SURFACE EFFECTS ON SPINODAL DECOMPOSITION IN THE FRAMEWORK OF A LINEARIZED THEORY

Free surfaces of binary mixtures (AB) have a profound effect on phase separation kinetics, since typically one species (say, A) will be preferentially attracted to the surface. Both experiments and numerical simulations have given ample evidence that in the initial stages a (damped) concentration wave forms, in the direction normal to the surface; the amplitude of these concentration oscillations is rapidly damped as one moves into the bulk. We discuss these phenomena in the framework of a Linearized theory of spinodal decomposition, where the usual Cahn-type treatment is supplemented by the appropriate boundary conditions. It is shown that the predicted wavelength of the concentration oscillations is compatible with the numerical treatment of the full nonlinear equations. We discuss how these phenomena depend both on the boundary conditions and the bulk state of the mixture to which the quenching experiment leads (temperature, concentration). Extension to thin film geometry and application to experiment are briefly discussed.