Thermal conductivity of aligned polymers with kinks

TL;DR

This paper theoretically investigates phonon transport in aligned kinked polymers, revealing how molecular conformation affects thermal conductivity and identifying regimes of ballistic, localized, and superdiffusive heat transport.

Contribution

It introduces a numerical model for phonon scattering in kinked polymers, explaining the impact of kinks on thermal conductivity across different length scales.

Findings

Thermal conductivity scales as κ ∝ L^{1/3} in long, aligned polymers.

At short lengths, thermal conductivity increases due to ballistic phonon transport.

Intermediate lengths show decreased conductivity due to phonon localization.

Abstract

Thermal conductivity of aligned polymer molecules can be exceptionally high along the alignment direction due to energy transport through strong covalent bonds. At the same time, it is highly sensitive to molecular conformation, varying by orders of magnitude as a result of gauche kinks. Here, we theoretically investigate phonon transport in kinked polymers by numerically evaluating thermal conductivity and interpreting the results in terms of phonon scattering from randomly distributed kinks. For strongly aligned polymers with restricted deviations from a linear backbone, we find that heat transport becomes superdiffusive at long lengths, with thermal conductivity scaling as $\kappa \propto L^{1/3}$. At shorter lengths, thermal conductivity exhibits non-monotonic behavior: it increases at very short scales due to ballistic transport of almost all phonons, then decreases at intermediate lengths due to the Anderson localization of most phonon modes. These results are consistent with experiments and molecular dynamics simulations, and they elucidate the microscopic mechanisms governing heat transport in polymers.