Self-healing transparent ionogel polymerized by liquid metal for strain sensor

Abstract

Flexible electronic devices, sensing human movement and monitoring physiological signals, might be useful for performing research in the area of intelligent detection. Gallium (Ga), a liquid metal (LM), is often used as a soft conductive material in the form of droplets because of its unique properties. Herein, a liquid metal-induced ionogel is synthesized by polymerizing acrylic acid (AA) with the existence of poly(diallyldimethylammonium chloride) (PDDA) and Ga droplets. In the system, the free radical formed from Ga oxidation process initiates the polymerization of AA. Meanwhile, the Ga3+ produced by Ga oxidation forms a coordination with the –COO− on PAA chains. The coordination crosslinking sites create slip when the gel is exposed to external force, increasing the stretchability (5000 %) of the ionogel. When the Ga droplets are completely oxidized to Ga3+, the gel changes from silvery gray to transparent (80 %). In addition, the ionic liquids and the electrostatic interactions within the network enable the resultant ionogel anti-dehydration (98 %) and self-healing performances in a wide temperature range (-20 ∼ 20 °C). The liquid metal-induced ionogel can be assembled into a flexible sensor with adequate sensitivity, rapid response time (240 ms), and cyclic stability, demonstrating human movement patterns with accuracy to keep track of physiological signs.