Angell Fragility of Glass Formers

Angell's plot: log η vs T_g/T. "Strong" liquids (SiO₂, m≈20) follow Arrhenius; "fragile" liquids (o-terphenyl, m≈81) deviate dramatically. The steepness index m = d(log η)/d(Tg/T)|_{Tg} quantifies fragility.

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Fragility m 50 VFT Divergence T₀/Tg 0.75

m index: 50

Class: intermediate

SiO₂ (m=20, strong)

GeO₂ (m=35)

Glycerol (m=53)

o-Terphenyl (m=81)

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