Percolation Behavior of Nonionic Reverse Micellar Solution

We report the percolation behavior of nonionic surfactant reverse micelles (RMs) composed of sorbitan laurate (Span20) and poly(oxyethylene) sorbitan monooleate (Tween80) in isopropyl myristate (IPM) in presence of a trace amount of water and electrolyte (KCl). Abrupt increase of conductivity above 20 degrees C for oil/surfactant = 8/2 and Span20/Tween80 = 3/2 composition is an indication of the typical percolation behavior. The dynamic percolation behavior was suggested based on the scaling analysis of the conductivity change around the percolation temperature. Contrary to the ionic surfactant RMs, conductivity maxima was observed in the present nonionic RM system. Small-angle X-ray scattering (SAXS) data showed sphere-to-rod-type RM microstructure transition with increasing temperature in the lower temperature region. On the other hand, RM shrunk in the high temperature region due to dehydration of poly(oxyethylene) chains. It is anticipated that this characteristic feature of nonionic surfactant led to the depercolation at high temperatures.