Thermal Casimir Force

Finite Size Scaling at Criticality

red ballCorrelation lengths diverge at a critical point:

yellow ball Finite-size contribution of long-wavelength fluctuations at criticality:

M.E. Fisher and P.-G. de Gennes, C. R. Acad. Sci. Ser. B 287, 207 (1978)

yellow ball This thermal analog of the Casimir effect should lead to observable effects in wetting phenomena near critical points:

M.P. Nightingale and J.O. Indekeu, Phys. Rev. Lett. 54, 1824 (1985)

Colloidal particles in a critical binary mixture

red ball  "Direct measurement of critical Casimir forces,"

Hertlein, Helden, Gambassi, Dietrich & Bechinger, Nature 451, 172 (2008)

 

red ball Depending on boundary conditions, these forces can be attractive or repulsive:

"Critical Casimir forces in colloidal suspensions on chemically patterned surfaces,"

F. Soyka, O. Zvyagolskaya, C. Hertlein, L. Helden, & C. Bechinger, Phys. Rev. Lett. 101, 208301 (2008) (movie)

  

Wetting by a Superfluid Film

red ballGarcia and Chan monitored thickness of a wetting film of helium near the superfluid transition.

"Critical Fluctuation-Induced Thinning of He Films near the Superfluid Transition,"

R. Garcia and M.H.W. Chan, Phys. Rev. Lett. 83, 1187 (1999)

yellow ballThickness of the film (denoted by d) is obtained by minimizing its energy, as

yellow ballThe film is thinner at the transition, and in the superfluid phase