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 it s glass transition temperature Tg). A visco penetrometer and a dielect ric spectrometer built in our laboratories allowed us to obtain experi mental 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 temperatu re on twelve decades; they are well fitted by the Cohen and Grest rela tion. These fits obtained on a large temperature range show that there is a strong correlation between viscosity and dielectric relaxation t ime. Furthermore it appears that the dielectric relaxation time distri bution is broadening in the vicinity of Tg.