Capillary waves

(Thermal) capillary waves are oscillations of an interface which have a thermal origin (there are also capillary waves that are ordinary waves excited in an interface, such as ripples in a water surface.)

Capillary wave theory (CWT) is a classic account of how thermal fluctuations distort an interface. It starts from some intrinsic surface that is distorted. A well-known prediction is that the width of the interface is bound to diverge with its area. On the other hand ,this divergence is extremely weak, and is damped by the presence of an external field. For example, the action of gravity is sufficient to keep the width fluctuation on the order of one molecular diameter for areas about 1mm$^{2}$ (Ref. 1).

Recently, a procedure has been proposed to obtain a molecular intrinsic surface from simulation data (Ref. 2). The density profiles obtained from this surface are, in general, quite different from the usual ones (the mean density profiles.)

References

1. J. S. Rowlinson and B. Widom "Molecular Theory of Capillarity". Dover 2002 (originally: Oxford University Press 1982)
2. Chacón E, Tarazona P "Intrinsic profiles beyond the capillary wave theory: A Monte Carlo study", Physical Review Letters 91 p. 166103 (2003)