The potential range switches between anion and cation-driven actuation: comparative study of three actuating polypyrrole materials in organic media

Abstract

Three different polypyrrole (PPy) material films: polypyrrole-polyanions (PPy-PA) generated by simultaneous electropolymerization, polypyrrole-dodecylbenzenesulfonate (PPy/DBS) and Polypyrrole-bis(trifluoromethylsulfonyl)imide (PPy/TFSI), were electrogenerated and then characterized as linear actuators (strain evolution) in propylene carbonate solutions by cyclic voltammetry and square potential waves. Four different potential ranges (1, 0.65V to -0.25V; 2, 0.65V to -0.6V, 3, 1.0V to -0.45V and 4, 1.0V to -0.8V) were studied. Oxidation and reduction charges were in balance whatever the material or the applied potential range. The PPy-PA actuator gives a mainly anion-driven linear actuation in the potential range 1 shifting to cation-driven actuation in the potential range 2, having mixed ion actuation in the potential ranges 3-4. This fast experimental shift of the actuation mechanism open a new way for both, applications and chemical kinetic study of those biomimetic reactions. The PPy/DBS actuator gives a mainly anion-driven actuation and some minor mixed-ion actuation, while PPy/TFSI showed consistent anion-driven in the four studied potential ranges. The evolution of the strain/specific charge ratio (actuator efficiency) can allow, in absence of parallel irreversible reactions, a quantitative description of the mixed actuation here and of the different Faradaic actuators in the future. The three studied materials give Faradaic actuators (charge/strain linear dependency) and closed loops strain/charge responses (without creeping) allowing a good actuation control and low degradation. Further material characterization such as scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), energy dispersive X-ray spectroscopy (EDX), electronic conductivity or ionic diffusion coefficient determinations are conducted.