RHEOLOGICAL BEHAVIOR AND BIREFRINGENCE INVESTIGATIONS ON DRAG-REDUCING SURFACTANT SOLUTIONS OF TALLOW-(TRIS-HYDROXYETHYL)-AMMONIUM ACETATE SODIUM-SALICYLATE MIXTURES

Rheological and flow birefringent properties of a drag-reducing mixtur e of tallow-(tris-hydroxiethyl)-ammonium acetate (ETHOQUAD T/13-50) an d sodiumsalicylate (NaSal) have been studied as a function of the conc entration 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-induc ed supermicellar 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 concen tration c exceeds c, i.e., the concentration where the volumes of rot ation of the individual rodlike micelles start to overlap. The validit y of the stress optical law is discussed. A switch from a reptation-co ntrolled stress relaxation to a kinetically controlled mechanism takes place at x almost-equal-to 2.5 for this system.