Shape‐Memory Photonic Thermoplastics from Cellulose Nanocrystals

Abstract Responsive materials prepared using shape‐memory photonic crystals have potential applications in rewritable photonic devices, security features, and optical coatings. By embedding chiral nematic cellulose nanocrystals (CNCs) in a polyacrylate matrix, a shape‐memory photonic crystal thermoplastic (CNC‐SMP) allows reversible capture of different colored states is reported. In this system, the temperature is used to program the shape‐memory response, while pressure is used to compress the helical pitch of the CNC chiral nematic organization. By increasing the force applied (≈140–230 N), the structural color can be tuned from red to blue. Then, on‐demand, the CNC‐SMP can recover to its original state by heating it above the glass transition temperature. This cycle can be performed over 15 times without any loss of the shape‐memory behavior or mechanical degradation of the sample. In addition, multicolor readouts can be programmed into the chiral nematic CNC‐SMP by using a patterned substrate to press the sample, while the glass transition temperature of the CNC‐SMP can be tuned over a 90 °C range by altering the monomer composition used to prepare the polyacrylate matrix.