Search

In the theoretical model it is assumed that a graphite disk electrode is covered by a thin film of the solution of decamethylferrocene and some supporting electrolyte in nitrobenzene and immersed in an aqueous solution of the same electrolyte. Oxidation of decamethylferrocene is accompanied by the transfer of anions of the electrolyte from water into nitrobenzene. The flux of decamethylferrocenium cations at the electrode surface and the flux of anions at the liquid/liquid interface are separated by the thickness of the film, but the electroneutrality is ensured by the migration of ionic species through the film. Theoretical concentration profiles of ionic species in the film are reported for cyclic voltammetry. Keywords: Liquid/liquid interface, Ionic transfer, Migration, Diffusion, Cyclic voltammetry, Decamethylferrocene

The aim of the present work is to trace adhesion response of single particles without influence of electron redox-exchange at the electrode. We have studied amperometric response of single cell adhesion in real time, from the initial attachment to a finite state of spread cell at the growing mercury drop electrode. The technique is based on measurement of double-layer charge displacement. The only hypothesis used in interpreting the signals is the validity of the electrical double-layer model. The flow of compensating current reflects the dynamics of adhesive contact formation and subsequent spreading of a cell. The rate of adhesion and spreading of cells is enhanced by the hydrodynamic regime of electrode’s growing fluid interface. The spike-shaped signals have the peak current in ľA range, duration of 5-10 ms and displaced charge in nC range. The electrochemical technique thus allows a precise measurement of the contact area between the cell and the electrode. The distance of the closest approach of an adhered cell can be estimated with certainty as equal or smaller than the outer Helmholtz plane i.e. 0.3-0.5 nm. There is clear evidence of cell rupture in the potential range of maximum attractive interaction, which is around the potential of zero charge. A surprising similarity to adhesion signals of droplets of liquid hydrocarbons (C12 – C18) suggest that collective properties of cell exterior govern the dynamics of adhesion and rate of spreading, with fluidity playing a major role. Our results demonstrate a general significance of adhesion phenomena in single particle - electrode interaction. When electroactive molecules reside in an organized microenvironment, such as colloidal particles, microdroplets or vesicles, their redox reaction at the electrode is preceded by adhesion step that is likely to become rate-determining.

Dissolved organic molecules and nano-particles in aquatic environments are traced through their collective adsorption response. We will show that individual micro-particles can be studied through current spikes caused by adhesion at a localized fraction of the mercury electrode/aqueous electrolyte interface. Adhesion and spreading of a micro-particle at DME causes double-layer charge displacement and a dramatic decrease of interfacial tension at the contact interface, followed by a transient local increase in the interfacial turbulence which results in a current transient at millisecond time-scale. The amplitude of the spike-shaped signal (adhesion signal) reflects the particle size and magnitude of adhesion forces. Particle abundance in the medium can be determined from the signal frequency expressed as the average number of signals per drop-life. The electrochemical technique is based on chronoamperometry of oxygen reduction at the potentials of streaming maximum at DME. This is a modification of a widely used polarographic technique for measurements of dissolved surfactants founded by Gosmann and Heyrovsky in 1931 as the Adsorption Analysis.