Micro-corrugated chiral nematic cellulose nanocrystal films integrated with ionic conductive hydrogels leads to flexible materials for multidirectional strain sensing applications

Multidirectional strain sensors are of technological importance for wearable devices and soft robots. Here, we report that flexible materials capable of multidirectional anisotropic strain sensing can be constructed leveraging diffusion-induced infiltration of monomers and in situ polymerization of metal ion-containing double network hydrogels in and on the surface of micro-corrugated chiral nematic cellulose nanocrystal/glucose films. Integrating the micro-corrugated cellulose nanocrystal/glucose chiral nematic films with ionic conductive hydrogels of PAA-co-AAm/sodium alginate/Al³⁺ endows the materials with multidirectional mechanoelectrical resistivity and mechanochromism anisotropy. The anisotropic responses to multidirectional stress, which are sensitive, swift and reversible, are owing to the synergistic effects of micro-corrugation, helicoidal arrangement, one-dimensional photonic bandgap, mobility of Al³⁺ ions, and water-rich architecture. These flexible materials hold promises as multidirectional and multimodal anisotropic strain sensors in wearable electronics and soft robotic applications.