1. Department of Chemistry, Surface Chemistry, Royal Institute of Technology, Drottning Kristinas väg 51, SE-100 44 Stockholm, Sweden, and YKI, Institute for Surface Chemistry, Box 5607, SE-114 86 Stockholm, Sweden, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark, and Danish Polymer Center, Risø National Laboratory, DK-4000 Roskilde, Denmark