The equilibrium penetration of monolayers. Is equilibrium really established?

Barnes, G. T. (2001). The equilibrium penetration of monolayers. Is equilibrium really established?. In: Colloids And Surfaces A-physicochemical And Engineering Aspects. 10th International Conference o Colloid and Interface Science, Bristol, United Kingdom, (145-151). 23-28 July 2000. doi:10.1016/S0927-7757(01)00674-4


Author Barnes, G. T.
Title of paper The equilibrium penetration of monolayers. Is equilibrium really established?
Conference name 10th International Conference o Colloid and Interface Science
Conference location Bristol, United Kingdom
Conference dates 23-28 July 2000
Proceedings title Colloids And Surfaces A-physicochemical And Engineering Aspects
Place of Publication Amsterdam
Publisher Elsevier
Publication Year 2001
Sub-type Fully published paper
DOI 10.1016/S0927-7757(01)00674-4
ISBN 0927-7757/01
Volume 190
Issue 1-2
Start page 145
End page 151
Total pages 7
Language eng
Abstract/Summary In studying the penetration of water-soluble surfactants into water-insoluble monolayers the main theoretical problem is to find a relationship that would enable the amount of surfactant that has entered the monolayer to be calculated from a set of equilibrium surface pressure-area isotherms. Despite many attempts, no current theory gives satisfactory results when applied to experimental data (Langmuir 14 (1998) 2148). One possible reason is that equilibrium had not been established when the surface pressure-area curves were measured. The three experiments reported here suggest that equilibrium is extremely difficult to establish in such systems when the area is low or the surface pressure is high. The essence of these experiments is to try to reach the same final condition by two different routes. In the first route, the one nearly always used in equilibrium penetration measurements, the surfactant is injected under the expanded monolayer, which is then slowly compressed in steps, with time allowed at each step for a steady surface pressure to be attained. In the second procedure, the monolayer is first compressed to a high surface pressure and the surfactant then injected. A stepped expansion isotherm may then be observed. Surface pressure-area per monolayer molecule isotherms, reflection spectra, and slow neutron reflectivity data all show the same pattern: if the surfactant was allowed to penetrate while the monolayer was in an expanded state, it was not completely removed when the monolayer was compressed; but if the monolayer was in a highly compressed state when exposed to the surfactant little penetration took place until the film was expanded. There thus appear to be very large energy barriers to the ejection of surfactant from a compressed monolayer and to the penetration of surfactant into a compressed monolayer. Although these experiments have some limitations, it now seems likely that at least some of the penetration data used in evaluating the various thermodynamic treatments of equilibrium penetration were not equilibrium data. (C) 2001 Elsevier Science B.V. All rights reserved.
Subjects C1
250103 Colloid and Surface Chemistry
780103 Chemical sciences
0306 Physical Chemistry (incl. Structural)
Keyword Chemistry, Physical
Monolayers
Penetration By Surfactants
Penetration Of Monolayers
Equilibrium In Monolayer Penetration
Penetration Equilibrium
Air-water-interface
Insoluble Monolayers
Thermodynamics
Surfactant
System
Q-Index Code C1

Document type: Conference Paper
Collection: School of Chemistry and Molecular Biosciences
 
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Created: Tue, 14 Aug 2007, 15:24:31 EST