Unusual effects of counterion to surfactant concentration ratio on viscoelasticity of a cationic surfactant drag reducer

One-to-one molar ratio sodium salicylate (5 mM)/Arquad S-50 (5 mM) solution was investigated in comparison to the sodium salicylate (12.5 mM)/Arquad S -50 (5 mM) or 2.5:1 solution, which was previously reported to be drag redu cing yet non-viscoelastic [9]. Results showed a dramatic influence of the c ounterion to surfactant concentration ratio on the viscoelasticity of the s urfactant drag reducing systems. The 1:1 solution has normal surfactant dra g reducer characteristics such as viscoelastic properties and thread-like m icellar networks and branches. This is the first cationic surfactant/counte rion drag reducing system found, for which excess counterion makes the solu tion non-viscoelastic, while the microstructure of thread-like micellar net works is apparently unchanged. (C) 2000 Elsevier Science B.V. All rights re served.