Facile fabrication of dual-conductivity, humidity-responsive single-layer membranes: towards advanced applications in sensing, actuation, and energy generation

Abstract

Humidity sensors and actuators have recently gained significant attention, largely owing to their broad applicability in innovative fields. This study presents the fabrication of smart single-layer membranes with mixed conductivity and high responsiveness to humidity. Utilizing a water-based processing method, partially-carboxylated multi-walled carbon nanotubes (CNTs-COOH) were incorporated into flexible cross-linked composite membranes, alongside sodium poly(4-styrene sulfonate-CO-glycidyl methacrylate) (P(SSNa-CO-GMA40)) and polyacrylic acid (PAA). This approach led to membranes with mixed conductivity, where CNTs were employed for electronic conductivity and P(SSNa-CO-GMA40) provided ionic conductivity and humidity responsiveness. The developed membranes were thoroughly studied, in terms of microstructure morphology, physicochemical, mechanical and humidity sensing properties, while an extensive conductivity study was conducted as well. These smart composite membranes with responsive humidity-driven deformation show potential applications such as non-contact switches or soft-robotics materials. Furthermore, membranes with 30 wt% CNTs are considered an effective hygroelectric generator, providing an environmentally friendly and cost-effective new approach for moisture electricity generators (MEGs).