Kalathi Jagannathan T, Kumar Sanat K, Rubinstein Michael, Grest Gary S
Department of Chemical Engineering, Columbia University , New York, New York 10027, United States.
Department of Chemistry, University of North Carolina , Chapel Hill, North Carolina 27599, United States.
Macromolecules. 2014 Oct 14;47(19):6925-6931. doi: 10.1021/ma500900b. Epub 2014 Sep 15.
We use molecular dynamics simulations of the Kremer-Grest (KG) bead-spring model of polymer chains of length between 10 and 500, and a closely related analogue that allows for chain crossing, to clearly delineate the effects of entanglements on the length-scale-dependent chain relaxation in polymer melts. We analyze the resulting trajectories using the Rouse modes of the chains and find that entanglements strongly affect these modes. The relaxation rates of the chains show two limiting effective monomeric frictions, with the local modes experiencing much lower effective friction than the longer modes. The monomeric relaxation rates of longer modes vary approximately inversely with chain length due to kinetic confinement effects. The time-dependent relaxation of Rouse modes has a stretched exponential character with a minimum of stretching exponent in the vicinity of the entanglement chain length. None of these trends are found in models that allow for chain crossing. These facts, in combination, argue for the confined motion of chains for time scales between the entanglement time and their ultimate free diffusion.
我们使用长度在10至500之间的聚合物链的Kremer-Grest（KG）珠簧模型以及一个允许链交叉的密切相关类似模型进行分子动力学模拟，以清晰描绘缠结对聚合物熔体中长度尺度依赖的链松弛的影响。我们使用链的Rouse模式分析所得轨迹，发现缠结强烈影响这些模式。链的松弛速率显示出两种极限有效单体摩擦，局部模式经历的有效摩擦远低于较长模式。由于动力学限制效应，较长模式的单体松弛速率大致与链长成反比。Rouse模式的时间相关松弛具有拉伸指数特征，在缠结链长度附近拉伸指数最小。在允许链交叉的模型中未发现这些趋势。综合这些事实，表明在缠结时间和最终自由扩散之间的时间尺度上，链存在受限运动。
