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Shift of Thin film ODT (c N) film-ODT ~7.94 ( c N) bulk-ODT =10.5

Ordering Transition of Block Copolymer Thin Films Abraham Arceo, Peter F. Green The University of Texas at Austin (DMR-0072897). BULK PHASE DIAGRAM ( c N) bulk-ODT =10.5.

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Shift of Thin film ODT (c N) film-ODT ~7.94 ( c N) bulk-ODT =10.5

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  1. Ordering Transition of Block Copolymer Thin FilmsAbraham Arceo, Peter F. GreenThe University of Texas at Austin (DMR-0072897) BULK PHASE DIAGRAM (cN)bulk-ODT=10.5 • A-b-B diblock copolymers self-organize into a range of geometrical patterns (spheres, lamellae etc.) below an order-disorder transition temperature, TODT. For bulk symmetric copolymers, which form lamellae of spacing L, the transition occurs when N>10.5, where N is the number of monomers per chain and  (~1/T) is an energetic interaction parameter. • Finding: • The transition occurs when N>7.94 for a film (h<2L) of PS-b-PMMA copolymer supported by SiOx, corresponding to a decrease of TODT by approximately 250 degrees. • In a solvent environment, supercritical CO2, which exhibits a preferential affinity for PMMA, the TODT is shifted significantly below the bulk, and below that of the supported film in air/vacuum. Lamellar (order) disorder Shift of Thin film ODT (cN)film-ODT~7.94 (cN)bulk-ODT=10.5 Journal of Physical Chemistry B (LETTER),109, 6958 (2005)

  2. Broader Impact • A-b-B diblock copolymers, depending on the chemical characteristics of the A and B components, are used for a wide range of applications, from devices and sensors to structural applications. Many of the new applications involve thin films. Upon increasing temperature, these materials self-organize. Our results show that the ordering temperature for thin, supported films, can be considerably lower, ~200 degrees, than the bulk ordering temperature (enhanced incompatibility between the A/B segments). • Secondly, solvents are often used to process block copolymers because they not only plasticize the copolymer, but they also make the system thermodynamically more compatible. Our results reveal that in cases where the solvent exhibits a preferential affinity for one component (PMMA in this case), that the thin, supported, film may become more incompatible than one would anticipate. This could have significant implications for low temperature processing of these systems.

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