PEDOT/Polypyrrole Core–Sheath Fibers for Use as Conducting Polymer Artificial Muscles

Electropolymerized polypyrrole (PPy) is considered as one of the promising polymers for use in ionic-electroactive or conducting polymer (CP) actuators. Its electromechanical properties surpass those of other prominent CPs such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) or polyaniline. However, freestanding and linear contracting actuator fibers made solely of electropolymerized PPy are not available yet. This work therefore targets the development of all-CP-based actuator fibers: electromechanically active PPy is electropolymerized on the surface of wet-spun, also electromechanically active PEDOT/PSS fibers. The thickness of the PPy fiber sheath is varied by using different electropolymerization durations. Mechanical and actuation properties of the different PEDOT/PPy core-sheath actuator fibers are investigated via tensile tests and isotonic actuation strain and isometric actuation force measurements, respectively. The fiber actuators show high tensile stability in both dry and aqueous conditions, rendering them highly suitable for actuation in aqueous electrolyte media. Regarding linear, untwisted, and uncoiled CP fiber actuators, the presented actuation measurements demonstrate to the best of our knowledge the highest reported linear contractile actuation strains of up to 2.2% in electrolytes and remarkable tensile actuation stresses of 1.64 MPa, as well as a high long-term cyclic actuation stability using varying actuation durations. This renders the fibers as a highly promising material, particularly with regard to their further structural textile processing for use in actuating wearables or soft robots.