Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion-like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder-order phase transition and order-order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.

Transmission electron microtomography (TEMT) has proven to be useful for investigating three-dimensional (3D) nanostructures in polymeric systems. However, the conventional TEMT that uses a tilt series around an axis occasionally fails to reconstruct nanostructures, especially when the nanostructure is highly anisotropic. Namely, if a certain geometrical relationship between orientation of the nanostructure and the tilt axis is fulfilled, the nanostructure does not appear in the 3D reconstruction. This problem can be solved by tilting the specimen around two (orthogonal) tilt axes and combining the resulting two 3D reconstructions after precise alignment between them. The strategy, called "dual-axis tomography", is used to observe one of the commonly observed anisotropic polymer nanostructures, cylindrical morphology, of poly(styrene-block-isoprene) block copolymer. It was experimentally observed that the cylindrical nanodomains that were "missing" in one of the two tomograms were complementary reconstructed in the other tomogram obtained from the tilt series using the orthogonal tilt axis to the first data set. Subsequently, the two 3D reconstructions were combined to generate a new 3D reconstruction, in which the cylinders at any orientation were successfully imaged with improved image quality. Although the single-axis tomography gave always lower volume fraction of the cylindrical microdomains than the predicted one calculated on the basis of known molecular composition, an excellent agreement was obtained between the two in the dual-axis tomography. In addition, 3D images taken by the TEMT were shown to be quite effective to determine the nanostructure, i.e., cylindrical structure, which otherwise could be assigned to be lamellar nanostructure by other (surface) observation technique such as AFM or SEM.

The control of microphase-separated structures in a poly(styrene-block-butadiene-block-methyl methacrylate) (SBM) was investigated in three dimensions by transmission electron microtomography. Neat SBM self-assembled into a double-helical structure of polybutadiene (PB) domains around hexagonally packed core polystyrene (PS) cylinders in a poly(methyl methacrylate) matrix. When PS homopolymer with a lower molecular weight than that of the PS block in SBM was added to the SBM, the PB domains transformed from double-helical structures to spherical domains, while maintaining the helical trajectories. In contrast, adding a higher molecular weight PS to the SBM changed the helical structures from double- to triple-stranded structures and even to four-stranded structures. The helical structures of the PB domains were strongly affected by the distribution of the blended polystyrenes in the core cylindrical PS domains.

The effect of confinement on microphase-separated structures of a diblock copolymer is investigated in nanoparticles serving as a three-dimensional (3D) confinement system. We succeeded in preparing nanoparticles having various types of complex structures from hydrophobic diblock copolymers by a simple solvent evaporation method. The detailed 3D structural analysis of the nanoparticles by transmission electron microtomography (TEMT) revealed that complex structures were found only to form in the nanoparticle surface region, the thickness of which corresponded to the single-molecule length of the block copolymer in the bulk state. These results indicate that 3D confinement fundamentally affects block copolymer self-assemblies most strongly in the surface region of nanoparticles but only weakly in the central region.