TEMPERATURE-INDUCED, ELECTRIC FIELD-INDUCED AND SOLUTE-INDUCED PERCOLATION IN WATER-IN-OIL MICROEMULSIONS

We report investigations on the percolation of the aqueous phase in wa ter-in-oil microemulsions, comparing systems stabilized by ionic AOT a nd non-ionic Igepal amphiphiles. First, we briefly review the opposite effect of temperature on the two systems and compare electric conduct ivity with viscosity data. In the second part, we show that percolatio n can be induced by high electric fields resulting in a shift of the p ercolation curve. The electric field measurements allow to investigate the dynamics of clustering of the water droplets to form a network of percolating channels. We examine the slow build-up and the fast decay of the percolating structure, monitoring simultaneously electric cond uctivity and electric birefringence. In the third part we discuss the effect of some solutes on the percolation curve, especially of small m olecules which act as protein denaturants and of native and denatured proteins like methemoglobin, chymotrypsin and gelatin. The spectroscop ic determination of the dimerization of hemin, released from denatured hemoglobin, reflects the incorporation of the hemin monomers in the s urfactant monolayer. In the gelatin system time resolved electric bire fringence shows that even at low concentrations it is the macromolecul e which determines the structure of the aqueous domain. In the appendi x, a simple estimate of the intrinsic Ken-constant is given for microe mulsion droplets deformed in an electric field.