1. Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
2. Department of Physics, University of Ioannina, P.O. Box 1186, 45110 Ioannina, Greece
3. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany