Deviations from the mean-field predictions for the phase behaviour of random copolymers melts

¹ Institut für Physik, Johannes Gutenberg Universität - D–55099 Mainz, Germany
² Max Planck Institut für Polymerforschung - D-55021 Mainz, Germany

Received: 8 January 2002
Accepted: 15 March 2002

Abstract

We investigate the phase behaviour of random copolymers melts via large-scale Monte Carlo simulations. We observe macrophase separation into A- and B-rich phases as predicted by the mean-field theory only for systems with a very large correlation λ of blocks along the polymer chains, far away from the Lifshitz point. For smaller values of λ, we find that a locally segregated, disordered microemulsion-like structure gradually forms as the temperature decreases. As we increase the number of blocks in the polymers, the region of macrophase separation further shrinks. The results of our Monte Carlo simulation are in agreement with a Ginzburg criterium, which suggests that the mean-field theory becomes worse as the number of blocks in polymers increases.