Microstructures Of Diblock Copolymers Under Confinements

Microstructures of diblock copolymers play important roles in the applications including the microstructure fabrications, drug deliveries and photonic crystals. The microstructures and corresponding transitions of diblock copolymers under cylindrical and spherical confinement are studied using the self-consistent field theory (SCFT), which focus on the phase behaviors of block copolymers influenced by the volume fraction, segregation degree, confinement degree and the surface fields.For the cylindrical confinement, microphase structures and the corresponding behaviors of diblock copolymers are studied in the two-dimensional space. And to begin with, the effects of volume fraction and segregation degree acting on the phase behaviors of diblock copolymers are studied. According to the new phase diagram, the phase boundaries are almost similar to those in the bulk one, but the corresponding phase structures are quite different from those in bulk, appearing new microstructures inaccessible in bulk. Then, the effect of the confinement degrees and surface fields acting on the phase behaviors of the copolymers are investigated, and observed the numbers of the layers and the outmost layers for the assembled structures are different in different sizes of cylinders. The assembled microstructures are also different for the various surface fields. For the surface field preferring to the short-blocks, most of the structures are similar as those under neutral cylinders. However, the microstructures of diblock copolymers are strongly influenced by the surface fields preferring to long-blocks. Especially, under a certain degree of confinement and strength of the surface field the copolymers formed square structure which is observed for the first time.For the spherical confinement, the microphase structures and the corresponding behaviors of cylinder-forming diblock copolymers are studied by systematically varying confinement degree and surface fields. First, the self-assembled structures of diblock copolymers in neutral nanospheres are studied with various diameters, and observed that most of the microstructures are core-shell formed, but the number of the shells and the blocks spatial arranged are quite different in different sizes of nanospheres; Then, the diblock copolymers confined in the nanospheres with the surface preferring to the minority blocks are studied, in which the outermost layers of those microstructures are observed to tend to form perforated or perfect spherical surfaces, but inner layers are almost unchanged; At last, the diblock copolymers under surface fields preferring to the majority blocks are studied, where we observed the outermost layer of those morphologies became non-spherical surface, and the inner layers were deformed, even the numbers of the inner layers were changed, at the same time the square and particles structures are observed. The results show that the self-assembled structures of diblock copolymers under confinement are mainly influenced by the bulk periods of the copolymers, the symmetries and sizes of the confined structures as well as the property and strength of surface fields. Therefore, artificially controlling the relevant parameters of confined structures can obtain the expected microstructures, which is helpful to experimentally fabricate the order nanostructures.