Interfaces in immiscible polymer blends: A Monte Carlo simulation approach on the CRAY T3E

Abstract

Polymeric materials pose a challenge for Monte Carlo simulations because of the widely spread length and time scales involved. Using large scale computer simulations we investigate the interfacial structure in a partially compatible polymer mixture. The problem is studied in the framework of a coarse grained lattice model - the bond fluctuation model on the simple cubic lattice, choosing N = 32 and lattice linear dimensions L × L × D up to 512 × 512 × 64. We employ a two dimensional geometric decomposition scheme to implement this algorithm on the CRAY T3E. The algorithm scales very well with the number of processors. The structure of polymer coils near interfaces between coexisting phases of symmetrical polymer mixtures (AB) is discussed, as well as the structure of symmetric diblock copolymers of the same chain length N adsorbed at the interface. Distribution functions for monomers at the chain ends, in the center of the copolymer chain, and in the center of the individual blocks are obtained. These are compared to the predictions of the self consistent field theory. For low copolymer concentration (“mushroom regime”) the copolymer extends its blocks into the appropriate bulk phases; individual blocks are only mildly perturbed (“dumb-bell”-like). At higher copolymer concentration, the copolymer displaces the homopolymer from the interface (“dry brush”).