Radiation synthesis of rapidly self-healing, durable, and flexible poly(ionic liquid)/MXene gels with anti-freezing property for multi-functional strain sensors

As a new type of flexible electronic materials, conductive gels have attracted considerable interest because of their distinctive physical and chemical properties. In this work, the ILs with -C=C- double bond function as monomer and crosslinker, respectively; while the two-dimensional (2D) transition metal carbides/nitrides (Ti3C2Tx MXene) functioned simultaneously as a “crosslinker” and nanofiller, then a series of new poly(ionic liquid)/MXene (Cn-PIL/MXene) gels with stable covalent and non-covalent cross-linking structures based on n-alkyl-imidazolium (n = 2, 8) ionic liquid and MXene are fabricated by a one-step radiation method. The results reveal that the gel containing shorter alkyl (C2-PIL/MXene) is more suitable for flexible materials. Additionally, the C2-PIL/MXene gel exhibits remarkable stretchability (nearly 600%), good conductivity (4.9 mS cm−1), rapidly self-healing ability (within 8 min), excellent adhesion (266.9 kPa), and a fast response time (within 100 ms) due to the stable covalent bonding and abundant hydrogen bonding in the gel network. Notably, the C2-PIL/MXene gel also shows an excellent anti-freezing property (−60 °C), excellent durability (90 days at room temperature), and outstanding antibacterial activity against E. coli (99.82%) and S. aureus (99.98%). In addition, the multi-functional sensor based on the C2-PIL/MXene gel exhibits a real-time and rapid response to detect various human activities, recognize writing strokes, and realize the encrypted transmission of information, thus showing considerable potential in flexible smart wearable devices.