1. Laboratory of Polymer Technology, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
2. The Rudolf Peierls Centre for Theoretical Physics, Oxford University, 1 Keble Road, Oxford OX1 3NP, U.K.
3. Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
4. Laboratoire de Spectrometrie Physique, Universite J. Fourier, Grenoble 1, BP87, 38402 St Martin d’Heres, France
5. Philips Research Laboratories, High Tech Campus 4, 5656 AE Eindhoven, The Netherlands