Strain effects on the anisotropic thermal transport in crystalline polyethylene

Abstract

Thermal transport in the axial direction of polymers has been extensively studied, while the strain effect on the thermal conductivity, especially in the radial direction, remains unknown. In this work, we calculated the thermal conductivity in the radial direction of a crystalline polyethylene model and simulated the uniaxial strain effect on the thermal conductivity tensor by molecular dynamics simulations. We found a strong size effect of the thermal transport in the radial direction and estimated that the phonon mean free path can be much larger than the prediction from the classic kinetic theory. We also found that the thermal conductivity in the axial direction increases dramatically with strain, while the thermal conductivity in the radial direction decreases with uniaxial strain. We attribute the reduction of thermal conductivity in the radial direction to the decreases in inter-chain van der Waals forces with strains. The facts that the chains in the crystalline polyethylene became stiffer and more ordered along the chain direction could be the reasons for the increasing thermal conductivity in the axial direction during stretching. Besides, we observed longer phonon lifetime in acoustic branches and higher group velocity in optical branches after uniaxial stretching. Our work provides fundamental understandings on the phonon transport in crystalline polymers, the structure-property relationship in crystalline polymers, and the strain effect in highly anisotropic materials.

Chain rotation significantly reduces thermal conductivity of single-chain polymers

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Thermal Transport in Polyethylene: The Effect of Force Fields and Crystallinity

“…One of the most prominent successes was the prediction of high thermal conductivities of PE, which was later confirmed by experiments . Since then, a substantial number of MD simulations have been performed ,− to investigate the thermal transport in PE and to understand what affects it. However, the different studies use systems that are often either purely crystalline and focusing on single chains ,, or purely amorphous .…”

Manufacturing process design of high-pressure graphite-blasting for mechanical production of turbostratic graphene

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