Direct Flow Visualization of Colloidal Gels in Microfluidic Channels.

The behavior of colloidal gels under pressure-driven flow in square microchannels is quantified by microscopic particle image velocimetry (PIV) and compared to predictions of available rheological models. The gels consist of hydrophobically modified silica microspheres ( 0.15−0.33) suspended in a refractive index-matched fluid along with fluorescent tracers to aid visualization. Measured velocity flow profiles show a transition from plug flow to more fluid-like behavior with increasing volumetric flow rate (Q) at all . This transition is not captured by theoretical predictions of the flow profile based on the Herschel−Bulkley model. Rather, a model that accounts for gel breakup into a suspension of clusters at elevated shear rates by assuming a finite viscosity at infinite shear is needed to accurately predict the flow behavior of colloidal gels at large Q. [ABSTRACT FROM AUTHOR]