A Method to Measure Viscosity of Fluids in Microchannels

In this paper, we present a microfluidic-based rheometer that uses in-situ pressure signals to measure the shear viscosity of liquids. The shear-viscosity is measured using a PDMS-based microfluidic device that consists of a channel layer and a sensing membrane integrated with an array of piezoresistive pressure sensors via plasma surface-treatment. The micro-pressure sensors are fabricated using conducting particles-PDMS composites, synthesized by mixing 82 wt% micrometer-sized silver particles (1–3 μm in diameter) with PDMS gels. The simple design and fabrication enable nearly perfect bonding of a 120 μm-thick sensing membrane to different channel geometries that map the pressure differences at various locations within the channel in order to measure the fluid shear stress in-situ and to estimate the fluid viscosity. Experimental validation of this microfluidic-based rheometer is performed using calibration oil of known viscosity as well as macroscopic rheometric data, both of which achieve good consistency. The present work allows in-situ measurements of rheological properties of fluids at low Re.