Size-Dependent Interfacial Tension of Polymer Blends with Broad Composition Polydispersity

The surface tension as a function of system size of a pure blend with chemically polydisperse compatibilizer is investigated by simulation. The main finding is that such compatibilizers adsorb readily at the interface between the bulk phases giving rise to very broad interfacial zones. This phenomenon leads to a marked size dependence of the interfacial tension. However the adsorption only leads to a decrease of 40% of the interfacial tension of the blend without compatibilizer. The limited effect on interfacial tension is explained by the observation that a considerable fraction of the compatibilizing chains do not contribute to the interfacial tension, instead these chains become part of an inhomogeneous phase with extensive thermodynamic properties.