The first electrochemical series in a deep eutectic solvent (DES) is described. Speciation resulting from the unusual chemistry of the choline chloride based DES is used to explain both similarities and differences from aqueous media. We give examples of how these differences can be exploited in technologically important systems.

We derive a lurnped-elemen~equivalent-circuit model for the thickness shear mode (TSM) resonator with a viscoelastic film. This modified ButterWorth-Van Dyke model includes in the motional branch a series LCR resonator, representing the quartz resonance, and a parallel LCR resonator, representing the film resonance. This model is valid in the vicinity of film resonance, which occurs when the acoustic phase shift across the film is an odd multiple of 7d2radians. This model predicts accurately the frequency changes and darnping that arise at resonance and is a reasonable approximation away fi-om resonance. The elements of the model are explicitly related to film properties and can be interpreted in terms of elastic energy storage and viscous power dissipation.The model leads to a simple graphical interpretation of the coupling between the quartz and film resonances and facilitates understanding of the resulting responses. These responses are compared with predictions fi-omthe transmission-line and the Sauerbrey models. KEYWORDSThickness-shear mode resonatoq quartz crystal microbakmce; viscoelasticity; film resonance; equivalent circuit; lumped-element model; transmission-line model.

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We report the results of X-ray absorption spectroscopy studies on electrochemically deposited iridium oxide films. The emphasis of the study is the correlation of X-ray derived structural data with electrochemically controlled charge state. Data were acquired for films subject to redox cycling in neutral and alkaline aqueous media. In both cases, cyclic voltammetric responses show two redox couples, coulometrically of roughly equal magnitude. Assays of the iridium population (based on the iridium L(3) absorption edge amplitude) and the charge injected (based on integration of the voltammetric response) show that overall an average of ca. one electron per iridium atom is transferred. The absorption edge shifts indicate that the formal charge on the iridium changes, on average, from ca. 3.5+ to ca. 4.5+ across the entire process. EXAFS-derived changes in mean Ir-O distance and their mean square variation have been interpreted in terms of a two-site model, in which the two types of site have distinct redox potentials. Variations of local structure and disorder with potential are discussed and a generic model for structural disorder (parameterized via Debye-Waller factor) with diagnostic capability is developed.

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We describe a new strategy for interpreting frequency responses of thickness shear mode resonators loaded with spatially uniform viscoelastic films. This procedure leads to unambiguous extraction of the four parameters that characterize such a film: its thickness, density and shear modulus components (storage and loss moduli). The interpretational difficulty is that the experimental frequency response (impedance spectrum) can only provide two parameters; thus, the problem is underdetermined. Previous interpretations employed various approximations and assumptions for two (or more) film parameters to effectively reduce the problem to a two-parameter fit. Such approaches are clearly imperfect. Our new strategy splits the problem into two separate two-parameter sub-problems, each of which is solved by the measurement of two different experimental responses. The result is a unique fit to the data without the need to make approximations or assumptions for film parameters. First, in the acoustically thin regime, measured frequency shift and film charge are combined to provide a unique solution for film thickness and density; shear moduli components do not affect the response in this regime. Second, film density is carried forward directly, and the film thickness-charge relationship is extrapolated into the acoustically thick regime. Third, with film density and thickness held fixed, crystal impedance data in the acoustically thick regime provide unambiguous shear modulus components. The method is generalized to any other (nonelectrochemical) probe that provides film thickness data and validated using crystal impedance data for poly(3-methylthiophene) films exposed to propylene carbonate.

The visualization of latent fingerprints on a metallic (stainless steel) surface is described by means of spatially selective deposition of an electrochromic polymer (polyaniline). Inhibition of electrochemical processes on areas of the surface masked by the fingerprint results in polymer deposition generating a negative image of the fingermark. By variation of the applied potential, the polymer optical characteristics can be continuously and reversibly adjusted to optimize visual contrast of the fingerprint.