Structure and aggregation of colloids immersed in critical solvents

TL;DR

This paper investigates how critical Casimir forces influence the structure and stability of colloidal suspensions in near-critical solvents, providing a theoretical framework for understanding colloidal aggregation driven by solvent fluctuations.

Contribution

It introduces a method to analyze colloidal organization using effective pairwise critical Casimir forces, advancing understanding of colloid aggregation near critical points.

Findings

Calculated radial distribution functions for colloids

Identified conditions for colloidal aggregation due to CCFs

Linked theoretical results to experimental observations

Abstract

We consider an ensemble of spherical colloidal particles immersed in a near-critical solvent such as a binary liquid mixture close to its critical demixing point. The emerging long-ranged fluctuations of the corresponding order parameter of the solvent drive the divergence of the correlation length. Spatial confinements of these critical fluctuations by colloidal solute particles, acting as cavities in the fluctuating medium, restrict and modify the fluctuation spectrum in a way which depends on their relative configuration. This results in effective, so-called critical Casimir forces (CCFs) acting on the confining surfaces. Using the available knowledge about CCFs we study the structure and stability of such colloidal suspensions by employing an approach in terms of effective, one-component colloidal systems. Applying the approximation of pairwise additive CCFs we calculate the radial distribution function of the colloids, which is experimentally accessible. We analyze colloidal aggregation due to CCFs and thus allude to previous experimental studies which are still under debate