Simulation of first‐ and second‐order transitions in asymmetric polymer mixtures

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Abstract
The critical properties of dense asymmetric binary polymer mixtures are studied by grand canonical simulations within the framework of the 3‐dimensional bond fluctuation lattice model. The monomers interact with each other via a potential ranging over the entire first peak of the pair distribution. An asymmetry is realized by giving the ratio of interactions λ = ∈AA/∈BB between monomers of the A‐species and of the B‐species a value different from 1. Using multiple histogram extrapolation techniques for the data analysis, the two phase region, which is a line of first‐order transitions driven by the chemical potential difference, and the critical point are determined for a mixture of chains with 32 monomers each. At a critical potential difference Δμc unmixing occurs below a critical temperature Tc. It is found that Δμc is proportional to the asymmetry (1 ‐ λ) and that the quantity 4kBTc/(3 + λ)∈ is independent of the asymmetry, consistent with the prediction of the Flory theory.