Bioinspired cholesteric CNC-based photonic hydrogels with enhanced mechanical properties and dynamic structural color for multifunctional optical applications

Abstract

The natural bouligand architecture endows crustacean exoskeletons with an exceptional combination of mechanical strength and vibrant chiroptical characteristics. However, fabricating photonic hydrogels that possess both mechanoresponsive color-changing capabilities and excellent mechanical strength remains a significant challenge. Herein, intelligent cellulose nanocrystal (CNC)-based photonic hydrogels with enhanced mechanical properties are obtained through a one-step synthesis process. Precise control over equilibration time of CNC and acrylamide (AM) precursors is essential for achieving long-range ordered structures within the hydrogels, which is also necessary for their mechanochromic response to pressure and tensile forces. The resulting hydrogels demonstrated high strength (257 KPa), toughness (405 KJ m⁻³), and elasticity (310 %), which far exceed the hydrogels with short-range ordered and completely disordered structures. These results are attributed to the ordered and stiff chiral nematic structure of CNCs, which are seamlessly embedded into the physically crosslinked soft PAM matrix due to favorable dynamic hydrogen bonding. Distinctive stress sensitivities in structural color of hydrogels are realized by controlling the reassembly angles of CNC and AM precursors. Furthermore, two types of anticounterfeiting labels are constructed by applying their mechanochromic characteristics and specific stress sensitivities, which offer enhanced information encryption over traditional labels.