Interaction of opposing layers in lamellar superstructures of block copolymers

The interaction of opposing brushes in bilayers is studied by numerically solving the self-consistent field theory equations. It was shown that the main entropy effect is due to elimination of the restrictions imposed on local conformations of chains on the surface. The effect depends on the density of brushes, which determines the number of surface segments. The interpenetration region of brushes is symmetric both for symmetric layers consisting of similar brushes and for asymmetric bilayers comprised of brushes differing in the chain length or the grafting density of chemically equivalent polymer chains. The contribution to the free energy associated with the depth of interpenetration of brushes is rather small. The asymmetry of bilayers due to the difference in the chain lengths makes the interaction unfavorable, whereas the asymmetry due to the difference in the grafting density makes the interaction favorable. In the latter case, the effect is due to the additional effective asymmetry of a layer as a whole, which is induced by the contact of brushes.