Fragility from Enthalpy Fluctuations and Fictive-Temperature Dynamics

Biman Bagchi

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arXiv · 2609.07396

Fragility from Enthalpy Fluctuations and Fictive-Temperature Dynamics

Biman Bagchi

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Abstract

Fragility and fictive temperature are two central measures of glass formation, but their connection is usually expressed indirectly through structural relaxation times or cooling-rate dependence. Here we formulate this connection in terms of configurational enthalpy fluctuations. The time evolution of the fictive temperature during cooling or aging is controlled by the enthalpy--enthalpy correlation function that also determines the frequency-dependent configurational heat capacity. Fragility enters through the strong temperature dependence of the structural relaxation time and therefore controls how rapidly the corresponding enthalpy-relaxation spectrum shifts to long times near the glass transition. This leads to a direct time-domain description of the onset and growth of the fictive-temperature lag, including the Debye limit, and connects calorimetric relaxation, fragility, and nonequilibrium structural arrest within a common framework.

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Biman Bagchi. 2026-09-07. Fragility from Enthalpy Fluctuations and Fictive-Temperature Dynamics. https://arxiv.org/abs/2609.07396

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