Field-Induced Percolation in Microemulsions

Abstract

Microemulsions of water in oil exhibit an insulator-conductor transition: a slight increase of the concentration of nanodroplets increases the conductivity with several orders of magnitude^1–6. The basic phenomenon^7–9 is percolation of clusters of water droplets throughout the system, although the volume concentration is often too low for continuum percolation. Safran, Webman and Grest⁸ have shown that the weak mutual attraction of the droplets lowers the density treshold for percolation. There is experimental evidence that in presence of a strong electric field the electric conductivity is enhanced. Indeed, recent experiments⁵ have shown that the electric current in the insulator phase consists of two contributions: a fast response due to diffusion of charged droplets, and a slow response due to changes in the shape of the clusters induced by the electric field.