Shear-Aligned Tunicate Cellulose Nanocrystals Reinforced Hydrogels with Mechano-Thermo-Chromic Properties

Developing cellulose nanocrystals (CNCs) based responsive optical materials with highly durable structure colors have received growing attentions. However, stimuli-responsive optical hydrogels with chiral nematic arranged CNCs are insufficient in practical application, such as long-time assembly and agglomeration caused by higher percentage of CNCs. Herein, mechano-thermo-chromic hydrogels with uniform interference colors are fabricated by directional shearing tunicate cellulose nanocrystals (TCNCs) and sequential locking the aligned TCNCs in poly(N-isopropylacrylamide) (PNIPAM) networks. Due to the higher aspect ratio and crystallinity of TCNCs, iridescence birefringence appeared at a lower concentration. The shear-oriented TCNCs with the moderate concentration (~5 wt%) not only endow uniform interference colors, but also improve the mechanical properties of nanocomposite hydrogels. The oriented TCNCs/PNIPAM hydrogels display reversible and distinct responsiveness to tensile force, compression, and temperature. This work offers a new strategy to design TCNCs-based sustainable and stretchable responsive optical devicesfor sensors, environmental monitoring, and anti-counterfeiting labels.