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

Abstract

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 ∼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 × 10⁻⁵ S cm⁻¹) w.r.t PVIM–PPA (1.25 × 10⁻⁵ S cm⁻¹) and it can retain ∼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.