We have examined the effect of deuterium labeling on surface interactions in mixtures of random olefinic copolymers
Based on surface segregation data we have determined a surface energy difference s between pure blend constituents. In each binary mixture components have different fractions x 1 , x 2 of the group C 2 H 3 (C 2 H 5 ), and one component is labeled by deuterium (dx) while the other is hydrogenous (hx). The mixtures are grouped in four pairs of structurally identical blends with swapped labeled constituent (dx 1 /hx 2 , hx 1 /dx 2 ). For each pair the surface energy parameter s increases when the component with higher fraction x is deuterated, i.e., s (dx 1 /hx 2 ) ΟΎ s (hx 1 /dx 2 ) for x 1 ΟΎ x 2 . A similar pattern has been found previously for the bulk interaction parameter . This is explained by the solubility parameter formalism aided by the lattice theory relating the surface excess to missingneighbor effect. s has also an additional contribution, insensitive to deuterium swapping effect, and related to entropically driven surface enrichment in a more stiff blend component with a lower fraction x. Both enthalpic and entropic contributions to s seem to depend on the extent of chemical mismatch between blend components.