COLLECTIVE AND SINGLE-CHAIN CORRELATIONS NEAR THE BLOCK COPOLYMER ORDER-DISORDER TRANSITION

The concentration pair correlation function and the order-disorder transition in a diblock copolymer melt are studied in the framework of a self-consistent one-loop approximation. In contrast with earlier work, no simplifying assumption on the wave vector dependence of the correlation functions is made. This allows us to calculate the shift in the peak of the fluctuation spectrum recently observed in neutron scattering experiments. Quantitative agreement with experimental results is found. We also present a new calculation of how the collective concentration fluctuations influence single chain statistics in the copolymer melt. It is shown that even in the disordered phase, strong deviations from Gaussian statistics can be expected for finite molecular weights. A local segregation between monomers of the two different blocks results in an increase in the copolymer radius of gyration.