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Two factors governing fragility: stretching exponent and configurational entropy
Prabhat K Gupta1, John C Mauro
1Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA.
Summary
Supercooled liquid fragility arises from thermodynamic and kinetic factors. The stretching exponent beta provides a lower limit for fragility, influenced by configurational entropy.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Physical Chemistry
Background:
- Supercooled liquids exhibit complex dynamics near the glass transition.
- Fragility quantifies the abruptness of viscosity changes with temperature.
- Glassy relaxation is often described by nonexponential functions like the Kohlrausch-Williams-Watts (KWW) function.
Purpose of the Study:
- To derive an analytical expression for supercooled liquid fragility.
- To elucidate the relationship between thermodynamic and kinetic contributions to fragility.
- To resolve discrepancies in the literature regarding fragility and relaxation dynamics.
Main Methods:
- Derivation of an analytical expression for fragility.
- Analysis of the thermodynamic and kinetic contributions to liquid dynamics.
- Quantification of relaxation nonexponentiality using the KWW stretching exponent (beta).
Main Results:
- Fragility is determined by both configurational entropy changes (thermodynamic) and relaxation stretching (kinetic).
- Non-Arrhenius viscosity scaling does not directly correlate with glassy relaxation nonexponentiality.
- The temperature dependence of beta sets a lower bound for fragility, modifiable by configurational entropy.
Conclusions:
- The derived expression reconciles conflicting findings on the correlation between beta and fragility.
- Understanding both thermodynamic and kinetic factors is crucial for predicting supercooled liquid behavior.
- The study provides a framework for analyzing the origins of liquid fragility.
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