Comparison of mechanical and dielectric relaxation processes in laser-deposited poly(methyl methacrylate) films

Abstract

Dynamic loss spectra for laser-deposited poly(methyl methacrylate) (PMMA) films are investigated at a frequency of 5.4 kHz with dielectric spectroscopy and mechanical torsional spectroscopy using a double-paddle oscillator as a substrate in a temperature range from room temperature up to 530 K. By comparing both methods, the coupling mechanism of the external force to the molecules and the resulting relaxation processes are discussed. Differences in both loss spectra are ascribed to a different weighting of the contributions of primary and secondary relaxation in the relaxation peak. During annealing above the glass temperature, the local structure of the disordered molecular system is changed. This is accompanied by hardening processes as demonstrated by showing the isothermal development of the mechanical frequency shift and the internal friction of the film. For even higher temperatures, irreversible changes in the polymeric structure occur as observed by infrared spectroscopy and by a weight loss of the film.