FLUCTUATION EFFECTS IN THE DENSITY-FUNCTIONAL THEORY OF ORDER-DISORDER TRANSITIONS IN BLOCK-COPOLYMERS

The determination of the phase diagram of diblock copolymer is of tremendous current interest. Many procedures have been presented which account for different essential features of the problem. In general, there are two kinds of fluctuations to account for. The recent density functional theory of Melenkevitz, Lescanec, and Muthukumar ignored composition fluctuations. By making the local approximation for T3 and T4 as in Ohta-kawasaki and FRH but including full chain fluctuations in T2, they found crossover between the weak and strong segregation limits with a well-pronounced intermediate regime. These calculations are extended in this paper to include composition fluctuations following the random-phase approximation of Brazovskii.