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

Abstract

Due to their unique chiral nematic structure and special optical property, cellulose nanocrystals (CNCs) have drawn enormous attention. However, the inherent brittleness and rigidity limit their application in coatings or free-standing films. In this work, we designed and fabricated a novel iridescent coating with multiple-stimuli-responsive coloration through photochemical cross-linking with CNCs, poly(ethylene glycol) diacrylate (PEGDA), and erythritol. The as-prepared coatings exhibited improved mechanical strength because of the introduction of covalent organic frameworks and the internal hydrogen-bonding interaction of CNCs, cross-linked PEGDA networks, and erythritol that provided efficient energy dissipation. Interestingly, the CNC coating was able to distinguish similar organic liquids, including the skeletal isomers (1-propanol/2-propanol), halogenated hydrocarbons (chloroform/dichloromethane), and homologous compounds (methanol/ethanol), quickly by the change in surface color when immersed in various organic solvents. In addition, the CNC coating exhibited reversible humidity sensitivity with wide color changes from cyan to yellow-green, salmon pink, red, and colorless under 30–98% air relative humidity (RH). Based on the reversible discoloration of CNC coating, the anti-counterfeiting performance on CNC coating was presented, and the handwriting of saline solution appeared reversibly when stimulated with ethanol. Thus, the reversible allochroic CNC-based coating platform with multiple-stimuli-responsiveness has the potential to be developed as solvent sensors, test papers, and encryption tools.