On the derivation of dynamical equations for a system with an interface

Dynamical equations for the Gibbs surface excesses and bulk fields are derived using linear response theory for one-component systems. Boundary conditions linking the dynamics of the gas and liquid phases to that of the surface are obtained. In the limit where the equilibrium interfacial profile is a step function the usual boundary conditions (i.e. stick) result. Corrections give correlation function expressions for the surface transport coefficients as well as constitutive relations for the surface fluxes. A new microscopic expression for the surface tension is obtained and various symmetries are examined. Acoustic scattering and dispersion equations for the surface modes when surface structure is included are considered and the connection to possible light scattering experiments is discussed.