Strong and fragile glasses: A powerful classification and its consequences

Abstract

In the strong versus fragile classification of simple liquids near their glass transition, a simple model is used to quantify this distinction, which sheds light on mechanisms in glass-forming liquids near freezing. From this model it is shown that the fragility parameter, one of the most important material constants, can be mapped onto the fluctuation of the coordination number, Δz: Δz=0 for network glasses; hence they are strong glasses. Systems with Δz>0 are always fragile. Implications on the relaxation behavior are shown to be in qualitative and quantitative agreement with experimental results. The proposed model supports the idea that glass-transition phenomena have universal features.