Chang Yi-Yen, Yu Hsiu-Yu
Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
Langmuir. 2021 Mar 23;37(11):3331-3345. doi: 10.1021/acs.langmuir.0c03422. Epub 2021 Mar 13.
We investigate the chain configuration and segmental dynamics in interacting solvent-free polymer brushes using molecular dynamics simulations. The brush systems are designed to mimic the interstitial space between a pair of neighboring polymer-grafted nanoparticles in solvent-free nanoparticle-organic hybrid materials. Each brush consists of uniformly grafted chains formed by a given number of monomer beads. In monodisperse systems, two opposing brushes have the same chain length and grafting density. In mixed conditions, we consider binary systems with two surfaces being separately grafted with polymers of distinct chain lengths at different grafting densities as well as bidisperse systems with polymers of two different lengths being tethered to the surfaces at a fixed grafting density. We demonstrate that the brush configuration and interpenetration are both governed by the need that monomer beads have to uniformly fill the space. For systems with longer chain lengths and/or higher grafting densities, the larger interwall separation yields more stretched brush conformations and reduced extents of interbrush mixing. As a result, the polymer configurational entropy is generally decreased and the segment-to-segment relaxation dynamics is slowed down accordingly. The grafting of chains at a high density not only makes the relaxation dynamics deviate from the standard Rouse prediction but also leads to distinct relaxation times for the free and tethered segments. The more slowly relaxing tethered segments play a more important role in determining the overall end-to-end fluctuations. Moreover, the two distinct relaxation processes are consistent with the two-stage decay in the Rouse mode fluctuation autocorrelation function. In the presence of brush bidispersity, the collaboration between polymers of different lengths is evidently observed in the brush profiles. The variations of the chain configuration for the two polymers are complementary, and the associated relaxation dynamics of the two species are significantly coupled.
我们使用分子动力学模拟研究了无溶剂相互作用聚合物刷中的链构型和链段动力学。这些刷系统旨在模拟无溶剂纳米颗粒 - 有机杂化材料中一对相邻聚合物接枝纳米颗粒之间的间隙空间。每个刷由给定数量的单体珠子形成的均匀接枝链组成。在单分散系统中，两个相对的刷具有相同的链长和接枝密度。在混合条件下，我们考虑二元系统，其中两个表面分别以不同的接枝密度接枝不同链长的聚合物，以及双分散系统，其中两种不同长度的聚合物以固定的接枝密度连接到表面。我们证明，刷的构型和相互渗透均受单体珠子必须均匀填充空间这一需求的支配。对于链长较长和/或接枝密度较高的系统，较大的壁间间距会产生更伸展的刷构象，并减少刷间混合的程度。因此，聚合物的构型熵通常会降低，链段间的弛豫动力学也会相应减慢。高密度接枝链不仅使弛豫动力学偏离标准的Rouse预测，还导致自由链段和接枝链段具有不同的弛豫时间。弛豫较慢的接枝链段在决定整体端到端波动方面起着更重要的作用。此外，这两个不同的弛豫过程与Rouse模式波动自相关函数中的两阶段衰减一致。在存在刷双分散性的情况下，在刷的轮廓中明显观察到不同长度聚合物之间的协同作用。两种聚合物的链构型变化是互补的，并且两种聚合物相关的弛豫动力学显著耦合。
