Induction of a lamellar phase by the addition of a hydrocarbon to an isotropic ternary surfactant system

The effect of solubilization of the hydrocarbon decane into a ternary surfactant system composed of tetradecyldimethylamine oxide (TDMAO)/benzyl alcohol/water has been investigated. Studies along the isotropic L-phase region connecting the aqueous corner of the phase diagram with the benzyl alcohol side show an increasing concentration of the cosurfactant benzyl alcohol at first only leads to a moderate increase of the solubilization capacity and for intermediate amounts even to a minimum whereas for larger concentrations of benzyl alcohol large amounts of decane can become solubilized. The most interesting effect is that for compositions of the minimum solubility one finds upon further addition of decane the formation of a lamellar phase instead of a microemulsion phase. A SANS study not only confirmed the phase progression from L-phase to the lamellar phase but also showed that in the range of higher benzyl alcohol still a similar trend is observed, i.e. the addition of decane to the surfactant system enhances its amphiphilic strength. Evidently the incorporation of the decane molecules into the amphiphilic bilayer increases its rigidity thereby stabilizing the formation of liquid crystalline lamellar phases. As an effect the combination of the short chain alcohol and the hydrocarbon has a similar influence on the phase behavior as addition of a longer chain alcohol would have.