Tunability of Critical Casimir Interactions by Boundary Conditions

TL;DR

This paper demonstrates that critical Casimir forces in colloidal systems can be continuously tuned by boundary conditions, showing a response to surface property changes beyond temperature variations.

Contribution

It introduces an experimental method to tune critical Casimir interactions via boundary conditions in colloidal systems with a surface property gradient.

Findings

Interaction potentials change from attraction to repulsion.

Critical Casimir forces respond to surface property variations.

Forces can be tuned continuously by boundary conditions.

Abstract

We experimentally demonstrate that critical Casimir forces in colloidal systems can be continuously tuned by the choice of boundary conditions. The interaction potential of a colloidal particle in a mixture of water and 2,6-lutidine has been measured above a substrate with a gradient in its preferential adsorption properties for the mixture's components. We find that the interaction potentials at constant temperature but different positions relative to the gradient continuously change from attraction to repulsion. This demonstrates that critical Casimir forces respond not only to minute temperature changes but also to small changes in the surface properties.