Anisotropic cellulose nanocrystal hydrogel with multi-stimuli response to temperature and mechanical stress

Conventional hydrogels with isotropic polymer networks usually lack selective response to external stimuli and that limits their applications in intelligent devices. Herein, hydrogels with distinctive anisotropic optical characteristics combined with thermosensitivity were prepared through in situ photopolymerization. Self-assembled cellulose nanocrystals (CNCs) with chiral nematic ordered structure were embedded in polyethylene glycol derivatives/polyacrylamide polymer networks. The arrangement of CNCs showed a strong dependence on the self-assembly angle and standing time, enabling the fabrication of hydrogels with customizable CNCs arrangements. Increasing the self-assembly angle from 0° to 90° changed the CNCs arrangement from chiral nematic to symmetrical nematic order which, together with CNCs dynamic arrangement from isotropic to annealed chiral nematic phase at longer standing time, provided versatile ways to produce CNCs hydrogels with tunable anisotropic properties. In addition, the obtained hydrogel displayed reversible temperature and compression response, showing excellent promise to be used as soft mechanical stress and temperature sensors or novel anti-counterfeiting materials.