A comprehensive light scattering study of the glass former toluene

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Abstract
We present depolarized light scattering data of the glass former toluene as obtained from tandem Fabry–Perot interferometry and Raman scattering covering a frequency range 0.5 GHz<v<5000 GHz. A large temperature interval of the (supercooled) liquid (Tg=117 K<T<295 K) as well as of the glass (7 K<T<117 K) is measured. Testing the scaling laws of idealized mode coupling theory (MCT) we find that MCT provides a satisfying interpolation up to the fluid regime (T/Tg=2.5) and a critical temperature Tc≅153 K is extracted. Deviations from the high-temperature MCT laws below Tc can be identified by constructing a master curve for the α-process. The deviations are attributed to spectral contributions from the high-frequency wing of the α-process and/or of the slow β-process which appear apparently only below Tc. A comparison with dielectric spectroscopy data, exhibiting a strong β-process, confirms this. Furthermore, we carry out a phenomenological analysis which assumes additivity of the susceptibility of α-process and fast dynamics. This approach allows us to single out the fast dynamics spectrum and to determine the nonergodicity parameter f. Whereas 1−f(T) is essentially constant above 160 K, a sharp decrease is observed below 160 K. This decrease stops at T=Tg and only a weak temperature dependence survives below Tg. Thus, the fast dynamics changes its characteristics at Tc and Tg. We speculate on the possibility of an ideal glass state exhibiting no relaxation any longer, and finally we comment on reasons for the large scatter of Tc data reported for some glass formers so far.