Multifunctional triple-network ionic hydrogel sensors engineered by Al/Zn bimetallic salt solution: From cellulose...

Ionic conductive hydrogels show promise for flexible sensors in wearables and e-skins, but balancing mechanical strength with high conductivity remains challenging. Herein, a triple-network ionic conductive hydrogel based on poly(acrylic acid) (PAA) was developed, synergistically reinforced by dissolved cellulose (dCel) and aramid nanofibers (ANF), with Al/Zn bimetallic ions serving as the conductive medium. Intriguingly, dCel was in-situ generated using the concentrated Al³⁺/Zn²⁺ bimetallic salt solutions as the cellulose solvent, following the complete dissolution of the pulp fibers driven by the intensive ionic hydration of Al³⁺/Zn²⁺ ions. Subsequently, aramid nanofibers (ANF) were uniformly dispersed in the dCel/AlCl₃-ZnCl₂ solution, while acrylic acid (AA) rapidly polymerized at room temperature to form the triple-network hydrogel (PAA/dCel/ANF/AlCl₃-ZnCl₂) in a single-step process. The high-concentration Al³⁺ and Zn²⁺ bimetallic salt solution, through its intensive ionic hydration, not only facilitated the uniform dispersion of dCel and ANF with PAA, but also functioned as the ionic conductor for the hydrogel, thereby endowing it with multifunctionality. The resultant hydrogel exhibited integrated properties of high toughness, excellent conductivity, freeze resistance, moisture retention, and antibacterial functionality. It demonstrated an excellent compressive strength of 431.80 kPa and an ionic conductivity of 13.74 S/m. Based on these advantages, the multifunctional hydrogel is employed in flexible sensors to achieve multi-mode sensing functions, including strain, compression, and temperature sensing. This work introduces a simple and efficient method to obtain a multifunctional ionic conductive hydrogel that meets the requirements of flexible sensing devices.