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

摘要

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 (25-35 deg) as a function of alkyl chain-length of co-surfactant (n-alkanols,C_4OH-C_8OH) and oil (n-alkanes,C_5-H-C_7H).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) 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)_(oil) ratio (V_c) where the microemulsion is about to breakdown,was calcualted with the help of viscosity measurements.