Correlation between dynamic fragility and glass transition temperature for different classes of glass forming liquids

Here we compile literature data for dynamic fragility m for six types of glass forming liquids: polymers, small molecule organics, hydrogen bonding organics, inorganics, ionic and metallic glass formers. Our analysis of the data shows that different categories of glass forming liquids exhibit different behaviors in terms of the correlation between m and Tg, a correlation not previously examined. For example, for hydrogen bonding organics, polymeric and metallic glass formers, there is an approximately linear increase in m with increasing Tg. While for inorganic glass formers, m appears almost independent of Tg, remaining nearly constant over a wide range in Tg. At the same time, another important parameter, the apparent activation energy Eg at Tg has been investigated. It was found that Eg increases with Tg to the 2nd power for hydrogen bonding organics, polymeric and metallic glass forming liquids, while Eg of inorganic glasses has a linear dependence on Tg.