Dynamics of salol at elevated pressure

The dielectric alpha relaxation was measured in salol over a range of temperatures at pressures as high as 0.7 GPa. The application of pressure causes a shift of the excess wing, relative to the primary a peak, indicating that the two processes have a distinct origin. Over all measured conditions, the response to pressure of the alpha relaxation and the dc-conductivity can be described as a volume-activated process, with the respective activation volumes exhibiting the same temperature dependence. When these results are compared to published viscosity data for salol, decoupling is observed at higher pressures and lower temperatures. The steepness index (T-g-normalized temperature dependence of the alpha-relaxation times) decreases with pressure by -0.011 per MPa. Near T-g, the relaxation is governed equally by volume and by thermal energy, the usual result for molecular glass formers in the absence of extensive intermolecular hydrogen bonding.