https://doi.org/10.1007/s100510050578
Flow birefringence and stress optical law of viscoelastic solutions of cationic surfactants and sodium salicylate
Laboratoire de Physique des Liquides et Interfaces, Groupe rhéophysique des
Colloïdes, Université de Metz 1,
boulevard D.F. Arago, 57078 Metz, France
Corresponding author: a decruppe@lpli.sciences.univ-metz.fr
Received:
18
February
1998
Revised:
23
June
1998
Accepted:
22
July
1998
Published online: 15 December 1998
The optical and rheological properties of different viscoelastic solutions of
surfactant are studied in order to gather experimental data used to
calculate the value of the stress optical coefficient C. Three surfactants
of the same family (CTAB) have been chosen; they differ by the length of
the hydrocarbon chain; it concerns the
dodecyltrimethylammonium bromide (C15H34BrN or DoTAB),
the myristyl trimethyl ammonium bromide (C17H38BrN or MyTAB),
and the hexadecyltrimethylammonium bromide (C19H42BrN or CTAB).
Different parameters like the temperature of the solution and the salinity
of the solvent have been made to vary.
Flow birefringence experiments and rheological
measurements are performed on these solutions in order to study the
dependence of the extinction angle χ, of the birefringence intensity
and of the shear stress 
with the shear rate
. These data are used to check the stress optical law which
turns out to be valid in a wide range of shear rates. The stress optical
coefficient C is then computed: it is found to vary with the salinity of the
solvent and the temperature of the solution for a given surfactant.
Then, for all solutions of this work the variations of C are related
to the variations of the polarizability anisotropy and the persistence length.
PACS: 78.20.Fm – Birefringence / 82.70.D – Colloids / 83.85.Cg – Rheological measurements
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1998
