Molecular dynamics simulations of concentrated polymer solutions in thin film geometry. I. Equilibrium properties near the glass transition.
Molecular dynamics simulations of concentrated polymer solutions in thin film geometry. I. Equilibrium properties near the glass transition.
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DOI：
10.1063/1.3158608
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发表时间：
2009-07
期刊：
影响因子：
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通讯作者：
S. Peter;H. Meyer;J. Baschnagel
中科院分区：
文献类型：
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作者：
S. Peter;H. Meyer;J. Baschnagel
我们报告的分子动力学模拟结果支持的聚合物薄膜与明确的溶剂。模拟中聚合物用珠弹簧链表示，溶剂粒子用单体表示。聚合物和溶剂之间的相互作用有利于混合。我们发现溶剂起着增塑剂的作用。玻璃化转变温度T（g）相对于纯聚合物膜降低。在T（g）附近，我们探索了平衡性质与温度和溶剂浓度的函数关系。我们发现，薄膜的结构和动力学的空间异质性。溶剂密度在支撑壁处和膜与溶剂蒸气平衡的自由表面处富集。在这两个接口的溶剂动力学是快速的，但顺利地跨越到散装动力学时，从界面向中心的膜。一个平滑的梯度，从增强的动态在界面上的批量行为在膜中心也被发现的单体。我们表明，用于参数化的纯聚合物膜中的动态的空间梯度相同的公式也可以应用于这里。此外，我们确定的浓度依赖性的弛豫时间的溶剂在膜的中心，并比较这种依赖性在文献中提出的模型。
We report on results of molecular dynamics simulations for supported polymer films with explicit solvent. The simulation represents the polymers by bead-spring chains and the solvent particles by monomers. The interaction between polymer and solvent favors mixing. We find that the solvent acts as a plasticizer. The glass transition temperature T(g) is reduced relative to the pure polymer film. Near T(g) we explore equilibrium properties as a function of temperature and solvent concentration. We find that the structure and dynamics of the films are spatially heterogeneous. The solvent density is enriched at the supporting wall and at the free surface where the film is in equilibrium with solvent vapor. At both interfaces the solvent dynamics is fast, but smoothly crosses over to bulk dynamics when moving from the interfaces toward the center of the film. A smooth gradient from enhanced dynamics at the interfaces to bulk behavior in the film center is also found for the monomers. We show that the same formula used to parametrize the spatial gradient of the dynamics in the pure polymer film may also be applied here. Furthermore, we determine the concentration dependence of the relaxation time of the solvent in the center of film and compare this dependence to models proposed in literature.