Segmental Interaction Parameters of Binary Polymer Mixtures Evaluated from Binodals and from Surface-Segregation Profiles:  Comparison with Small-Angle Neutron Scattering

We compare segmental interaction parameters χ<INF>AB</INF> in binary polyolefin mixtures extracted from a fit to the binodal&sbd;as deduced from composition−depth profiling of thin films&sbd;with values extracted from small-angle neutron scattering (SANS), on the self-same blends. We find good quantitative agreement as regards both absolute values and compositional dependence of χ<INF>AB</INF>. We also compare values of χ<INF>AB</INF> obtained from composition−depth profiles of surface segregation in isotopic polystyrene mixtures with values deduced from SANS from these mixtures, and again we find good agreement between them. These results point to the use of thin-film composition−depth profiling, which is potentially a more accessible technique and requires far smaller quantities of material, as a convenient, accurate, and widely applicable alternative to SANS for measuring segmental interactions in binary polymer mixtures.