Molecular dynamics study on interfacial heat transport in carbon nanotube/conjugated polymer composites

Abstract

For applications as electrodes and flexible thermoelectric materials, conjugated polymers are commonly introduced into macro-scale carbon nanotube (CNT) assemblies, such as CNT yarns, CNT films and CNT forests, to achieve both high electrical conductivity and good structural stability. However, despite significant improvements observed in electrical aspects, the effects of conjugated polymer addition on the thermal properties of CNT-based composites still remain unclear. In this work, we comprehensively investigated the underlying mechanisms of interfacial thermal transport in CNT/conjugated polymer composites through molecular dynamics (MD) simulations. To enhance the accuracy of the calculation, we adopted a force field that was parametrically optimized through density functional theory (DFT) calculations. Starting with a comparative study of across-tube thermal conductivity in neat CNT and CNT/conjugated polymer composite systems, we further investigated the effects of the chain length and doping state of the conjugated polymers, as well as the chirality of the nanotubes, on across-tube heat conduction in the composite systems. The results demonstrated that the across-tube thermal conductance increased as the chain length of the conjugated polymers increased, while the enhancements were constantly more pronounced in the composites with conjugated polymer chains in the neutral state than those in the doped state. In addition, the nanotubes with a high degree of symmetric axial chirality were found to be more conducive to across-tube heat conduction than those with asymmetric off-axial chiralities. These results were further analyzed by calculating the phonon vibrational density of states and the phonon participation ratio. This study elucidates the fundamental mechanisms for regulating interfacial heat transfer in CNT/conjugated polymer composites, providing a theoretical basis for the interface engineering of composite systems tailored for specific thermal-conductivity requirements in different applications.