1. M. Muthukumar is in the Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003–4530, USA. C. K. Ober is in the Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853–1501, USA. E. L. Thomas is in the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139–4307, USA.