Rheological behavior and birefringence investigations on drag-reducing surfactant solutions of tallow-(tris-hydroxyethyl)-ammonium acetate/sodiumsalicylate mixtures

Rheological and flow birefringent properties of a drag-reducing mixture of tallow-(tris-hydroxiethyl)-ammonium acetate (ETHOQUAD T/13-50) and sodiumsalicylate (NaSal) have been studied as a function of the concentration and of the salt/surfactant molar ratio x. The optimum molar ratio x for drag reduction is around 2.5. It is shown that shear-induced supramicellar structures (SIS) which are believed to be responsible for friction reduction in turbulent pipe flow develop in the presence of NaSal. It was observed that SIS are also formed even if the concentration c exceeds c^*, i.e., the concentration where the volumes of rotation of the individual rodlike micelles start to overlap. The validity of the stress optical law is discussed. A switch from a reptation-controlled stress relaxation to a kinetically controlled mechanism takes place at x 2.5 for this system.