Nanostructures Inside Colloidal Particles of Block Copolymer/Homopolymer Blends

Colloidal spheres with unique internal morphologies were prepared by blending symmetrical poly(styrene)- block -poly(butadiene) (PS- b -PB) and polystyrene homopolymer ( h PS) in emulsion droplets and carrying out subsequent solvent evaporation. We found various unprecedented microphases in these spherically confining geometries that depend on the ratio ( r ) of the molecular weight of h PS relative to that of the PS block of PS- b -PB and the ratio of the diameter ( D ) of the emulsion drop to the feature spacing ( L 0 ) of the phase-separated periodic domains. In particular, the effect of spherical confining geometry was pronounced for D / L 0 < 15, in which directionally oriented structures such as helices and hoops were observed. For r < 1, the PB domains exhibit transitions between morphological microphases of lamellae, perforated lamellae, cylinders, and spheres, in that order, as the weight fraction of h PS (φ) is increased. The lamellae or perforated lamellae are ordered in concentric shells. Interestingly, cylindrical domains of PB blocks consisting of circular helices or stacked hoops were observed for 0.38 ≤ φ ≤ 0.54, in which the particle shape is slightly deformed from spherical to accommodate the ordered regular packing of the hoops and helices. For r ∼ 2, concentric spherical lamellae are produced for φ up to 0.30, above which macrophase separation occurs and the spherical lamellae are either nonconcentric or deformed into a domelike structure. For r ∼ 4, an onion-like structure is present for the entire range of φ, with a lamellar spacing that is nearly independent of φ due to macrophase separation. In particular, for r ∼ 1, spherical lamellar morphology is present up to φ = 0.30, and complex anomalous structures such as multiply jointed hoops are present for φ ≥ 0.32 because of the combined effects of micro- and macrophase separations.