Water-in-oil microemulsion: influence of co-surfactant chain-length and nature of emulsifier

Two types of water-in-oil (w/o) microemulsions : anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) have been studied at various temperatures (25-35degrees) as a function of alkyl chain-length of co-surfactant (n-alkanols, C4OH-C8OH) and oil (n-alkanes, C5H-C7H). The free energy of transfer of co-surfactant from the continuous oil phase to the interfacial region (DeltaG(s)(0)) has been reported and the adsorption free energy per methylene group of the alkanols (DeltaG(s,alkanol)(0)/Ch(2)) has been computed. With increase in the water content the appearance of microemulsion systems changed from a clear solution to bluish which finally became turbid. The transitions were identified on the basis of specific resistance measurements. A significant change in specific resistance was observed at the transitions. The critical n(water)/n(oil) ratio (V-c) where the microemulsion is about to breakdown, was calculated with the help of viscosity measurements.