Highly conductive Faradaic artificial muscle based on nanostructured polypyrrole-bis(trifluoromethylsulfonyl)imide synthesized onto electrospun polyurethane nanofibers

Abstract

Conductive polymer-based artificial muscles have attracted enormous interest in various fields due to their unique properties such as electroactivity and biocompatibility. In this study, a bending artificial muscle was fabricated by chemical synthesis of polypyrrole (PPy) onto nanofibrous polyurethane (PU) structures using bis(trifluoromethylsulfonyl)imide (TFSI) anions as dopant. First, PU nanofibers were prepared by electrospinning and then coated with a layer of polypyrrole via in-situ polymerization to produce core-shell nanofibers of PU/PPy-TFSI. The actuation performance of the PU/PPy-TFSI nanofibers in 1M LiClO4 aqueous solution was analyzed based on their cyclic voltammetric, coulo-voltammetric, dynamo-voltammetric, coulo-dynamic and chronopotentiometric responses. FESEM images showed that the surface of all PU nanofibers has been coated with a uniform layer of PPy in the form of semi-spherical nanostructures. Doping using TFSI anions resulted in an excellent electrical conductivity in nanofibers (314.55 S/cm). The examination of electrochemomechanical properties showed that for the produced electroactive nanofibers, reversible oxidation and reduction processes occur under the potential cycle between -0.8 V and 0.5 V. It was demonstrated that during the oxidation and reduction reactions, the dominant volume variation mechanism can be best explained based on the exchange of perchlorate anions, which yields a reversible angular displacement of 160°. However, a weak mechanism involving the absorption of small lithium cations was also observed at low cathodic potentials. The results demonstrated that the produced nanofibrous artificial muscle could be considered as a Faradaic motor, as its bending angle and velocity are completely controlled by the consumed charge and the applied current, respectively.