J. Phys. I France
Volume 5, Numéro 3, March 1995
Page(s) 365 - 377
DOI: 10.1051/jp1:1995131
J. Phys. I France 5 (1995) 365-377

Fluctuation Theory of Random Copolymers

Andrey V. Dobrynin1 and Igor Ya. Erukhimovich2

1  Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627-0011, U.S.A.
2  Department of Physics, Moscow State University, Moscow 117234, Russia

(Received 28 April 1994, revised 30 August 1994, accepted 23 November 1994)

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.

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