Surface Enrichment in an Isotopic Polymer Blend

Forward-recoil spectrometry reveals that the surface of a blend of deuterated polystyrene ($d$-PS) and protonated polystyrene (PS) is enriched with $d$-PS relative to the bulk; the surface excess of $d$-PS increases almost linearly with the bulk volume fraction $\phi$ of $d$-PS at 184°C. The results may be interpreted quantitatively with mean-field theory, and yield a form of the bare surface energy of the blend consistent with the surface enrichment being driven by a surface-energy difference between $d$-PS and hydrogenated polystyrene ($h$-PS) of isotopic origin.