(396c) Effect of Counter-Ion Concentration on the Rheology of Shear-Thickening Surfactant Solutions

Vasudevan, M., Washington University in St. Louis
Khomami, B., Washington University in St. Louis
Shen, A., University of Washington
Sureshkumar, R., Syracuse University

It is well known that certain wormlike surfactant solutions (e.g. CTAB, CTAT) can undergo a phase transition from a solution phase to a gel-like phase upon increasing the shear rate above a critical value [Wunderlich and co-workers (1987), Liu and Pine (1996), Hartmann and Cressely (1997,1998,2000), and Bandyopadhyay and Sood (2001)]. The apparent viscosity of the solution increases (i.e. the solution shear-thickens) as a result of such phase transitions. The critical shear rate and the extent of viscosity enhancement in such systems are very sensitive to salt concentration. In this study, the effect of salt (NaSal) concentration on surfactant (CTAB) solution rheology has been investigated in the shear thickening regime. Experimental data have been analyzed to obtain power-law relationships for the critical shear rate and apparent relaxation time of the shear-thickened solution as a function of salt concentration Cs. Secondly, a procedure has been developed to collapse viscosity vs. shear rate data at various values of Cs into a single master curve. Effect of Cs on the elastic properties of the shear-thickened solutions is discussed for different surfactant concentrations. Comparisons of experimental data for the time constants of the system with those predicted by linear stability analysis of "gel-fluid" models [Shankar and Kumar (2004), Kumaran and Muralikrishnan (2000), and Eggert and Kumar (2004)] are also provided.


1. Wunderlich I., Hoffmann H., Rehage H., Flow birefringence and rheological measurements on shear induced micellar structures, Rheo. Acta., 26: 532-542 (1987)

2. Liu C., Pine D.J., Shear Induced Gelation and Fracture in Micellar Solutions., PRL 77, 10, 2121-2124 (1996)

3. Hartmann V., Cressely R., Influence of sodium salicylate on the rheological behaviour of an aqueous CTAB solution, Coll. Surf. A: Physicochemical and Engineering Aspects 121 151-162(1997) , Hartmann V., Cressely R., Occurance of shear thickening in aqueous micellar solutions of CTAB with some added organic counterions, Coll. Polym. Sci. 276 169-175 (1998), and Cappelaere E., Cressely R., Influence of NaClO3 on the rheological behavior of a micellar solution of CPCl, Rheo. Acta 39: 346-353 (2000)

4. Bandyopadhyay R., Sood A., Chaotic dynamics in shear-thickening surfactant solutions, Europhys.Lett.,56 (3), 447-453 (2001)

5. Shankar, V. and S. Kumar Instability of Viscoelastic Plane Couette Flow past a Deformable Wall, J. Non-Newtonian Fluid Mech. 116, 371-393 (2004)

6. Kumaran, V. and R. Muralikrishnan, Spontaneous Growth of Fluctuations in the Viscous Flow of a Fluid past a Soft Interface, Phys. Rev. Lett., 84, 3310 (2000)

7. Eggert, M.D. and S. Kumar Observations of Instability, Hysteresis, and Oscillation in Low-Reynolds Number Flow past Polymer Gels, J. Colloid Interface Sci. 278, 234 (2004).