Microstructure and humidity response of polyethylene glycol/cellulose nanocrystal composite liquid crystal films
[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.[Ch,6 fig.25 ref.]
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