Subzero Conductivity in Antifreeze-Free Ionic Gels from Liquid Crystalline Cellulose-Protein Networks

The development of sustainable, bioderived, conductive ionic gels for low-temperature applications remains a critical challenge, particularly in eliminating reliance on ethylene glycol-based antifreezing agents. This study introduces a cellulose-based ionic gel system that leverages a hierarchical network of multiscale interactions to achieve exceptional mechanical robustness and ionic conductivity across a broad low temperature range (RT to -60 °C). The gel was synthesized from cellulose nanocrystals (CNCs) chemically conjugated with cyanobiphenyl liquid crystalline (LC) units, coordinated with ZnCl₂, and covalently crosslinked with bovine serum albumin (BSA) via EDC coupling in an ionic liquid mixture. The optimized gel (25 wt % ZnCl₂, 7.5 wt % BSA) delivers ionic conductivities of 11.4 mS cm^-1 at 25 °C, 5.48 mS cm^-1 at -20 °C, and 4.25 mS cm^-1 at -40 °C, outperforming the neat ionic liquid. This unique architecture integrates (i) thermotropic LC ordering, (ii) Zn²⁺ mediated ionic coordination, (iii) protein-based covalent crosslinking, and (iv) hydrogen bonding and supramolecular assembly within the ionic liquid, resulting in a homogeneous and highly conductive gel. Notably, the immobilization of LC units in the isotropic phase enhances local structural order and elasticity without compromising conductivity. This work pioneers an environmentally benign, mostly bioderived, antifreeze-free ionic gel platform for applications in soft electronics, cryogenic energy devices, deep-sea and space technologies, and biomedical cryo-preservation.