Preparation of Inorganic/Organic Double-Network Ion Gels Using a Cross-Linkable Polymer in an Open System

Tough micro-double-network (μ-DN) ion gels, composed of interpenetrating inorganic and organic networks swollen with 80 wt % of an ionic liquid, were fabricated in an open system using nonvolatile materials: silica nanoparticles for the inorganic network, a cross-linkable polymer for the organic network, and an ionic liquid. The cross-linkable copolymer, poly­(N,N-dimethylacrylamide-co-N-succinimidyl acrylate) synthesized by reversible addition–fragmentation chain transfer polymerization, was cross-linked in situ with a diamine to form the organic network. On the application of load, the inorganic network was partly destroyed resulting in substantial energy dissipation, but the organic network acted as hidden length to suppress the macroscopic destruction of the μ-DN ion gel. The modulus, fracture strength, and strain-to-break of the μ-DN ion gels were tuned by varying the cross-linking degree of the organic network, which could be controlled by changing either the succinimidyl acrylate content of the cross-linkable polymer or the cross-linkable polymer concentration in the precursor solution.