1. Laboratory of Materials and Interface Chemistry, Soft Matter Cryo-TEM Research Unit, Laboratory of Polymer Technology, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands, Dutch Polymer Institute, P.O. Box 902, NL-5600 AX Eindhoven, The Netherlands, and FEI Company, Achtseweg Noord 5, NL-5651 GG Eindhoven, The Netherlands