Ouyang Yulou, Zhang Zhongwei, Xi Qing, Jiang Pengfei, Ren Weijun, Li Nianbei, Zhou Jun, Chen Jie
Center for Phononics and Thermal Energy Science, China-EU Joint Lab for Nanophononics, School of Physics Science and Engineering, Tongji University Shanghai 200092 People's Republic of China
Institute of Systems Science and Department of Physics, College of Information Science and Engineering, Huaqiao University Xiamen 361021 People's Republic of China.
RSC Adv. 2019 Oct 18;9(57):33549-33557. doi: 10.1039/c9ra07563a. eCollection 2019 Oct 15.
Thermal transport properties of amorphous polymers depend significantly on the chain morphology, and boundary chain folding is a common phenomenon in bulk or lamellar polymer materials. In this work, by using molecular dynamics simulations, we study thermal conductivity of lamellar amorphous polyethylene (LAPE) with varying chain length ( ). For a short without boundary chain folding, thermal conductivity of LAPE is homogeneous along the chain length direction. In contrast, boundary chain folding takes place for large , and the local thermal conductivity at the boundary is notably lower than that of the central region, indicating inhomogeneous thermal transport in LAPE. By analysing the chain morphology, we reveal that the boundary chain folding causes the reduction of both the orientation order parameter along the heat flow direction and the radius of gyration, leading to the reduced local thermal conductivity at the boundary. Further vibrational spectrum analysis reveals that the boundary chain folding shifts the vibrational spectrum to the lower frequency, and suppresses the transmission coefficient for both C-C vibration and C-H vibration. Our study suggests that the boundary chain folding is an important factor for polymers to achieve desirable thermal conductivity for plastic heat exchangers and electronic packaging applications.
非晶态聚合物的热输运性质在很大程度上取决于链形态，而边界链折叠是块状或层状聚合物材料中的常见现象。在这项工作中，我们通过分子动力学模拟研究了不同链长（ ）的层状非晶态聚乙烯（LAPE）的热导率。对于没有边界链折叠的短链，LAPE的热导率沿链长方向是均匀的。相比之下，对于长链会发生边界链折叠，边界处的局部热导率明显低于中心区域，这表明LAPE中的热输运是不均匀的。通过分析链形态，我们发现边界链折叠导致沿热流方向的取向序参数和回转半径都减小，从而导致边界处局部热导率降低。进一步的振动光谱分析表明，边界链折叠使振动光谱向低频移动，并抑制了C-C振动和C-H振动的传输系数。我们的研究表明，边界链折叠是聚合物在塑料热交换器和电子封装应用中实现理想热导率的一个重要因素。
