Adsorption of surfactants and the structure of the electrical double layer at the mercury/water interface

✍ Scribed by I.R. Miller

• Publisher: Elsevier Science
• Year: 1964
• Tongue: English
• Weight: 969 KB
• Volume: 9
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(64)85027-1

✦ Synopsis

Differential capacitance of the electrical double layer of the mercury surface in contact with salt solutions containing different surfactants at various concentrations was measured. The potential of the desorption maximum (dl?/dE)B,fl.,t. cone. = maximum, which is always nearer to the electrocapillary maximum than the capacitance peak potential, was determined for each surfactant concentration.

It was found that the desorption maximum potential (&es) is a linear function of the logarithm of the surfactant concentration.

Assuming a Langmuir-type adsorption isotherm or its Frumkin modification, a correlation between the dependence of the desorption potential on concentration and of the variation of the standard free energy with potential is derived.

The electrical part of the free energy is a function of the surface charge densities and of the local dielectric constants in the surface domain occupied by water and surfactant molecules. From the variation of &ee with surfactant concentration, the local dielectric constant in the Helmholz plane of the double layer was estimated to be between 8.3 and 6.9. The non-electrical part of the standard free energy increases with length of the paraffinic chain at a rate of 1.5 kT per CH,.

an der Oberflache. Aus der Anderung von Ed,,. mit der Konzentration wurde die lokale Dielektrizitatskonstante in der Hehnholtz-Ebene der Doppelschicht zu 6,9 bis 8,3 abgescbatzt. Der nicht-elektrische Teil der freien Enthalpie nimmt mit der Lange der paraffiischen Kette urn 1,5 kT pro CH, zu.