Tough and conductive double-network hydrogel based on PVA/poly(ionic liquids) strengthened by metal ion complexation for flexible sensors

Abstract

Hydrogels have attracted extensive attention for their promising applications as flexible sensors. Developing conductive hydrogels with excellent mechanical properties still remains a significant challenge. Herein, double-network (DN) hydrogels composed of poly(vinyl alcohol) (PVA) and poly(ionic liquids) (PILs) are prepared through repetitive freezing/thawing process. The hydrogels are further treated with Fe³⁺ ions to enhance the mechanical properties due to the complexation between carboxyl groups and Fe³⁺ ions. The influence of the amount of PILs and concentration of Fe³⁺ on mechanical properties and conductivity is investigated. The optimal DN hydrogel P(VMCA-AA)₁/PVA-Fe³⁺₄ shows excellent mechanical properties, whose tensile strength, elongation at break, and toughness are 2.2 MPa, 350%, and 3.5 MJ m⁻³, respectively. P(VMCA-AA)₁/PVA-Fe³⁺₄ also displays a good conductivity of 1.04 S m⁻¹. Moreover, the hydrogel demonstrates a high sensing sensitivity with a gauge factor (GF) of 3.36, indicating its application potential as a flexible sensor.