School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan, 689-798, South Korea.
Sci Rep. 2017 Aug 21;7(1):9004. doi: 10.1038/s41598-017-08712-5.
In this work, we analyzed the individual chain dynamics for linear polymer melts under shear flow for bulk and confined systems using atomistic nonequilibrium molecular dynamics simulations of unentangled (CH) and slightly entangled (CH) polyethylene melts. While a certain similarity appears for the bulk and confined systems for the dynamic mechanisms of polymer chains in response to the imposed flow field, the interfacial chain dynamics near the boundary solid walls in the confined system are significantly different from the corresponding bulk chain dynamics. Detailed molecular-level analysis of the individual chain motions in a wide range of flow strengths are carried out to characterize the intrinsic molecular mechanisms of the bulk and interfacial chains in three flow regimes (weak, intermediate, and strong). These mechanisms essentially underlie various macroscopic structural and rheological properties of polymer systems, such as the mean-square chain end-to-end distance, probability distribution of the chain end-to-end distance, viscosity, and the first normal stress coefficient. Further analysis based on the mesoscopic Brightness method provides additional structural information about the polymer chains in association with their molecular mechanisms.
在这项工作中，我们使用无缠结（CH）和轻度缠结（CH）聚乙烯熔体的非平衡分子动力学模拟，分析了剪切流下线性聚合物熔体在本体和受限体系中的单个链动力学。虽然本体和受限体系在聚合物链对施加流场的响应的动力学机制方面表现出一定的相似性，但受限体系中边界固体壁附近的界面链动力学与相应的本体链动力学有很大的不同。在广泛的流动强度范围内对单个链运动进行详细的分子水平分析，以表征三种流动状态（弱、中和强）下本体和界面链的固有分子机制。这些机制实质上是聚合物体系各种宏观结构和流变性质的基础，例如均方末端到末端距离、末端到末端距离的概率分布、粘度和第一法向应力系数。基于介观亮度法的进一步分析提供了与分子机制相关的聚合物链的附加结构信息。
