Effect of temperature on the viscosity of cationic micellar solutions in the presence of added salts

Abstract

The effect of temperature on the viscosities of cetyltrimethylammonium salts (CTA X, X =Br-, NO3-, Tosylate) in the presence of added salts is presented. It was found that plots of 1n of relative viscosity vs 1/T was linear and the activation free energy (ΔG*) of the viscous flow was obtained from the slopes of such plots. The activation enthalpies (ΔH*) and entropies (ΔS*) for the viscous flow were also calculated and the entropic contribution was found to be negligible. The ΔG* are interpreted in terms of the energy required to create a hole or an activated transition micellar structure capable of being transformed into smaller micelles and finally into spherical micelles. The ΔG* and ΔH* values are highly dependent on the nature of the counterions. The more strongly bound counterions produce the greatest effect on the energy of the rod-to-sphere transition. © 1987 Academic Press, Inc.