1. Laboratory of Disperse Systems and Interfacial Phenomena, Institute of Photographic Chemistry, Academia Sinica, Beijing 100101, People's Republic of China, Laboratoire de Physico-Chimie des Surfaces, UMR CNRS 8612, 5 rue J. B. Clément, 92296 Châtenay-Malabry Cedex, France, and Laboratoire de Physico-Chimie Curie, UMR CNRS 168, Institut Curie, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France