Fragility (glass physics)

This article is about the property of glass forming liquids. For other uses, see Fragility.
The glass transition temperature Tg-scaled Arrhenius plot of fragility of glass forming liquids indicate the distinct behavior of strong and fragile liquids. This representation of fragility is known as an "Angell Plot".

In glass sciences, fragility or "kinetic fragility" is a concept proposed by the Australian-American physical chemist C. Austen Angell. Fragility characterizes how rapidly the viscosity of a glass forming liquid approaches a very large value approximately 1012 Pa s during cooling. At this viscosity, the liquid is "frozen" into a solid and the corresponding temperature is known as the glass transition temperature Tg. Materials with a higher fragility have a more rapid increase in viscosity as approaching Tg, while those with a lower fragility have a slower increase in viscosity. Fragility is one of the most important concepts to understand viscous liquids and glasses. Fragility may be related to the presence of dynamical heterogeneity in glass forming liquids, as well as to the breakdown of the usual Stokes–Einstein relationship between viscosity and diffusion. Fragility has no direct relationship with the colloquial meaning of the word "fragility", which more closely relates to the brittleness of a material.