Alexandr Lhotský

Ac impedance analysis of tetraethylammonium ion transfer at liquid/liquid microinterfaces

The kinetics of ion transfer reactions at the microhole-supported water/nitrobenzene interface have been studied by an ac impedance technique. A thin layer approximation of diffusional impedance has been derived for the geometry of the hole. In contrast to the large-area interface, the charge transfer resistance at the liquid microinterface is comparable in magnitude with the electrolyte resistance, which makes its determination more reliable. The apparent rate constant of tetraethylammonium ion transfer, kapp= 0.22 cm s–1, as determined at the liquid microinterface with an area ranging from 100 to 1000 µm2, has been found to be about twice as high as that previously reported.

Surface complex formation at the water/1,2-dichloroethane interface

Abstract Surface tension measurement at an aqueous drop/1,2-dichloroethane interface was used to study adsorption and surface reactions of calix[4]arene ligands. The found difference in surface tension in acidic and alkaline medium was ascribed to a difference in charge of the adsorbed ligand. Formation of a surface complex with Ba 2+ and Ca 2+ cations reduces the change in surface tension as compared to an adsorbed dissociated ligand with higher charge. A mechanism of the surface reaction is proposed.

Interfacial tension and impedance measurements of interfaces between two immiscible electrolyte solutions

Abstract Interfacial tension and impedance measurements were used to study the electrochemical properties of the interface between 0.1 M LiCl in water and 0.05 M tetrabutylammonium tetraphenylborate in nitrobenzene in the absence and the presence of various tetraalkylammonium ions. While the presence of these ions has no effect on the interfacial tension, the interfacial capacity can be considerably enhanced. This enhancement appears to be an artefact arising from the inadequate representation of the interface or the electrochemical cell by the Randles equivalent circuit employed for impedance data analysis. Modifications to this equivalent circuit are discussed.

Formation of a polymer layer from monomers adsorbed at a liquid|liquid interface

Polymerization of adsorbed monomers at the water 1,2-dichloroethane interface was studied with a series of surface active derivatives of pyrrole. Polymerization was induced by an electron transfer reaction between a monomer dissolved in the organic phase and Ce(SO)4 dissolved in the aqueous phase. The formation of a polymer layer at the interface was monitored by surface tension measurement and by cyclic voltammetry in the presence of transferable ions. It was found that in contrast to a simple adsorbed layer, an interfacial tension in the presence of a polymer layer becomes independent of the applied potential and that a polymer layer strongly inhibits ion transfer reactions.

Specific ion adsorption at liquid | liquid interfaces : effect of the ionic charge

The effect of the charge of adsorbed ions on their surface concentration was examined for a series of negatively charged ions at the water 1,2-dichloroethane (DCE) interface. Langmuir and Frumkin isotherms and Coulomb law were used to fit the experimental data. The limiting surface concentration Γ s , as determined from the surface tension measurements, was found to be related to the charge number z of the adsorbed ions, in agreement with the derived formula Γ s = 1.42 × 10 -6 /z 4/3 mol m -2 . Application of this formula to the determination of the dissociation and equilibrium constants of surface reactions is demonstrated for slightly soluble calix[4]arene ligands.

Langmuir-Blodgett monolayers at an aqueous pendant drop

The aqueous pendant drop has been used to determine surface area per molecule of insoluble surface active substances. A slow and continuous decrease of surface area has been achieved by the drop evaporation. The surface area per molecule of myristic acid inferred from a compression diagram (surface tension versus time dependence) has been in close agreement with that obtained by the Langmuir-Blodgett (LB) technique. The surface tension versus surface concentration isotherms (γ-c) and the area per molecule of two calix[4]arene ligands with a different number of carboxylic groups in the hydrophilic part have been determined. It has been found that compressibility of a surface film is proportional to the number of carboxylic groups interacting with water. The surface tension decreases hy 7 mN m -1 per one carboxylic group in a molecule. The evaporation rate has been but slightly influenced by the surface films under study.

Peculiar correlation between the interfacial capacity and faradaic admittance of the ion transfer across an interface between two immiscible electrolyte solutions

Surface tension and impedance measurements were used to study the electrochemical properties of the interface between 0.01 M LiCI in water and 0.01 M tetrabutylammonium tetraphenylborate in 1,2-dichloroethane in the absence and the presence of the Cs + or tetraethylammonium ion. While the presence of these ions has no effect on the surface tension, the interfacial capacity is considerably enhanced and exhibits a peculiar correlation with the faradaic admittance of the Cs + or tetraethylammonium ion transfer reaction. Changes in the capacity appear to be artefacts arising from the inadequate description of the electrical behaviour of the interface in terms of the Randles-type equivalent circuit employed in the analysis of experimental impedance data. A more convenient description is provided by our model, which links the measured impedance to the mechano-electric oscillations in the interfacial region during the a.c. impedance measurements.