Colloidal motility and pattern formation under rectified diffusiophoresis

TL;DR

This study experimentally investigates colloidal and DNA motion under controlled solute gradients, revealing how temporal solute variations induce particle segregation and pattern formation through an osmotic rectification mechanism.

Contribution

It demonstrates the use of microfluidic technology to control and analyze particle behavior under dynamic solute gradients, uncovering a new rectification mechanism for pattern formation.

Findings

Particles can be trapped by solute-induced potentials.

Pattern shapes depend on solute temporal and spatial symmetry.

Solute contrasts drive out-of-equilibrium soft matter processes.

Abstract

In this letter, we characterize experimentally the diffusiophoretic motion of colloids and lambda- DNA toward higher concentration of solutes, using microfluidic technology to build spatially- and temporally-controlled concentration gradients. We then demonstrate that segregation and spatial patterning of the particles can be achieved from temporal variations of the solute concentration profile. This segregation takes the form of a strong trapping potential, stemming from an osmotically induced rectification mechanism of the solute time-dependent variations. Depending on the spatial and temporal symmetry of the solute signal, localization patterns with various shapes can be achieved. These results highlight the role of solute contrasts in out-of-equilibrium processes occuring in soft matter.