화학공학소재연구정보센터
Macromolecules, Vol.53, No.20, 9131-9141, 2020
Impact of Thin-Film Confinement on the Packing of Low-Coordinate Spheres in Bulk
The self-assembly of a purposely designed AB-type multiblock copolymer melt under the confinement of thin film with two identical surfaces attractive to minority A-blocks is investigated using self-consistent field theory. This copolymer can form some nonclassical spherical phases of low coordination numbers (CNs) in the bulk, e.g., simple cubic (SC), cubic diamond (DSC) and irregularly layered hexagonal-packing (iHP), due to the synergistic effect of stretched bridging block and released packing frustration. With the bulk SC phase, an interesting transition sequence of the packing of spheres in thin film is predicted with increasing film thickness, which consists of alternating hexagonal and tetragonal morphologies. Most of the multilayer hexagonal and tetragonal morphologies are composed of normally aligned but not shifted layers. This reentrant transition sequence is in striking contrast to the single transition from hexagonal to orthorhombic morphologies observed with the bulk body-centered cubic (BCC) phase. As the coordination number (CN) is an important characteristic of spherical morphology, we rationalize the transition mechanism between different morphologies in terms of CN. Our results reveal that these transitions are governed by the change of CN with the film thickness, whereas the CN of each sphere is contributed by its in-plane and out-plane neighbors. In addition, we find that the multilayer hexagonal morphologies with shifted arrangements start to form as the bulk phase transfers to higher-CN phase, while new spherical morphologies composed of graphene-like spherical layers are formed for the bulk DSC phase. It necessary to stress that the monolayer tetragonal lattice of spheres predicted in this work exhibits promising applications in the semiconductor industry.