| Issue |
J. Chim. Phys.
Volume 88, 1991
|
|
|---|---|---|
| Page(s) | 515 - 536 | |
| DOI | https://doi.org/10.1051/jcp/1991880515 | |
| Published online | 29 May 2017 | |
Description quantitative de l'agrégation micellaire dans les systèmes mixtes anionique-cationique
Laboratoire de Physicochimie des Systèmes Polyphasés, URA 330, Université de Montpellier II, Sciences et Techniques du Languedoc, place Eugène Bataillon, 34095 Montpellier Cedex 05, France.
L’agrégation en solution du système mixte dodécylsulfate de sodium - bromure de dodécyltriméthylammonium (SDS/DTAB) a été étudiée quantitativement par diffusion quasiélastique de la lumière et autodiffusion par traceur radioactif.
La concentration en SDS libre, l’évolution de la taille et de la forme des agrégats mixtes, la liaison des contre-ions sodium aux agrégats mixtes ont été étudiées.
Le système SDS/DTAB présente une augmentation de la taille des agrégats et une diminution de la liaison des ions sodium lorsque DTAB est ajouté au SDS alors que les agrégats restent de petite taille lorsque SDS est ajouté à DTAB.
Abstract
Tracer self diffusion and Quasielastic Light Scattering measurements were performed in order to obtain a quantitative description of the aggregation in the mixed system sodium n-dodecyl sulfate - dodecyl- trimethylammonium bromide.Tracer self diffusion and Quasielastic Light Scattering measurements were performed in order to obtain a quantitative description of the aggregation in the mixed system sodium n-dodecyl sulfate - dodecyl- trimethylammonium bromide.
The structural change of mixed micelle size has been studied. The SDS/DTAB system shows a large size increase when DTAB is added to SDS. The mixed aggregates stay constant and globular as SDS is added to DTAB. Using a two sites model we deduced the concentrations of free and micellar SDS ions and sodium counterions. In the SDS rich domain the concentration of free SDS monomers is smaller than the critical micellar concentration of the pure anionic surfactant and it decreases with the molar fraction of DTAB.
The degree of sodium binding depends on the addition of DTAB, it decreases abruptly at a molar fraction of DTAB corresponding to the change in the mixed micelle size. At the limit of solubility when the precipitation is occuring there is no binding of sodium ions.
In the DTAB rich domain the excluded volume of mixed micelles for the sodium ions are twice the calculated one.
The observed break in the surface tension curves is related to the precipitate formation.
© Elsevier, Paris, 1991