MICELLAR AND MICROEMULSION SYSTEMS TO PERFORM HETEROGENEOUS REACTIONS, BIPHASIC EXTRACTION AND SOLUTE TRANSPORT

This paper is reviewing recent developments in the field of applicatio ns of self-organized systems (essentially micelles and microemulsions) for the modelling of heterogeneous biphasic reactions, the pseudo-bip hasic extraction of metal ions and the use of micellar particles as tr ansfer agents. All these processes are related to the solubilizing pro perties of micelles which are governed by the free energy of associati on of the solutes considered. Stopped-flow kinetic results are used to demonstrate the relation between the rate of metal/extractant complex formation in these systems and the partitioning of the reagents. A di scrimination between the possible mechanisms involved (interface or bu lk aqueous phase) is shown to be possible in some cases. The practical removal of metal ions using micellar extraction coupled with ultrafil tration is examined from both a thermodynamic and a kinetic point of v iew, in relation with the preceding observations. In a second part we consider the use of micellar particles as carrier agents in liquid mem brane transport experiments which demonstrate a strong analogy with th e ''facilitated diffusion'' of solutes classically observed with macro cyclic carriers. The factors affecting the transfer rates and the natu re of the interfacial transfer mechanisms are discussed. The final par t briefly examines the future of micellar processes and suggests some directions for further investigations. (C) 1997 Elsevier Science B.V.