A stress-controlled microfluidic shear viscometer based on smartphone imaging

Abstract

We report a stress-controlled microfluidic shear viscometer with flow visualization aided by smartphone technology. The method involves driving the fluid into a microchannel at constant pressure and using the smartphone camera to track the fluid front in a glass capillary attached to the microchannel. We find that videos of interface propagation from the smartphone are of sufficient resolution that accurate pressure drop-flow rate relations can be determined to quantify the viscosity curves for complex fluids. We demonstrate that this simple ‘iCapillary’ device measures the shear viscosity of Newtonian and polymeric fluids over a broad range of shear rates (10–10,000 s−1) that is in quantitative agreement with rotational rheometry. We further show that the simplicity of the iCapillary device allows for parallel analysis of viscosity of several samples. We performed multiplexed measurements of concentration dependence of high shear rate viscosity of globular protein solutions, and the results are in good agreement with models of suspension rheology as well as prior experimental data. Our approach is unique, since no on-chip sensing element is required other than the smartphone camera. This sensor-less approach offers the potential to create inexpensive and disposable devices for point-of-care rheology of complex fluids and biological samples.