β-Relaxation in polymethylacrylate studied by light scattering

Summary The relaxation processes of glass-forming polymethylacrylate have been studied in a wide temperature range above the glass transition temperatureT _g by means of light scattering measurements. Experimental spectra give evidence of a self-similar behaviourI(ω) ∝ ω^−(1−a) over a spectral range of 2–3 decades, consistent with the predictions of the mode-coupling theory. Different from the prediction of the theory, the value ofa is strongly temperature dependent. This behaviour has been attributed to the presence of a slow secondary relaxation located in the GHz frequency region, whose strength progressively increases with temperature. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.