Hana Jänchenová

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.

Electrochemically controlled formation of a silicate membrane at a liquid|liquid interface

Abstract A new method is described for the preparation of a silicate membrane. Its principal idea lies in the separation of the template and precursor ions participating in sol–gel processes, by the interface between two immiscible electrolyte solutions (ITIES). The sol–gel process is initiated by potential-controlled adsorption of the template ions at the interface and their transfer from the organic to the aqueous phase. Association of the positive template ions with the silicate ions at the aqueous side of the interface produces neutral species which condense and form a compact layer at the interface. The thickness of the layer can be controlled by the magnitude of the electrical charge passed.

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.