Light-scattering study of a supercooled epoxy resin

The dynamics of the fragile glass-forming liquid diglycidyl ether of bisphe nol-A was studied by depolarized Rayleigh-Brillouin light-scattering and ph oton correlation spectroscopy above the glass transition, in the temperatur e range from 261 to 473 K and in the frequency range from 1 Hz to 300 GHz. The structural (alpha-) relaxation process was revealed and no signature of the secondary relaxation previously evidenced by dielectric spectroscopy a t about 0.1 GHz was observed. The characteristic time of the ct process dif fers from that determined by dielectric spectroscopy of an amount, which in creases with increasing temperature. The relaxation times were compared wit h viscosity data to test the predictions of the classic Stokes-Einstein-Deb ye model. The tau proportional to eta behavior was verified for dielectric data, while a fractional power law of viscosity tau proportional to eta(0.8 9) was obtained for light-scattering relaxation times, extending over more than seven decades in viscosity and time. This deviation of light scatterin g from viscosity data could be interpreted in terms of cooperative motion i n the supercooled liquid with a characteristic length xi(a)proportional to( T- T-0)(-upsilon) where T-0 = 229 K is the Vogel temperature and upsilon is close to 2/3 which is consistent with the prediction of the fluctuation th eory of glass transition. [S1063-651X(99)04009-X].