Institute of Polymer Materials;
School of Material Science and Engineering;
Qingdao University;
Qingdao 266071;
China;
Shanxi Province Key Laboratory of Functional Nanocomposites;
North University of China;
Taiyuan 030000;
China;
School of Chemistry and Materials Science;
Ludong University;
Yantai264025;
China;
Carbon fibers; Polymer-matrix composites; Interface; Hierarchical structure; Gradient modulus;