小分子开关耦合PNIPAm响应自组装调控宏观相变及粘结性研究

Poly(N-isopropylacrylamide) (PNIPAm) is the most widely studied thermoresponsive polymers. The general architecture of photo/thermoresponsive systems is using covalently connected azobenzene moieties to side or end positions of polymer chains. However, as self assembling process of PNIPAm will bring azobenzene chains out of ionic liquids(ILs) together, photoisomerization of the azobenzene chains will be prevented, and even worse, leading to an irreversible self-assembly. Herein, azobenzene moieties as photoresponsive switches was proposed to achieve light controlled self-assembly of PNIPAm, whereas photoisomerization would no longer be negatively constrained by self-assembly behaviors of PNIPAm. This project will carefully study how structures and contents of azobenzene molecules influence the photo/thermo response of PNIPAm as well as the mechanism of light controlled self-assembly in a molecular dynamics view. Based on these responsive behaviors, PNIPAm containing block copolymers could demonstrate light controlled sol-gel transitions in ILs. Also, adhesive strength as an important interface character will be studied to establish a relationship between micromesophases and adhesive properties. The feature of the current project is using molecular switches to control self-assembly of PNIPAm, which will provide a reference to build intelligent systems as well as scientific data and fundamental knowledge for stimuli responsive self-assembly in ILs.

聚N-异丙基丙烯酰胺(PNIPAm)是研究最为广泛的温敏聚合物，在其侧链或末端位置以共价键的方式引入偶氮苯基可构造温敏体系光响应性，但当PNIPAm响应自组装析出时，会连带偶氮苯基聚合物在离子液体中析出聚集，阻碍偶氮苯基异构，甚至导致自组装不可逆。于是，本研究采用偶氮苯基小分子作分子开关，构造PNIPAm光响应体系。从结构上独立光敏、温敏基元，保障偶氮苯基光致异构可逆，不受限于PNIPAm自组装行为。研究拟探讨偶氮苯基结构、含量对光控自组装行为影响的科学规律，从分子动力学角度阐明光控自组装机理，并利用该响应自组装特性实现PNIPAm嵌段聚合物在离子液体中光控溶胶凝胶转变，探讨自组装过程中凝胶界面粘结强度的变化规律，建立微相形态与性能的构象关系。该项目创新性地使用小分子异构触发PNIPAm自组装，不仅为智能体系的构建提供一定借鉴，也为小分子光控大分子自组装研究提供科学数据与基础知识。

刺激响应材料因其智能响应行为及其在选择性分离、控制释放、智能开关等领域的潜在应用，因而受到了广泛关注，研究多功能离子液体基材料的刺激响应体系对于开发材料新功能具有重要意义。聚N-异丙基丙烯酰胺(PNIPAm)作为最具有代表性的热响应聚合物，在离子液体中具有高临界溶解温度(UCST)相转变行为(低温析出、高温溶解)。将光响应基元通过共聚或末端修饰的方法引入PNIPAm的主链或侧链上，可赋予热敏聚合物光控自组装响应。但是，光响应基元的含量很容易影响相变温度，需要进行多次聚合反应以优化响应温度，极大地制约了光/热响应材料的发展。为了克服这些缺点，本研究提出了利用偶氮苯(Azo)小分子异构调控聚合物自组装的方法来构建光/热响应体系。研究发现偶氮苯基异构极性变化可以调控PNIPAm自聚集/自溶解行为, 揭示了小分子异构调控大分子自组装的机理。并且借助PNIPAm光敏自组装特性，构建了离子液体体系的宏观的光控溶胶凝胶转变，可以用于界面粘结性性质调控，实现绿色可循环粘结剂的构建，而且基于宏观离子液体相变，离子液体的传导率性质可大幅调控，应用于逻辑电路的光电信号转化应用，对光电器件的发展具有重要作用。