Repulsive and attractive critical Casimir forces

When confining vacuum fluctuations between two identical walls, the Casimir force manifests itself as a mutual attraction of the walls. When confining concentration fluctuations of a binary liquid mixture, an analogous force should exist near the critical temperature T C ; it is called the critical...

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Bibliographic Details
Published in:Physica A 2007-12, Vol.386 (1), p.31-35
Main Authors: Rafaï, Salima, Bonn, Daniel, Meunier, Jacques
Format: Article
Language:English
Subjects:
Condensed Matter
Critical Casimir effect
Critical phenomena
Finite size effects
Phase transitions
Physics
Soft Condensed Matter
Wetting
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Summary:When confining vacuum fluctuations between two identical walls, the Casimir force manifests itself as a mutual attraction of the walls. When confining concentration fluctuations of a binary liquid mixture, an analogous force should exist near the critical temperature T C ; it is called the critical Casimir force. Here we show experimentally that this purely entropic force can be either attractive or repulsive, depending on the boundary conditions for the fluctuations. For symmetrical boundary conditions an attractive force is found while asymmetrical ones lead to a repulsive force. This is observed directly by confining the fluctuations in a thin ( ≈ 100 A ˚ ) wetting film. Depending on the boundary conditions either a thinning or a thickening of the film is observed when T → T C .
ISSN:0378-4371
1873-2119
0378-4371
DOI:10.1016/j.physa.2007.07.072