木质纳米纤维热致调光智能膜的多维结构调控与响应机制研究

The intelligent strategy of wood cellulose nanofiber is the new strategic direction of high value-added utilization of wood fiber, and it is a new idea and method for the special function of wood material. In this project, a thermally light-adjusting wood nanofiber based smart membrane with the multi-dimensional structure will be constructed by the method of molecular design and biomimetic and hierarchical self-assembly. This project proposes a new strategy of using asymmetric flow field flow-static light scattering instrument separation from multiple perspectives to regulate the micro scale of cellulose nanofibril and master the law of structure regulation. Surface temperature sensitive controlled modification of the CNFs will be achieved through Activators ReGenerated by Electron Transfer Atom Transfer Radical Polymerization (ARGET ATRP). The multi dimension structure membrane was constructed by combining ARGET ATRP with biomimetic and hierarchical self-assembly strategy. The formation mechanism of multi dimensional structure under the synergistic action of micro scale of CNFs, copolymer chain structure and polymerization process will be revealed. This project will study the thermal behavior of smart film systematically and demonstrate the synergistic relationship among the microstructure of CNFs, copolymer chain structure, multi-dimensional structure, intelligent film solar light modulation ability, visible light transmittance, critical temperature, temperature response properties, mechanical properties and dimensional stability, illuminating the temperature response mechanism, to achieve the basic application theory of wood cellulose nanofiber based green-efficient thermally light-adjusting smart membrane and devices. This project provides a scientific theoretical guidance for the development of the wood cellulose nanofiber based smart materials with excellent performance, greens environmental protection and resource saving.

木质纳米纤维智能化是木质纤维高附加值利用的新型战略方向，是赋予木质材料特殊功能的新理念。项目从分子层面出发，结合生物层次自组装构筑木质纳米纤维多维结构热致调光智能膜。通过优化非对称流场流-静态多角度光散射分离技术调控木质纳米纤维纤丝（CNFs）的微观尺度，掌握结构调控规律；采用连续电子转移活化再生催化剂原子转移自由基聚合（ARGET ATRP）实现CNFs表面温敏可控修饰，借助自组装策略构筑多维结构膜材，揭示CNFs微观尺度、共聚物链结构和聚合工艺协同作用下多维结构可控形成机制；系统研究智能膜热致调光行为，揭示CNFs微观结构、共聚物链结构和多维网络与智能膜太阳光调制能力、临界温度、力学性能和尺寸稳定性等性能的协同增效关系，探明温度响应机制，获得木质纳米纤维绿色高效热致调光材料与器件的应用基础理论。本项目为性能优良、绿色环保和资源节约的木质纳米纤维智能材料的开发提供理论指导。

木质纳米纤维智能化是木质纤维高附加值利用的新型战略方向，是赋予木质材料特殊功能的新理念。项目从分子层面出发，结合生物层次自组装构筑木质纳米纤维多维结构热致调光智能膜。主要研究结果为：（1）通过优化酸解-研磨-均质工艺调控木质纳米纤维纤丝（CNFs）的微观尺度，掌握结构调控规律。高压均质后的纤维素长度为8-15nm，直径均匀，具有高长径比，网络结构纵横交错。（2）通过红外分析可知，CNFs上大量羟基作为引入功能段的活性点，通过原位自由基聚合，以异丙基丙烯酰胺（NIPPAm）为功能单体，实现表面接枝和化学交联。由于纳米纤维素具有较大的长径比和高度缠结，在水凝胶结构中化学交联、物理缠结以及氢键是共存的，提出了水凝胶交联网络形成机理。（3）通过对复合水凝胶力学性能分析可知，CNFs作为功能骨架材料可以将负载从PNIPAM基体转移从而显著提高水凝胶的弯曲强度、压缩强度和开裂强度。此外，CNFs链上的硫酸根基团(-O-SO3-1)会增加PNIPAm分子链的交联密度，进一步增强复合水凝胶的网络结构。（4）聚合方式对凝胶的结构起着决定性的作用，在未完全交联的聚合物链中形成的冰晶有利于形成互穿孔结构，可为水分子扩散提供更短的通道和更大的储存空间。深层冻结对互穿孔结构有破坏作用，增加冻融次数降低水凝胶的溶胀速率和ESR。而在无冰晶的情况下，网络结构的形成仅依赖于化学交联，反应温度升高，交联密度增加，溶胀速率和ESR越高。（5）通过分析平衡溶胀率（ESR）分析可知，在I~V模式下制备的水凝胶均具有温度响应性，在32℃~ 35℃之间，由PNIPPAm链段构象的变化，引起的ESR发生突变。并且互穿三维交联结构有利于提高响应灵敏度。当环境温度由20℃升高到35℃，三维网状结构消失，并伴随着透明度和体积的降低。提出了水凝胶形态演化机理。本项目为性能优良、绿色环保和资源节约的木质纳米纤维智能材料的开发提供理论指导。