Size Effects in the Thermal Conductivity of Amorphous Polymers
Size Effects in the Thermal Conductivity of Amorphous Polymers
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DOI：
10.1103/physrevapplied.14.044023
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发表时间：
2020-10-14
影响因子：
4.6
通讯作者：
Shrestha, Som S.
中科院分区：
文献类型：
--
作者：
Feng, Tianli;He, Jixiong;Shrestha, Som S.
通过纳米工程控制热导率对先进技术至关重要，如软机器人、人造皮肤、可穿戴电子产品、电池、隔热材料和热电材料。在这里，通过研究非晶态聚合物，包括聚苯乙烯、聚丙烯、聚乙烯和乙烯醇，使用分子动力学模拟，我们发现非晶态聚合物的热导率可以通过尺寸效应降低到其非晶态极限以下。非晶材料中与尺寸相关的热输运被分解为结晶、结晶到非晶和非晶状态。在非晶状态下，热载体的平均自由程可以从几十纳米到超过100纳米，占总导热系数的16%-36%。提出了一种不结合尺寸效应（即扩散和局部）和尺寸效应（即传播）的双通道模型来解释尺寸相关的导热系数。我们还发现，由于静电相互作用，聚合物中带电分子的存在会显著影响热导率及其尺寸效应。这项工作为非晶聚合物的导热性提供了见解，这将对各种能源相关应用的聚合物的纳米和化学工程产生广泛的影响。
Manipulating thermal conductivity through nanoengineering is of critical importance to advance technologies, such as soft robotics, artificial skin, wearable electronics, batteries, thermal insulation, and thermoelectrics. Here, by examining amorphous polymers, including polystyrene, polypropylene, polyethylene, and ethylene vinyl alcohol, using molecular dynamics simulations, we find that the thermal conductivities of amorphous polymers can be reduced below their amorphous limit by size effects. Size-dependent thermal transport in amorphous materials is decomposed into crystalline, crystalline-to-amorphous, and amorphous regimes. In the amorphous regime, the mean free path of propagating heat carriers can range from tens of nanometers to more than 100 nm, contributing 16%-36% of the total thermal conductivity. A two-channel model that combines no size effect (i.e., difusons and locons) and size effect (i.e., propagons) is proposed to account for size-dependent thermal conductivity. We also find that the presence of charged molecules in polymers can significantly affect the thermal conductivity and its size effects due to electrostatic interactions. This work provides insights into the thermal conductivity of amorphous polymers that will have a broad impact on the nano- and chemical engineering of polymers for various energy-related applications.