Monte Carlo simulation of a homopolymer-copolymer mixture interacting with a surface:: Bulk versus surface micelles and brush formation

Using Monte Carlo simulations of the bond fluctuation model, we study the formation of micelles in a confined mixture of asymmetric AB-diblock copolymers and homopolymers. The composition of the sphere-forming AB-diblock copolymers is f(A) = 1/8. The mixture is confined into a thin film. The film surfaces attract the minority component of the diblock with strength, epsilon(W). To efficiently sample the micelle size distribution and establish equilibrium between the surface and the bulk, we work in the semigrandcanonical ensemble, i.e. at fixed density and fixed chemical potential difference between the two types of chains, choosing a large incompatibility chi N similar or equal to 100 (strong segregation regime). The composition of the mixture is controlled by the chemical potential difference, delta mu = mu(cop) - mu(hom), between copolymers and homopolymers. We,study the morphology as a function of the surface interaction, epsilon(W), and the chemical potential, delta mu. Only in a limited regime of parameters-i.e., in the vicinity of the adsorption transition of the minority component at the surface and slightly below the critical micelle concentration in the bulk-surface micelles are formed. We characterize the shape of the adsorbed micelles by the tensor of gyration and radial density profiles.