a
Institute of Polymer Science and Technology, (CSIC), Juan de la Cierva, 3, Madrid, Spain
E-mail: rverdejo@ictp.csic.es
;
Fax: +34 91 5644853
;
Tel: +34 91 258 7424
b
Cellular Materials Group (CellMat), Condensed Matter Physics Department, University of Valladolid, Valladolid, Spain