1. George and Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA
2. Department of Mechanical Engineering, Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, Pennsylvania 15213, USA
3. Deparmtent of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA