STABILITY OF ORDERED PHASES IN DIBLOCK COPOLYMER MELTS

The stability of the diblock copolymer ordered phases is investigated by means of a novel theory of anisotropic composition fluctuations. Th e analogy between a polymer chain in a periodic structure and an elect ron in crystalline solid is exploited in the development of the theory . This theory allows the calculation of the spinodal lines, the most u nstable modes, and the scattering functions of the ordered phases. The one-phase regions of the lamellar, cylindrical, and spherical phases are found to be within their corresponding stability regions. On the o ther hand, the hexagonally-perforated lamellar phase is unstable along the lamellar-cylindrical phase boundary. The most unstable fluctuatio n modes are readily identified and are used to infer the kinetic pathw ays of the order-order phase transitions. We speculate that the experi mentally observed modulated and/or perforated layered states along the lamellar-cylindrical phase boundary are a consequence of the infinite ly degenerate fluctuation modes of the lamellar phase. The scattering functions of all ordered phases are calculated. The stability of the d ouble gyroid phase is also investigated.