Xugang Guo1, Antonio Facchetti2,3. 1. Department of Materials Science and Engineering, Southern University of Science and Technology (SUSTech), Shenzhen, Guangdong, China. guoxg@sustech.edu.cn. 2. Flexterra Corporation, Skokie, IL, USA. a-facchetti@northwestern.edu. 3. Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, IL, USA. a-facchetti@northwestern.edu.