Bioinspired Cholesteric\nPhotonic Crystals with 3D\nCross-Linked Network Structure for Humidity Sensors

Inspired by photonic crystals found in nature, smart\nhumidity sensors\nwith structural colors were designed. These sensors differed from\nconventional ones by excluding memory metals in the construction process\nand eliminating the need for energy input during the response phase.\nThey were notable for low cost and ease of fabrication into label-like\nlayers, offering strong competition to advanced electronic sensors\nand carrying significant research implications. In this study, with\nhydrophilic monomer 1-vinyl-2-pyrrolidone (NVP) as a precursor of\nstimulus-response component, cellulose nanocrystals ((CNC)-NVP) cholesteric\nphotonic crystal materials were formed through coevaporation-introduced\nself-assembly of cellulose nanocrystals (CNCs) and NVP, followed by\nultraviolet (UV) curing. The effect of varying poly-NVP contents on\nthe optical properties, chemical properties, microstructure, and humidity\nresponse behavior of photonic crystal materials was systematically\ninvestigated, and a humidity response mechanism was proposed. Compared\nto composite materials using small molecular substances as stimulus-response\ncomponents, the materials developed in this study formed a three-dimensional\n(3D) cross-linked network, which mitigated the risks of component\nmigration, environmental pollution, and performance deterioration.\nThis research contributed to the development of environmentally friendly,\nlow-cost, and sustainable intelligent sensors.