Observation of a dynamic anomaly in the liquid-glass transformation range by Brillouin scattering

The temperature dependence of the nonergodicity parameter ${\mathit{f}}_{\mathit{q}}$ in the ‘‘fragile’’ glass-former propylene carbonate has been investigated using a wide-frequency-window Brillouin-scattering technique. A critical decrease of ${\mathit{f}}_{\mathit{q}}$ is revealed at temperatures well above the calorimetric glass transition in accordance with mode-coupling theories for the liquid-glass transition. The determined critical temperature (270±5 K) is, however, significantly higher than that obtained using incoherent neutron scattering (210±15 K); this does not agree with the universal ${\mathit{T}}_{\mathit{c}}$ in the mode-coupling theory.