1. Surface Engineering Laboratory, Department of Polymer Physics, National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba Ibaraki 305, Japan
2. Department of Molecular Engineering, National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba Ibaraki 305, Japan
3. Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra A.C.T. 0200, Australia