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

Abstract

We have performed dielectric loss measurements at 1 kHz on thin films of isotactic poly(methyl methacrylate). A key distinction of our studies is that the samples measured were supported films with one free surface rather than films that have metallic electrodes covering both surfaces. This unique sample geometry allows us to eliminate any effects due to evaporation of metal onto the top film surface and provides a unique opportunity to make direct comparisons between dielectric loss and glass transition measurements. Film thicknesses in the range from 6 microm to 7 nm were prepared on Al coated substrates. The dielectric loss peak and ellipsometric glass transition temperature of all films were measured. The dielectric loss was found to exhibit no discernible film thickness dependence in either the temperature of the maximum loss value or the shape of the loss curve. In contrast, the measured T(g) values were found to decrease with decreasing film thickness with a maximum shift of 10 K for a 7-nm film. Dielectric measurements were also made on Al coated films and these samples also showed no shift in the temperature of the loss peak. Finally, the T(g) measurements were also made on Si substrates. These values exhibited an increasing T(g) value with film thickness with a maximum increase of approximately 15 K being measured for a 7-nm film.