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

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

Evaluation of Laser Treatment on Reline-Base Composites

The effects of different laser treatments on some mechanical properties of acrylic resin and soft liner were investigated. A total of 60 test specimens were fabricated according to test requirements. The specimens were roughened with Potassium-ticanyl-Phosphate (KTP), Er:YAG, and Nd:YAG lasers before application of soft liner. The flexural, peel, and tensile bond strengths were measured using a universal testing machine. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) spectra of surfaces were also obtained to evaluate changes on the lased surfaces. No significant difference was apparent between the tensile bond strength values of the groups. Although peel strength values obtained for each of the laser types were lower than those of the control group, flexural strength values were higher than those of the control specimens. The spectra of specimens showed that lasing led to some chemical changes on the resin surfaces. Physical changes on the treated surfaces were visualized by scanning electron microscopy (SEM) analysis. Results of this study suggest that such treatments may be warranted because of the increase in flexural strength