Actuation of polypyrrole films in propylene carbonate electrolytes

Abstract

The actuation properties of free standing PPy films polymerised from propylene carbonate (PC) solutions of tetrabutylammonium triflouromethanesulfonate (TBACF3SO3) and tetrabutylammonium hexaflourophosphate (TBAPF6) electrolytes were investigated by means of electrochemomechanical deformation (ECMD) measurements during cyclic voltammetry (CV) and chronoamperometry. The ECMD properties of the films were studied in PC/TBAPF6 and PC/TBACF3SO3 electrolytes to determine the effect of both the preparation and cycling electrolytes. Most systems showed mixed-ion actuation, although PPy/TBACF3SO3 films exhibited greater cathodic actuation. However, the extent of anodic actuation exceeded the cathodic actuation in all cases. When the cycling electrolyte was different from the preparation electrolyte it was found that the size of the anion at preparation had a critical effect: smaller PF6− anions in PPy/TBAPF6 films cannot be easily ion-exchanged for the larger CF3SO3−, which also had a tendency to stay entrapped in the polymer network, resulting in decreased anodic actuation and an increase in cathodic (cation-driven) actuation. On the contrary, significant cathodic movement for PPy/TBACF3SO3 films was suppressed when the cycling electrolyte was changed to PC/TBAPF6. Chronoamperometry was used to examine the kinetics of actuation in the positive potential region and electrochemical potential step experiments to investigate the long-term stability of the studied systems.