Gum arabic-CNT reinforced hydrogels: dual-function materials for strain sensing and energy storage in next-generation supercapacitors

Abstract

Recent advancements in the field of conductive hydrogels have made the hydrogels promising candidates for the development of human motion sensors, as well as for energy storage in soft and flexible electronic devices, owing to their excellent mechanical properties such as flexibility, bioavailability, and biocompatibility. However, limitations such as resilience, resistance to fatigue, toughness, flexibility, and stretchability have hampered their sensing capabilities and long-term operation. To address these limitations, we introduced an ionically and electronically conductive hydrogel composite, which is aimed at enhancing mechanical performance and responsiveness to human motion, ranging from finger bending to epidermal motion sensing. This hydrogel was synthesized by incorporating an unmodified electroactive material, carbon nanotubes (CNTs), stabilized by the biopolymer gum arabic (GA) within the hydrophobically associated hydrogels of lauryl methacrylate (LM) and polyacrylamide (p(Am)). The dispersion of both LM and CNTs was facilitated by the anionic surfactant sodium dodecyl sulfate (SDS). The introduction of CNTs and varying the concentration of GA highly enhanced the mechanical property of the synthesized hydrogel, which in turn brilliantly improved its stretchability up to 1380%, with an antifatigue character and a toughness of 661.5 kJ m⁻³. The high tensile strain sensitivity of the hydrogel material, with a gauge factor (GF) of 9.45 at 1000% strain, demonstrated its remarkable sensitivity. The composite hydrogels exhibited impressive sensing capabilities, including differentiation in language, response to high and low pitches and stresses, drawing various shapes, writing different words, and detection of various human actions. The critical strain study of the present materials underscored their excellent rheological properties. The hydrogels with CNT addition and higher concentrations of GA demonstrated specific capacitance (Cs) values of 171.25 F g⁻¹ from CV at 20 mV s⁻¹, 113.7 F g⁻¹ from GCD at a current density of 0.3 A g⁻¹, and a resistance of 7.656 Ω measured via EIS at a frequency of 5 mV. These electrochemical properties highlight the potential use of hydrogels for energy storage in soft wearable electronic devices.