B.H. Chen, M.X. Wang, M.D. Dickey
North Carolina State University,
United States
Keywords: ionogel, lightweight materials, glassy gel
Summary:
Conventional gels, such as hydrogels, are typically solvent-rich, which inherently renders them a lightweight material. However, the liquid acts as a plasticizer, weakening the interchain interactions and resulting in extreme softness. Here, we present a new type of ionogel, glassy gel, which defies the trade-off of solvent content and mechanical properties. Despite the liquid content of glassy gel being more than 50% liquid, it remains in a glassy state at room temperature, and the mechanical properties (e.g., Young’s modulus ~ 600 MPa and a fracture strength ~ 42 MPa) are comparable to classical thermoplastics, such as polypropylene and polyethylene. These unique properties of glassy gels arise from the abundant and strong non-covalent interactions between the ionic liquid and polymer chains—a phenomenon described as solvent toughening. Through this toughening mechanism, glassy gels achieve low polymer density yet mechanical robustness without relying on structural porosity, in stark contrast to conventional lightweight strategies based on foams or fiber-reinforced composites. Moreover, the exceptional adhesion strength of glassy gel allows for the replacement of metallic fasteners or commercial pressure-sensitive adhesives (PSAs), further reducing structural weight and simplifying assembly. Glassy gels also possess a range of additional features, including ionic conductivity, optical transparency, and self-healing ability, which can be harnessed through versatile processing approaches. They can be readily processed into films, coatings, or fibers through photopolymerization or melt-based techniques, enabling scalable fabrication and integration into diverse devices. These characteristics endow glassy gels with broad application potential across multiple fields. More broadly, they offer a molecular-level design strategy for lightweight materials—achieving low density and high mechanical efficiency without relying on structural porosity—thereby opening new directions for advanced lightweight materials.