Role of Chain Morphology and Stiffness in Thermal Conductivity of Amorphous Polymers

Abstract

Designing thermally conductive polymer is of scientific interest and practical importance for applications like thermal interface materials, electronics packing, and plastic heat exchangers. In this work, we study the fundamental relationship between the molecular morphology and thermal conductivity in bulk amorphous polymers. We use polyethylene as a model system and performed systematic parametric study in molecular dynamics simulations. We find that the thermal conductivity is a strong function of the radius of gyration of the molecular chains, which is further correlated to persistence length, an intrinsic property of the molecule that characterizes molecular stiffness. Larger persistence length can lead to more extended chain morphology and thus higher thermal conductivity. Further thermal conductivity decomposition analysis shows that thermal transport through covalent bonds dominates the effective thermal conductivity over other contributions from nonbonded interactions (van der Waals) and translation of molecules disregarding the morphology. As a result, the more extended chains due to larger persistence length provide longer spatial paths for heat to transfer efficiently and thus lead to higher thermal conductivity. In addition, rigid rod-like polymers with very large persistence length tend to spontaneously crystallize and form orientated chains, leading to a thermal conductivity increase by more than 1 order of magnitude. Our results will provide important insights into the design of thermally conductive amorphous polymers.

High thermal conductivity in electrostatically engineered amorphous polymers

“…It is likely that the predominant vibrational transfer of heat along the covalently bonded polymer backbone afforded by the extended and stiffened chain morphology as well as enhanced interchain conductance due to stronger ionic bonds result in the substantial increment in κ. The measured increases in κ are consistent with a recent computational study that predicts large enhancements in κ with increasing persistence length in amorphous polyethylene ( 36 ). To further confirm the contributions of extended chain morphology of the ionized PAA chains to measured thermal conductivity, we performed solvent vapor annealing (SVA) on spin-cast PAA films.…”

Role of Ionization in Thermal Transport of Solid Polyelectrolytes

“…This is because thermal transport in amorphous polymer is dominated by the covalent bonds along the chain backbones and when such backbones are extended, thermal conductivity increases. 14,15 In bulk condensed polyelectrolytes, where the counterion concentration is high and the interchain interaction is strong, the counterion condensation theory suggests that the polymer chain will collapse. [16][17][18] Thus, the observed thermal conductivity increase (in Fig.…”

Temperature effects in the thermal conductivity of aligned amorphous polyethylene—A molecular dynamics study

“…To study thermal transport in amorphous PE, the structure of the amorphous polymer is carefully constructed 13 (Fig. 1) by first equilibrating a single extended polyethylene chain of 1000 C atom length at 300 K for 1 ns to form a compact relaxed chain.…”