3 research outputs found
A Study of the “Spurt Effect" in Wormlike Micelles Using Nuclear Magnetic Resonance Microscopy
The non-Newtonian flow properties of the wormlike surfactant system, cetyl pyridinium
chloride/sodium salicylate in water, have been studied using dynamic and steady rheometry and
nuclear magnetic resonance velocity imaging. The NMR measurements of velocity profiles across a
5.0Â mm diameter glass tube reveal a discontinuity in the flow behaviour, once a critical shear
strain rate of around 1 s is exceeded, a manifestation of the so-called “spurt effect".
Rheological measurements show that three characteristic regimes are observed. Below 0.2Â s the
system is near-Newtonian. Between 0.2 and 0.8Â s, shear-thinning behaviour is observed. Above
this a multi-valued shear-rate regime is found at constant stress. This “spurt" regime exhibits
shear rates up to values of around 50 to 100Â s, at which an upturn in the shear stress is
found. The rheological flow curves are characteristic of those predicted by a Wagner model and in
turn are found to be broadly consistent with the velocity profiles as measured by NMR