CONNECTION BETWEEN QUASI-ELASTIC RAMAN-SCATTERING AND FREE-VOLUME IN POLYMERIC GLASSES AND SUPERCOOLED LIQUIDS

Quasielastic light scattering (QLS) in the frequency interval 100-1000 GHz is measured in some polymers: polycarbonate, polybutadiene, polys tyrene, and poly(methyl methacrylate). To describe the spectra, a mode l of the fast picosecond relaxation processes responsible for the QLS, which is based on the damping of the boson peak vibrations by the dyn amic hole volume fluctuations, is used. Within the frame of the model, the intensity of the fast relaxation process is proportional to the f ractional dynamic hole volume (which above the glass transition temper ature Tg is known as the fractional free volume). The hole volumes can be measured using the positron annihilation lifetime spectroscopy (PA LS). The comparison of the literature PALS data in the four polymers w ith the QLS shows an apparent correlation between the relaxation stren gth and the fractional dynamic hole volume in good agreement with the predictions of the model. (C) 1997 American Institute of Physics.