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.
Highlights
DEUTSCHE PHYSIKALISCHE GESELLSCHAFT the temperature range from room temperature up to 530 K
We investigate films that are produced by pulsed laser deposition (PLD)
In the first part of this paper, we introduce briefly the experimental method of getting the complex shear modulus of thin films by using a double-paddle oscillator (DPO) as a substrate and the dielectric measurement technique
Summary
DEUTSCHE PHYSIKALISCHE GESELLSCHAFT the temperature range from room temperature up to 530 K. In figure 2, as a typical example, the temperature-dependent shear modulus of a 1.75 μm-thick PMMA film is shown during heating. The absolute value of G (figure 2(a)) is about 11 GPa at room temperature, which is higher than in bulk material, where Muzeau et al [10], for example, determined G to be about 1 GPa. The huge difference can be explained by massive structural changes and partial cross-linking occurring during the deposition process and various foregoing tempering steps that lead to a hardening as will be discussed below.
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