Effect of Metal Ions and Compounds on the Rheological Properties of a Drag-Reducing Cationic Surfactant Solution...

The effect of various metal ions and compounds on the viscoelasticity of a 12.5/5 mM sodium salicylate (NaSal)/tris(2-hydroxyethyl) tallowalkyl ammonium acetate (TTAA) surfactant solution has been studied phenomenologically. This solution normally exhibits shear-induced structure formation and strong drag reduction properties. The viscosity and N1 buildup times under a constant shear rate increase monotonically with the concentration of added Zn(OH)2, Cu(OH)2, or Fe(OH)3. The magnitude of N1 and the viscosity do not change significantly with the addition of Zn(OH)2, but decrease dramatically with increasing Cu(OH)2, Cu2(OH)2CO3, and Fe(OH)3 concentrations. The effect is believed to be due to adsorption on insoluble particulates and to reaction between copper compounds and NaSal. Mg2+ and Cu2+ do not change the steady-state viscosity and N1, whereas Na+, Zn2+, and Ca2+ decrease these quantities significantly at low shear rates. The loss of viscoelasticity in the NaSal/TTAA solution due to Cu(OH)2 and Cu2(OH)2CO3 can be recovered, however, by adding the chelating agent ethylenediaminetetraacetate to the contaminated solution. The rheological results are consistent with drag reduction experiments. The results show that chemical contamination may be an important issue for drag-reducing cationic surfactant additives used in industrial applications where such contaminants are present.