Reversible Trapping of Colloids in Microgrooved Channels via Diffusiophoresis under Steady-State Solute Gradients

TL;DR

This paper introduces a reversible, rapid trapping method for sub-micron colloids in dead-end micro-grooves using steady-state salinity gradients, combining diffusiophoresis and hydrodynamics for applications in analysis and recovery.

Contribution

It demonstrates for the first time steady-state gradient-based particle focusing in dead-end microstructures, enabling reversible trapping through flow control.

Findings

Particles are trapped at flow recirculation zones due to diffusiophoresis.

The trapping is reversible and cyclic with salt concentration control.

Particles are continuously transported in and out of the focusing point.

Abstract

The controlled transport of colloids in dead-end structures is a key capability that can enable a wide range of applications, such as bio-chemical analysis, drug delivery and underground oil recovery. This letter presents a new trapping mechanism that allows the fast (i.e., within a few minutes) and reversible accumulation of sub-micron particles within dead-end micro-grooves by means of parallel streams with different salinity level. For the first time, particle focusing in dead-end structures is achieved under steady-state gradients. Confocal microscopy analysis and numerical investigations show that the particles are trapped at a flow recirculation region within the grooves due to a combination of diffusiophoresis transport and hydrodynamic effects. Counterintuitively, the particle velocity at the focusing point is not vanishing and, hence, the particles are continuously transported in and out of the focusing point. The accumulation process is also reversible and one can cyclically trap and release the colloids by controlling the salt concentration of the streams via a flow switching valve.