HIGH-FREQUENCY DIELECTRIC-SPECTROSCOPY ON GLYCEROL

Dielectric spectroscopy has been performed on supercooled glycerol for frequencies 3 mu Hz less than or equal to v less than or equal to 40 GHz and temperatures between 100 K less than or equal to T less than o r equal to 500 K. Hence, the absorptive part of the dielectric suscept ibility was measured at comparable frequencies as the dynamic suscepti bility obtained by neutron and light scattering techniques. The charac teristic timescales obtained from all experimental techniques essentia lly agree. However, the dielectric data as measured on the high-freque ncy wing of the loss spectra are not consistent with neutron and light scattering results which probe density fluctuations. We conclude that in glycerol at high frequencies the density fluctuations are dominate d by local vibration excitations which are fully decoupled from the di polar reorientations. The temperature dependence of the dielectric los s traces that of the spin-lattice relaxation times measured with NMR t echniques and exhibits almost frequency-independent signatures near th e calorimetric glass transition.