Dielectric properties of microemulsions and of their liquid crystalline mesophases

Abstract

Isotropic w/o microemulsions as well as the liquid crystalline (LC) phase that develops in the former upon water addition, were investigated as a function of increasing water concentration, mass fraction, in the interval 0.024-0.8. We measured: the complex permettivity in the frequency range 16Hz–50MHz; concentration dependence of both ϵ′ and ϵ′ at the different frequencies; the thermally stimulated dialectric polarization release (TSD); and the electro-optical behavior. The different structures that develop in isotropic microemulsions as water is added, were analyzed. An accurate description of the temperature-dependent relaxation processes occuring both in the isotropic state and in the LC phase of these systems was obtained and their activation energy and relaxation time calculated. Two different structures, of lyotropic nature, respectively of cylindrical and lamellar type, were identified; their concentration range of existence and temperature domain were determined. The concentration regions where the transition occurs from an isotropic microemulsion to an LC mesophase (0.3–0.48) and from the first to the second lyotropic LC structure (0.580-0.605) were also investigated.