THE EFFECTS OF SALTS ON THE RHEOLOGICAL CHARACTERISTICS OF A DRAG-REDUCING CATIONIC SURFACTANT SOLUTION WITH SHEAR-INDUCED MICELLAR STRUCTURES

The effect of the counterion salt sodium salicylate (NaSal) on the tra nsient rheological properties of a drag-reducing surfactant system tri s (2-hydroxyethyl) tallowalkyl ammonium acetate (TThA) has been studie d with both rheometric and rheo-optical methods. Three types of transi ent. behavior for N-1 and viscosity were identified in 5 mM TTAA solut ions depending on the counterion concentration: induction and growth ( below equimolar concentration); overshoot and growth (above equimolar concentration); and over-shoot then plateau (al high concentrations of MaSal). The transient flow birefringence and orientation angle show t rends similar to chose of the viscosity and N-1. The second type of tr ansient behavior suggests a two-stage alignment and shear thickening p rocess. The SIS buildup lime from the quiescent state, the rebuilding time after a strong preshear, and the relaxation time were also obtain ed from N-1 measurements, and show a maximum around equimolar conditio ns. The initial N-1 and viscosity immediately after the flow startup, on the other hand, show a maximum around a ratio of 2.5 eo 3 NaSal/TTA A. For solutions with a NaSal concentration in the ratio 1.5 to 3, the steady state values of N-1 and viscosity do not show much variation w ith NaSal concentration over the shear rate range covered, however. Th e effect of an addition of sodium chloride (NaCl) to an equimolar NaSa l/TTAA solution on the characteristic times and steady state values wa s also quantified. These rheological results provide us with tools to determine the optimal concentration ratio for practical drag reduction applications.