Monte Carlo Study of the Stabilization of Complex Bicontinuous Phases in Diblock Copolymer Systems

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• 作者：Francisco J. Martí ; nez-Veracoechea ; Fernando A. Escobedo
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：October 2, 2007
• 年：2007
• 卷：40
• 期：20
• 页码：7354 - 7365
• 全文大小：998K
• 年卷期：v.40,no.20(October 2, 2007)
• ISSN：1520-5835

文摘

Lattice Monte Carlo simulations are used to study the stabilization of different ordered bicontinuousphases in A-B diblock copolymer systems. The stabilization approach involves attempting to reduce the packingfrustration inside the nodes of the bicontinuous phases by the addition of an A-component "additive". Two differentstrategies are considered which entail the addition of (1) explicit selective-solvent particles and (2) homopolymerof a length equal to 80% that of the diblock copolymer chains. Approximate phase boundaries were found viafree-energy calculations, and great care was taken to enact the commensurability of system size with the unit-celldimensions of distinct candidate phases. A very contrasting phase behavior is observed upon increasing the amountof the A-component additive in the two different strategies. With the first strategy (i.e., addition of solvent particles)we observed the progression gyroid perforated lamella lamella reversed gyroid, including a long-livedmetastable orthorhombic cocontinuous phase known as O⁵². With the second strategy (i.e., addition ofhomopolymer) we observed the progression of morphologies gyroid double diamond plumber's nightmare.In the latter two bicontinuous phases, the homopolymer concentrates preferentially in the nodes not only to reducethe nodal packing frustration but also to enhance the homopolymer's conformational entropy. At high homopolymervolume fractions, a novel morphology was observed, wherein cylinders of two different diameters alternate in atetragonal (square) packing; however, it remains unclear whether this "alternating diameter cylinder" phase isjust a long-lived metastable or a truly stable phase at some of the conditions examined. The dissimilarity in theresulting phase behavior for the two strategies considered is rationalized in terms of the difference in the degreeof penetration of the two additives into the diblock copolymer layer, which is a direct consequence of the disparityin translational entropy exhibited by the homopolymers and by the solvent particles.