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 surfa ctant system composed of tetradecyldimethylamine oxide (TDMAO)/benzyl alcoh ol/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 concentratio ns of benzyl alcohol large amounts of decane can become solubilized. The mo st interesting effect is that for compositions of the minimum solubility on e finds upon further addition of decane the formation of a lamellar phase i nstead 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 streng th. Evidently the incorporation of the decane molecules into the amphiphili c bilayer increases its rigidity thereby stabilizing the formation of liqui d crystalline lamellar phases. As an effect the combination of the short ch ain alcohol and the hydrocarbon has a similar influence on the phase behavi or as addition of a longer chain alcohol would have. (C) 2001 Elsevier Scie nce B.V. All rights reserved.