Catalogo Articoli (Spogli Riviste)

OPAC HELP

Titolo:
The equilibrium penetration of monolayers. Is equilibrium really established?
Autore:
Barnes, GT;
Indirizzi:
Univ Queensland, Dept Chem, Brisbane, Qld 4072, Australia Univ QueenslandBrisbane Qld Australia 4072 Brisbane, Qld 4072, Australia
Titolo Testata:
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
fascicolo: 1-2, volume: 190, anno: 2001,
pagine: 145 - 151
SICI:
0927-7757(20010930)190:1-2<145:TEPOMI>2.0.ZU;2-9
Fonte:
ISI
Lingua:
ENG
Soggetto:
AIR-WATER-INTERFACE; INSOLUBLE MONOLAYERS; THERMODYNAMICS; SURFACTANT; SYSTEM;
Keywords:
monolayers; penetration by surfactants; penetration of monolayers; equilibrium in monolayer penetration; penetration equilibrium;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
14
Recensione:
Indirizzi per estratti:
Indirizzo: Barnes, GT Univ Queensland, Dept Chem, Brisbane, Qld 4072, Australia Univ Queensland Brisbane Qld Australia 4072 ld 4072, Australia
Citazione:
G.T. Barnes, "The equilibrium penetration of monolayers. Is equilibrium really established?", COLL SURF A, 190(1-2), 2001, pp. 145-151

Abstract

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 appliedto 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 ofthese 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 eachstep 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 themonolayer 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 equilibriumdata. (C) 2001 Elsevier Science B.V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 04/07/20 alle ore 21:11:31