Janus-type ionic conductive gels with single-sided adhesiveness prepared by a “one-step” method for strain/pressure sensors

Abstract

Flexible sensors have been widely studied for their huge potential applications in health monitoring, soft robots and electronic skin. However, the simple and rapid preparation of Janus-type flexible adhesive sensors with adhesive properties on one side and no adhesive properties on the other side is still a great challenge. In this work, we first used the different solubilities of silk fibroins in water and the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] ([EMIM][Tf₂N]) to prepare Janus-type ionic conductive gels by a “one-step” method of UV irradiation. In this system, the noncovalent bond interaction between poly(N,N-dimethylacrylamide) (PDMA) and [EMIM][Tf₂N] and the substrate endows the gel with strong adhesion, and the ionic liquid [EMIM][Tf₂N] endows the gel with conductivity and bactericidal properties. However, silk fibroins in ionic gels have a ladder distribution due to different solubilities and are concentrated on the other side of the gel so that the side of the gel does not have adhesion. Additionally, the β-sheet structure of silk fibroins gives the ionic gel greater toughness. Janus-type ionic conductive gels prepared by this method have super tensile properties (2671%), excellent bactericidal properties (99.99%) and strong adhesion to a variety of substrates (such as glass, rubber, metal, and plastic) and skin. Moreover, the Janus-type ionic conductive gel has excellent electromechanical properties, such as good sensitivity, low hysteresis and good repeatability, when used as a sensor and can realize multifunctional detection of the human body's various strain movements and pressure changes. Based on the simple and easy-to-operate preparation method and the endowed excellent electromechanical characteristics of the Janus-type ion-conductive gel, it has broad application prospects in the fields of multifunctional wearable sensors.