Dielectric investigation of the temperature dependence of the nonexponentiality of the dynamics of polymer melts

Abstract

Using broad band dielectric spectroscopy [Formula Presented] Hz), combining time domain and frequency domain techniques, we study the temperature dependence of the non-Debye character of the [Formula Presented] relaxation of polymer melts in the glass transition temperature [Formula Presented] range. The [Formula Presented] relaxation process is described in terms of the Kohlrausch-Williams-Watts relaxation function which has a single parameter [Formula Presented] to characterize the nonexponentiality of the relaxation. At high temperatures, [Formula Presented] remains nearly insensitive to temperature changes, whereas in the vicinity of [Formula Presented] a nearly linear increasing of [Formula Presented] with temperature is found. The temperature range where the change of the [Formula Presented] behavior occurs is located for all the polymers investigated around [Formula Presented] Moreover, our results indicate a common value of [Formula Presented] at the temperature where the relaxation time diverges. The [Formula Presented] behavior near [Formula Presented] is discussed in terms of a “rugged landscape” phase space which allows us to rationalize both the [Formula Presented] behavior observed as well as the similarities of our findings near [Formula Presented] with the results reported in simulations on Ising spin glasses and other model systems. © 1999 The American Physical Society.