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

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Developing sustainable, bioderived, conductive ionic gels for low-temperature applications is challenging, especially avoiding ethylene glycol-based antifreezes.
• Existing materials often fail to maintain conductivity and mechanical integrity at sub-zero temperatures.

Purpose of the Study:

• To introduce a novel cellulose-based ionic gel system with enhanced mechanical robustness and ionic conductivity for a wide low-temperature range (room temperature to -60 °C).
• To create an environmentally benign, antifreeze-free platform for advanced applications.

Main Methods:

• Synthesized a gel using cellulose nanocrystals (CNCs) conjugated with liquid crystalline (LC) units, coordinated with zinc chloride (ZnCl2), and crosslinked with bovine serum albumin (BSA) using EDC coupling in an ionic liquid.
• Optimized gel composition (25 wt % ZnCl2, 7.5 wt % BSA).

Main Results:

• The optimized gel exhibited superior ionic conductivity compared to the neat ionic liquid across the tested temperature range (e.g., 11.4 mS cm-1 at 25 °C, 4.25 mS cm-1 at -40 °C).
• The gel's hierarchical structure, integrating LC ordering, ionic coordination, protein crosslinking, and supramolecular assembly, ensures homogeneity and high conductivity.
• Immobilization of LC units improved local structural order and elasticity without sacrificing conductivity.

Conclusions:

• Pioneered an environmentally friendly, largely bioderived, antifreeze-free ionic gel platform.
• Demonstrated the potential of this gel for applications in soft electronics, cryogenic energy devices, deep-sea/space technologies, and biomedical cryo-preservation.