Polydisperse Polymer Brushes: Internal Structure, Critical Behavior, and Interaction with Flow
Polydisperse Polymer Brushes: Internal Structure, Critical Behavior, and Interaction with Flow
复制标题
DOI：
10.1021/acs.macromol.6b02026
复制
发表时间：
2016-12-27
期刊：
影响因子：
5.5
通讯作者：
Schmid, Friederike
中科院分区：
文献类型：
--
作者：
Qi, Shuanhu;Klushin, Leonid I.;Schmid, Friederike
我们通过解析理论、数值自一致场方法和蒙特卡罗模拟研究了多分散性对聚合物刷体结构的影响。多分散性用schulz - zimn链长分布表示。我们特别关注三种不同的多分散体，它们代表尖锐、中等和极宽的链长分布，并推导出这些刷的链端分布的显式解析表达式。结果与自洽场计算和蒙特卡罗模拟的数值结果吻合得很好。随着多分散性的增加，刷体密度曲线由凸形变为凹形，对于给定的平均链长N-n和接枝密度sigma，在广泛的多分散性指数N-w/N-n -n范围内，刷体高度H的比例为(H/H-mono - 1) α (N-w/N-n - 1)(1/2)（这里H-mono为相应的单分散刷体高度）。发现链端波动在非常小的多分散性下已经被强烈抑制。在此观察的基础上，我们引入了电刷作为近临界系统的概念，该系统具有两个参数（缩放变量），即（N-n sigma(2/3)）（-1）和（N-w/N-n -1）（1/2），控制到临界点的距离。这种方法很好地描述了仿真数据。最后，我们研究了流动中刷涂表面的水动力穿透长度l(p)。我们发现它通常随着多分散性的增加而增加。单分散和弱多分散刷子的结垢行为从类似于N-n(1/2) σ(-1/6)的l(p)跨越到类似于N-n（2/3）的强多分散刷子的l(p)。
We study the effect of polydispersity on the structure of polymer brushes by analytical theory, a numerical self consistent field approach, and Monte Carlo simulations. The polydispersity is represented by the Schulz-Zimrn chain-length distribution. We specifically focus on three different polydispersities representing sharp, moderate, and extremely wide chain length distributions and derive explicit analytical expressions for the chain end distributions in these brushes. The results are in very good agreement with numerical data obtained with self-consistent field calculations and Monte Carlo simulations. With increasing polydispersity, the brush density profile changes from convex to concave, and for given average chain length N-n and grafting density sigma, the brush height H is found to scale as (H/H-mono - 1) alpha (N-w/N-n - 1)(1/2) over a wide range of polydispersity indices N-w/N-n (here H-mono is the height of the corresponding monodisperse brush). Chain end fluctuations are found to be strongly suppressed already at very small polydispersity. On the basis of this observation, we introduce the concept of the brush as a near-critical system with two parameters (scaling variables), (N-n sigma(2/3))(-1) and (N-w/N-n - 1)(1/2), controlling the distance from the critical point. This approach provides a good description of the simulation data. Finally, we study the hydrodynamic penetration length l(p) for brush-coated surfaces in flow. We find that it generally increases with polydispersity. The scaling behavior crosses over from l(p) similar to N-n(1/2)sigma(-1/6) for monodisperse and weakly polydisperse brushes to l(p) similar to N-n(2/3) for strongly polydisperse brushes.