Synchrotron radiation studies of the dynamics of polymer films

X-ray photon correlation spectroscopy, an emerging technique for studying the slow dynamics of condensed matter, has been employed to probe surface fluctuations on thin supported polymer films as a function of in-plane wavevector, film thickness, temperature, and molecular weight of the polymer. The measurements were performed on thin polystyrene (PS) films of thicknesses ranging from 84 to 333 nm above the glass transition temperature. The lateral length scales probed are at least ten times smaller than those accessible in conventional dynamic light scattering. We find excellent agreement between the measured surface dynamics and the theory of overdamped thermal capillary waves on thin viscoelastic films. The values of the viscosity obtained from these data show good agreement with those of bulk PS.