Solvent coarsening around colloids driven by temperature gradients

TL;DR

This study uses simulations and theory to explore how solvent structures around colloids evolve after temperature quenches, revealing different mechanisms based on colloid surface properties and solvent composition.

Contribution

It introduces a phenomenological model that explains asymmetric solvent structuring around Janus colloids under temperature gradients, aligning with recent experimental observations.

Findings

Neutral colloids show alternating phase behavior near surface over time.

Janus colloids induce asymmetric concentration gradients even above the critical temperature.

Model captures experimental results of solvent behavior under laser-induced temperature gradients.

Abstract

Using mesoscopic numerical simulations and analytical theory we investigate the coarsening of the solvent structure around a colloidal particle emerging after a temperature quench of the colloid surface. Qualitative differences in the coarsening mechanisms are found, depending on the composition of the binary liquid mixture forming the solvent and on the adsorption preferences of the colloid. For an adsorptionwise neutral colloid, as function of time the phase being next to its surface alternates. This behavior sets in on the scale of the relaxation time of the solvent and is absent for colloids with strong adsorption preferences. A Janus colloid, with a small temperature difference between its two hemispheres, reveals an asymmetric structure formation and surface enrichment around it, even if the solvent is within its one-phase region and if the temperature of the colloid is above the critical demixing temperature $T_c$ of the solvent. Our phenomenological model turns out to capture recent experimental findings according to which, upon laser illumination of a Janus colloid and due to the ensuing temperature gradient between its two hemispheres, the surrounding binary liquid mixture develops a concentration gradient.