Phase separation of binary homopolymer and ternary homopolymer-copolymer mixtures through Gibbs ensemble simulations

A Gibbs ensemble algorithm is implemented for mixtures of homopolymers and copolymers in a cubic lattice with coordination number z=26. We consider sy mmetric binary mixtures of homopolymer chains and also study the influence of the presence of symmetric diblock copolymers on these mixtures. All the chain lengths in a given mixture are identical (chains up to 128 units are included). A certain proportion of vacancies is introduced in each simulati on. The phase separation curves are characterized by fitting the coexistenc e data to theoretical expressions. The dependence of the critical temperatu re on chain length, fraction of vacancies and also on the volume fraction o f the copolymer in the mixture has been analyzed. Despite differences betwe en models, the conclusions with this algorithm are similar to those obtaine d from previous simulations performed with techniques in which finite size interfacial effects may be important. Since the computational cost of our a lgorithm is reasonable, the present method can be considered an efficient w ay to study phase separation in different types of polymer mixtures. (C) 20 01 American Institute of Physics.