1. State Key Laboratory for Mechanical Behaviour of MaterialsShaanxi International Research Center for Soft MatterXi'an Jiaotong University Xi'an 710049 P. R. China
2. Institute of ChemistryMartin-Luther-University Halle-Wittenberg Kurt-Mothes-Straße 2 06120 Halle Germany
3. Department of Materials Science and EngineeringUniversity of Sheffield Sheffield S1 3JD UK
4. Department of PhysicsZhejiang Sci-Tech University Hangzhou 310018 P. R. China