Strong-segregation theory of bicontinuous phases in block copolymers

Abstract
We compute phase diagrams for diblock copolymers in the strong-segregation regime as a function of volume fraction φ. We include the ordered bicontinuous double-diamond (OBDD) phase, which is found to be stable between cylinders and lamellae, consistent with experiment, for φ (or 1-φ) between 0.19 and 0.27. Our phase diagram relies on taking into account the hexagonal shape of the unit cell for the cylindrical phase, and the unique geometry of the OBDD phase.