A model is developed to account for the viscous flow of glass-forming liquids. We consider that a supercooled glass-forming liquid is composed of a liquid phase and some solidlike clusters which have a higher activation energy for viscous flow than the liquid regions. This approach yields a fitting equation for viscosity with a simple form #eta#=#eta#_0 exp(E/k_BT)exp(#PHI#T/T_g), where E is the activation energy for viscous flow at low temperatures, and #PHI# represents the fragility of a glass-forming systm. Our results suggst that kinetic viscous flow of glass-forming liquids is closely related to their thermodynamics.
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