1. State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China
2. University of Chinese Academy of Sciences, Beijing 100080, P. R. China
3. Key Laboratory of Eco-Environment-Related Polymer Materials
of Ministry of Education, Key Laboratory of Polymer Materials of Gansu
Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730000, P. R. China