密度泛函理论探索溶剂响应型二元聚合物刷的“熵-焓”协同机制

Two problems will be involved in the application of binary polymer brushes to surface tuning: one is whether the structure of brush can be stimuli-responsive, and the other is the sensitivity of the response to the strength of stimulating signal. For the layered segregation of the solvent-responsive binary polymer brushes, so far most theoretical studies have focused on the incompatibility in different polymer brush species (enthalpic effect). We note that the configurational entropy effect due to the difference in molecular architecture plays an important role in the solvent response of binary polymer brushes. Changing the molecular architecture will change the synergy between entropy and enthalpy, adjust the sensitivity of the layer structure of binary polymer brushes to the solvent selectivity, and consequently change the controllability of binary polymer brushes. Therefore, this project intends to construct a lattice/free-space density functional theory of the polymer density distributions and the configuration distributions of binary non-linear copolymer brushes to investigate the synergic relationship between the molecular architecture and incompatibility, and construct the structure-function relationship between the molecular architecture and solvent response (degree of layered segregation and sensitivity to the solvent selectivity) of binary polymer brushes which can provide guiding principle for the molecular architecture optimization in the design of solvent-responsive binary polymer brushes.

将二元聚合物刷应用于材料表面开关性能的调控时，会涉及到两个重要的问题：其一，二元刷的结构能否在环境刺激下产生特定的响应；其二，响应对刺激信号强度的敏感性。对于溶剂响应型二元刷的层状分相，迄今大多数研究关注的是组分间的不相容性(焓效应)的影响。我们注意到：高分子结构差异引起的构型熵效应对二元聚合物刷的溶剂响应特性也有重要影响，二元刷的溶剂响应是熵和焓的协同效应。通过改变分子结构可以改变熵和焓的协同性，从而调节二元刷的层状结构对溶剂选择性的敏感性，进而改变二元刷的可控性。本项目拟建立非线形共聚高分子二元刷的密度分布和构型分布的密度泛函理论，探索分子结构与组分间不相容性的协同关系，建立从分子结构到溶剂响应效果（层状相分离程度和对溶剂选择性的敏感性）的"构－效"关系，为溶剂响应型二元聚合物刷膜的设计提供分子结构优化的指导原则。

由于长链高分子体系所涉相结构尺度通常在纳米级以上，如果主要关注聚合物在表界面受限下的相行为，那么链节分子的形状细节就变得次要，这使得格子空间模型在聚合物相行为预测方面获得广泛应用。本项目所发展的格子密度泛函理论直接适用于此类模型，这就为聚合物刷体系的理论研究提供了一个简单方便的分析工具。运用此工具，我们就溶剂响应型聚合物刷的“温控类型预测”、“基底增益效应”、“闭锁/开锁机制”、“共非溶调控机制”、“双重热响应共聚物调控”等焓驱动问题建立了适用于实验研究的定量规律，这些规律是将溶剂响应性二元刷应用于温控表面开关、表面传感器、表面开关性能的复杂或多重调控方式等热点问题的基础，如果根据实验条件进一步改进理论模型及相应参数，可望挖掘出更多具体的有待实验验证的问题和规律。