Synchrontron X-ray studies of the statics and dynamics of fluctuations at the surfaces of polymer films

Full text: Studies of surface (capillary wave) fluctuations on polymer films using the techniques of x-ray scattering have yielded a number of intriguing results over the last few years and indicate that, unlike the surfaces of simple liquids, the dynamics of polymer surfaces and interfaces need to be understood in greater detail. In particular, issues such as interaction with the substrate, chain entanglement effects, and the approach to the glass transition all affect the dynamics at the surface. We shall review some recent results on polystyrene films of different thicknesses and at different temperatures obtained from studies of off-specular diffuse (static) scattering (which measures the static height-height correlation function) and also using the relatively new technique of X-Ray Photon Correlation Spectroscopy (XPCS) which is the analogue of Dynamical Light Scattering and which measures the dynamical height-height correlation function. Both these techniques extend the lateral length-scales, which can be probed to at least an order of magnitude smaller than those observable with light scattering. We shall discuss to what extent these results can be described by the ordinary capillary wave theory for liquid surfaces