Morphology and internal structure control of rod–coil copolymer aggregates by mixed selective solvents

Abstract

The molecular packing of rod–coil copolymers, which relates closely to their aggregate morphology, significantly influences their optoelectronic properties. The morphological phase diagram of rod–coil block copolymers in mixed selective solvents and the internal structures of the resulting aggregates are studied by using dissipative particle dynamics. The coil-selective solvent is mixed well with the rod-selective solvent and the effective solvent quality can be tuned by their relative amount. The diverse morphologies and morphological transitions of structural aggregates induced by mixed solvents depend on the mixed solvent composition, rod-block length, and copolymer concentration. Our simulation results show that while the overall morphology of the aggregate is controlled primarily by the rod length and polymer concentration, the domain morphology within the aggregate, as well as the degree of local rod alignment, are primarily controlled by the rod length and solvent quality. Specifically, we observe that spheres, cylinders, perforated sheets, and three-dimensional networks are sequentially formed with increasing rod length or copolymer concentration irrespective of the solvent quality. On the other hand, changing the solvent quality influences the morphology within an aggregate both by determining any preference for the exposed surface of the aggregate, and also because the rod-selective solvent tends to disrupt the orderly packing of the rod blocks. The range of morphologies within the aggregate is even richer, and interesting structures, such as an inverted vesicle, a structural sphere, an inverted cylindrical vesicle, a segmented cylinder, and a segmented network are observed. Unique segmented-like structures exhibiting the most ordered conformation in the rod domains appear when roughly equal amounts of rod- and coil-selective solvents are used.