Dynamics at a Buried Polymer Interface

We present a further development of X-ray Photon Correlation Spectroscopy (XPCS) technique to study polymer interfaces. We have probed capillary wave dynamics not just at a free surface, but also at buried polymer/polymer interface within a bilayer film. The bilayer was chosen so that the critical angle of the top layer is smaller than that of the bottom layer. When X-rays are incident below the critical angle of the top layer, only the structure and dynamics of the top surface are probed. When X-rays are incident above the critical angle of the top layer but below that of the bottom layer, a standing wave is set up. The phase of this standing wave can be adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. Consequently, one can isolate for the first time the static and dynamic scattering from a single buried layer. Results on a system consisting of a 100nm polystyrene film on top of an 100nm poly(4-bromo styrene) film, supported on a Si substrate will be discussed.