2017/01/10 by Wang, Xinjiang, Kaviany, Massoud, Huang, Baoling
#FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
paper · doi:10.48550/arxiv.1701.02428
We calculate the thermal conductivity (\kappa) of both bulk crystalline and single-chain polyethylene (PE) using the first-principles-based anharmonic lattice dynamics. Despite its low \kappa in amorphous state, the predicted bulk crystal has high axial \kappa (237 W/m-K) at room temperature. The much lower measured \kappa is attributed to the small size of nanocrystallites (~10 nm) in synthesized semi-crystalline PE. For the 1-D chain, the predicted \kappa is much larger and yet finite (1400 W/m-K at room temperature). The reduction of scattering phase space caused by the diminished interchain van der Waals interactions explains this larger \kappa. It is also found that the transverse phonon branches with quadratic dispersion make minor contribution to this, due to their vanishing group velocity in the long-wavelength limit. Moreover, the low-frequency bending and twisting phonon modes are strongly coupled and dominate anharmonic phonon scatterings, leading to the finite \kappa. The predicted high \kappa of bulk and chain PE crystals enable polymer usage in thermal management and the above phonon scatterings provide guide for their nano-designs.