Although tremendous efforts have been devoted to enhance thermal conductivity in polymer fibers, correlation between the thermal-drawing conditions and the resulting chain alignment, crystallinity, and phonon transport properties have remained obscure. Using a carefully trained coarse-grained force field, we systematically interrogate the thermal-drawing conditions of bulk polyethylene samples using large-scale molecular dynamics simulations. An optimal combination of moderate drawing temperature and strain rate is found to achieve highest degrees of chain alignment, crystallinity, and the resulting thermal conductivity. Such combination is rationalized by competing effects in viscoelastic relaxation and condensed to the Deborah number, a predictive metric for the thermal-drawing protocols, showing a delicate balance between stress localizations and chain diffusions. Upon tensile deformation, the thermal conductivity of amorphous polyethylene is enhanced to 80% of the theoretical limit, that is, its pure crystalline counterpart. An effective-medium-theory model, based on the serial-parallel heat conducting nature of semicrystalline polymers, is developed here to predict the impacts from both chain alignment and crystallinity on thermal conductivity. The enhancement in thermal conductivity is mainly attributed to the increases in the intrinsic phonon mean free path and the longitudinal group velocity. This work provides fundamental insights into the polymer thermal-drawing process and establishes a complete process–structure–property relationship for enhanced phonon transport in all-organic electronic devices and efficiency of polymeric heat dissipaters.

尽管已致力于提高聚合物纤维的导热性的巨大努力，但热拉伸条件与所得链取向，结晶度和声子传输性质之间的相关性仍然不清楚。使用经过严格训练的粗粒度力场，我们使用大规模分子动力学模拟系统地询问了散装聚乙烯样品的热拉伸条件。发现适度的拉伸温度和应变速率的最佳组合可实现最高程度的链排列，结晶度和所产生的热导率。通过粘弹性弛豫的竞争效应使这种组合合理化，并浓缩为Deborah数，Deborah数是热拉伸方案的一种预测指标，在应力局部化和链扩散之间显示出微妙的平衡。在拉伸变形时，无定形聚乙烯的热导率提高到理论极限的80％，即其纯结晶的对应物。在此基础上，开发了一种基于半结晶聚合物的串行-平行导热性质的有效介质理论模型，以预测链排列和结晶度对导热率的影响。导热系数的提高主要归因于本征声子平均自由程和纵向基团速度的增加。