高分子/棒状纳米粒子复合物的分子动力学模拟

Molecular Dynamics Simulation of Polymer/rod Nanocomposite

采用非平衡态分子动力学模拟研究了剪切场下棒状纳米粒子对高分子基体的结构、动力学和流变性质的影响.通过比较多种体积分数(0.8%~10%)的纳米复合物及纯熔体的模拟结果发现,随着纳米粒子的增加,高分子链的扩散和松弛逐渐受到抑制,而链尺寸几乎保持不变.从Weissenberg number(Wi)角度看,在剪切流场下,高分子链的结构性质(如归一化的均方回转半径、回转张量和取向抑制参数)几乎与纳米粒子的体积分数无关,而高分子链的Tumbling运动受到抑制.研究还发现,纳米复合物与纯熔体的剪切黏度曲线趋势基本一致,即Wi=1将曲线分为平台区和剪切变稀区.纳米棒的加入仅定量地改变了流体的剪切黏度.

The effects of nanorods on the structural,dynamical,and rheological properties of polymer matrix were investigated under shear flow via nonequilibrium molecular dynamics simulation.By comparing the re⁃sults of nanocomposites(with volume fractions from 0.8%to 10%)and pure melts,it is found that the diffu⁃sion and relaxation of polymer chains are gradually limited with the increase of nanoparticles,while the poly⁃mer size keeps almost unchanged.Under shear flow,it is found that the structural properties such as the mean-square radius of gyration,main components of gyration tensor and the orientation resistance parameter are almost independent of the volume fractions of nanoparticles,from the perspective of Weissenberg number(Wi),while the tumbling motion of polymer chains is restricted.In addition,we also find the shear viscosity curve of nanocomposites is essentially the same with that of the pure melt,that is,Wi=1 divides the curve into the plateau region and the shear thinning region.The introduction of nanorods merely changes the shear viscosi⁃ty of the fluid quantitatively.