CHARACTERIZATION OF MICELLAR STRUCTURE DYNAMICS FOR A DRAG-REDUCING SURFACTANT SOLUTION UNDER SHEAR - NORMAL STRESS STUDIES AND FLOW GEOMETRY-EFFECTS

Some surfactant solutions have been observed to exhibit a strong drag reduction behavior in turbulent flow. This effect is generally believe d to result from the formation of large cylindrical micelles or micell ar structures. To characterize and understand better these fluids, we have studied the transient theological properties of an efficient drag -reducing aqueous solution: tris (2-hydroxyethyl) tallowalkyl ammonium acetate (TTAA) with added sodium salicylate (NaSal) as counterion. Fo r a 5/5 mM equimolar TTAA/NaSal solution, there is no measurable first normal stress difference (N-1) immediately after the inception of she ar, but N, begins to increase after a well-defined induction time - pr esumably as shear-induced structures (SIS) are formed - and it finally reaches a fluctuating plateau region where its average value is two o rders of magnitude larger than that of the shear stress. The SIS build up times obtained by first normal stress measurements were approximate ly inversely proportional to the shear rate, which is consistent with a kinetic process during which individual micelles are incorporated th rough shear into large micellar structures. The SIS buildup after a st rong preshear and the relaxation processes after flow cessation were a lso studied and quantified with first normal stress difference measure ments. The SIS buildup times and final state were also found to be hig hly dependent on flow geometry. With an increase in gap between parall el plates, for example, the SIS buildup times decreased, whereas the p lateau viscosity increased.