Transient-electric-birefringence study of rodshaped water-in-oil microemulsions

Transient electric-birefringence (TEB) and smallangle neutron-scattering (SANS) studies have been carried out on w/o microemulsions stabilised by the nickel salt of di(ethyl)hexylsulphosucclnate Ni(AOT)2. The system fonns rods at low water contents, which convert to more spherical aggregates as the concentration of water is increased. TEB data have been obtained as a function of volume fraction and water content, both below and above the entanglement regime. The asymptotic decay of birefringence is well described by a stretched-exponential function [1]. The dynamic data have been analysed following consideration of the theory by Cates [2] assuming that the rods are rigid, polydlsperse and can undergo reversible scission. The static data have been interpreted developing a theoretical model to calculate the polarizabilities along and orthogonal to the symmetry axis of the rod [3]. With the aid of this model, we can justify an apparent collective effect In the specific Kerr constant and compare the rod dimensions measured by SANS and by TEB. A reasonably good agreement is obtained.