Using the first-principles-based anharmonic lattice dynamics, we calculate the thermal conductivities (κ) of both bulk and single-chain polyethylene (PE) and characterize the mode-wise phonon transport and scattering channels. A significantly higher room-temperature axial thermal conductivity in single-chain PE (1400 W m⁻¹ K⁻¹) is observed compared to bulk PE crystals (237 W m⁻¹ K⁻¹). The reduction of scattering phase space caused by the diminished inter-chain van der Waals interactions explains the much larger κ in single-chain PE. Different from many previous studies, the thermal conductivity of single-chain PE is predicted to converge at a chain length of ∼1 mm at 300 K. The convergence is explained by the indirect thermal resistance from momentum-conserving scatterings of long-wavelength phonons. It is also found that longitudinal phonon modes dominate the thermal transport in PE chains, while transverse phonon branches with quadratic dispersions contribute little to κ due to their vanishing group velocities and limited lifetimes in the long wavelength limit. The predicted high κ of bulk crystalline and single-chain PE show great potential for use of polymers in thermal management, and the unveiled phonon transport mechanisms offer guides for their molecule-level design.

中文翻译：

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单个聚乙烯链中的声子耦合和传输：与块状晶体的比较研究

使用基于第一原理的非调和晶格动力学，我们计算了本体和单链聚乙烯（PE）的热导率（κ）并表征了模态声子传输和散射通道。与块状PE晶体（237 W m ^-1 K ^-1）相比，单链PE（1400 W m ^-1 K ^-1）的室温轴向导热系数明显更高。链间范德华相互作用减弱导致的散射相空间减少说明了更大的κ在单链PE中。与以前的许多研究不同，单链PE的热导率预计在300 K时在约1 mm的链长处会聚。会聚是通过长波子声子的动量守恒散射产生的间接热阻来解释的。还发现纵向声子模式主导了PE链中的热传输，而具有二次分散的横向声子分支由于其消失的基团速度和在长波长范围内的有限寿命而对κ的贡献很小。预测的块状结晶和单链PE的高κ值显示了在热管理中使用聚合物的巨大潜力，而最新的声子传输机制为它们的分子级设计提供了指导。