Simulating network phase formation in diblock bottlebrush copolymers

Block polymers are a powerful system to create self-assembled, interpenetrating network phases with potential applications in separations and photonics. Double gyroid (DG) is the most common network phase, consisting of two enantiomeric networks with three-fold connectors. In linear diblock copolymers, both experiments and self-consistent field theory indicate that DG appears between the cylinder and lamellar phases. In contrast, for diblock bottlebrush copolymers, SCFT predicts minimal changes to the phase behavior while experiments show an extinction of the DG phase window. This disagreement is attributed to SCFT’s inability to account for backbone crowding. To go beyond the mean-field limit of SCFT, we will present dissipative particle dynamics simulation data for A- and B-side chains grafted to a C-backbone, where the stiffness of each moiety is controlled via three separate bending potentials. The DG window shrinks as the side chains become longer, and DG is supplanted at times by perforated lamellae. Surprisingly, the simulations produce a stability window of single diamond for stiff backbones. Further allowing the stiffness of the backbone to vary with the graft identity significantly enlarges the single diamond window.