Partition and water/oil adsorption of some surfactants.
Adsorption isotherms have been determined at the water/oil interface for five biphasic systems involving surfactants (non-ionic and ionic) present in both phases at partition equilibrium. The systems studied were polyoxyethylene(23)lauryl ether (Brij35) in water/hexane and four ionic surfactants, hexadecyltrimethylammonium bromide (CTAB), and a series of three tetraalkylammonium dodecylsulfate (TEADS, TPADS, and TBADS) in water/CH 2Cl 2. Interfacial tension measurements performed at the water/air and water/oil interfaces provided all the necessary information for the determination of the adsorption parameters by taking partition into account. These measurements also allowed the comparison of the adsorption properties at both interfaces which showed an increase of the adsorption equilibrium constant and a decrease of the maximum surface concentration at the water/oil interface compared to water/air. The values of the critical aggregation concentration showed, in all cases, that only the surfactant dissolved in the aqueous phase contribute to the decrease of the water/oil interfacial tension. In the case of the four ionic surfactants, the critical aggregation concentration obtained in biphasic conditions were lowered because of the formation of mixed surfactant-CH 2Cl 2 aggregates.
Tadmouri
Rawad
R
Laboratoire des IMRCP, UMR au CNRS No. 5623, Service Commun d'HPLC, FR 2599, and Service Commun de Spectroscopie IR et Raman, FR 2599, Universite Paul Sabatier, 118 route de Narbonne, Toulouse Cedex, France.
Zedde
Chantal
C
Routaboul
Corinne
C
Micheau
Jean-Claude
JC
Pimienta
Véronique
V