(747f) Fluctuations/Correlations in Disordered Symmetric Diblock Copolymers: Direct Comparisons between Simulations and Theories

While the polymer self-consistent field theory has gained great success in describing various inhomogeneous polymeric systems, particularly the self-assembled morphologies of block copolymers, for spatially homogeneous systems it reduces to the Flory-Huggins theory and gives the simplest, yet often qualitatively incorrect, predictions. We therefore directly compare, without any parameter-fitting, the thermodynamic and structural properties of the disordered phase of symmetric diblock copolymers obtained from fast off-lattice Monte Carlo (FOMC) simulations [Q. Wang and Y. Yin, J. Chem. Phys. 130, 104903 (2009)], reference interaction site model (RISM) and polymer reference interaction site model (PRISM) theories, and Gaussian-fluctuation theory for the same model system of discrete Gaussian chains interacting with soft, finite-range repulsions as commonly used in the dissipative particle dynamics simulations. The compared quantities include the internal energy, entropy, Helmholtz free energy, pressure, constant-volume heat capacity, chain/block dimensions, and various structure factors in the system. Our comparisons unambiguously and quantitatively reveal the consequences of various theoretical approximations and the validity of these theories in describing the fluctuations/correlations in disordered diblock copolymers.