Rheo-PIV of shear-thickening wormlike micelles

Benjamin M. Marin-Santibanez^1,2, Jose Perez-Gonzalez^1*, Lourdes de Vargas¹,

FranciscoRodriguez-Gonzalez^1,2, Guadalupe Huelsz³

¹Laboratorio de Reologia, Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, Apdo. Postal 118-209, C. P. 07051,

Mexico D. F. MEXICO. ²Posgrado en Ciencia e Ingenieria de Materiales, UNAM, Mexico D. F., MEXICO.

³Centro de Investigacion en Energia, UNAM, Temixco, Morelos, MEXICO.

The shear thickening behavior of an equimolar semidilute aqueous solution of 40 mMol/l cetylpyridinium chloride and sodium salicylate was studied in this work by using a combined method of rheometry and particle image velocimetry (PIV). Experiments were conducted at 27.5 C with Couette, vane-bob, and capillary rheometers in order to explore a wide shear stress range, as well as the effect of boundary conditions and time of flow on the creation and destruction of shear induced structures (SIS). The use of the combined method of capillary rheometry with PIV allowed the detection of fast spatial and temporal variations in the flow kinematics, which are related to the shear thickening behavior and the dynamics of the SIS, but are not distinguished by pure rheometry. A rich in details flow curve was found for this solution, which includes five different regimes. Namely, at very low shear rates a Newtonian behavior was found, followed by a shear thinning one in the second regime. In the third, shear banding was observed, which served as a precursor of the SIS and shear thickening. The fourth and fifth regimes in the flow curve were separated by a spurt-like behavior, and they clearly evidenced the existence of shear thickening accompanied by stick-slip oscillations at the wall of the rheometer, which subsequently produced variations in the shear rate under shear stress controlled flow. Such a stick-slip phenomenon prevailed up to the highest shear stresses used in this work, and was reflected in asymmetric velocity profiles with spatial and temporal variations linked to the dynamics of creation and breakage of the SIS. Increasing the residence time of the fluid in the flow system enhanced the shear thickening behavior.