Adsorption at liquid interfaces

The generalized Frumkin isotherm and interfacial structure

M. I. Volkova-Gugeshashvili, A. G. Volkov, V. S. Markin

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The thermodynamics of adsorption of amphiphilic surface-active compounds at the interface between two immiscible liquids is considered. At the interface, these molecules are supposed to replace a few of the adsorbed molecules of both solvents. Classical isotherms of adsorption (Frumkin, Frumkin-Damaskin, Langmuir, Henry) were based on the model of non-penetrable interface, where an adsorbate can substitute only molecules of one solvent. At the interface between two immiscible electrolytes, nonpolar oil/water interfaces, and liquid membranes amphiphilic molecules can substitute molecules of both solvent and classic isotherms cannot be used. The generalization of Frumkin isotherm for permeable and non-permeable interfaces, known as the Markin-Volkov isotherm, gives the possibility to analyze adsorption in a general case. The adsorption isotherms of pentafluorobenzoic acid at the octane/water interface at different pHs were measured by the drop-weight method. The thermodynamic parameters of pentafluorobenzoic acid (PFBA) adsorption at octane/water interface were determined. From the measurements of PFBA adsorption, the structure of the octane/water interface was determined. Substitution of one adsorbed octane molecule requires approximately three adsorbed PFBA molecules. This result shows that the orientation of solvent molecules at the interface is different from the bulk. Adsorbed octane molecules have a lateral orientation with respect to the interface. Gibbs free energy of adsorption equilibrium and thermodynamic parameters of PFBA adsorption show that the adsorption of PFBA at the octane/water interface is accompanied by a reduction in the attraction between adsorbed PFBA molecules as the pH decreases to the acidic region.

Original languageEnglish (US)
Pages (from-to)1073-1078
Number of pages6
JournalRussian Journal of Electrochemistry
Volume42
Issue number10
DOIs
StatePublished - Oct 2006

Fingerprint

Isotherms
Adsorption
Molecules
Liquids
Acids
Water
Thermodynamics
Liquid membranes
Gibbs free energy
Adsorbates
pentafluorobenzoic acid
Adsorption isotherms
Electrolytes
octane
Oils
Substitution reactions

Keywords

  • Adsorption
  • Frumkin isotherm
  • Liquid/liquid interface
  • Markin-Volkov isotherm

ASJC Scopus subject areas

  • Electrochemistry

Cite this

Adsorption at liquid interfaces : The generalized Frumkin isotherm and interfacial structure. / Volkova-Gugeshashvili, M. I.; Volkov, A. G.; Markin, V. S.

In: Russian Journal of Electrochemistry, Vol. 42, No. 10, 10.2006, p. 1073-1078.

Research output: Contribution to journalArticle

Volkova-Gugeshashvili, M. I. ; Volkov, A. G. ; Markin, V. S. / Adsorption at liquid interfaces : The generalized Frumkin isotherm and interfacial structure. In: Russian Journal of Electrochemistry. 2006 ; Vol. 42, No. 10. pp. 1073-1078.
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