Highly robust ion gels, termed double-network (DN) ion gels, composed of inorganic/organic interpenetrating networks and a large amount of ionic liquids (ILs), are fabricated. The DN ion gels with an 80 wt% IL content show extraordinarily high mechanical strength: more than 28 MPa of compressive fracture stress. In the DN ion gel preparation, a brittle inorganic network of physically bonded silica nanoparticles and a ductile organic network of polydimethylacrylamide (PDMAAm) are formed in the IL. Because of the different reaction mechanisms of the inorganic/organic networks, the DN ion gels can be formed by an easy and free-shapeable one-pot synthesis. They can be prepared in a controllable manner by manipulating the formation order of the inorganic and organic networks via not only multistep but also single-step processes. When silica particles form a network prior to the PDMAAm network formation, DN ion gels can be prepared. The brittle silica particle network in the DN ion gel, serving as sacrificial bonds, easily ruptures under loading to dissipate energy, while the ductile PDMAAm network maintains the shape of the material by the rubber elasticity. Given the reversible physical bonding between the silica particles, the DN ion gels exhibit a significant degree of self-recovery by annealing.

Tough inorganic/organic composite network gels consisting of a partially developed silica-particle network and a large amount of an ionic liquid, named micro-double-network (μ-DN) ion gel, are fabricated via two methods. One is a one-pot/one-step process conducted using a simultaneous network formation via sol-gel reaction of tetraethyl orthosilicate and free radical polymerization of N, N-dimethylacrylamide in an ionic liquid. When the network formation rates of the inorganic and organic networks are almost the same, the μ-DN structure is formed. The second method is simpler and involved the use of silica nanoparticles as the starting material. By controlling the dispersion state of the silica nanoparticles in an ionic liquid, the μ-DN structure is formed. In both μ-DN ion gels, silica nanoparticles partially aggregate and form network-like clusters. When a large deformation is induced in the μ-DN ion gels, the silica-particle clusters rupture and dissipate the loaded energy. The fracture stress and Young's modulus of the μ-DN ion gel increase as the size of the silica nanoparticles decreases. The increment in the mechanical strength would have been caused by the increase in the total van der Waals attraction forces and the total number of hydrogen bonding in the silica-particle networks.

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Development of SiO2-d-PK membrane via electrostatic attraction forced strategy for oil–water emulsions separation.

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,Ndimethylacrylamide-co-N-succinimidyl acrylate) synthesized by reversible additionfragmentation 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.