Role Of Angular Bending Freedom In Regulating Thermal Transport In Polymers

Polymers, despite their desirable structural properties, suffer from low thermal conductivity, which restricts their use. Previous studies have indicated that the strong bond-stretching and angular-bending interactions along the chain are believed to have saturated the maximum achievable thermal conductivity in the along-the-chain direction. Contrary to this belief, our results show an improvement in thermal conductivity. By increasing the bond and angle potential, we studied the effect on the thermal conductivity of polyethylene using non equilibrium molecular dynamics simulations. In comparison to restricting the bond stretching, we found that restricting angular bending freedom plays a crucial role in improving the thermal transport along the chain. We observed significant changes in the morphology of the polyethylene chains when the angle potential was increased. We also found a remarkable increase in the phonon group velocity accompanied by large shifts in the longitudinal acoustic branch of the dispersion curve. These results when coupled with the structural changes strongly support the argument that thermal conductivity can be controlled by restricting the angular bending freedom.