Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids

TL;DR

This study demonstrates that the diffusiophoresis of colloidal ellipsoids depends on their shape and orientation, challenging the assumption of shape independence and revealing complex behaviors under ionic gradients.

Contribution

It provides experimental evidence and theoretical insights into shape- and orientation-dependent diffusiophoresis of ellipsoids beyond the thin Debye layer approximation.

Findings

Ellipsoidal particles exhibit shape- and orientation-dependent diffusiophoretic mobility.

Mobility varies with eccentricity and orientation relative to solute gradients.

Nonmonotonic diffusiophoresis occurs under strong confinement.

Abstract

We present the diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Contrary to the common expectation that diffusiophoresis is shape independent, here we show experimentally that this assumption breaks down when the thin Debye layer approximation is relaxed. By tracking the translation and rotation of various ellipsoids, we find that the phoretic mobility of ellipsoids is sensitive to the eccentricity and the orientation of the ellipsoid relative to the imposed solute gradient, and can further lead to nonmonotonic behavior under strong confinement. We show that such a shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids can be easily captured by modifying theories for spheres.