ELECTRONIC DENSITY-FLUCTUATIONS IN DISORDERED-SYSTEMS .1. EFFECT OF THERMAL TREATMENTS ON THE DYNAMICS AND LOCAL MICROSTRUCTURE OF POLY(METHYL METHACRYLATE)

The density fluctuations in poly(methyl methacrylate) are investigated by small-angle X-ray scattering (SAXS) as a function of temperature a nd microstructural state with time-resolved accuracy, by means of sync hrotron radiation. We show for the first time the differences in elect ronic density fluctuations between quenched and annealed samples in re lation to their dynamic behavior. At low temperature, the microstructu ral state slightly influences the electronic density fluctuations, whe reas differences between both samples appear in the glass transition r ange. SAXS is thus essentially sensitive to fluctuations of dynamic na ture. These features are understood and related to the differences obs erved directly in the relaxational behavior, as revealed by high resol ution mechanical spectroscopy and differential scanning calorimetry me asurements.