Conductivity of reverse micellar systems of water/AOT + Brij-56 or Brij-58/IPM and their percolation under varied concentrations of amphiphiles and different additives

Abstract

The conductivity of AOT/Brij-56 or Brij-58/IPM/water reverse micellar systems as a function of temperature, ([water]/[AOT + Brij]) and X non-ionic (mole fraction of non-ionic in total surfactant) has been studied. The addition of non-ionic surfactants (Brij-56 and Brij-58) exhibits temperature-induced percolation in conductance in non-percolating AOT/IPM/water system at constant compositions (i.e. at fixed total surfactant concentration, ω and X non-ionic). The influence of total surfactant concentration (micellar concentration), water content ( ω) and content of non-ionic surfactants on the temperature-induced percolation behaviors of these systems have been investigated. The effect of Brij-58 is more pronounced than that of Brij-56 in inducing percolation. The threshold percolation temperature, T p has been determined for these systems in presence of additives of different molecular structures, physical parameters and/or and interfacial properties. The additives have shown both assisting and resisting effects on the percolation threshold. The additives, bile salt (sodium cholate), urea, formamide, cholesteryl acetate, cholesteryl benzoate, toluene, a triblock copolymer (pluronics, L64), polybutadiene, sucrose esters (sucrose dodecanoates, L-1695 and sucrose monostearate S-1670) and formamide distinctively fall in the former category, whereas sodium chloride, cholesteryl palmitate, crown ether and ethylene glycol constitute the latter for both systems. Sucrose dodecanoates (L-595) had almost marginal effect on the process. The activation energy, E p for the percolation process has been evaluated. E p values for the AOT/Brij-56 systems have been found to be lower than those of AOT/Brij-58 systems. The concentration of additives influence the parameters T p and E p for both systems. A preliminary report on the percolation phenomenon in mixed reverse micelles in presence of additives has been suggested on the basis of these parameters ( T p and E p).