Giant Iontronic Flexoelectricity in Soft Hydrogels Induced by Tunable Biomimetic Ion Polarization

Abstract

Flexoelectricity features the strain gradient‐induced mechanoelectric conversion using materials not limited by their crystalline symmetry, but state‐of‐the‐art flexoelectric materials exhibit very small flexoelectric coefficients and are too brittle to withstand large deformations. Here, inspired by the ion polarization in living organisms, we report the giant iontronic flexoelectricity of soft hydrogels where the ion polarization is attributed to the different transfer rates of cations and anions under bending deformations. The flexoelectricity is found to be easily regulated by the types of anion‐cation pairs and polymer networks in the hydrogel. A polyacrylamide (PAM) hydrogel with 1 M NaCl achieves a record‐high flexoelectric coefficient of ∼1160 μC/m, which can even be improved to ∼2340 μC/m by synergizing with the effects of ion pairs and extra polycation chains. Furthermore, the hydrogel as flexoelectric materials can withstand larger bending deformations to obtain higher polarization charges owing to its intrinsic low modulus and high elasticity. A soft flexoelectric sensor is then demonstrated for object recognition by robotic hands. Our findings greatly broaden the flexoelectricity to soft, biomimetic and biocompatible materials and applications.This article is protected by copyright. All rights reserved