Fluctuation Theory of Random Copolymers

We investigate the behavior of symmetric AB random copolymer melt near the point of microphase separation in the framework of a one-loop (Hartree-Fock) approximation, that exactly solves the problem. We have shown that composition fluctuations result to complete elimination of the microphase separation predicted in the framework a mean-field approximation [1-5]. Using variational techniques the temperature dependence of the density-density correlation function and its length scales are calculated. The diagonal in the replica space correlation function is stable with respect to the off-diagonal perturbation (glass-like order parameter). We discuss the general relation between microphase separation in random copolymers and spinodal decomposition in a mixture of A and B unconnected monomer units below their critical demixing point