Polymer brushes in competing solvents: phase transitions and switching.

在润湿聚合物方面竞争的两种良溶剂的混合物可导致聚合物链的崩溃和弹性聚合物材料中的相变。这种现象在文献中被称为“共非溶剂”，并且可以在溶剂组成的小变化下为聚合物材料（例如凝胶和聚合物层）的切换打开新的选择。另一方面，复杂的多组分溶剂混合物也是生命系统的特征。在这个项目中，我们想研究和理解的性质下，共非溶剂使用计算机模拟和分析模型的影响下，密集接枝聚合物刷。除了它们的技术潜力外，聚合物刷是研究聚合物物理中集体性质和相变的一个极好的和定义明确的模型系统。我们开始分析和合理化的条件下，一个单一的聚合物刷的非连续相变的存在下，一个共同的非溶剂。之后，应研究由两个相对取向的刷组成的聚合物刷双层。 这与在平衡条件下研究该纳米通道的切换的可能性有关。最后，我们想在溶剂混合物简单流动的条件下研究这种通道的非平衡性质。这里，特别感兴趣的是通过改变流动条件来研究通道的可能切换，即使用通道作为可能的刺激响应阀。将使用基于粗粒度聚合物模型的分子动力学模拟，并进一步开发给定的问题。该模型的实施的基本要素已经开发的初步工作，以及一个简化的理论模型，用于描述在一个均匀的聚合物刷的崩溃过渡。该项目的最终目标是开发使用竞争溶剂的溶液切换定制纳米通道的概念，并实现对聚合物刷中“共同非溶解性”的普遍理解。

The mixture of two good solvents which are competing in wetting the polymer can lead to collapse of polymer chains and to phase transitions in elastic polymer materials. This phenomenon is called ''co-non-solvenc'' in the literature, and can open novel options for the switching of polymer materials such as gels and polymer layers under a small variation of the solvent composition. On the other hand, complex multi-component solvent mixtures are a characteristic property of living systems too. In this project we want to study and to understand the properties of densely grafted polymer brushes under the influence of co-non-solvents both using computer simulations and analytical models. Besides their technological potential polymer brushes being an excellent and well defined model system to study collective properties and phase transition in polymer physics. We start to analyze and rationalize the conditions of discontinuous phase transitions of a single polymer brush in the presence of a co-non-solvent. After that polymer brush double-layers consisting of two oppositely oriented brushes shall be studied. This is related with the possibility to investigate switching of this nano-chanel under equilibrium conditions. Eventually, we want to study the non-equilibrium properties of such channels under the condition of simple flow of the solvent mixture. Here, it is of particular interest to investigate the possible switching of the channel by changing the flow conditions, i.e. using the channel as a possible stimuli-responsive valve. Molecular dynamics simulations based on a coarse-grained polymer model will be used and further developed for the given problem. Essential elements of the implementation of this model have been developed in preliminary work, as well as a simplified theoretical model for the description of the collapse transition in a homogeneous polymer brush. The ultimate goal of the project is to develop concepts for switching of tailored nano-channels using solutions of competing solvents and to achieve a universal understanding of ''co-non-solvency" in polymer brushes.