High-frequency dielectric spectroscopy on glycerol

Dielectric spectroscopy has been performed on supercooled glycerol for frequencies 3 μHz ⩽ ν ⩽ 40 GHz and temperatures between 100 K ⩽ T ⩽ 500 K. Hence, the absorptive part of the dielectric susceptibility was measured at comparable frequencies as the dynamic susceptibility obtained by neutron and light scattering techniques. The characteristic timescales obtained from all experimental techniques essentially agree. However, the dielectric data as measured on the high-frequency 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 dominated by local vibration excitations which are fully decoupled from the dipolar reorientations. The temperature dependence of the dielectric loss traces that of the spin-lattice relaxation times measured with NMR techniques and exhibits almost frequency-independent signatures near the calorimetric glass transition.