Decanol Effect on Micellar Structure and Phase Transitions

Concentrated micellar solutions of the binary system sodium lauryl sulfate−water and the ternary system sodium lauryl sulfate−water−decanol have been studied by X-ray diffraction in the vicinity of the isotropic (I)−type I hexagonal (H<INF>α</INF>) liquid-crystal phase transitions. Results show how decanol affects the I → H<INF>α</INF> phase transition. In the binary system there is a close packing of micelles in a local hexagonal order in the I phase, and the H<INF>α</INF> phase has a behavior typical of finite/hard objects. In contrast, in the ternary system the close packing is relaxed through a micellar growth, and the H<INF>α</INF> phase has a behavior typical of infinite/flexible objects. An intriguing phase sequence H<INF>α</INF>−nematic cylindrical (N<INF>c</INF>) with an increase in the decanol content is also investigated, and it is attributed to a combined effect of micellar growth and change in rigidity with decanol addition.