A Monte Carlo simulation of asymmetric random copolymers at an immiscible interface

The distribution of a random copolymer P(Af-r-B1-f) at the interface between immiscible A and B phases as a function of the copolymer composition, denoted by the fraction f of A monomers, and as a function of the monomer-monomer interactions, or χ values, has been studied via lattice Monte Carlo simulations. A symmetric distribution of the copolymer was found for compositionally symmetric chains (f = 0.5) when the χ values were independent of the copolymer composition. In contrast, an asymmetric distribution of the copolymer was found for a compositionally asymmetric copolymer (f = 2/3) with composition-independent χ values. It was found that a symmetric distribution of the compositionally asymmetric copolymer can result only when the χ values are allowed to depend upon the copolymer composition. Such a symmetric distribution of a compositionally asymmetric copolymer is in qualitative agreement with miscibility, neutron reflectivity, and adhesion studies of polystyrene/poly(methyl methacrylate) systems.