1. Department of Physics, University of Ioannina, P.O. Box 1186, 451 10 Ioannina, Greece
2. Bergische Universität Wuppertal, 42119 Wuppertal, Germany
3. Max Planck Institute for Polymer Research, 55128 Mainz, Germany
4. Institute of Materials Science and Computing, University Research Center of Ioannina (URCI), 45110 Ioannina, Greece