Induced electric birefringence and viscosity studies in microemulsions

The Kerr constant was determined for the AOT-water-dodecane water-in-oil microemulsion. The goal of these experiments has been to test the validity of the theoretical approach of van der Linden, S. Geiger and D. Bedaux, Phys. A., 156 (1989) 130, which explains the electro-optical process through an elastic deformation of the droplets. The bending modulus of the curved surfactant monolayer along different paths of the phase diagram was measured. It was concluded that for concentrations relatively far from phase transition regions the theory can account for the experimental results. However, we have measured the Kerr constant, relaxation times and viscosity in microemulsion-based (gelatin) gels. These magnitudes have been measured as a function of gelatin concentration. For low biopolymer concentrations, Kerr constants do not vary too much, whereas in a certain concentration range (about 3-4%), they increase abruptly. This behaviour is similar to those of electric conductivity and viscosity. We have estimated the characteristic size of anisotropic microstructures. The possibility of the presence of a branched structure has been analysed by using a stretched-exponents approach proposed by M. Daoud and J. Klafter, J. Phys. A: Math. Nucl. Gen., 23 (1990) L981.