Charge Transport in Percolated Water-in-Oil Microemulsions

Abstract

Charge transport studies in percolated water-in-oil microemulsions near the percolation limit have been carried out. We have investigated in particular CmE5/water/oil systems where either sodium chloride or the surface-active electrolyte AOT were added as carrier electrolytes. We find a markedly different behavior regarding these electrolytes, which is interpreted quantitatively by the different chemical environment of C12E5 imbedding the AOT molecules. Charge transport may be visualized to occur in both systems through droplet/droplet contacts in the interconnected network of chains of nanodroplets. In the systems containing NaCl as carrier electrolyte, the conductivity is found to be proportional to the NaCl concentration, as expected for strong electrolytes. The systems containing AOT as carrier electrolyte, on the other hand, show a strongly nonlinear dependence on concentration. A quantitative consideration of dissociation and association equilibria of AOT yields a dissociation constant of 6 × 10-4, which conforms to typical weak electrolytes such as, e.g., formic acid.