1. Laboratoire de Physicochimie Macromoléculaire, Université Pierre et Marie Curie, CNRS URA No. 278, ESPCI, 10 rue Vauquelin, F-75231 Paris Cedex 05, France; and Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-22100 Lund, Sweden