The Electrochemical Quartz Crystal Microbalance

Abstract

This chapter reviews the development and use of the electrochemical quartz crystal microbalance (EQCM) as an in situ probe of interfacial processes involving the formation, properties, and redox switching of multilayer films. For films that are sufficiently rigid and/or thin (termed acoustically thin ), the EQCM functions as a quantitative gravimetric probe of surface population changes. This well‐established methodology is now being used to explore both thermodynamic and kinetic aspects of film compositional changes, for example, in response to electrochemical stimuli. Correlation of mobile species (ion and solvent) population changes—within the effectively static film matrix—with electrochemical control and response functions (potential, current, and charge) now provides mechanistic information. Combination with other in situ (e.g. optical or spectroscopic) techniques is a developing area and can facilitate separation of individual ion and solvent transfers. For films that are softer and/or thicker (termed acoustically thick ), the acoustic wave is attenuated during passage across the film, which in turn undergoes acoustic deformation. The EQCM now responds primarily to film viscoelastic properties, that is, film (rather than mobile species) dynamics. This is a developing area, but it is now possible to extract film shear modulus components (storage and loss moduli); these are found to respond significantly to the film redox state (controlled via potential or charge), temperature, timescale (frequency), and environment (both solvent and electrolyte ions). These effects are reviewed with selected examples from a diverse range of materials, encompassing metals, metal oxides, semiconductors, metal coordination complexes, and redox, conducting, and insulating polymers.

Effect of electrochemical control function on the internal structure and composition of electrodeposited polypyrrole films: A neutron reflectometry study

“…Detailed structure and composition depend on deposition conditions, notably electrode material, solvent, pH, temperature and control function [4,20,22]. We note that the EQCM [23,24], yields changes in film mass and thus changes in mobile species populations, but not absolute populations. When the observational timescale is shorter than the equilibration timescale, such that repetitive cycling results in a ratchetting of mobile species populations [25,26], rationalisation of film responses becomes extremely complicated [27,28].…”

Electrochemical techniques for investigating redox active macromolecules

“…In addition to studying the ion movement in dependence of the redox state, viscoelastic properties of polymer films have been investigated with EQCM impedance studies in respect to redox state in various films [58]. For example, EQCM impedance studies of Os(byp) 2 ClPyCH 2 NH 2 -poly(allylamine)hydrogel (Os-PAA) cross-linked with glucose oxidase (GOx) revealed that swelling of the film during Os II oxidation resulted in a mass uptake and a decrease of shear modulus [61].…”

Electrochemical Quartz Crystal Nanobalance

“…The deviation from the linearity regarding the m vs. Q function is related to the appearance of the viscoelastic effect. By the help of impedance measurements the viscoelastic characteristics of the surface film can also be tested [4,5,6,7,10]. In the absence of any deposition the change of the density and viscosity in the double layer or in the diffusion layer may cause 0.1-10 Hz frequency change.…”