Dimitrov D I, Milchev A, Binder Kurt, Klushin Leonid I, Skvortsov Alexander M
Inorganic Chemistry and Physical Chemistry Department, University of Food Technology, Maritza Blvd. 26,4002 Plovdiv, Bulgaria.
J Chem Phys. 2008 Jun 21;128(23):234902. doi: 10.1063/1.2936124.
We revisit the classical problem of a polymer confined in a slit in both of its static and dynamic aspects. We confirm a number of well known scaling predictions and analyze their range of validity by means of comprehensive molecular dynamics simulations using a coarse-grained bead-spring model of a flexible polymer chain. The normal and parallel components of the average end-to-end distance, mean radius of gyration and their distributions, the density profile, the force exerted on the slit walls, and the local bond orientation characteristics are obtained in slits of width D=4/10 (in units of the bead diameter) and for chain lengths N=50/300. We demonstrate that a wide range of static chain properties in normal direction can be described quantitatively by analytic model-independent expressions in perfect agreement with computer experiment. In particular, the observed profile of confinement-induced bond orientation is shown to closely match theory predictions. The anisotropy of confinement is found to be manifested most dramatically in the dynamic behavior of the polymer chain. We examine the relation between characteristic times for translational diffusion and lateral relaxation. It is demonstrated that the scaling predictions for lateral and normal relaxation times are in good agreement with our observations. A novel feature is the observed coupling of normal and lateral modes with two vastly different relaxation times. We show that the impact of grafting on lateral relaxation is equivalent to doubling the chain length.
我们从静态和动态两个方面重新审视了受限在狭缝中的聚合物的经典问题。我们通过使用柔性聚合物链的粗粒化珠簧模型进行全面的分子动力学模拟，证实了一些众所周知的标度预测，并分析了它们的有效性范围。在宽度D = 4/10（以珠直径为单位）的狭缝中，对于链长N = 50/300，获得了平均端到端距离、平均回转半径及其分布的法向和平行分量、密度分布、施加在狭缝壁上的力以及局部键取向特征。我们证明，在法向方向上，广泛的静态链性质可以由与计算机实验完全一致的解析模型无关表达式进行定量描述。特别是，观察到的受限诱导键取向轮廓与理论预测密切匹配。发现受限的各向异性在聚合物链的动态行为中表现得最为显著。我们研究了平移扩散和横向弛豫的特征时间之间的关系。结果表明，横向和法向弛豫时间的标度预测与我们的观察结果吻合良好。一个新的特征是观察到具有两个截然不同弛豫时间的法向和横向模式的耦合。我们表明，接枝对横向弛豫的影响相当于链长加倍。
