Cellulose-Based Photonic Crystal Film with Multiple Stimulus-Responsive Performances

Inspired by the Chameleon's skin with tunable color and flexibility, this work designs a ternary supramolecular ensemble (cellulose nanocrystals-poly(ethylene glycol) acrylate-pentanediol) to biomimic this unique inner structure. The incorporated flexible additives form the compact hydrogen-bonding percolating network, which ensures excellent mechanical properties and optical sensitivity. The film color almost covers the entire visible region by tuning the photonic bandgap. The film can respond to multiple stimuli, including humidity, wetting gas, solvent, and pressure, and the corresponding chromaticity variation reflects the degree of stimulation. Besides, the film shape varies in the stimuli, which curves to one side when exposed to the wetting gas and recovers upon drying. External pressure makes the film structure shrink and color blue-shift, and the change degree is related to the pressure intensity. The compressed film can recover to its original state by immersing it in an ethanol solution and evaporating the solvent slowly. This green-manufactured optical biofilm shows considerable mechanical performance and stimulus-induced optical signal switching, which broaden applications in displays, sensors, and coating.