Composite colloidal assembly by critical Casimir forces

TL;DR

This paper explores how critical Casimir forces influence the phase behavior and crystallization of colloidal mixtures with chemically modified particles, revealing complex, reversible phase transitions akin to atomic alloys.

Contribution

It demonstrates the use of temperature-dependent critical Casimir forces to control and sample the phase diagram of colloidal mixtures with particle-specific interactions.

Findings

Critical Casimir forces induce complex crystallization behavior.

Temperature dependence allows reversible phase control.

Microstructure annealing mimics atomic alloy processes.

Abstract

We investigate the phase behaviour of mixtures of two populations of colloidal particles dispersed in a binary solvent system near its critical composition. The surfaces of particles are chemically modified to elicit a specific solvent affinity for one of the solvents. In this way, fluid-mediated interactions, which involve the critical Casimir effect, become particle population specific. As a result, the colloidal mixture shows a complex crystallization behavior reminiscent of the crystallization of atomic alloys. We show that the exquisite temperature dependence and reversibility of the critical Casimir interaction allows sampling the entire phase diagram of the binary system, and can be even used to anneal the crystalline microstructure analogous to temperature cycling of atomic alloy phases.