EFFECT OF ANNEALING TIME, FILM THICKNESS, AND MOLECULAR-WEIGHT ON SURFACE ENRICHMENT IN BLENDS OF POLYSTYRENE AND DEUTERATED POLYSTYRENE

Surface-enhanced Raman scattering (SERS) was used to investigate surfa ce segregation in blends of polystyrene (PS) and deuterated polystyren e (DPS) following annealing at temperatures above the upper critical s olution temperature (UCST). Blends of PS and DPS were spin-coated onto cleaned silicon wafers from toluene solutions and annealed at tempera tures above the UCST. Silver island films were then evaporated onto th e blend films, and SERS spectra were obtained. The relative intensitie s of the bands near 1015 and 975 cm-(1), which were characteristic of PS and DPS, respectively, were used to determine the relative amounts of PS and DPS at the surface of the blend films. When the blends consi sted of PS and DPS with the same molecular weight, DPS segregated to t he free surface after annealing. Moreover, the extent of surface segre gation increased when the annealing time, the film thickness of the bl ends, and the molecular weight of the polymers in the blends were incr eased. When blends contained PS and DPS with different molecular weigh ts, DPS always segregated to the free surface as long as PS had molecu lar weights that were greater than DPS. However, PS segregated to the surface when PS had a relatively small molecular weight, indicating th at the surface free energy of polymers, which caused surface segregati on in blends of PS and DPS, was determined by both molecular weight an d isotopic effects.