Interfacial energy effects on the electric field alignment of symmetric diblock copolymers

The alignment of diblock copolymer microdomains by an electric field depends on the segmental interaction between two blocks and the difference in the interfacial energies of each block with the substrate. Morphologies having mixed orientations are predicted when the difference in the interfacial energies of the two blocks is large. By modifying a surface with random copolymer brushes, interfacial energies were controlled and the influence of interfacial energy on the orientation of the copolymer microdomains by an electric field was examined. Complete alignment of the lamellar microdomains was achieved only when the interfacial, interactions were balanced. In all other cases, lamellae adjacent to the substrate were oriented parallel to the substrate surface, whereas in the center of the sample the lamellae oriented in the direction of the applied field. These results can be ascribed to a pathway-dependent alignment and a high energetic barrier to achieve complete reorientation of the lamellae adjacent to the surface.