Observation of shear banding in worm-like micelles by NMR velocity imaging
Department of Physics, Massey University - Palmerston North, New Zealand
Accepted: 8 November 1996
We report an observation of shear-banding, under Couette flow, of the worm-like surfactant system cetyl pyridinium chloride/sodium salicylate (respective concentrations of 100 mM and 60 mM in pure water). The method, based on NMR velocity imaging, allows the direct measurement of velocity, and consequent calculation of shear rate, at a spatial resolution of around , sufficient to resolve apparent slip at the inner wall from shear banding within the bulk of the fluid. Above a critical shear rate (around ) a high shear rate band is observed in the annulus between concentric rotating cylinders, the width of the band being of order with a corresponding shear rate of order . The precise location of the band is sensitive to boundary conditions at the inner wall and is shown to be susceptible to significant broadening.
PACS: 76.60.Pc – NMR imaging / 61.25.Hq – Macromolecular and polymer solutions; polymer melts / 47.27.Lx – Wall-bounded thin shear flows
© EDP Sciences, 1996