Characterization of structural transitions in the SLS/n-alcohol/water system

Abstract

Ternary systems sodium dodecylsulphate (SLS)/n-alcohol/water with alcohols of different chainlengths and a constant water content of 55% have been investigated by polarized optical microscopy and small-angle x-ray scattering. Upon addition of cosurfactant a hexagonal phase with constant lattice parameter transforms via a two-phase region into a lamellar phase. If surfactant and cosurfactant have similar chainlengths only a small two-phase region is observed and at low cosurfactant content a temperature-sensitive lamellar structure is formed. This structure can be described as a defective one with water-filled pores. At higher alcohol content the well-known behavior of a “classical” lamellar phase with bilayers of great lateral extension is observed. The maximum mole fraction of cosurfactant the lamellar phase of our system can incorporate is 0.77.