1. Frontier Institute of Science and Technology; and State Key Laboratory of Electrical Insulation and Power Equipment; Xi'an Jiaotong University; Xi'an Shaanxi 710054 China
2. School of Science; Xi'an Jiaotong University; Xi'an Shaanxi 710049 China
3. State Key Laboratory of Polymer Physics and Chemistry; Changchun Institute of Applied Chemistry; Chinese Academy of Sciences; Changchun 130022 China