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Title: What sets the fragility of a glass-forming liquid
Plain: Some liquids, such as molten silica, slow down smoothly as they approach the glass point, while others, such as many organic liquids and polymers, slow down abruptly; this steepness is called fragility. Why liquids differ so much is not known.
Precise: The kinetic fragility m = d log10(tau_alpha) / d(T_g/T) evaluated at $T = T_g$ ranges from about 20 for SiO2 to above 150 for some polymers. Identify the microscopic determinants of $m$ (softness of the repulsion, network connectivity, vibrational anharmonicity, the heat-capacity jump $\Delta C_p$ at $T_g$) and give a predictive relation for $m$ tested across a set of chemically different liquids.
Settled by: A relation predicting m from microscopic or thermodynamic inputs that holds within experimental error across a large database of molecular, network, polymeric and metallic glass formers.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)