1. State Key Laboratory of Polymer Physics and ChemistryChangchun Institute of Applied ChemistryChinese Academy of Sciences Changchun Jilin 130022 P. R. China
2. University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. University of Science and Technology of China Hefei Anhui 230027 P. R. China
4. Department of Mechanical EngineeringUniversity of Akron Akron OH 44325‐3903 USA