Surface-directed spinodal decomposition

The spinodal decomposition of mixtures of poly(ethylenepropylene) (PEP) and perdeuterated poly-(ethylenepropylene) has been studied near the surface using forward-recoil spectrometry. Instead of the composition waves with randomly oriented wave vectors (and random phases) found in the bulk, we observe composition waves with wave vectors normal to, and which propagate inwards from, the surface, maintaining coherence for several wavelengths. We argue that these surface-directed spinodal decomposition waves are caused by the preferential attraction of the d-PEP to the surface.