Trajectory of particles exposed to a tilted-angle washboard potential: application to high-throughput acoustophoresis in microchannels

Abstract

A wide variety of tilted washboard potentials based on acoustic waves, electric fields, optical patterns and so on have been applied to sort particles in microchannels. In this paper, we present a theoretical analysis of the particles trajectory in a washboard potential making a tilt angle $\hat{I}¸$ with the flow. Depending on the sorting to drag force ratio $\hat{I}\mu$, we identified a transition threshold $\hat{I}\mu =\cos (\hat{I}¸)$ between two distinct regimes of particles motion: drift and locked modes. In drift mode, the particles follow an oscillating trajectory which slope is given by $\frac{\hat{I}{\mu }^2}{2}\tan (\hat{I}¸)$, while in locked mode the trajectory slope is given by $1/\tan (\hat{I}¸)$. These theoretical predictions agree quantitatively well with previously published experimental data and may help in the design of high-performance microfluidic sorting devices.