Adsorption de l'adenosine a l'electrode de mercure—I. Etude cinetique du processus de condensation observe aux faibles densites de charge
✍ Scribed by G. Quarin
- Publisher
- Elsevier Science
- Year
- 1984
- Tongue
- English
- Weight
- 731 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
R&urn&
-A l'&ctrode de mercure et aux faibles densitds de charge, l'adsorption des mol6cules d'adbnosine se manifeste par l'apparition d'un puits capacitif r&&ant de la formation d'une phase conden&. La largeur du puits capacitif croIt avec la concentration en surfactant. La brusque transition de phase entre les deux structures superficielles qui se diff&encient par I'arrangement spatial et la mobilit des mol6cules adsorties est Btudi& en technique de saut potentiostatique. Les processus cin&iques caractCristiques de La formation de la phase condensde sont contr6lGs par des ph&nom&nes de nuclCation et croissance bidimensionnelles. Lesvitesses derelaxation mesur&s en fonction du potentiel final pr&entent un maximum dont I'amplitude depend de la concentration en surfactant. En admettant que la force motrice qui contr6le le processus de nucleation est la diK&ence de tension interfaciale SAy entre l'ttat final et l'ttat mttastable qui prd&de la relaxation, on etablit qu'il existe effectivement pour chaque potcntiel un parall&sme Ctroit entre la diff&ence de tension interfaciale et la vitesse de relaxation. Abstract-At the mercury electrode and for low charge densities, the capacity curves show a pit which results from the formation of a condensed film of adsorbed adenosine molecules. The width of the capacity pit increases with the concentration of the surfactant. The sudden phase transition between the two superficial structures differing by the spatial arrangement and the mobility of the adsorbed molecules is studied by the potential-step method. The kinetics of condensed phase formation are controlled by a two-dimensional nucleation and growth process.
The rate of relaxation measured in function of the final potential presents a maximum whose amplitude increases with organic molecules concentration.
In agreement with the fact that the driving force which controls the nucleation process is the dilference SAy of superficial tension between the final state and the metastable state preceding the relaxation, a meaningful relation between the interfacial tension and the rate of relaxation has been observed at every potential.