Surface enrichment-depletion duality in a binary polymer blend

We have measured the surface segregation towards the vacuum in films of a binary mixture of deuterated E 48 EE 52 (d52)—and hydrogenous E 38 EE 62 (h66)—random olefinic copolymers. Here E and EE are the linear ethylene and branched ethyl ethylene groups (C 4 H 8 ) and [C 2 H 3 (C 2 H 5 )], respectively. The d52 copolymer is enriched at the surface when d52 is the minority component in the blend. On the contrary, the surface is depleted in the d52 chains, when they constitute a majority of the mixture. We have determined two branches of the segregation isotherm corresponding to the enrichment and the depletion. A mean-field Cahn model describes consistently these two isotherm branches. The observed enrichment-depletion duality modifies a common viewpoint on surface segregation.