Enhanced thermal conductive and interfacial performance of M40X carbon fiber/epoxy composites with multi-dimensional liquid crystalline interphase: A combined method of experimental analysis and molecular simulation

The construction of thermally conductive interphase without sacrificing interfacial properties remains challenging for the fabrication of high-performance carbon fiber-reinforced polymer (CFRP) composites. In this work, one-dimensional clavate liquid crystalline polymer (1D C-LCP) and two-dimensional discotic liquid crystalline polymer (2D D-LCP) were synthesized and applied to construct structural-functional interphase in M40X carbon fiber/epoxy (CF/EP) composite, and the correlations of the LCP dimensionality with thermal conductive and interfacial performance were experimentally analyzed and molecularly simulated. The smectic C-LCP and columnar D-LCP improved the surface roughness and chemical activity of M40X CF. Compared to pristine CF/EP composites, the experimental out-of-plane and simulated interfacial thermal resistance of C-LCP-CF/EP and D-LCP-CF/EP composite were respectively alleviated by 45.1 %, 32.2 % and 53.1 %, 52.9 % due to the construction of unidirectional and multichannel thermal conductive pathways at the interphase. The dominant in-plane vibration mode facilitated the parallel phonon transmission, which led to the 163.2 % and 85.8 % improvement in interfacial phonon coupling and interfacial interaction energy of C-LCP-CF/EP composite. Comparatively, the multi-directional phonon transport channels were established by the synergy of out-of-plane and in-plane vibration mode, which induced 26.7 % and 77.5 % increase in interfacial phonon coupling and π-electron accumulation density, leading to the highest thermal conductive and interfacial performance of D-LCP-CF/EP composite.