Influence of sodium salicylate on the rheological behaviour of an aqueous CTAB solution

We have experimentally studied the rheological behaviour of an aqueous cetyltrimethylammonium bromide (CTAB) solution with sodium salicylate (NaSal) as added salt. The CTAB concentration C-D was fixed at 0.1 M, and in this work we observe the evolution of the linear and non-linear rheological behaviour of the solution when the salt concentration C-s is below or equal to C-D, varying between 0.015 and 0.1 M. We observe two very different kinds of behaviours. For the low C-s concentration, we can obtain a shear-thickening effect. The critical shear rate at which this occurs is a function of the temperature T, and C-s. We give here the evolution of this critical parameter. When C-s increases and reaches a limit value, this behaviour disappears and we obtain a shear-thinning effect with a shear stress plateau for a certain range of shear rate. In the plateau domain an induced shear-banding structure must exist: bands of high and low shear rate co-exist under flow. (C) 1997 Elsevier Science B.V.