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

A recent scaling-law analysis using τ∝(T−Tc)−γ with Tc<Tg 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 3ns to over 1 year. In contrast to Colby's conclusions, the observed temperature dependence rules out a temperature-invariant exponent γ as well as a clear cut critical temperature Tc.