SURFACE SEGREGATION AMPLIFICATION IN MISCIBLE POLYMER BLENDS NEAR CRITICALITY

In atomic, small molecule or polymeric multicomponent materials, surfa ce compositions naturally differ from the bulk because one component ( or phase) will generally favor the surface region. Binary polymer blen ds represent a model system to investigate surface enrichment because segregation is enhanced by the small combinatorial entropy of mixing a nd amplified by chain connectivity (relative to small-molecule systems ). Therefore, polymers are advantageous systems for probing the thermo dynamic complexities underlying surface enrichment in mixtures. In thi s work, the surface excess of binary polymer blends is studied as a fu nction of composition and temperature in the vicinity of the critical point. Although the surface excess away from criticality behaves as an ticipated, it is found to grow slower than expected as criticality is approached from the one-phase region. These results suggest that the s urface and bulk thermodynamics are coupled.