SHEAR VISCOSITY AND DIELECTRIC-RELAXATION TIME OF DIBUTYL PHTHALATE DOWN TO GLASS-TRANSITION TEMPERATURE

We studied the shear viscosity and the main dielectric relaxation time of dibutyl phthalate from 97 degrees C down to -96 degrees C (near its glass transition temperature Tg). A visco penetrometer and a dielectric spectrometer built in our laboratories allowed us to obtain experimental data in the ranges 10-10(9) Pa.s for viscosity and 1 mHz-2 MHz for dielectric relaxation time. All these data and those of different authors give viscosity and dielectric relaxation time versus temperature on twelve decades; they are well fitted by the Cohen and Grest relation. These fits obtained on a large temperature range show that there is a strong correlation between viscosity and dielectric relaxation time. Furthermore it appears that the dielectric relaxation time distribution is broadening in the vicinity of Tg.