Parametric instability of a liquid-vapor interface close to the critical point

An experimental study of the parametric instability of a liquid-vapor interface close to the critical point is presented. A cell containing carbon dioxide at the critical density is vertically vibrated sinusoidally; the acceleration amplitude ${\mathit{a}}_0$ and the instabiilty wavelength ${\lambda }_0$ at the instabiilty onset are measured with respect to the excitation frequency and the critical temperature difference ${\mathit{T}}_{\mathit{c}}$-T. These measurements provide a simple way to determine the surface tension and the density difference between the two phases. When ${\mathit{T}}_{\mathit{c}}$-T diminishes ${\lambda }_0$ decreases and reaches a finite value whereas ${\mathit{a}}_0$ diverges. The shape of the wave pattern appears to depend on ${\mathit{T}}_{\mathit{c}}$-T.