Rapid self-healing and superior toughness in ionically crosslinked polymer ionogels and strain sensing applications

Self-healing polymeric ionogel/hydrogel materials are mostly viscoelastic and lack high mechanical toughness; however, simultaneous rapid self-healing and robust mechanical properties are essential for various applications. Herein, an ionically crosslinked polymer ionogel comprising poly(vinylimidazol) [PVIM] and polyphosphoric acid [PPA] having a dual interpenetrating network of ionic and hydrogen bonding interactions is reported. The designed ionogel PVIM-PPA shows rapid and repeatable self-healing within a few seconds without any external stimulus, realizes exceptional mechanical properties such as high tensile strength (30 +/- 1 MPa), superior toughness (43.3 +/- 0.5 MJ m-3), and fracture energy (4100 J m-2) with similar to 90% of healing efficiency and possesses intrinsic flexibility, transparency, and fire-resistant properties. In addition, the mechanical and self-healing properties of the polymer were also investigated by incorporating Ca-ions into the PVIM-PPA ionogels. The PVIM-PPA-Ca ionogel shows an enhancement of the tensile strength to 39 +/- 1 MPa and fracture energy of 4700 J m-2 with >= 87% self-healing efficiency. The ionic conductivity of the PVIM-PPA-Ca polymer membrane increases almost five times (5.93 x 10-5 S cm-1) w.r.t PVIM-PPA (1.25 x 10-5 S cm-1) and it can retain similar to 90% of the conductivity after self-healing. The recovery efficiency remains almost constant from the second cycle up to the sixth subsequent failure-recovery cycle for these ionogels. Furthermore, a wearable strain sensor was designed using the designed ionogels to detect various human motions accurately and reliably. The designed ionogel comprising poly(vinyl imidazole) and polyphosphoric acid exhibits rapid self-healing with robust mechanical properties that could further be enhanced by incorporation of Ca-ions into the matrix.