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Self-assembly via a complex phase transition in mixtures of polystyrene-block -polybutadiene block copolymer and poly(methyl vinyl ether)
Authors:Takeji Hashimoto  Tatsuo Izumitani  Katsuaki Oono
Abstract:The self-assembly of a binary mixture of polystyreneblock-polybutadiene (SB) and poly(methyl vinyl ether) (PVME) was studied by transmission electron microscopy and time-resolved light scattering. The self-assembly studied involved first microphase separation, in which a microdomain structure composed of polybutadiene block chains (PB) was formed in a matrix composed of polystyrene block chains (PS) and PVME homopolymers, and subsequently macrophase separation of the PVME from the microdomain phase of SB. The microphase separation was induced in a film preparation process using a solution cast method at room temperature. The macrophase separation was induced by rapidly heating the film specimens to above a critical temperature where PVME and PS undergo spinodal decomposition (SD). This complex phase transition, involving microphase separation followed by macrophase separation, was found to generate a superlattice structure (or a modulated structure) with two characteristic spacings: Amacro associated with the SD and Amicro associated with the microphase separation, both being generally time-dependent. The growth of the “macrodomains” was found to be pinned at Amacro ? 840 nm due to the elastic effect of the microdomain structure. The microdomain structure with Amicro ? 57 nm was found to undergo a morphological transition (a transition between two ordered phases of block copolymers) as a consequence of the local composition change of the two polymers induced by the SD.
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