Inertial hydrodynamic ratchet: Rectification of colloidal flow in tubes of variable diameter

TL;DR

This paper presents an analytical study of a microfluidic device that uses inertial hydrodynamics and Brownian motion to create a ratchet effect, enabling size-dependent colloidal particle sorting in a tube with variable diameter.

Contribution

It introduces a novel inertial hydrodynamic ratchet mechanism that leverages tube geometry and particle size for effective colloidal sorting.

Findings

Average particle current is highly sensitive to particle size.

The ratchet mechanism enables directional transport despite zero net fluid flow.

The device can be used for efficient colloidal particle separation.

Abstract

We investigate analytically a microfluidic device consisting of a tube with non-uniform but spatially periodic diameter, where a fluid driven back and forth by a pump carries colloidal particles. Although the net flow of the fluid is zero, the particles move preferentially in one direction due to ratchet mechanism, which occurs by simultaneous effect of inertial hydrodynamics and Brownian motion. We show that the average current is strongly sensitive to particle size, thus facilitating colloidal particle sorting.