Microphase Separation of Star-diblock Copolymer Films: a Dissipative Particle Dynamics Simulation

Abstract

The microphase-separating behaviors of two types of star-diblock copolymers (Ax)4(By)4 and (AxBy)4 in thin films are studied using the simulation technique of dissipative particle dynamics. A variety of ordered mesostructures have been observed and the simulated phase diagrams show obvious symmetries for the (Ax)4(By)4 films and asymmetries for the (AxBy)4 films, besides, it is easier for the (Ax)4(By)4 than for the (AxBy)4 to carry out microphase separation under the same conditions, which has been recognized in bulk and can be ascribed to the structural difference between the two types of star copolymers. There are some correspondences between the mesostructures formed in the film and those formed in bulk at the same composition fraction. Decreasing the thickness of film and strengthening the A-B repulsion both help the mesostructures enhance the degree of order. Composition fraction dependences of the mean-square radius of gyration in the two types of star copolymer films are almost contrary, which can be attributed to the differences in their respective structures. These findings can provide a guide to designing novel microstructures involving star-diblock copolymers via geometrical confinement.