Super-Arrhenius viscosity divergence and fragility in glass-forming polymers
T = 600 K | log₁₀(η) = — | State: liquid
The VFT equation η(T) = η₀ exp(B/(T−T₀)) describes the dramatic super-Arrhenius viscosity increase as a glass-former approaches Tg. "Fragility" m = d(log η)/d(Tg/T)|_{T=Tg} distinguishes strong (silica, Arrhenius) from fragile (polymers, steep VFT) glass-formers. At Tg, the structural relaxation time exceeds ~100 s and the material becomes kinetically arrested.