Bioinspired\nBouligand-Structured\nCellulose Nanocrystals/Poly(vinyl\nalcohol) Composite Hydrogel for Enhanced Impact Resistance

Impact-protective materials are gaining\nimportance because\nof the\nwidespread occurrence of impact damage. Hydrogels have emerged as\npromising candidates owing to their lightweight and flexible nature.\nHowever, achieving soft impact-resistant hydrogels with exceptional\nstiffness, strength, and toughness remains a challenge. Inspired by\nthe Bouligand structure found in the smasher dactyl club of stomatopods,\nwe propose a straightforward multiscale hierarchical structural design\nstrategy. This strategy integrates self-assembly and salting-out techniques\nto enhance the impact resistance of soft hydrogels. Rigid cellulose\nnanocrystals (CNCs) self-assemble into Bouligand-like structures within\nsoft poly(vinyl alcohol) (PVA) matrix via supramolecular interactions.\nThis rational structural design combines the CNC Bouligand structure\nwith a cross-linked network of soft PVA crystalline domains, resulting\nin a composite hydrogel with impressive mechanical properties: high\ntensile fracture strength (30.2 MPa), elastic modulus (62.7 MPa),\nand fracture energy (75.6 kJ m<sup>–2</sup>), surpassing those\nof other tough hydrogels. Moreover, the multiscale hierarchical structure\nfacilitates various energy dissipation mechanisms, including crack\ntwisting, tortuous crack paths, and PVA chain orientation, resulting\nin notable force attenuation (80.4%) in the composite hydrogel. This\nbiomimetic design strategy opens new avenues for developing soft and\nlightweight impact-resistant materials.