WEAKLY SEGREGATED BLOCK-COPOLYMERS - ANISOTROPIC FLUCTUATIONS AND KINETICS OF ORDER-ORDER AND ORDER-DISORDER TRANSITIONS

We discuss the kinetics of order-order and order-disorder transitions in weakly segregated diblock copolymers. A theory is developed based o n the anisotropic fluctuations in the ordered phases. These fluctuatio ns play two crucial roles: first, they determine the stability limit o f the initial structure and, second, they are responsible for the emer gence of new structures, whether these are the final equilibrium state s or transient states during the transition. A linear stability analys is allows us to identify the largest fluctuation modes under both equi librium and nonequilibrium conditions. By combining the order paramete r of the initial structure with the largest fluctuation modes into a s implified multimode model we are able to describe qualitatively the fu ll nonlinear evolution of the system after sudden temperature jumps be yond the spinodal of the initial phase. Our theory successfully explai ns our earlier results from direct Cahn-Hilliard-type numerical simula tions. Our predicted kinetic scenarios are in accord with available ex periments. (C) 1998 Elsevier Science Ltd. All rights reserved.