Relaxation dynamics in orthoterphenyl:: comparing βK from extended mode coupling theory and phenomenological analyses

Depolarized light scattering susceptibility spectra of orthoterphenyl (OTP) were analyzed using the idealized and extended versions of mode coupling theory (MCT). The extended MCT fits were combined with KWW fits to the alpha peaks to provide combined alpha-beta fits from which the KWW stretching coefficient beta(K) was determined. beta(K) was found to be nearly independent of temperature, in agreement with the asymptotic prediction of MCT. The spectra were also analyzed with a five-function phenomenological model developed by Patkowski et al. [J. Non-Cryst. Solids 172-174 (1994) 52]. While this model gives excellent fits to the spectra, we found that it is not able to determine beta(K) uniquely unless other parameters are artificially constrained. Here, and in comparing light scattering and dielectric data for salol, we find the claim that beta(K) approaches 1 at high temperatures not to be justified by the experimental data. (C) 1998 Elsevier Science B.V. All rights reserved.