Polymer brushes in competing solvents: phase transitions and switching.

两种相互竞争润湿聚合物的好溶剂的混合物会导致聚合物链的断裂和弹性聚合物材料的相变。这种现象在文献中被称为‘’共非溶解‘’，并且可以在微小的溶剂组成变化下为诸如凝胶和聚合物层之类的聚合物材料的切换开辟新的选择。另一方面，复杂的多组分混合溶剂也是生命系统的一个特征。在这个项目中，我们希望通过计算机模拟和分析模型来研究和了解共非溶剂影响下稠密接枝聚合物刷子的性能。除了它们的技术潜力，聚合物刷是研究聚合物物理中集体性质和相变的一个很好的和定义良好的模型系统。我们开始分析和合理的条件下，单一的聚合物刷的不连续相变存在共非溶剂的存在。在此之后，应研究由两个相对取向的刷子组成的双层聚合物刷子。这与研究这种纳米香奈儿在平衡条件下开关的可能性有关。最后，我们想要研究在简单的混合溶剂流动条件下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，即将通道用作可能的刺激响应阀。对于给定的问题，将使用并进一步发展基于粗粒聚合物模型的分子动力学模拟。在前期工作中，已经开发了实现该模型的基本要素，以及描述均匀聚合物刷中坍塌转变的简化理论模型。该项目的最终目标是开发使用竞争溶剂的解决方案来切换定制的纳米通道的概念，并实现对聚合物刷子中“共不溶”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.