Fragility and Vogel-Fulcher-Tammann parameters near glass transition temperature

Abstract

The strength parameter D, ideal glass transition temperature T0, and fragility parameter m are vital parameters and frequently used to analyze significant problems in various glass-forming liquids. It is found that parameters D, T0 and m will have great difference when these values for the same glass-forming liquid are obtained by fitting the measured viscosity data in different temperature ranges near glass transition temperature Tg. In order to obtain accurate parameters (T0, D and m), the temperature dependences of viscosity in different temperature ranges are studied. The results show that in the temperature range 0.97Tg~1.16Tg, the fitting viscosity data obtained by the measured data in temperature ranges (f)~(k) and Plazek's expression are close to the measured viscosity data. However, there are still great difference between the minimum and maximum values for fluctuant T0 and D values, which are 28.61 K and 24.91, respectively. The study further finds that parameters obtained using the measured viscosity data in temperature ranges (g)~(i) and (k) by VFT relation are more accurate and the maximal fluctuations of T0 and D parameters are decreased to 10.57 K and 10.79, respectively. Furthermore, parameters obtained by the measured data in (g) are the most accurate than those obtained by the measured data in any temperature range.