Glassy dynamics and glass transition in thin polymer layers of PMMA deposited on different substrates

Broadband Dielectric Spectroscopy (BDS) and spectroscopic Vis-Ellipsometry are combined to study the glassy dynamics and the glass-transition of thin layers of atactic poly(methylmethacrylate) (PMMA) prepared under identical conditions. The interfacial interactions are systematically modified ranging from strong attractive interactions for covalently bonded PMMA brushes with high grafting densities to weak and strong repulsive interactions as realized by Au-coated and silanized SiO$_{x}$--surfaces, respectively. Down to layer thicknesses of $\sim $ 10 nm and independently from the substrate used, both methods deliver -- within the experimental accuracy ($\pm $1.0 K for BDS and $\pm $2 K for Ellipsometry) -- the coinciding result that the glassy dynamics and the glass transition are not altered due to the geometrical confinement in thin polymer layers.