Influence of disorder on viscosity of undercooled melts

The influence of disorder on shear viscosity of undercooled melts is described by the formula η=η0⋅exp(θ/T )a. It is shown that this expression reproduces the existing experimental data with a reasonable accuracy for a broad range of substances of various nature (silicates, borates, germanates, phosphates, Se, glucose, glycerin, As2Se3, etc.). Angell and Sichina [Ann. NY Acad. Sci. 279, 53 (1976)] distinguish between ‘‘strong’’ and ‘‘fragile’’ liquids on the basis of their heat capacity. The present model provides a physical ground for such classification. Also the isostructural viscosity of glasses is easily described. The present approach gives a natural explanation to the empirical rule of Bimen and Kauzmann.