Structural phase transformations induced by the addition of decanol to the hexagonal phase of the binary sodium decyl sulphate/water system

Abstract

Abstract The hexagonal phase of the sodium decyl sulphate/water system transforms into a lamellar phase on the introduction of decanol. This transformation occurs in several steps. We present here a study of the sequence of the corresponding phase transformations. The various phases are identified according to their textures by optical microscopy. It can be seen that, as the decanol/soap ratio increases the two dimensional hexagonal phase is followed by two dimensional rectangular phases before the one dimensional lamellar phase is reached. The symmetries of the structures of the phases and the shapes of their aggregates of amphiphilic molecules were determined by small angle X-ray and neutron scattering studies (SAXS and SANS). Two rectangular phases with cmm and pgg symmetries show up successively between the hexagonal and lamellar phases. The shape of the aggregates evolves along the sequence in an unexpected manner. In the two dimensional hexagonal phase, the aggregates are cylinders with an isotropic...