A nanofibrous hydrogel templated electrochemical actuator: From single mat to a rolled-up structure

A flexible conducting polymer actuator was fabricated using an electrospun poly(vinyl alcohol) (PVA) nanofibrous mat followed by in situ chemical polymerization with aniline. The PVA/polyaniline (PVA/PANi) hybrid mat consisted of nanostructured PANi grown on the surface of individual PVA nanofibers. The resulting structure with large surface area and porosity enabled the easy diffusion of ions to cause efficient electrochemical reaction. The PVA/PANi hybrid mat showed an electrical conductivity of 2.35 S/cm and a single strip produced a maximum linear actuation strain of 1.8% while cycling the potential between specified ranges in 1 M methane sulfonic acid solution. The hybrid mat could be stably actuated during extended electrochemical cycling up to 250 cycles. Actuation performance of the hybrid fibrous mat (for a single strip) was explained from the viewpoint of mechanical properties, and it was demonstrated that the flexible structure can generate higher strain than the brittle structure such as a carbon nanotube/conducting polymer composite actuator. Based on the flexible nature and the mechanical stability provided by highly entangled hydrogel nanofibers, the PVA/PANi hybrid mat was conveniently rolled-up into multilayered assembly of cylindrical structures. The interlayer spacing of the rolled-up structure and the huge surface area per unit volume accessible to electrolytes contributed to high current and enabled enhanced actuation performance and fast response.