The rheological properties of wormlike micellar solutions formed by the pseudo-ternary system sodium dodecyl sulfate (SDS)-Al(NO3)(3)-H2O have been studied at a fixed molar ratio Al(NO3)(3):SDS = 5.92:1 as a function of surfactant concentration. The linear data show that solutions behave as a Maxwell fluid and there are two well-defined domains characterized by scaling laws for surfactant concentration, with a maximum in the viscosity-surfactant concentration curve. Prior to the maximum, the system consists of linear micelles, and eta(0) (zero-shear rate viscosity) and tau(R) (relaxation time) are found to scale with surfactant concentration with exponents higher than those predicted by the theory of Cates. The results in the second domain are not reflected by the dynamic behavior of entangled wormlike micelles, and they are interpreted in terms of formation of connected micelles. The nonlinear rheology is governed by the shear banding effect occurring for viscous entangled wormlike micellar solutions and branched micelles, and the properties identified by reduced stress sigma(p)/G(0) and the Weissenberg number, y(c)tauR, are compared to the values predicted on the basis of the theoretical model.
Subject classification (UKÄ)
- Physical Chemistry