OBSERVATION OF A DYNAMIC ANOMALY IN THE LIQUID-GLASS TRANSFORMATION RANGE BY BRILLOUIN-SCATTERING

The temperature dependence of the nonergodicity parameter f(q) in the "fragile" glass-former propylene carbonate has been investigated using a wide-frequency-window Brillouin-scattering technique. A critical decrease of f(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 T(c) in the mode-coupling theory.