Tunability of Critical Casimir Interactions by Boundary Conditions

Understand

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.