Equilibrium properties of a diblock copolymer lamellar phase confined between flat plates

We study theoretically the equilibrium behavior of the lamellar phase of an A-B diblock copolymer melt. Each lamellar layer is an A-B,B-A repeat unit and n such layers are confined between, and parallel to, two identical flat plates. We find that the configurations with a half-odd-integer number of layers occur only when the difference between the two polymer-plate surface tensions is small, and then only below some critical plate separation. We calculate the discontinuity in the pressure at the transition point between two different values of n.