Polyvinyl alcohol/sodium alginate hydrogels with tunable mechanical and conductive properties for flexible sensing applications

Abstract

Despite the significant advantages of conductive hydrogels in flexible sensing, their further development is often hindered by limitations in strength and conductivity. In this work, the ionic conductive hydrogels with tunable mechanical and conductive properties were designed by utilizing sodium alginate (SA) to reinforce the polyvinyl alcohol (PVA) networks, followed by the respective introduction of Li₂SO₄, ZnSO₄, and Fe₂(SO₄)₃, leveraging the Hofmeister effect and metal coordination. Consequently, the mechanical properties (σ = 0.40-2.70 MPa) and conductivity (IC = 0.18-1.02 S/m) can be extensively tuned by adjusting the metal salts with varying oxidation states. Notably, Fe³⁺ ions can significantly enhance the mechanical properties, while Li⁺ ions more effectively improve conductivity. Interestingly, the PVA/SA/Zn²⁺ hydrogel achieves a balance between mechanical properties (σ = 1.86 MPa, ε = 1110 %) and conductivity (0.92 S/m), ascribing it to the multiple interactions including densification of polymer networks, formation of nanocrystalline domains, and ionic coordination effects. Furthermore, the conductive hydrogel also exhibits low strain detection limit (2.0 %), and demonstrated enormous potential in personal health monitoring and information transmission applications. This work presents a highly efficient and eco-friendly strategy for constructing hydrogels with tunable properties, while elucidating the mechanisms behind the enhanced mechanical and conductive performance.

Keywords: Flexible sensing; Hydrogels; Mechanical properties; Sodium alginate; Tunable.