Liquid Metal–Ionic Liquid Composite Gels for Soft, Mixed Electronic–Ionic Conductors

Abstract

Mixed electronic–ionic conductors with high flexibility and stretchability can serve as key materials in rapidly emerging applications such as soft electronics and soft robotics. The combined use of two functional liquid materials, ionic liquids (ILs) and liquid metals (LMs), is of significant interest in the development of highly deformable mixed conductors. In this study, composite gels embedded with both IL and LM are prepared for the first time using a Ga–In eutectic (eGaIn), 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide, and poly(vinylidene fluoride-co-hexafluoropropylene) as the LM, IL, and polymer matrix, respectively. The composite gels exhibit low electronic conductivities of the order of 10−3 S cm−1. The addition of an optimal amount of Ni particles (NiPs) improve the electronic conductivity to ≈25 S cm−1 while retaining mechanical flexibility. The electronic conductivity is further enhanced upon elongation due to the reversible alignment and elongation of the LM in the gel matrix along the stretching direction. Owing to a bicontinuous structure composed of the IL-based gel and metal component phases, the composite gels exhibit high ionic conductivity of the order of 10−3 S cm−1. This study demonstrates a rational approach for designing stretchable mixed conductors using ILs and Ga-based LMs.