Tunability of critical Casimir interactions by boundary conditionsU. Nellen1, L. Helden1 and C. Bechinger1, 2
1 2. Physikalisches Institut, Universität Stuttgart - Pfaffenwaldring 57, 70550 Stuttgart, Germany, EU
2 Max-Planck-Institut für Metallforschung - Heisenbergstr. 3, 70563 Stuttgart, Germany, EU
received 22 September 2009; accepted in final form 8 October 2009; published October 2009
published online 22 October 2009
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.
68.35.Rh - Phase transitions and critical phenomena.
82.70.Dd - Colloids.
81.16.Dn - Self-assembly.
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