Okuda Satoru, Inoue Yasuhiro, Masubuchi Yuichi, Uneyama Takasi, Hojo Masaki
Department of Mechanical Engineering and Science, Kyoto University, Kyoto 606-8501, Japan.
J Chem Phys. 2009 Jun 7;130(21):214907. doi: 10.1063/1.3140941.
In condensed polymeric liquids confined in slit channels, the movement of chains is constrained by two factors: entanglement among the chains and the excluded volume between the chains and the wall. In this study, we propose a wall boundary (WB) model for the primitive chain network (PCN) model, which describes the dynamics of polymer chains in bulk based on coarse graining upon the characteristic molecular weight of the entanglement. The proposed WB model is based on the assumptions that (i) polymers are not stuck but simply reflected randomly by the wall, and (ii) subchains below the entanglement length scale behave like those in bulk even near the wall. Using the WB model, we simulate the dynamics of entangled polymer chains confined in slit channels. The results show that as the slit narrows, the chains are compressed in the direction normal to the wall, while they are expanded in the parallel direction. In addition, the relaxation time of the end-to-end vector increases, and the diffusivity of the center of mass decreases. The compression in the normal direction is a natural effect of confinement, while the expansion is introduced by a hooking process near the wall. The trends revealed that the relaxation time and diffusivity depend on the increase in friction due to an increased number of entanglements near the wall, which is also associated with the hooking process in the PCN model. These results are expected within the assumptions of the PCN model. Thus, the proposed WB model can successfully reproduce the effects of wall confinement on chains.
在限制于狭缝通道中的凝聚态聚合物流体中，链的运动受到两个因素的制约：链之间的缠结以及链与壁之间的排除体积。在本研究中，我们针对原始链网络（PCN）模型提出了一种壁边界（WB）模型，该模型基于对缠结特征分子量的粗粒化来描述本体中聚合物链的动力学。所提出的WB模型基于以下假设：（i）聚合物不会粘附在壁上，而是简单地随机反射，以及（ii）低于缠结长度尺度的子链即使在靠近壁处的行为也与在本体中类似。使用WB模型，我们模拟了限制在狭缝通道中的缠结聚合物链的动力学。结果表明，随着狭缝变窄，链在垂直于壁的方向上被压缩，而在平行方向上则被拉伸。此外，端到端矢量的弛豫时间增加，质心的扩散系数减小。垂直方向上的压缩是限制的自然效应，而拉伸是由壁附近的钩连过程引起的。这些趋势表明，弛豫时间和扩散系数取决于壁附近缠结数量增加导致的摩擦增加，这也与PCN模型中的钩连过程相关。在PCN模型的假设范围内可以预期这些结果。因此，所提出的WB模型能够成功再现壁限制对链的影响。
