STABILITY OF ORDERED PHASES IN WEAKLY SEGREGATED DIBLOCK COPOLYMER SYSTEMS

Stability of ordered phases in diblock copolymer melts is studied usin g a theory of anisotropic fluctuations, which bears a useful similarit y with energy band theory in solids. We calculated stability lines of all ordered phases and found the hexagonally perforated lamellar phase to be unstable around the lamellar-cylindrical (LC) phase boundaries. We used fluctuation analysis to obtain dynamical pathways between ord ered phases and argue that the observed modulated layered states along LC boundary regions are due to infinitely degenerate fluctuation mode s of the lamellar phase.