Picu R C, Rakshit A
Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
J Chem Phys. 2007 Apr 14;126(14):144909. doi: 10.1063/1.2719196.
The dynamics of entangled polymeric chains in a polymer filled with nanoparticles is studied by means of molecular dynamics simulations of a model system. The primary objective is to study to what extent the reptation of polymers not in direct contact with fillers is modified with respect to the neat material. To this end, two systems are considered: A regular filled material in which the filler-polymer affinity is controlled, and a system in which the beads in contact with the filler at the beginning of the production phase of the simulation are tethered to the filler surface. This second system represents the limit case of long polymer-filler attachment time. In this case attention is focused on the free chains of the melt. The dynamics in the two models is different. In the filled system uniform slowing down for all Rouse modes is observed. The effect varies monotonically with the filler-polymer affinity. Up to saturation, this behavior may be captured by usual models with an effective, affinity-dependent, friction coefficient. In the system with grafted chains, the free chain Rouse dynamics is identical to that in the neat material, except for the longest modes which are significantly slowed down. More interestingly, the dynamics of the free chains depends in a nonmonotonic way on the polymer-filler affinity, although the free chains do not come in direct contact with the filler. This effect is due to small changes in the structure of the polydisperse brush upon modification of the affinity. Specifically, the density of the brush and the amount of interpenetration of free and grafted chains depend on the filler-polymer affinity. The use of a reptation model with modified tube diameter to capture this behavior is discussed.
通过对一个模型系统进行分子动力学模拟，研究了填充纳米颗粒的聚合物中缠结聚合物链的动力学。主要目的是研究与填料没有直接接触的聚合物的蠕动相对于纯材料而言在多大程度上被改变。为此，考虑了两个系统：一个是填料 - 聚合物亲和力可控的规则填充材料，另一个是在模拟生产阶段开始时与填料接触的珠子被束缚在填料表面的系统。第二个系统代表了聚合物 - 填料附着时间长的极限情况。在这种情况下，注意力集中在熔体的自由链上。两个模型中的动力学是不同的。在填充系统中，观察到所有Rouse模式都有均匀的减速。这种效应随填料 - 聚合物亲和力单调变化。在达到饱和之前，这种行为可以用具有有效、依赖亲和力的摩擦系数的常用模型来描述。在接枝链的系统中，自由链的Rouse动力学与纯材料中的相同，除了最长的模式明显减速。更有趣的是，尽管自由链不与填料直接接触，但其动力学以非单调方式依赖于聚合物 - 填料亲和力。这种效应是由于亲和力改变时多分散刷结构的微小变化。具体来说，刷的密度以及自由链和接枝链的互穿量取决于填料 - 聚合物亲和力。讨论了使用具有修改管直径的蠕动模型来描述这种行为。
