Rheometric investigation on the temporal shear thickening of dilute micellar solutions of C14‐, C16‐, and C18TAB∕NaSal

Abstract

The rheological behavior and especially the rheopexy phenomena of dilute self-assembled solutions in the presence of a counterion are examined in stationary and transient shear flows. In the first part, a continuous and gradually increasing strain is applied on the same sample. We study the effect of the initial shear rate, the temporal variation of the viscosity, and the hysterisis between charge and discharge curves. The results show that the properties of shear thickening are independent of the initial shear rate. In the second part, fresh samples are successively subjected to increasing shear strains; this method allows us to follow the evolution of the rheological characteristics during long measuring durations and gives us a distinct picture of the behavior per shear rate. In both cases, we confirm that the chain length has a strong influence on the emergence and amplitude of the shear thickening. It was also found by studying the start-up flow behavior that the structure at equilibrium is composed of bigger structures for longer chain lengths. The maximum of the viscosity in the shear thickening transition occurs in a range of lower shear rates when enough time is given to the system to undertake the formation of the shear induced structure. Considering this result, we introduce the concept of "temporal shear thickening transition." © 2008 The Society of Rheology.