On the Limits of High-Speed Microthermal Focusing Field-Flow Fractionation

Abstract

The migration of microparticles exposed to gravitational-buoyancy force and lift force and transported by the flow of the carrier liquid inside microfluidic conduits was studied from the viewpoint of the transient period (the relaxation) between the moment at which the particles start to be transported by the hydrodynamic flow and the time at which they are focused at an equilibrium position. Relaxation times were calculated theoretically by the incremental numerical method and the results were compared with the experimental data obtained on two microfluidic channels of different lengths and for different average linear velocities of the carrier liquid. It has been found that the maximal linear velocity of the carrier liquid in a microthermal field-flow fractionation channel whose dimensions were already optimized is of the order of a few cm/s under the investigated experimental conditions. At this velocity, the contribution of the secondary relaxation time is negligible compared to the retention time of the micrometer-sized particles.