From the dynamic to the static glass transition via hypersonic measurements using Brillouin spectroscopy

For the fragile, low-molecular-weight liquid diglycidyl ether of bisphenol A (DGEBA), we report on the dynamic glass transition and a further acoustic anomaly in the vicinity of the thermal glass transition based on hypersonic investigations of the longitudinal elastic modulus using Brillouin spectroscopy. This additional acoustic anomaly of the longitudinally polarized phonon is confirmed by the occurrence of an anomaly of the shear phonon at the same thermal glass transition temperature. Analysis of the generalized Cauchy relation suggests that both anomalies are coupled to a glass transition phenomenon independent of the so-called α-relaxation process.