Single-chain conformations in symmetric binary polymer blends:: Quantitative comparison between self-consistent field calculations and Monte Carlo simulations

Single-chain properties in a symmetric binary polymer blend are studied by self-consistent field calculations and Monte Carlo simulations. Within the self-consistent field scheme, the statistical mechanics of a cluster of neighboring polymers is solved. Interactions among the polymers of a cluster and composition fluctuations within a cluster are incorporated exactly, a mean field approximation is invoked for intercluster interactions and long-range fluctuations. The results are compared to large scale Monte Carlo simulations for a broad range of chain lengths. While we find nearly quantitative agreement for single chain properties-e.g., the reduction of the chain dimensions of the minority component-only qualitative agreement is achieved for thermodynamic quantities-e.g., the critical temperature. The temperature and composition dependence of the chain conformations are attributed to a balance between the entropy loss upon contraction and the exchange of intermolecular and intramolecular contacts. The calculations suggest that the relative reduction of the spatial extension of the minority chains depends on the parameter chi root N for not too large incompatibilities chi. The scaling limit is, however, approached only for very long chain lengths N.