Rheological behaviour and shear thickening exhibited by aqueous CTAB micellar solutions

In this experimental work we carefully investigate the rheological behaviour and in particular the shear thickening exhibited by aqueous micellar solutions of CTAB with NaSal as added counterion. We are particularly interested in the evolution of the critical shear rate (gamma) over dot(C) (at which shear thickening occurs) versus C(D), the surfactant concentration. We show that (gamma) over dot(C) , at fixed salt concentration C(S), increases with C(D) following a power law evolution with a positive exponent of +5.8. On the other hand we show that if the ratio C(D)/C(S) is fixed (gamma) over dot(C) decreases with C(D) with a negative exponent of -2.0. Nevertheless investigations of the zero shear viscosity eta(0) indicate that in all situations (implying variation of the surfactant concentration C(D), or the salt concentration C(S) or the temperature) (gamma) over dot(C) is a decreasing function of the length of the micelles. All these evolutions are compatible with a gelation mechanism which could possibly be associated with entanglement effects of large interacting flowing structures.