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

TL;DR

This paper provides a theoretical analysis of particle trajectories in tilted washboard potentials, revealing a transition between drift and locked modes based on the force ratio and tilt angle, aiding microfluidic device design.

Contribution

It introduces a theoretical framework predicting particle motion regimes in tilted washboard potentials, validated against experimental data, for improved microfluidic sorting device design.

Findings

Transition threshold at b5 = b7( heta) between drift and locked modes

Trajectory slope in drift mode: (b5^2/2) an( heta)

Trajectory slope in locked mode: 1/ an( heta)

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 $\theta$ with the flow. Depending on the sorting to drag force ratio $\epsilon$, we identified a transition threshold $\epsilon = \cos(\theta)$ 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 $\frac{\epsilon^2}{2}\tan(\theta)$, while in locked mode the trajectory slope is given by $1/\tan(\theta)$. These theoretical predictions agree quantitatively well with previously published experimental data and may help in the design of high-performance microfluidic sorting devices.