Analysis of non-Newtonian liquids using a microfluidic capillary viscometer.

We have used a self-calibrating microfabricated capillary viscometer to analyze non-Newtonian power law fluids. The capillary viscometer can generate a wide range of shear rates during a single experimental run enabling quick and accurate analysis of non-Newtonian liquids. The measurement of viscosity is based on monitoring the capillary pressure-driven movement of fluid sample whose mean velocity and, therefore, shear rate varies with time. The device has been successfully tested for accuracy and robustness with dilute as well as semidilute solutions of flexible elastic polymers including poly(ethylene oxide) and hydrolyzed polyacrylamide to an aqueous solution of a stiff rodlike polymer molecule of xanthan gum, a popular emulsifier and food thickener, as well as with ink-jet printing inks. Viscosities in the range of 1-600 cP were measured, and shear rates varying from 5 to 1000 s(-1) have been obtained on the microfabricated viscometer with the current geometry and channel dimensions. The total measurement time varied between 2 and 8 min and less than 1 microL of sample volume was required. Such a microfabricated capillary viscometer would have possible applications in quality control and manufacturing where rapid and repeated measurements need to be made using limited sample volume.