CASIMIR FORCES IN BINARY-LIQUID MIXTURES

If two or more bodies are immersed in a critical fluid, critical fluct uations of the order parameter generate long-ranged forces between the se bodies. Due to the underlying mechanism these forces are close anal ogs of the well-known Casimir forces in electromagnetism. For the spec ial case of a binary liquid mixture near its critical demixing transit ion, confined to a simple parallel plate geometry, it is shown that th e corresponding critical Casimir forces can be of the same order of ma gnitude as the dispersion (Van der Waals) forces between the plates. I n wetting experiments or by direct measurements with an atomic force m icroscope. The resulting modification of the usual dispersion forces i n the critical regime should therefore be easily detectable. Analytica l estimates for the Casimir amplitudes Delta in d=4-epsilon are compar ed with corresponding Monte Carlo results in d=3, and their quantitati ve effect on the thickness of critical wetting layers and on force mea surements is discussed.