Pointwise observations for rheological characterization using nuclear magnetic resonance imaging

This study focuses on development of a nuclear magnetic resonance (NMR) imaging based viscometric technique using pulsed gradient NMR for characterizing fluid materials under steady tube flow conditions. By simultaneously measuring velocity profiles and pressure gradients it is possible to characterize complex fluids locally. Shear viscosity-shear rate data, ranging from one to over two decades of shear rate from one combined velocity profile/pressure drop per unit tube length measurement, are provided for five fluids that exhibit both Newtonian and shear thinning characteristics. The resolution of the velocity data controls the accuracy of the measured shear viscosity whereas the radial resolution prescribes the number of shear viscosity-shear rate data points and the minimum shear rate. Velocity profile measurements with a velocity resolution of 1 mm/s and radial resolutions which provided from 22 to 110 spatially resolved velocity data points accurately characterized fluids for shear rates greater than 0.1 s(-1). Dynamic yield values measured from velocity data for a microfibrous cellulose solution were within 2% of those measured with a conventional rheometer using the controlled shear rate method and a vane attachment. (C) 1999 The Society of Rheology. [S0148-6055(99)00601-X].