Dielectric and ellipsometric studies of the dynamics in thin films of isotactic poly(methylmethacrylate) with one free surface

A detailed study on thin films of i-PMMA was performed using dielectric loss measurements and ellipsometry. By studying supported films on the same substrate material, it was possible to make detailed comparisons between dielectric loss measurements and ellipsometrically determined Tg values. The temperature corresponding to the peak in the 1-kHz dielectric loss was found to be independent of film thickness. Al coated samples were also studied and found not to exhibit a discernible difference in the dielectric loss peak from supported films. Ellipsometric studies on both Al and Si substrates show a qualitative change in the Tg behavior with substrate similar to that demonstrated in other studies. Finally, reasonable quantitative agreement between the ellipsometry measurements on Al substrates, and the extrapolation of dielectric measurements reported by Hartmann et al. was observed.