1. Department of Physics, University of Ioannina, 451 10 Ioannina, Greece
2. Laboratory of Polymer Chemistry and Technology, Department of Chemistry, Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Macedonia, Greece
3. Chemistry Department, University of Ioannina, P.O. Box 1186, 45110 Ioannina, Greece