Viscosity measurement of organic glasses below and above glass transition temperature

The viscosity of organic glasses, polystyrene (PS), poly (methylmethacrylate) (PMMA), and polycarbonate (PC) was measured, and the results were compared with those of inorganic glasses previously studied. The measurement was carried out in the pure shear deformation mode using a sandwich method from room temperature (RT) to the glass transition temperature Tg. Two relaxations of thermal activation type appeared in the lower and higher temperature regions (double relaxation). The temperature dependence of the viscosity was found to be sensitive to the mechanical and thermal treatments the specimen received. The compensation effect, a linear relation between the logarithm of the preexponential factor and the activation energy, was observed for the two viscosity relaxations. The shear viscosity measurement was also carried out above Tg using a rotation disk viscometer. The viscosity was in the hydrodynamic regime above Tg and was in the hopping regime below Tg; a crossover occurred near Tg. The overall characteristics of the viscosity of the organic glasses were quite similar to those of inorganic glasses such as metaphosphate glass.