具有环形拓扑结构聚合物刷的分子动力学研究

Molecular Dynamics Study of Polymer Brushes with Ring Topology

摘要: 运用分子动力学模拟，研究了不同拓扑结构的环形聚合物刷的静态结构，并对聚合物刷进行了等温压缩模拟。发现不同拓扑结构的聚合链的回转半径与链长的标度行为在不同方向的分量是不同的。对于回转半径z分量与链长的关系，不同拓扑结构的环形聚合物的标度值ν有些差别，但区分度不是特别的大。然而，对于回转半径的横向分量，不同拓扑结构的聚合链，所获得的标度值有明显的不同，而且随着拓扑限制变量的增大，所获得的标度值越来越小。聚合物刷的等温压缩模拟结果表明，聚合物刷在无外界压力或是在较小的压力压缩情况下，单体密度分布轮廓曲线是抛物线状，但随着压力的增大，单体密度分布是阶梯状。而且在压力很大的情况下，聚合物刷的拓扑效应会消失。

Abstract: Static properties of polymer brushes with different topological ring structures are studied by using molecular dynamics simulation, and a compression of the brushes in isothermal process is carried out. It is found that the scaling behaviors between the radius of gyration and the chain length are very different in different directions. The scaling behavior between the gyration radii in the z-direction and the chain length shows little difference for different topological structures. While the transverse components reveal a quite different result. Furthermore, as the topological constraint becomes stronger, one obtains smaller scaling exponent. From the simulation of iso-thermal compression of the brush, we find that the profile of the monomer density is a step function rather than a parabolic one without compression. With force increasing, the topological effect will disappear in the brush system.