Anomalies in the scaling of the dielectric α-relaxation

By measuring the complex dielectric function over 15 decades in frequency we evaluate the scaling of the \ensuremath{\alpha}-relaxation for several glass-forming liquids including propylene carbonate. The temperature dependence of the mean relaxation time and of the relaxation strength of the relaxation function displays two dynamical regions being separated by a crossover temperature. The observed findings are essentially not in accordance with predictions of the mode-coupling theory and light scattering results for propylene carbonate [M. Elmroth et al., Phys. Rev. Lett. 68, 79 (1992)].