1. Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Research Campus Golm, 14424 Potsdam, Germany, Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, P.O. Box 331, 10002 Zagreb, Croatia, and Department of Materials, Swiss Federal Institute of Technology (ETH) Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland