DOI: 10.1051/jp2:1996188
J. Phys. II France 6 (1996) 375-393

A Study of the "Spurt Effect" in Wormlike Micelles Using Nuclear Magnetic Resonance Microscopy

P.T. Callaghan¹, M.E. Cates², C.J. Rofe¹ and J.B.A.F. Smeulders<sup>3

1</sup>  Department of Physics, Massey University, Palmerston North, New Zealand
²  Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK
³  Department of Physics and Astronomy, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh EH9 3JZ, UK

(Received 19 June 1995, revised 9 October 1995, accepted 12 December 1995)

Abstract
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 5.0 mm diameter glass tube reveal a discontinuity in the flow behaviour, once a critical shear strain rate of around 1 s ^-1 is exceeded, a manifestation of the so-called "spurt effect". Rheological measurements show that three characteristic regimes are observed. Below 0.2 s ^-1 the system is near-Newtonian. Between 0.2 and 0.8 s ^-1, 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 100 s ^-1, 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.

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