1. Chemistry Department, Molecular and Nanomaterials, Catholic University of Leuven, Celestijnenlaan 200F, B3001 Heverlee, Belgium; Laboratoire de Physique des Polymères, CP-223, Université Libre de Bruxelles, Bld. du Triomphe, B-1050, Brussels, Belgium; Institude of Textile Engineering and Polymer Materials, University of Bielsko-Biala, ul. Willowa 2, 43-300 Bielsko-Biala, Poland; and DUBBLE-CRG/ESRF, Netherlands Organization for Scientific Research (NWO), B.P. 220, F-38043 Grenoble Cedex, France