ANALYSIS OF THE ACTIVATION-ENERGY SPECTRUM FOR THE ENTHALPY RELAXATION OF A GLASSY LIQUID-CRYSTALLINE POLYMER

The phenomenology of the physical ageing of glassy materials can be de scribed by using the activation energy spectrum model. This model was originally developed for relaxations in metallic and oxide glasses and this paper applies it to a liquid crystalline polymer, poly(diethylen e glycol p, p'-bibenzoate) (PDEB), in the glassy state. PDEB samples w ere quenched from above T-g and isothermally annealed in a differentia l scanning calorimetry (DSC) equipment, and a description of the entha lpy relaxation of PDEB was achieved by means of the Kohlrausch-William s-Watts (KWW) equation. The results show that the relaxation time decr eases when the annealing temperature increases and can be explained in terms of an Arrhenius-type equation. The predicted value for the appa rent activation enthalpy (0.98 eV) is lower than those reported for ot her polymers. This approach assumes that a unique elemental process wi th a relaxation time tau(0) = 1.3 x 10(-13) min controls the evolution of the system. Energy spectra demonstrate that the activation energy values for the mechanisms controlling the relaxation are lower than 1. 1 eV and the spectra present a maximum for an activation energy close to 0.98 eV. The total number of available relaxation processes (measur ed by the area below the curves) decreases if the sub-T-g annealing te mperature increases. Moreover, the results show that the distributions widen if the shape parameter of the KWW equation decreases.