Vincent J. Cunnane

Electron and ion transfer potentials of ferrocene and derivatives at a liquid-liquid interface

The electrochemistry of ferrocene, dimethyl ferrocene and decamethyl ferrocene at the interface of immiscible electrolytes has been investigated. The aqueous redox electrolyte was the hexacyanoferrate couple. It has been found that the study of the electron transfer reaction can be complicated by both the transfer of the ferricenium ion formed in the organic phase (1,2-dichloroethane) during oxidation, and by oxidation of the organic base electrolyte anion. However, by using a high concentration of aqueous electrolyte, the difference between ionic and electronic transfer potentials can be increased sufficiently to observe these two processes separately. Ionic transfer potentials of the ferricenium ion have been measured by preparing the corresponding FeCl−4 salts. For decamethyl ferrocene, no electron transfer reaction could be observed at the liquid/liquid interface and it is proposed that this is due to distance effects, which become more marked for this more hydrophobic ferrocene derivative.

Interfacial capacitance and ionic association at electrified liquid/liquid interfaces

The capacitance of the interface of immiscible electrolytes has been measured for the Li+, Na+, K+, Rb+ and Cs+ chlorides in 1,2-dichloroethane and nitrobenzene. Evidence for ionic specific adsorption at the interface is presented. The nature of the specifically adsorbed charge is discussed in terms of the formation of interfacial ion pairs between the aqueous and the organic ions. The contribution of specific ionic adsorption to the interfacial capacitance is calculated on the basis of an ionic associated model using the Bjerrum theory of ion-pair formation. A mixed solvent region with varying penetration of the ion pairs into it, dependent on their ionic radii, best represents the structure of these interfaces.

Electrosynthesis of polyphenylpyrrole coated silver particles at a liquid-liquid interface

This communication reports the production of polyphenylpyrrole coated silver nanoparticles at the liquid/liquid interface by an EC-type mechanism. In the electrochemical step of the reaction N-phenylpyrrole facilitates the transfer of the silver ion from an aqueous to an organic phase. This step is followed by a slow homogeneous electron transfer reaction from the N-phenylpyrrole to the silver ion followed by polymerization and metal cluster growth.

The kinetics of ionic transfer across adsorbed phospholipid layers

Abstract The inhibition to ion transfer by a monolayer of phospholipid at an immiscible electrolyte interface has been studied using the tetraethylammonium ion as a probe. The decrease of the rate constant for ion transfer has been analysed considering the work of pore formation and the calculated pore size is in agreement with the known dimensions of the probe ion. The proposed model has been used to study the kinetics of assisted transfer of K + with valinomycin as the ionophore.

Microstructural development and surface characterization of electrodeposited nickel/yttria composite coatings

The addition of yttria particles to a Watts nickel plating bath is shown to significantly change the surface morphology and preferred crystallographic orientation of the composite coatings deposited on Inconel 625 substrates. The typical morphology for nickel deposits from an additive-free Watts bath is pyramidal, however the addition of yttria particles in concentrations >2 g dm -3 changes this morphology to hemispherical. The preferred growth direction was also influenced by yttria with a change from a to a preferred growth direction occurring when the particle loading exceeded 2 g dm -3 . The results here show that both the nucleation and growth process of the nickel matrix was greatly influenced by the yttria additions. When yttria was absent from the electroplating bath the growth took place preferentially on (200) orientated planes. However, yttria acts to inhibit growth on grains of this orientation, leading to a requirement for additional nucleation, which takes place preferentially on (111) planes. This constant inhibition of growth and renucleation causes the changes to a hemispherical morphology observed.

Study of ion transfer across phospholipid monolayers adsorbed at micropipette ITIES

Abstract The transfer of tetraethylammonium cations across phospholilpid monolayers deposited at a micropipette ITIES (interface between two immiscible electrolyte solutions) was studied using short potential step techniques. The observed current transients consisted of a capacitive and a faradaic current component, which were separated using a non-linear fit to a model function. Fits were very good. From the capacitive component, the surface coverage of lipids was calculated by applying a simple model for the monolayer configuration. It appeared that the coverage varied between 80 and 99%. The rate of ion transfer was increased slightly after the lipid addition, but no significant variations between different lipids were found. The transfer mechanism is discussed briefly.

Influence of the presence of a gel in the water phase on the electrochemical transfer of ionic forms of β-blockers across a large water∣1,2-dichloroethane interface

The transfer of ionic species of three beta-blockers (propranolol, sotalol and timolol) has been studied by cyclic voltammetry at a macroscopic water 1,2-dichloroethane (1,2-DCE) interface. The aqueous solution has been gellified in order to study the effect of the gel on the transport properties of the drugs. The gelling agent also stabilizes the interface overcoming mechanical instability. The standard potential and standard Gibbs energy of transfer across the interface, the partition coefficient and the diffusion coefficient of each drug were determined in the presence of a gelled interface. The diffusion coefficients were shifted relative to those obtained at normal water 1,2-DCE interfaces (free of gel).

Electrochemical and morphological study of the effect of polymerization conditions on poly(tetrathiophene) with emphasis on carbon fiber microelectrodes: A cyclic voltammetry and atomic force microscopy study

Electropolymerization of tetrathiophene was carried out in various solvents on carbon fiber microelectrodes and platinum electrodes. Acetonitrile, dichloroethane and propylene carbonate were investigated as solvent systems for film formation, and solvent effect as well as the effect of other experimental conditions (scan rate, supporting electrolyte) on the electropolymerization has been discussed on the basis of the electropolymerization mechanism. Surface morphology was investigated by atomic force microscopy (AFM). Carbon fiber electrodes were found to be an effective microelectrode system for the electropolymerization of tetrathiophene, which was compared with polyterthiophene growth on carbon fibers.

Micro-cavity electrode : a new type of liquid-liquid microelectrode

Abstract A simple method for fabrication of microcavity electrodes is described, which provides an effective and inexpensive tool for exploring many aspects of the polarised liquid interface.

Electrochemical characterization of Si in tetra-methyl ammonium hydroxide (TMAH) and TMAH:Triton-X-100 solutions under white light effects

An experimental study of the electrochemical characteristics of the silicon/tetra-methyl ammonium hydroxide (TMAH) junction under dark and white light conditions are investigated for both n- and p-type Si. The presence of Triton-X-100 (TX100) in the TMAH solution under white light conditions is also studied. Cyclic voltammetry (CV) and ex situ atomic force microscopy (AFM) are employed to study the white light effects on the etching characteristics of silicon in TMAH and TMAH:TX100. It was found that the passivation peak potential shifted significantly for both n- and p-type Si under white light conditions. The positions of the flatband potential for n- and p-type Si were predicted by CV under illumination. Finally, etch rate studies and preliminary surface roughness measurements were performed on p(100) Si in TMAH under both dark and white light conditions. These latter studies concluded that a reduction in the vertical surface roughness occurred in the presence of white light.