Inertial Focusing and Ordering in Low Aspect Ratio Microchannels Using Reference Frame Tracking and Rotation Measurements

Inertial focusing and ordering in microchannel flows refers to the tendency of finite-sized particles to migrate across streamlines and to form linear, equally spaced trains in the direction of flow. This study utilizes a motorized microscope stage moving along the length of a low aspect ratio microchannel at up to 10 cm/s and provides a Lagrangian view of particles to obtain more complete time dependent trajectory and rotation histories from the channel inlet to outlet. We observe monodisperse particle dynamics, rotations, and interactions over time scales significantly longer (exceeding a 30-fold increase) than static reference frames. The results present new insight into particle interactions which show quasi-steady state equilibrium spacing which oscillates at a constant frequency at a fixed flow rate, which is different from the damped oscillatory interactions suggested in the literature. The average spacing shows little dependence on flow rate, but the oscillation frequency is dependent both on flow rate and particle size.