Critical Casimir Effect in Three-Dimensional Ising Systems: Measurements on Binary Wetting Films

Abstract

The critical Casimir force (CF) is observed in thin wetting films of a binary liquid mixture close to the liquid/vapor coexistence. X-ray reflectivity shows thickness (L) enhancement near the bulk consolute point. The extracted Casimir amplitude \(\Delta_{+-}\)=3\(\pm\)1 agrees with the theoretical universal value for the antisymmetric 3D Ising films. The onset of CF in the one-phase region occurs at L/\(\xi \sim\)5 regardless of whether the bulk correlation length \(\xi\) is varied with temperature or composition. The shape of the Casimir scaling function depends monotonically on the dimensionality.