FLUCTUATION EFFECTS ON MICROPHASE SEPARATION IN RANDOM COPOLYMERS

We study random copolymers consisting of two kinds of monomers with at traction between similar kinds. The mean-field analysis of this system indicates a continuous phase transition into a phase with periodic mi crodomain structure. It is shown,that the inverse of the renormalized propagator has a. minimum at non-zero wave numbers. consequently, ther e is an anomalously large contribution of fluctuations that make the d isordered phase locally stable. However, below a certain temperature, the ordered phase is shown to be locally stable and a weak first-order transition is possible, with qualitative differences from the weak cr ystallization theory developed by Brazovskii. These differences are du e to the peculiar form of the fourth-order vertex of the effective Ham iltonian for the system. We calculated the temperature region for the validity of the mean-field estimates of the amplitude and the scale of microphase separation.