Chain rotation significantly reduces thermal conductivity of single-chain polymers

Kevlar (polyparaphenylene terephthalamide) and PBDT (poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide))-derivatives have very similar chemical structures with aromatic rings. In this study, thermal conductivities of their single chains were calculated using molecular dynamics simulations. Chain rotation was found to be the key to reducing the thermal conductivity. By introducing a new chain rotation factor (CRF), we can easily quantify chain rotation level of single-chain polymers. We demonstrated that thermal conductivity decreases as the CRF increases. We performed further calculations on phonon properties and unveiled that the small thermal conductivity led by large chain rotation can be attributed to reduced phonon group velocities and shortened phonon mean free paths. Insights obtained in this study can be used for tuning thermal conductivity of various polymers and facilitating their various applications including thermal energy conversion and management.