Modulus, Confinement, and Temperature Effects on Surface Capillary Wave Dynamics in Bilayer Polymer Films Near the Glass Transition

We report relaxation times (tau) for surface capillary waves on 27-127 nm polystyrene (PS) top layers in bilayer films using x-ray photon correlation spectroscopy. At similar to 10 degrees C above the PS glass transition temperature (T-g), tau tracks with underlayer modulus, being significantly smaller on softer substrates at low in-plane scattering wave vector. Relative to capillary wave theory, we also report stiffening behavior upon nanoconfinement of the PS layers. At PS T-g + 40 degrees C, both effects become negligible. We demonstrate how neighboring polymer domains impact dynamics over substantial length scales.