A morphology map based on phase evolution in polymer blend films

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We present a novel morphology map based on pattern development mechanisms in polymer blend films. Six distinct mechanism are found for poly(methyl methacrylate) (PMMA):poly(styrene-ran-acrylonitrile) (SAN) films for thickness values and bulk compositions between 50-1000 nm and φ PMMA = 0.3-0.8, respectively. In regime A (φ PMMA = 0.3), PMMA is completely depleted from the midlayer by preferential wetting, resulting in a stable PMMA/SAN/PMMA trilayer. With increasing φ PMMA (0.4-0.7), pattern development is driven by phase separation in the midlayer, which produces circular domains, irregular domains, and bicontinuous patterns denoted as regimes B, C, and D, respectively. Here, shape factors are used for the first time to quantitatively distinguish these regimes. In regime E (φ PMMA = 0.8), the SAN phase is the minority component in the midlayer and breaks up into droplets in a smooth PMMA film. In regime F (φ PMMA = 0.4 or 0.5; d < 80 nm), films initially develop a trilayer structure, which then ruptures upon dewetting of the SAN midlayer. Trilayer stability is analyzed using a free energy model that attributes dewetting to capillary fluctuations at the PMMA/SAN interface. This study of pattern development mechanisms will serve as a guideline to control morphology shape and feature size, which are both critical design parameters for technological applications such as organic devices and membranes. © 2006 American Chemical Society.

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