Chremos Alexandros, Glynos Emmanouil, Green Peter F
Department of Chemical Engineering, Centre for Process Systems Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
J Chem Phys. 2015 Jan 28;142(4):044901. doi: 10.1063/1.4906085.
Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties.
通过珠簧模型的分子动力学模拟研究了星型熔体的结构和动力学性质。已知星型聚合物是不均匀的，但缺乏在接近玻璃化转变温度的熔体条件下对其性质进行系统模拟研究。为了探究它们的性质，我们将多布科夫斯基链长依赖相关函数[Z. 多布科夫斯基，《欧洲聚合物杂志》18, 563 (1982)]的适用性从线性聚合物扩展到了星型聚合物。基于实验室玻璃化转变的规范定义，密度和等动力学温度可以通过相关函数得到很好的描述，并且随着结构变得更加复杂，一种微妙的行为会显现出来。对于线性聚合物链和低官能度星型聚合物，我们发现臂长增加会导致密度和等动力学温度升高，但高官能度星型聚合物表现出相反的行为。对于短臂长，低官能度和高高官能度之间的影响更为明显。诸如比容和接触邻居数等补充结果为结构与动力学之间的微妙关系提供了进一步的见解。这些发现对于聚合物、胶体和纳米复合材料领域在无溶液条件下设计具有所需性质的材料具有重要价值。
