1. Department of Polymer Engineering, University of Akron, Akron, Ohio 44325 United States
2. Department of Chemistry, Howard University, Washington, District of Columbia 20059, United States
3. Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
4. Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States