Perfluoropolyether microemulsions: Conductivity behaviour of four-component water-in-oil systems

Abstract

The solubilization of water in a perfluoropolyether (PFPE) oil by a PFPE carboxylic surfactant is studied by performing conductivity measurements 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 corresponding water-surfactant-oil system, quantitatively described previously (A. Chittofrati, A. Sanguineti, M. Visca and N. Kallay, Colloids Surfaces, 63 (1992) 219), is the basis for discussion of the data. The results provide evidence for the role of the fourth component in the competition between charge fluctuation among closed water domains (droplets) and migration of hydrated/partially dissociated ionic species (counterions) in solution: one of the two conduction mechanisms becomes predominant, depending on the type of alcohol. The electroconductive properties mirror the structure-maker/breaker effect of each alcohol on the association of this PFPE surfactant, in analogy with hydrocarbon systems. The similarities between four-component PFPE systems and the corresponding three-component PFPE system upon variation of the packing parameter ( V/al as defined by Ninham and co-workers (J. Chem. Soc., Faraday Trans. 2, 72 (1976) 1525; 76 (1980) 201)) are discussed in detail.