Criticality and phase separation in a two-dimensional binary colloidal fluid induced by the solvent critical behavior

TL;DR

This study investigates how critical solvent fluctuations induce phase separation in a two-dimensional binary colloidal fluid, revealing a solvent-controlled demixing transition driven by critical Casimir forces.

Contribution

It combines experimental observations with theoretical modeling to demonstrate solvent-induced phase separation in colloids near criticality, highlighting the role of critical Casimir forces.

Findings

Critical Casimir forces induce phase separation.

Experimental results agree with free energy calculations.

Critical fluctuations lead to a demixing transition.

Abstract

We present an experimental and theoretical study of the phase behavior of a binary mixture of colloids with opposite adsorption preferences in a critical solvent. As a result of the attractive and repulsive critical Casimir forces, the critical fluctuations of the solvent lead to a further critical point in the colloidal system, i.e. to a critical colloidal-liquid--colloidal-liquid demixing phase transition which is controlled by the solvent temperature. Our experimental findings are in good agreement with calculations based on a simple approximation for the free energy of the system.