1. Max-Planck-Research Group for Colloids and Surfaces at the Institute of Ceramics, Glass and Construction Materials at the TU Bergakademie Freiberg, Chemnitzer Strasse 40, D-09599 Freiberg, Germany, Institute of Polymer Research Dresden, Hohe Strasse 6, D-01067 Dresden, Germany, and University of Sofia, Department of Physical Chemistry, 1126 Sofia, Bulgaria