SURFACE-TENSION AND INTERFACE FLUCTUATIONS IN IMMISCIBLE LATTICE GASES

Using a Boltzmann approximation, we calculate the surface tension as a function of population density in a momentum-conserving lattice-gas m odel of immiscible fluids in two dimensions. The calculation, which pr edicts that the surface tension vanishes below a critical density, is compared to measurements made from simulations of flat interfaces and bubbles; the fit of theory to data is qualitatively good. Equilibrium fluctuations of flat interfaces are also studied. The fluctuations are empirically observed to be classical, decaying like the inverse squar e of wavenumber and obeying qualitatively the equipartition of surface energy.