Nuclear magnetic resonance imaging for viscosity measurements of non-Newtonian fluids using a miniaturized RF coil

Abstract

This work reports on applications of a miniaturized RF coil combined with a capillary tube for the design of a portable on-line/in-line magnetic resonance imaging (MRI) based viscometer. A microfabricated Helmholtz RF coil with the average diameter of 7 mm and a Teflon tube with ID = 1.02 mm were utilized. Tube flows of two aqueous CMC polymer solutions (2% with MW = 250k and 1% with MW = 700k) of different viscosities at 1.99 µL s−1 volumetric flow rate were monitored. It was shown that the RF coil and the capillary permit measurement of shear thinning phenomena during flow. A constitutive power law model was used to analyse the tube flows. Viscosity was successfully measured for both the CMC solutions. The less viscous CMC solution was found to have the power index n = 0.77 ± 0.06 and the flow consistency coefficient K = 1.68, whereas the more viscous CMC solution exhibited n = 0.5 ± 0.03 and K = 7.23. The MRI measurements compared well with measurements of the same samples performed on a conventional rotational rheometer. The range of shear rates covered by the obtained MRI viscosity data was 3–20 s−1.