Effect of confinement on phase-separation processes in a polymer blend observed by laser scanning confocal microscopy

Structure self-assembling in the late stage spinodal decomposition of a polymer blend at its critical composition has been explored by laser-scanning confocal microscopy with particular emphasis on the effects of confinement (dimensionality) and preferential wetting of solid surface by one of the constituent polymers. A mixture of deuterated polybutadiene and polybutadiene (PB) with relatively narrow thickness [Formula presented] was observed in three dimensions over the entire thickness. Formation of a wetting layer was clearly observed near the glass surface, while a bicontinuous structure evolved in the middle of the specimen. Global as well as local features of the phase-separating structures were quantified by several structural parameters, e.g., characteristic length [Formula presented] structure factor [Formula presented] interfacial area per unit volume [Formula presented] probability densities of interfacial curvatures [Formula presented] etc. [Formula presented] is a phase-separation time). From the time evolution of these structural parameters, a deviation from the self-similar growth of a bicontinuous structure was found to occur at a transition time, [Formula presented] at which a scaled thickness, [Formula presented] approached unity. The breakdown of the self-similar growth was most sensitively observed by the local characteristics, i.e., [Formula presented] and [Formula presented] On the other hand, the global characteristic, [Formula presented] did not provide useful insight into the effects of dimensionality. It turned out that the bicontinuous structure, initially growing with dynamical self-similarity, eventually transformed into a “columnlike” structure (at [Formula presented] in which cylindrical PB-rich domains bridge the upper and lower PB wetting layers.