Complex self-assembled lattices from simple polymer blends

Abstract

Block copolymers having two or more polymer chains linked covalently have been extensively studied for various nanostructure fabrications. Highly symmetric body-centered cubic (bcc) packing lattice has been the only observed supramolecular spherical phase in compositionally asymmetric AB diblock copolymers for a long time. After 2010, the Frank−Kasper (F-K) σ (1) and A15 (2) phases featured by small volume asymmetry among constitutional supramolecular motifs have been discovered in some block copolymers, although with elaborately designed block conformation asymmetry or architectures. In PNAS, Cheong et al. (3) utilize the self-consistent field theory (SCFT) to demonstrate that thermodynamically stable F-K Laves phases with intrinsically large volume asymmetry can be realized by simply blending diblock copolymers with minority-block homopolymer in dry-brush mode. This rather convenient strategy potentially provides common block copolymer systems the access to those complex condensed phases with large volume asymmetry and upper length scale. F-K phases in soft matter are a family of complex spherical phases sharing similar lattice structures with some metallic alloys. They are tetragonally close-packed structures, with spherical motifs deformed into polyhedra to accommodate the lattice symmetry and maintain constant density. These polyhedra are combinations of coordination number 12 (CN12) polyhedron, CN14 polyhedron, CN15 polyhedron, or CN16 polyhedron (4). Discovery of F-K phases in soft matter can be traced back to the 1990s, and their observation in various soft matter systems and the deeper understanding of them has accelerated in recent years. So far, F-K phases have been identified in four main categories of soft matter, including small molecular surfactants (5, 6), dendrimers (7, 8), block copolymers (1, 2, 9), and giant amphiphiles (10⇓–12). A distinct feature of F-K phases in soft matter is that the constructing polyhedra are assembled from multiple, identical molecular constituents. These polyhedral, scaling from several to … [↵][1]1To whom correspondence may be addressed. Email: scheng{at}uakron.edu or huangmj25{at}scut.edu.cn. [1]: #xref-corresp-1-1