Stretchable and conductive polyacrylamide/sodium alginate dual-network hydrogels mediated by HNO3 for flexible capacitors and wearable sensors

Abstract

In recent years, hydrogels have been employed to fabricate flexible capacitors (FCs) and wearable sensors. However, achieving a balance between the electrochemical and mechanical properties of hydrogels remains a challenge. Herein, polyacrylamide/sodium alginate (PAM/SA) dual-network hydrogels with good mechanical properties and high electrochemical properties were obtained by nitric acid (HNO₃) mediation. The –COO– groups on the SA network inside the hydrogel are partially acidified to –COOH under the action of HNO₃, which increases the hydrogen bond density of the hydrogel. The PAM/SA hydrogel exhibited a maximum mechanical strength of 83.4 KPa and a maximum elongation at break of 471.3%. Furthermore, the conductivity (σ) of PAM/SA dual-network hydrogels increased from 36.48 mS cm⁻¹ to 96.4 mS cm⁻¹, and the specific capacitance of the flexible capacitor (FC) composed of the hydrogels increased by about 142.1%. Finally, the hydrogel was prepared as a wearable motion sensor, which is capable of accurately detecting the different motion states of a person. Consequently, the hydrogel has a multitude of applications in the field of FCs and wearable sensors.