Surface response functions for a thin-film between fluids with infinite boundaries and for a fluid-fluid interface between finite boundaries

Measuring the surface response function of a fluid allows us to ascertain many of its properties. Simplified surface response functions are presented for several interface conditions, including (a) a thin-film between two fluids of infinite extent, (b) the newly derived fluid-fluid interface between finite boundaries, and (c) the traditional fluid-fluid interface between infinite boundaries. The finite-boundary derivation indicates that wall effects are very short range. This portends that the effects of external vibrations, which traditionally make this measurement challenging, can be mitigated by scattering from thin fluid layers.