We synthesized polystyrene-[polystyrene-b-poly(2-vinylpyridine)] 3 miktoarm star copolymer [PS L -(PS S -b-P2VP) 3 ], where PS L and PS S are long and short PS chains, respectively, by the combination of anionic polymerization, atom transfer radical polymerization (ATRP), and click reaction. We changed the volume fraction of the PS block (f PS ) and the chain asymmetry of the PS chain τ = f PS,L /(f PS,L + f PS,S ). Phase behavior of PS-(PS-b-P2VP) 3 was investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Inverted gyroids consisting of PS chains were formed at f PS = 0.64 and τ = 0.65, while asymmetric lamellae were observed at f PS = 0.81 and τ = 0.79. Because a long PS chain (PS L ) and three short PS S -b-P2VP copolymer chains are linked at a single junction point, a huge configurational entropy penalty was expected, resulting in distorting the original phase boundaries observed for conventional AB diblock copolymer. PS S -b-P2VP chains are mainly located at the interface between PS and P2VP microdomains, whereas PS L chains fill the regions far from the interface, which causes a radial distribution to form interfacial curvature. Interestingly, the phase behavior was greatly affected by τ at a fixed f PS . For instance, at a fixed f PS (0.64), an inverted gyroid structure was formed at τ = 0.65, while a lamellar structure was observed at τ = 0.46. With the decrease in τ (or the difference of molecular weight between PS L and PS S becomes smaller), the interfacial curvature is not expected because all PS S -b-P2VP chains have no need to be arranged in the same direction. The experimental results are consistent with the predictions based on self-consistent field theory (SCFT).

Blending AB/AC diblock copolymers with B/C hydrogen bonding interactions provides a facile way to expand the Aspherical and A-cylindrical phase regions toward large volume fractions. However, it is still challenging for the AB/AC blend to form truly "inverted" A-cylinders and especially "inverted" A-spheres. In this work, we investigate the self-assembly of binary A(AB) 3 /AC blends using self-consistent field theory, focusing on the exploration of truly "inverted" A-cylinders and A-spheres. We found that the A-sphere and A-cylinder regions can be much more deflected to large volume fractions of A-blocks f ( ) A than those of the pure A(AB) 3 miktoarm star copolymer, leading to the formation of truly "inverted" A-cylinders as well as A-spheres. The volume fractions of both A-cylinders and A-spheres can exceed 0.7, causing severe deformations. Severely deformed A-cylinders and A-spheres even become partially connected to perforate the B-matrix. The main mechanism of amplifying the effect of spontaneous curvature is that the short A-block of AC diblock helps optimize the radial distribution of A-blocks within the curvature, further relieving the packing frustration. The effect of the adding short AC diblocks sensitively depends on the intrinsic spontaneous curvature of the A(AB) 3 copolymer. In addition, a number of intriguing novel phases are predicted, such as the double-diamond and Plumber's nightmare network phases. Our work not only deepens the understanding of the self-assembly of binary blends, but also provides a feasible way for the fabrication of truly "inverted" cylinders and spheres that may have promising applications.

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.