Surface ordering phenomena in block copolymer melts.

A mean field theory is presented for the description of surface ordering phenomena in diblock copolymers near the microphase separation transition (MST). We consider a near-symmetric diblock melt in the vicinity of a solid wall or free surface, such as a film-air interface. The surface is allowed to modify the Flory interaction parameter and the chemical potential in the adjacent copolymer layer. The composition profile normal to the surface is investigated both above and below the MST. In contrast to the surface critical behavior of binary fluids, we find interesting oscillatory profiles in copolymers that arise from the connectivity of the blocks. These composition profiles might be amenable to study by ellipsometry, evanescent wave-induced fluorescence, or by scattering techniques. Wetting and other surface phenomena and transitions in block copolymers are briefly discussed.