SIMULATION OF 1ST-ORDER AND 2ND-ORDER TRANSITIONS IN ASYMMETRIC POLYMER MIXTURES

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 lambda = epsilon(AA)/epsilon(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 DELTAmu(c) unmixing occurs;below a critical temperature T(c). It is found that DELTAmu(c). is proportional to the asymmetry (1 -lambda) and that the quantity 4k(B)T(c)/(3 + lambda)epsilon is independent of the asymmetry, consistent with the prediction of the Flory theory.