1. a Dept. de Física , Universitat de Girona , Campus Montilivi (EPS, P II), E-17071, Girona, Spain
2. b Dept. de Física , Universitat de Girona , Campus Montilivi (EPS, P II), E-17071, Girona, Spain
3. c Dept. Polymers Engineering , University of Minho , Minho, Portugal