Xin Wang acknowledges the China Scholar-ship Council for funding a scholarship. The first author would like to acknowledge the support from all staff members in Institute of Polymer Materials and Friedrich-Alexander-University Erlangen-Nuremberg, especially Yijing Qin and Muchao Qu for their helpful advice and life care, and also acknowledges Zhuoyu Zhang for illustrations. The authors appreciate the thoughtful input from both reviewers, which has improved the quality of this paper. The paper reflects the views and position of the authors, and not necessarily those of the funding entities. （）