Wavelength-Orthogonal Photoinitiated Polymerization-Induced Microphase Separation for Stepwise Ionogel Curing

Ionogels typically face a trade-off between stiffness and ionic conductivity, with phase separation being a potential solution. However, postmodification techniques to enhance stiffness after phase separation remain underexplored. To address this, we developed a stepwise ionogel curing strategy using wavelength-orthogonal photoinitiated polymerization-induced microphase separation (PIMS) to improve stiffness while preserving ionic conductivity. In the first curing step, blue light-initiated PIMS facilitated the formation of a bicontinuous nanodomain using macro-chain transfer agents of three different molar masses. A benzophenone-based acrylate acted as a latent cross-linker, polymerizing in the first step and triggering UV-induced radical cross-linking in the second. Fourier-transform infrared spectroscopy confirmed reaction orthogonality, while small-angle X-ray scattering and scanning electron microscopy validated the formation of bicontinuous nanodomains and demonstrated that their structure remained intact after the second curing. While preserving the nanostructure, the second curing significantly increased the cross-linking density and Young's modulus. After the second curing, the final ionogel exhibited a Young's modulus of 607 kPa and an ionic conductivity of 1.9 mS/cm, achieving a 140% increase in stiffness with a negligible (0.1%) change in conductivity, which was smaller than the measurement error. This approach provides a promising method for enhancing mechanical strength without sacrificing conductivity and is widely compatible with conventional single-step PIMS.