Phase separation in a grafted polymer layer

We examine equilibrium phase separation in a grafted polymer layer composed of mutually immiscible chains. Under symmetric melt conditions, we predict that there is a transition to a ``rippled'' phase--a density wave in composition running along the surface. This transition is expected for a molecular weight 2.27 times that for the same species in a simple blend at its demixing threshold. The ripple wavelength is 1.97 times the chain rms end-to-end distance. The lateral rippling is accompanied by a composition oscillation with depth.