3D Printing of Thermo‐Mechano‐Responsive Photoluminescent Noncovalent Cross‐Linked Ionogels with High‐Stretchability and Ultralow‐Hysteresis for Wearable Ionotronics and Anti‐Counterfeiting

Abstract

Ionogel has recently emerged as a promising ionotronic material due to its good ionic conductivity and flexibility. However, low stretchability and significant hysteresis under long‐term loading limit their mechanical stability and repeatability. Developing ultralow hysteresis ionogels with high stretchability is of great significance. Here, a simple and effective strategy is developed to fabricate highly stretchable and ultralow‐hysteresis noncovalent cross‐linked ionogels based on phase separation by 3D printing of 2‐hydroxypropyl acrylate (HPA) in 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4). Ingeniously, the sea‐island structure of the physically cross‐linked network constructed by the smaller nanodomains and larger nanodomain clusters significantly minimizes the energy dissipation, endowing these ionogels with remarkable stretchability (>1000%), ultra‐low hysteresis (as low as 0.2%), excellent temperature tolerance (−33–317 °C), extraordinary ionic conductivity (up to 1.7 mS cm−1), and outstanding durability (5000 cycles). Moreover, due to the formation of nanophase separation and cross‐linking structure, the as‐prepared ionogels exhibit unique thermochromic and multiple photoluminescent properties, which can synergistically be applied for anti‐counterfeiting and encrypting. Importantly, flexible thermo‐mechano‐multimodal visual ionotronic sensors for strain and temperature sensing with highly stable and reproducible electrical response over 20 000 cycles are fabricated, showing synergistically optical and electrical output performances.