Block copolymers in water or compatible solvents show micelles with various shapes, such as worm-like, vesicles, and spheres. In this study, we prepared core–satellite micelles by employing a polystyrene-block-polyisoprene-block-polystyrene-block-polyisoprene (S1I1S2I2) linear tetrablock copolymer. When a PS-compatible solvent, for example, dimethylacetamide or diethylphthalate, is used, the PI chains form the inside core, while the PS chains become a shell as long as the volume fraction of mid PI1 chains (f PI1) is large enough (0.2) to form a loop configuration, resulting in merging into spherical cores consisting of the PI2 chains. However, at smaller f PI1 (0.08), the short mid PI1 chains cannot merge into the PI2 core and therefore exist separately as small spherical micelles, which are referred to as the “satellite” micelles. Thus, the micelles consist of large central core spheres and smaller outside satellite spherical micelles.
Stacked split-ring resonators (SSRR) arrays exhibiting polarization-sensitive dichroic responses in both visible and near-infrared wavelengths are realized over a centimeter-scale large area. The SSRR arrays are derived from pagoda-like nanorods fabricated from the self-assembly of a lamellae-forming polystyrene-b-poly (methyl methacrylate) copolymer (PS-b-PMMA) confined in cylindrical pores of anodized aluminum oxide (AAO) template. Along the nanorod direction, PS and PMMA nanodomains were alternately stacked with the same distance. Silver crescents and semi-hemispherical covers, which are essential for SSRR with the polarization sensitivity, were obliquely deposited on the single side of the nanorod after removing the AAO template and reactive-ion etching treatment. These sophisticated nanoscale architectures made by bottom-up fabrication can be applied to structural color, optical anti-counterfeiting, and commercial optical components in a large area.
Among many possible nanostructures in block copolymer self-assembly, helical nanostructures are particularly important because of potential applications for heterogeneous catalysts and plasmonic materials. In this work, we investigated, via small-angle X-ray scattering and transmission electron microscopy, the morphology of a polystyrene-blockpolyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (S 1 IS 2 V) tetrablock terpolymer. Very interestingly, when the volume fraction of each block was 0.685, 0.125, 0.060, and 0.130, respectively, a multidomain double-stranded helical nanostructure (MH 2 ) was formed: P2VP chains became a core helix, and PI chains formed double-stranded helices surrounding the core helix. Core and double-stranded helices are connected by short PS 2 chains, and PS 1 chains become the matrix. The experimentally observed morphology is in good agreement with the prediction by self-consistent field theory. We believe that this multidomain helical structure will be pave the way to the creation of multifunctional helical structures for various applications such as metamaterials.
Block copolymers (BCPs) have attracted significant interest due to their ability to form various nanostructures, including lamellae, cylinders, gyroids, and spheres. But these nanostructures are only observed for limited range of the volume fraction of one block. Namely, lamellar microdomains are observed for symmetric volume fraction, whereas spherical microdomains are found for highly asymmetric volume fraction. To increase the potential applications of these nanostructures for next‐generation lithography, advanced optical materials, and high‐performance membranes, one should have these nanostructures beyond the limitation of the volume fraction. During the past decades, many directions, such as blends of two BCPs, design of complex chain architecture of BCP and introduction of favorable interactions between block components, have been suggested to greatly change the phase boundaries of conventional nanostructures. In this review, we focus on unconventional nanostructures, such as highly asymmetric lamellae, inverted cylinders and gyroids, and spherical microdomains at nearly symmetric volume fraction.
Hexagonally packed (HEX) cylindrical microdomains can be obtained through the self-assembly of block copolymers (BCPs) with a moderately asymmetric volume fraction of one block (f), resulting in the formation of minor cylinders. However, for next-generation lithography and high-density memory devices, it is desirable to obtain densely and tetragonally packed inverted cylindrical microdomains, which are composed of the major block in the minor matrix. The inverted cylinders differ from conventional HEX cylinders, which consist of the minor block in the matrix of the major block. In this study, we achieved this objective by utilizing a binary blend of a polystyrene-b-poly(4-vinylpyridine) copolymer (S4VP) and polystyrene-b-poly(4-hydroxystyrene) copolymer (SHS), where the P4VP block exhibited a strong hydrogen bonding interaction with the PHS block. By carefully controlling the molecular weight ratio of S4VP and SHS as well as the blend composition, we successfully observed tetragonally packed inverted PS cylinders with a square cross-section at a volume fraction of PS of 0.69.
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