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

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.