1. State Key Laboratory of Solidification Processing; Center of Advanced Lubrication and Seal Materials; Northwestern Polytechnical University; Xi'an Shaanxi 710072 P. R. China
2. School of Materials Science and Engineering; Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
3. Key Laboratory for Soft Chemistry and Functional Materials; Ministry of Education; Nanjing University of Science and Technology; Nanjing 210094 P. R. China