1. Institute of Technical and Macromolecular Chemistry, University of Hamburg, Bundesstr. 45, 20146 Hamburg, Germany; Max-Planck-Institute of Colloids and Interfaces, c/o HASYLAB at DESY, Notkestr. 85, 22603 Hamburg, Germany; HASYLAB at DESY, Notkestr. 85, 22603 Hamburg, Germany; and GKSS Research Center, Postfach 1160, 21494 Geesthacht, Germany