J. Phys. II France
Volume 7, Numéro 2, February 1997
Page(s) 257 - 270
DOI: 10.1051/jp2:1997123
J. Phys. II France 7 (1997) 257-270

Optical and Rheological Properties of a Semi-Diluted Equimolar Solution of Cetyltrimethylammonium Bromide and Potassium Bromide

J.P. Decruppe, E. Cappelaere and R. Cressely

Institut de Physique-Électronique et Chimie, Laboratoire de Physique des Liquides et des Interfaces, 1 boulevard D.F. Arago, 57070 Metz, France

(Received 26 July 1996, received in final form 15 October 1996, accepted 7 November 1996)

We report in this paper the results of rheological and optical experiments performed on a semi-diluted viscoelastic solution of cetyltrimethylammonium bromide (CTAB) in water with sodium bromide at a concentration of 0.3 M l -1 in surfactant and salt. This concentration in surfactant is much smaller than the concentration which gives a nematic phase at rest. The solution behaves like a Maxwell fluid with a single relaxation time. When submitted to a shear flow, this solution shows a behaviour typical of a system undergoing a phase transition. When observed between crossed polarizer and analyzer, the gap of the Couette cell appears divided in two bands the optical properties of which are different; in rheology, the curves $\sigma(\dot{\gamma})$ are also characteristic of these systems where the shear stress presents a plateau extending between two critical values, $\dot{\gamma}_{1{\rm c}}$, and $\dot{\gamma}_{2{\rm c}}$ of the shear rate. We finally compare the results with previous experiments performed on a concentrated solution of CTAB containing no salt.

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