The effect of substrate roughness on the orientation of lamellar microdomains of symmetric poly(styrene)-block-poly(methyl methacrylate) [PS-b-PMMA] was investigated. Thin films of three molecular weights of PS-b-PMMA were prepared on organic polyimide and inorganic indium tin oxide substrates whose surfaces were characterized for roughness and surface energy. It was shown, through cross-section transmission electron microscopy (TEM) and dynamic secondary ion mass spectroscopy (dSIMS), that above a critical substrate roughness all three molecular weights of PS-b-PMMA produced a perpendicular lamellar orientation. Using atomic force microscopy (AFM) and PS-b-PMMA thin films on an array of polyimide substrates of varied substrate roughness, a critical substrate roughness was identified, below which a parallel orientation was observed. This behavior was modeled simply and showed that the critical roughness determined by AFM represents an underestimate of the true critical roughness of the substrate. Finally, a series of TEM cross sections of thin films on rough and smooth substrates, annealed to different stages of reaching equilibrium, are shown and discussed in terms of the dynamics of ordering in block copolymer thin films.

The lamellar dimension, D, for pure and blended block copolymer (BCPs) thin films of symmetric poly(styrene)-block-poly(methyl methacrylate) was measured using atomic force microscopy analysis of surface patterns of perpendicularly oriented lamellar structures. It was approximately verified, using SAXS and AFM analysis, that perpendicular structures in lamellar thin films bounded by a neutral and a roughened interface did not significantly alter the bulk block copolymer phase separation thermodynamics. In the case of blends, it was also verified that there was a uniform distribution of blend components throughout the thin film. These checks allowed a detailed comparison of D as a function of the number of statistical segments (N) and blend composition using existing bulk phase predictions and experiments. In pure BCPs we observed the two characteristic regimes; strong (D ∼ N 0.66) and intermediate segregation regimes (D ∼ N 0.85). In addition, we observed a more complicated, weakly segregated regime where D does not scale as N 0.5 as expected for a random coil. In blended BCPs there was good agreement with existing theory when BCP components from the strongly segregated regime were used. In cases where intermediate or weakly segregating BCP components were used, an alternative semiempirical analytical function was developed. In cases where the ratio of N for the BCP blend components exceeds ∼5, macrophase separation was observed in the thin film with the smaller BCP component remaining at the air surface.