Smart strain sensing organic–inorganic hybrid hydrogels with nano barium ferrite as the cross-linker

Abstract

Regarding artificial intelligence and wearable soft electronics, increasing attention has been dedicated to hydrogel strain sensors. However, traditional hydrogels are insulating and fragile. To obtain a continuous and repeatable electrical signal output upon external stress or strain in a hydrogel, the combination of good mechanical property, good elasticity and high electrical conductivity is demanded. In order to apply hydrogel in the strain sensing field, in this work, a smart, flexible organic–inorganic polyanion polyacrylic acid (PAA) hybrid hydrogel is designed with nano barium ferrite (BaFe₁₂O₁₉) as a cross-linker without the addition of any chemically covalent or ionic cross-linkers, exhibiting a high ionic conductivity of 1.22 × 10⁻² S cm⁻¹. Due to high porosity as confirmed by scanning electron microscope (SEM), the BaFe₁₂O₁₉/PAA hybrid hydrogel demonstrates 100% recoverability and stable piezoresistive sensing performance with negligible hysteresis loops under cyclic compression loading tests compared with the N,N′-methylene bisacrylamide chemically cross-linked PAA hydrogel. This demonstrates that the BaFe₁₂O₁₉/PAA hydrogel is not only favorable to be used as a candidate for strain sensors in soft electronics but also facilitates the evolution of a new generation of flexible, wearable, and human-friendly intelligent devices.