Molecular dynamics simulation of thermal transport in semicrystalline polyethylene: Roles of strain and the crystalline-amorphous interphase region
Molecular dynamics simulation of thermal transport in semicrystalline polyethylene: Roles of strain and the crystalline-amorphous interphase region
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DOI：
10.1063/5.0067999
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发表时间：
2021-12-08
影响因子：
3.2
通讯作者：
Liu, Jun
中科院分区：
文献类型：
--
作者：
He, Jixiong;Liu, Jun
随着塑料热交换器和热界面材料等潜在的热管理应用的发展，导热聚合物在过去十年中重新引起了人们的兴趣。实验表明，超拉伸聚乙烯纤维和薄膜的导热率至少是其无定形对应物的两个数量级。然而，对拉伸半结晶聚合物（例如聚乙烯）中应变对热传输的影响的理论分子水平理解，尤其是结晶-非晶界面区域中不同层间链拓扑的作用，仍然难以捉摸。利用分子动力学模拟，我们研究了简化的夹层半晶结构中的应变对热导率和振动传输的影响。我们发现层间链的拓扑结构决定了热导率对应变的依赖性。比较层间结构不同区域的热阻，非晶区域的热阻不一定是最高的；从晶态到非晶态转变的相间区域可以具有更高的电阻。我们进行频域分析以获得晶体-非晶界面区域的热通量谱，发现由于复杂的层间链拓扑（例如环链），中频和高频的振动模式对总热通量的贡献比相对较低频率的振动模式更大。我们的工作提供了对半结晶聚合物与应变的结构-性能关系的分子水平理解，这可以帮助设计和开发用于热管理应用的导热聚合物。由 AIP Publishing 独家许可出版。
With potential thermal management applications, such as plastic heat exchangers and thermal interface materials, thermally conductive polymers have gained renewed interest in the past decade. Ultradrawn polyethylene fibers and films have been experimentally shown to have thermal conductivities at least two orders of magnitude of these in their amorphous counterparts. However, the theoretical molecular-level understanding of strain effects on the thermal transport in drawn semicrystalline polymers, such as polyethylene, especially the roles of different interlamellar chain topologies in the crystalline-amorphous interphase region, remains elusive. Using molecular dynamics simulations, we investigated the strain effects on the thermal conductivity and vibrational transport in a simplified sandwich semicrystalline structure. We found that the topology of the interlamellar chains determines the dependence of thermal conductivity on strains. Comparing thermal resistances at different regions in the interlamellar structure, thermal resistance at the amorphous region is not necessarily the highest; the interphase region with the transition from the crystalline to amorphous state can have a much higher resistance. We conducted the frequency domain analysis to obtain the heat flux spectrum in the crystalline-amorphous interphase region and found that the vibrational modes at intermediate and high frequencies can contribute more than these at relatively low frequencies to the total heat flux because of the complex interlamellar chain topologies (e.g., loop chains). Our work provides molecular-level understandings of the structural-property relationship in semicrystalline polymers with strains, which could assist the design and development of thermally conductive polymers for thermal management applications. Published under an exclusive license by AIP Publishing.