Rich Variety of Three-Dimensional Nanostructures Enabled by Geometrically Constraining Star-like Block Copolymers

The influence of star-like architecture on phase behavior of star -like block copolymer under cylindrical confinement differs largely from the bulk (i.e., nonconfinement). A set of intriguing self-assembled morphologies and the corresponding phase diagrams of star-like (AB)(f) diblock copolymers with different numbers of arms f (i.e., f = 3, 9, 15, and 21) in four scenarios (phi(A) = 0.3 and V-0 > 0; phi(A) = 0.3 and V-0 < 0; phi(A) = 0.7 and V-0 > 0; and phi(A), = 0.7 and V-0 < 0 (where phi(A) is the volume fraction of A block) and V-0 < 0 and V-0 > 0 represent that the pore wall of cylindrical confinement prefers the inner A block (i.e., A-preferential) and B block (i.e., B-preferential), respectively) were for the first time scrutinized by employing the pseudospectral method of self-consistent mean -field theory. Surprisingly, a new nanoscopic phase, that is, perforated-lamellae-on-cylinder (denoted PC), was observed in star -like (AB), diblock copolymer at ik = 0.3 and V-0 > 0. With a further increase in f, a single lamellae (denoted L1) was found to possess a larger phase region. Under the confinement of A -preferential wall (i.e., V-0 < 0) at phi(A) = 0.3, PC phase became metastable and its free energy increased as f increased. Quite intriguingly, when phi(A) = 0.7 and V0 > 0, where an inverted cylinder was formed in bulk, the PC phase became stable, and its free energy decreased as f increased, suggesting the propensity to form PC phase under this condition. Moreover, in stark contrast to the phase transition of C-1 L-1 -> PC (C-1, a single cylindrical microdmain) at OA = 0.3 and 170 > 0, when subjected to the A-preferential wall (phi(A) = 0.7), a different phase transition sequence (i.e., C-1 -> PC -> L1) was identified due to the formation of a double-layer structure. On the basis of our calculations, the influence of star-like architecture on (AB)/ diblock copolymer under the imposed cylindrical confinement, particularly the shift of the phase boundaries as a function off was thoroughly understood. These self-assembled nanostructures may hold the promise for applications as lithographic templates for nanowires, photonic crystals, and nanotechnology.