PERFLUOROPOLYETHER MICROEMULSIONS - CONDUCTIVITY BEHAVIOR OF 4-COMPONENT WATER-IN-OIL SYSTEMS

The solubilization of water in a perfluoropolyether (PFPE) oil by a PF PE carboxylic surfactant is studied by performing conductivity measure ments in the presence of ethanol, butanol, hexanol, nonanol and a PFPE alcohol. The insolubility of any alkanol in the PFPE oil enables the confinement of the fourth component in the aqueous phase, in the PFPE oil or at the interface. The electroconductive behaviour of the corres ponding water-surfactant-oil system, quantitatively described previous ly (A. Chittofrati, A. Sanguineti, M. Visca and N. Kallay, Colloids Su rfaces, 63 (1992) 219), is the basis for discussion of the data. The r esults provide evidence for the role of the fourth component in the co mpetition between charge fluctuation among closed water domains (dropl ets) and migration of hydrated/partially dissociated ionic species (co unterions) in solution: one of the two conduction mechanisms becomes p redominant, depending on the type of alcohol. The electroconductive pr operties mirror the structure-maker/breaker effect of each alcohol on the association of this PFPE surfactant, in analogy with hydrocarbon s ystems. The similarities between four-component PFPE systems and the c orresponding three-component PFPE system upon variation of the packing parameter (V/al as defined by Ninham and co-workers (J. Chem. Soc., F araday Trans. 2, 72 (1976) 1525; 76 (1980) 201)) are discussed in deta il.