Ionic solvent shell drives electroactuation in organic mixed ionic-electronic conductors

Abstract

Abstract The conversion of electrochemical processes into mechanical deformation in organic mixed ionic-electronic conductors (OMIECs) enables artificial muscle-like actuators but is also critical for degradation processes affecting OMIEC based devices. To provide a microscopic understanding of electroactuation, we introduce here the modulated electrochemical atomic force microscopy (mEC-AFM) as a novel characterization method for electroactive materials. The technique enables multidimensional spectroscopic investigations of local electroactuation and charge uptake giving access to the electroactuation transfer function. For poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based microelectrodes we combine the spectroscopic measurements with multichannel mEC-AFM imaging, providing maps of local electroactuation amplitude and phase as well as surface morphology. Our results demonstrate that the amplitude and timescales of electroactuation are governed by the drift motion of hydrated ions. Accordingly, slower water diffusion processes are not limiting, and the results illustrate how OMIEC microactuators can operate at sub-millisecond timescales.