Velocity Oscillations in Microfluidic Flows of Concentrated Colloidal Suspensions

We study the pressure-driven flow of concentrated colloids confined in glass microchannels at the single-particle level using fast confocal microscopy. For channel to particle size ratios 2a/D ≤ 30, the flow rate of the suspended particles shows fluctuations. These turn into regular oscillations for higher confinements (2a/D ≃ 20). We present evidence to link these oscillations with the relative flow of solvent and particles (permeation) and the effect of confinement on shear thickening.