Fabrication of Ion Gels with Enhanced Side-Chain Crystallization

초록

Polymeric network structures, such as hydrogels and ion gels, are increasingly employed across various applications in wearable electronics. Hydrogels, however, have a drawback of water evaporation over time, which makes it difficult to retain the given shape. In contrast, ionic liquids, composed of cations and anions, feature low volatility and high thermal stability. Extensive research has been conducted on ion gels, which consist of polymer networks and ionic liquids. The network formation in ion gels is achieved by one or combinations of chemical and physical cross-linking mechanisms. While chemical cross-linking involves polymerization of multifunctional molecules or post cross-linking of macromolecules, the self-assembly or hydrogen bonding may be utilized for physical cross-linking. These ion gels combine the non-flammability, electrochemical stability, and high ionic conductivity of ionic liquids with the excellent mechanical properties attributable to polymeric networks. This makes them suitable for various applications in electrochemical fields, such as transistors and sensors. Although crystallization has been implemented to realize network scaffolds in ion gels, crystallizable side-chain architecture has not been sufficiently explored for ion gels. The compositional dependence of semicrystalline copolymers, comprising crystalline and amorphous comonomers, exhibits a systematic variation in the physicochemical properties of the resulting networks. However, a few reports have indicated that the structure modulation of the amorphous monomers can significantly alter the crystalline structure and mechanical properties. In this study, we aimed to study the consequence of minimizing the steric hindrance for the amorphous comonomers, which led to enhanced crystallization in ion gels. We synthesized copolymers using monomers with long and short alkyl side chains and then mixed them with ionic liquids to fabricate ion gels. As we varied the composition of the amor