Light scattering study of a supercooled epoxy resin

The dynamics of the fragile glass-forming liquid diglycidyl ether of bisphenol-A was studied by depolarized Rayleigh-Brillouin light-scattering and photon correlation spectroscopy above the glass transition, in the tem- perature range from 261 to 473 K and in the frequency range from 1 Hz to 300 GHz. The structural ~a2! relaxation process was revealed and no signature of the secondary relaxation previously evidenced by dielectric spectroscopy at about 0.1 GHz was observed. The characteristic time of the a process differs from that determined by dielectric spectroscopy of an amount, which increases with increasing temperature. The relax- ation times were compared with viscosity data to test the predictions of the classic Stokes-Einstein-Debye model. The t }h behavior was verified for dielectric data, while a fractional power law of viscosity t }h 0.89 was obtained for light-scattering relaxation times, extending over more than seven decades in viscosity and time. This deviation of light scattering from viscosity data could be interpreted in terms of cooperative motion in the supercooled liquid with a characteristic length j a}(T2T0)2v where T05229 K is the Vogel tempera- ture and v is close to 2/3 which is consistent with the prediction of the fluctuation theory of glass transition.