1. Equipe mixte CEA-RP, RHODIA, 93308 Aubervilliers, France, Laboratoire PMMH, ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France; Physical Chemistry 1, Center for Chemistry and Chemical Engineering, University of Lund, P.O.B. 124, S 221 00 Lund, Sweden