Combined electrokinetic and shear flows control colloidal particle distribution across microchannel cross-sections

Recent experimental observations on combined electrokinetic and shear flows of colloidal suspensions in rectangular cross-section microfluidic channels have shown unusual cross-stream colloidal particle migration and dynamic assembly. Although a new electrophoresis-induced lift force has been postulated to cause the lateral migration of colloidal particles, little is known about how fluid properties and flow conditions impact this force and therefore subsequent colloidal particle migration. Furthermore, no experimental quantification of this electrophoresis-induced lift force is available. We report several key advances by demonstrating that the kinematic viscosity of the fluid can be used to modulate the spatial distribution of particles over the entire microchannel cross-section, with suppression of the colloidal particle migration observed with increase in fluid kinematic viscosity. Colloidal particle migration of similar to 10 mu m from not only the top and bottom microchannel walls but also from the side walls is shown with the corresponding electrophoresis-induced lift force of up to similar to 30 fN. The breadth of flow conditions tested capture the channel Reynolds number in the 0.1-1.1 range, with inertial migration of colloidal particles shown in flow regimes where the migration was previously thought to be ineffective, if not for the electrophoresis-induced lift force. The ability of the electrophoresis-induced lift force to migrate colloidal particles across the entire microchannel cross-section establishes a new paradigm for three-dimensional control of colloidal particles within confined microchannels.

Automated summary

Recent experimental observations have uncovered unusual cross-stream colloidal particle migration and dynamic assembly in rectangular cross-section microfluidic channels with combined electrokinetic and shear flows. The electrophoresis-induced lift force, postulated to cause lateral migration of colloidal particles, impacts fluid properties and flow conditions, with little experimental quantification available. The study demonstrates that fluid kinematic viscosity can modulate particle distribution, suppressing colloidal particle migration, with up to 30 fN electrophoresis-induced lift force allowing migration across the entire microchannel cross-section, establishing a new paradigm for three-dimensional control of colloidal particles.