Finite Size Effect (Critical Casimir Force)
We present experimental evidence for the Casimir effect within critical
films of binary liquid mixtures possessing opposite boundary conditions
(+-) by studying the thickness of these vapor-adsorbed films on a silicon
wafer as a function of temperature near the critical temperature. Our results
for two different critical mixtures demonstrate that the critical Casimir
pressure scaling function J +-(y)
scales with y=L/x, where L is the equilibrium film thickness and x is the
bulk correlation length. Additionally, on approaching the critical temperature
Tc an increase in the film thickness L is observed, implying that the sign
of the universal Casimir amplitude D+-=J+-(0)/2
at Tc is positive, consistent with theoretical predictions.
However, the magnitude of the Casimir amplitude that we measure is approximately
two orders of magnitude smaller than that given by prevailing theories.
Further readings: A. Mukhopadhyay
and B. M. Law, Phys. Rev. Lett. 83,
772 (1999),
A. Mukhopadhyay and B. M. Law, Phys. Rev.
E. 62, 5201 (2000).
Film thickness as a function of DT=T-Tc at fixed heights H=1.5 mm (diamond) and 3.3 mm (squares) for 2-methoxyethanol + methylcyclohexane (MM), and 3.4 mm (triangles) and 6.3 mm (inverted triangles) for methanol + hexane (MH), adsorbed on a vertical Si wafer. |
The Casimir pressure scaling function J+-( y) obtained from a vertical Si wafer in the one-phase region for the two mixtures MH and MM. The function J +-( y) exhibits excellent scaling as a function of y=L/x. |