Diffusiophoresis in a Near-critical Binary Fluid Mixture

TL;DR

This paper investigates how a rigid spherical particle moves in a near-critical binary fluid mixture due to composition gradients, revealing a diffusiophoresis mechanism influenced by critical fluctuations and adsorption layers.

Contribution

It introduces a novel diffusiophoresis mechanism in near-critical fluids, accounting for large susceptibility and adsorption layer effects, which were not considered in prior models.

Findings

Mobility depends on temperature and particle size.

A significant adsorption layer enhances diffusiophoresis.

The mechanism differs from classical diffusiophoresis models.

Abstract

We suppose that a rigid spherical particle is put into a binary fluid mixture with the critical composition in the homogeneous phase near the demixing critical point. A short-range interaction is assumed between each component and the particle surface, and one component is assumed to be attracted more than the other by the surface. The adsorption layer, where the preferred component is more concentrated, can be significantly thick owing to a large susceptibility. In this situation, an imposed composition gradient causes a particle motion, i.e., diffusiophoresis emerges from a mechanism not considered previously. We calculate how the mobility depends on the temperature and particle size.