1. Department of Physics, University of Ioannina, P.O. Box 1186, 45110 Ioannina, Greece
2. Department of Chemistry, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany
3. Max Planck Institute for Polymer Research, 55128 Mainz, Germany
4. University Research Center of Ioannina (URCI)─Institute of Materials Science and Computing, 45110 Ioannina, Greece