SURFACE DIRECTED SPINODAL DECOMPOSITION IN A PARTIALLY MISCIBLE POLYMER BLEND

We have studied the effect of the surface and interface on the phase s eparation of thin films of a blend of deuterated polystyrene and poly( alpha-methyl styrene) using He-3 nuclear reaction analysis. In the uns table region of the phase diagram, surface directed spinodal decomposi tion is observed. We describe the growth of the morphology and see tha t the depletion layer behind the wetting layer at the substrate grows faster than the wetting layer at the vacuum interface with power law g rowth exponents of 0.27 and 0.14, respectively. The early size of the wetting layer is compared with a theoretical zero-time spinodal wavele ngth. This wavelength decreases when the film is thinner than a critic al thickness in accord with other workers. (C) 1995 American Institute of Physics.