A NON-VISCOELASTIC DRAG-REDUCING CATIONIC SURFACTANT SYSTEM

The drag reducing cationic surfactant system, Arquad S-50 (5 mM)/sodiu m salicylate (12.5 mM), was found to have unusual rheological properti es. The system is highly drag reducing and birefringent. Cryo-TEM show s a network of thread-like micelles. However, the system shows no firs t normal stress difference, no recoil and no stress overshoot with she ar start-up, and thus does not appear to be viscoelastic, contradictin g 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 viscos ity ratios. These results indicate surfactant solutions which do not a ppear to be viscoelastic can be drag reducing, and that extensional vi scosity appears to be the key property controlling drag reducing abili ty. (C) 1997 Elsevier Science B.V.