INVESTIGATIONS ON L(2) PHASE AND CUBIC PHASE IN THE SYSTEM AOT 1-OCTANOL WATER

The properties of L(2) phase and cubic phase in the ternary system AOT /1-octanol/water have been studied by means of electrical conductivity , NMR self-diffusion experiments, theology, static and dynamic light s cattering, SANS, and DSC. L(2) phase and cubic phase are neighboring p hases that are both isotropic but vary largely with respect to their m acroscopic appearance; i.e., the L(2) phase is of low viscosity, where as the cubic phase is gel-like. At the phase transition, L(2) phase -- > cubic phase, no discontinuities were observed for the electrical con ductivity and the self-diffusion coefficient of water; i.e., both phas es should structurally be closely related and both are bicontinuous. S ANS showed that in the cubic phase the size of the structural units de creases with increasing AOT concentration. The self-diffusion coeffici ents of both water and octanol/amphiphile are decreasing in parallel w ith the size of the structural units. At the same time the shear modul us rises with increasing surfactant concentration, which can be explai ned in terms of a simple network theory, where each structural unit ac ts as a network point. At high temperatures the cubic phase melts to f orm the L(2) phase with transition enthalpies of typically 5-250 mJ/g. Finally, it was observed that for not too high AOT content such a pha se transition occurs also upon lowering the temperatures; i.e., a reve rse melting transition takes place. (C) 1995 Academic Press, Inc.