Imidazolium-based poly(ionic liquid)/poly(vinyl alcohol) multifunctional supramolecular gels with self-healing, shape memory, and strain sensing

The functional ionic liquid gels have attracted increasing attention in the fields of smart sensors, flexible wearable devices, and artificial sensors, but it is challenging to develop multifunctional gels to meet the complex applications requirement. The aim of this work was to develop the multifunctional poly(ionic liquid) gels (PILGs) with conductivity, self-healing, high stretchability, redox-driven shape memory, and strain sensing. Considering the designable structure and conductivity of the poly(ionic liquid) (PILs), we proposed one hypothesis. Is it possible to synthesize the PILs and to fabricate the multifunctional PILGs through supramolecular self-assemble strategy? Herein, imidazolium-based PILs was synthesized, and poly(vinyl alcohol) (PVA) was chosen to composite with PIL for fabricating the gels. Apart from the hydrophilic and nontoxic property of PVA, another important reason of choosing it is that the hydroxyl groups in PVA could form hydrogen bonds with the strongly electronegative atoms (N, F, and O) in PIL.

As expected, the PILs/PVA mixed solution was converted to gels in acidic condition at room temperature, and the gelation mechanism was studied. The reversible non-covalent bonds endowed the gels with satisfied self-healing, strains sensing, and stable mechanical properties. The addition of PILs facilitated the gelation and improved the self-healing and strength. The healed PILGs sensors could monitor the human joint movement, facial expression, and speech recognition etc. The one-step solution gel transition strategy will provide a universal approach for preparing multifunctional gels, which have great potential in strain sensors, soft electronic materials, and portable testing equipment etc.