Interface properties and bubble nucleation in compressible mixtures containing polymers

Using self-consistent field theory we investigate the properties of interfaces and of bubbles that nucleate in response to a pressure change. We use a simple phenomenological equation of state for a compressible mixture of two polymers. The parameters are chosen as to mimic the behavior of a polymer in a supercritical solvent and the phase behavior in the bulk corresponds to class III in the classification of Konynenburg and Scott. At low pressure, the density of the volatile solvent is small and the interface and nucleation properties are similar to a one-component fluid. At higher pressure, however, there is a triple point at which the polymer coexists with a vapor of the solvent and a mixed solvent-rich liquid. The vicinity of the triple point alters the interface and nucleation behavior: There is a thick wetting layer of the (metastable) solvent-rich liquid at the interface between polymer and vapor, and the solvent condenses into a solvent-rich liquid inside small bubbles. We explore the dependence of the nucleation barrier on temperature, pressure and molecular weight dispersity of the polymer and relate our findings to the binodal and spinodal of the bulk.