1. Adolphe Merkle Institute and Fribourg Center for Nanomaterials, University of Fribourg, Rte de l'Ancienne Papeterie, P.O. Box 209, 1723 Marly, Switzerland
2. Materials Science Centre and the Northwest Composites Centre, School of Materials, Paper Science Building, University of Manchester, Sackville Street, Manchester, M13 9PL, U.K.
3. Department of Macromolecular Science and Engineering, Case Western Reserve University, 2100 Adelbert Road, Cleveland, Ohio 44106-7202, United States