Dynamic mechanoelectrochemistry of polypyrrole membranes via shear-force tracking
Mechanoelectrochemistry is the study of elastic and plastic deformation of materials during reversible reduction and oxidation processes. In this article, we introduce shear-force tracking as a method to dynamically measure mechanical (strain), chemical (ion transport), and electrical (applied redox potentials) responses of the conducting polymer polypyrrole (PPy) during redox reactions. This tracking technique uses a control algorithm to maintain a set distance between a ultramicroelectrode (UME) tip and a surface via shear-force regulation. Due to the sensitivity of shear-force signals in the near field of substrate surfaces, a significantly improved signal to noise ratio (20 : 1) is possible and allows for nanoscale measurement of redox events. Chemomechanical coupling (the ratio of ion transport to resultant extensional actuation) is calculated for PPy-based membranes of various thicknesses based on a mechanistic interpretation of charge storage in redox active conducting polymers. The measured dynamic response demonstrates that chemomechanical coupling is not a constant, as assumed in literature, but is dependent on the polymers state of charge and the direction (ingress/egress) of ion transport.