PHASE-SEPARATION-INDUCED SURFACE PATTERNS IN THIN POLYMER BLEND FILMS

Atomic force microscopy (AFM), neutron reflection (NR) and secondary i on mass spectroscopy (SIMS) are used to examine phase separation in sy mmetrically segregating thin polymer blend films (less than or equal t o 1000 Angstrom). Phase separation in the film leads to undulations of the liquid-air interface, provided the film is sufficiently thin to s uppress surface-directed spinodal decomposition waves. Flattened dropl ets are formed at a very late stage of phase separation, and the aspec t ratio of these droplets can be rationalized by an interfacial free e nergy minimization argument.