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RESEARCH PRODUCT

Chain Conformations and Phase Behavior in Confined Polymer Blends

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We investigate the chain conformations and phase separation in binary polymer blends. Using large scale semi-grandcanonical Monte Carlo simulations and finite size scaling, we investigate the molecular extension and the intermolecular paircorrelation function in thin films with hard, non-preferentially adsorbing surfaces. The interplay between chain conformations, demixing and the validity of mean field theory is investigated for a large variation of chain lengths 16 ≤ N ≤ 512. Three regimes of film thickness D can be distinguished: (i) For film thicknesses much larger than the unperturbed chain extension R e, bulk behavior is observed, i.e., the critical temperature of demixing T c increases linearly with chain length, and the mean field theory becomes asymptotically correct for large N. (ii) For D ∼ R e, the critical temperature scales linearly, T c ∼ N, but the mean field theory overestimates the prefactor even in the limit N → ∞ (iii) For ultrathin films, the chain conformations are quasi-two-dimensional, T c ∼ √N and mean field theory completely fails.