Modulus, confinement, and temperature effects on surface capillary wave dynamics in bilayer polymer films near the glass transition

We report relaxation times (τ) for surface capillary waves on 27-127 nm polystyrene (PS) top layers in bilayer films using x-ray photon correlation spectroscopy. At ∼10°C above the PS glass transition temperature (T _g), τ 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°C, both effects become negligible. We demonstrate how neighboring polymer domains impact dynamics over substantial length scales.