1. Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025, IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, Physical Chemistry Laboratory, ETH-Zentrum, Universitätsstr 22, CH-8092, Zürich, Switzerland, and Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany