We compute phase diagrams for diblock copolymers in the mean-field weak-segregation regime as a function of the fraction f of A-monomers and the repulsive interaction χN. We include the ordered bicontinuous double-diamond (OBDD) phase [space group Pn3m] and the gyroid phase [space group Ia3d] as well as lamellae, hexagonal cylinders, and BCC spheres. We find a stable region of gyroid phase between cylinders and lamellae just above the mean-field critical point, in agreement with numerical mean-field calculations. The stability of gyroid depends on the presence of the next higher  reflections in addition to the  fundamental. The gyroid free energy is favored by terms of the form ψ3ψ and ψ2ψ; the analogous terms are not permitted for OBDD.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal de Physique I|
|State||Published - Dec 1 1997|
All Science Journal Classification (ASJC) codes
- Statistical and Nonlinear Physics