Cellulose Nanocrystals Chiral Nematic Coating with Reversible Multiple-Stimuli-Responsive Coloration

Due to their unique chiral nematicstructure and specialopticalproperty, cellulose nanocrystals (CNCs) have drawn enormous attention.However, the inherent brittleness and rigidity limit their applicationin coatings or free-standing films. In this work, we designed andfabricated a novel iridescent coating with multiple-stimuli-responsivecoloration through photochemical cross-linking with CNCs, poly-(ethyleneglycol) diacrylate (PEGDA), and erythritol. The as-prepared coatingsexhibited improved mechanical strength because of the introductionof covalent organic frameworks and the internal hydrogen-bonding interactionof CNCs, cross-linked PEGDA networks, and erythritol that providedefficient energy dissipation. Interestingly, the CNC coating was ableto distinguish similar organic liquids, including the skeletal isomers(1-propanol/2-propanol), halogenated hydrocarbons (chloroform/dichloromethane),and homologous compounds (methanol/ethanol), quickly by the changein surface color when immersed in various organic solvents. In addition,the CNC coating exhibited reversible humidity sensitivity with widecolor changes from cyan to yellow-green, salmon pink, red, and colorlessunder 30-98% air relative humidity (RH). Based on the reversiblediscoloration of CNC coating, the anti-counterfeiting performanceon CNC coating was presented, and the handwriting of saline solutionappeared reversibly when stimulated with ethanol. Thus, the reversibleallochroic CNC-based coating platform with multiple-stimuli-responsivenesshas the potential to be developed as solvent sensors, test papers,and encryption tools. Aneco-friendly chiral nematic coating with reversible multiple-stimuli-responsivecoloration prepared through co-assembly of CNCs, PEGDA, and erythritol.