Scaling vs. Vogel-Fulcher-type structural relaxation in deeply supercooled materials

A recent scaling-law analysis using tau proportional to (T - T-c)(-gamma) with T-c < T-g has concluded that the resulting fits are superior over the Vogel-Fulcher-Tammann temperature dependence as regards the structural relaxation time of supercooled liquids (Colby, Phys. Rev. E 61 (2000) 1783). This issue is investigated based on the dielectric retardation data of poly(vinylacetate) which cover 16 decades in time, from 3 ns to over 1 year. In contrast to Colby's conclusions, the observed temperature dependence rules out a temperature-invariant exponent <gamma> as well as a clear cut critical temperature T,. (C) 2000 Elsevier Science B.V. All rights reserved.