On the empirical functions describing the alpha-relaxation of glass-forming systems

In the present work a comparison among the different functions commonly use d to describe the alpha -relaxation in glass-forming systems has been estab lished. The main results obtained are: (i) By using a direct Fourier transf ormation we have corroborated previous results, which were obtained by diff erent means, connecting the Havriliak-Negami (HN) and Kohlrausch-Williams-W atts (KWW) descriptions. (ii) Ali equivalence between the latter descriptio n and the one obtained from the Rajagopal distribution has been established in a very wide range. Thus, an expression for the distribution function of relaxation times, valid for most of the stretched exponential behaviours e xperimentally found, has been derived. (iii) Comparing these three function s with the dielectric relaxation data from different systems, we proposed a criteria for the choice of the most appropriate function depending on the particular type of the glass former system. (C) 2001 Elsevier Science B.V. All rights reserved.