A non-viscoelastic drag reducing cationic surfactant system

Abstract The drag reducing cationic surfactant system, Arquad S-50 (5 mM)/sodium salicylate (12.5 mM), was found to have unusual rheological properties. The system is highly drag reducing and birefringent. Cryo-TEM shows a network of thread-like micelles. However, the system shows no first normal stress difference, no recoil and no stress overshoot with shear start-up, and thus does not appear to be viscoelastic, contradicting the general belief that there is a correlation between viscoelastic properties and drag reduction. On the other hand, the system has high extensional viscosity, with high extensional viscosity-to-shear viscosity ratios. These results indicate surfactant solutions which do not appear to be viscoelastic can be drag reducing, and that extensional viscosity appears to be the key property controlling drag reducing ability.