Entropic electrokinetics: recirculation, particle separation and negative mobility

TL;DR

This paper explores how electrokinetic flows in corrugated charged channels induce novel phenomena like particle separation, mixing, and negative mobility, especially when channel width is comparable to the Debye length, with implications for microfluidic and biological systems.

Contribution

It reveals the physical mechanisms behind entropic electrokinetics phenomena arising from electrostatic and geometrical interactions in confined electrolyte flows.

Findings

Electrokinetic flows cause particle separation and mixing.

Negative mobility can occur in confined electrolyte systems.

Phenomena are amplified when channel width matches the Debye length.

Abstract

We show that when particles are suspended in an electrolyte confined between corrugated charged surfaces, electrokinetic flows lead to a new set of phenomena such as particle separation, mixing for low-Reynolds micro- and nano-metric devices and negative mobility. Our analysis shows that such phenomena arise, for incompressible fluids, due to the interplay between the electrostatic double layer and the corrugated geometrical confinement and that they are magnified when the width of the channel is comparable to the Debye length. Our characterization allows us to understand the physical origin of such phenomena therefore shading light on their possible relevance in a wide variety of situations, ranging from nano- and micro-fluidic devices to biological systems.