanol (C8E0) 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 (CiEj) 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-CiEj 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.