聚乙二醇/纤维素纳米晶体复合液晶薄膜微观结构及湿度响应行为

Microstructure and humidity response of polyethylene glycol/cellulose nanocrystal composite liquid crystal films

【目的】探索聚乙二醇(PEG)对纤维素纳米晶体(CNC)液晶薄膜湿度响应的影响,阐明其响应机制,旨在为开发低成本、可重复使用和高灵敏度的PEG/CNC复合薄膜湿度传感器提供理论基础。【方法】将CNC与PEG共组装,制备了一种具有湿度响应性能的虹彩色手性向列相光子液晶薄膜,系统考察了PEG质量分数对液晶薄膜的微观结构、显色、力学性能及湿度响应的影响,在此基础上,研究了PEG/CNC复合液晶薄膜在不同湿度条件下的响应循环性能。【结果】对于纯CNC体系,CNC质量分数由3%增加到7%,CNC液晶薄膜的螺距减小,最大反射光波长由596.5 nm蓝移至511.0 nm;对于添加PEG的CNC体系,随着PEG质量分数的增加,PEG/CNC复合液晶薄膜的螺距由394.0 nm减小到244.0 nm,最大反射光波长由613.5 nm蓝移至350.5 nm,韧性先提升后下降,PEG质量分数为5%时为最佳,断裂能为31.9 J·m^(-2),较纯CNC薄膜提升了138%;液晶薄膜经过5次吸湿-解湿,表现出良好的湿度响应重复性,平衡波长的变化率小于0.6%。【结论】制备了一种对湿度具有敏感响应的虹彩色光子PEG/CNC复合液晶薄膜,PEG可以调控复合薄膜螺距,起到调节结构色的作用。

[Objective]Cellulose nanocrystalline(CNC)liquid crystal film,as a kind of photonic crystal with special optical properties,has a promising prospect in the fields of anti-counterfeiting technology,photoelectric functional materials and humidity responsive functional materials.This study,with an exploration of the influence of polyethylene glycol(PEG)on the humidity response of CNC liquid crystal films,is aimed to explain its response mechanism to provide a theoretical basis for the development of low-cost,reusable and highly sensitive PEG/CNC composite film humidity sensors.[Method]The chiral nematic photonic liquid crystal films with humidity response were prepared by evaporation-induced self-assembly of PEG/CNC suspension,and the effects of PEG content on the microstructure,color evolution,mechanical properties and humidity response of the PEG/CNC films were investigated.Then,the cyclic properties of PEG/CNC liquid crystal films under different humidity conditions were studied.[Result]For pure CNC film system,with the increase of CNC content from 3%to 7%,the pitch of CNC liquid crystal film decreased,and the maximum wavelength of reflected light shifted from 596.5 nm to 511.0 nm.For PEG/CNC films,with the increase of PEG content,the pitch of PEG/CNC composite liquid crystal film decreased from 394.0 nm to 244.0 nm while the maximum wavelength of reflected light moved from 613.5 nm to 350.5 nm.The toughness increased first and then decreased,the optimal PEG addition amount was 5%,the breaking energy was 31.9 J·m^(−2) which was 138%higher than that of pure CNC film.After 5 hygroscopic and dehumidifying experiments,the PEG/CNC film showed good humidity response repeatability with the change rate of the equilibrium wavelength being lower than 0.6%.[Conclusion]An iridescent photonic PEG/CNC liquid crystal film for humidity sensing were prepared,and it was found that PEG can regulate the structural colour by modulate the pitch of the composite film.