Effect of Molecular Asymmetry on the Formation of Asymmetric Nanostructures in ABC-Type Block Copolymers

Because domain geometry is dictated by the volume fraction of the block constituting it, an ABC linear triblock copolymer with unequal volume fractions of A and C blocks can form asymmetric ordered morphologies and even hybrid morphologies composed of A and C domains in different geometries. By constructing the triangular phase diagram of ABC triblock with fixed interaction parameters chi N-AB = chi N-BC = chi N-AC using self-consistent field theory, we predict a number of hybrid morphologies, including sphere-lamella, cylinder-lamella, perforated lamella-lamella, and sphere-cylinder. These hybrid morphologies exhibit relatively narrow stable regions as well as simple arrangements of A/C-domains. Furthermore, an interesting class of hybrid morphologies composed of spheres and network is absent, whose absence is mainly caused by the limited regions of sphere-containing hybrid morphologies. Accordingly, we introduce a topological asymmetry by branching BC-blocks at the A/B junction, forming an A(BC)(m) miktoarm star copolymer. In the phase diagram of A(BC)(2) we predict three interesting sphere-network hybrid morphologies in considerable regions, including sphere-diamond (SD), spheres within the double-gyroid networks, and sphere-perforated lamella. A stable SD over a sphere-gyroid is in striking contrast to stable alternating gyroids over alternating diamonds. When m = 2 is increased to m = 3, another new sphere-network morphology, that is, spheres within the double-diamond networks, is predicted in a considerable region. In addition, we find that the stability regions of these interesting sphere-network hybrid morphologies only shift slightly when chi N-AB = chi N-BC = chi N-AC is changed to chi N-AB = chi N-BC << chi N-AC. In brief, our work demonstrates that the combination of compositional asymmetry and topological asymmetry provides an opportunity for the fabrication of novel hybrid morphologies.

Automated summary

By constructing the phase diagram of ABC triblock copolymers using self-consistent field theory, various hybrid morphologies have been predicted. The combination of compositional asymmetry and topological asymmetry provides opportunities for fabricating novel hybrid morphologies.