Microscopic dynamics and viscous flow in a borosilicate glass-forming liquid

The connections between microscopic dynamical processes and macroscopic viscous transport are not well known in multi-component oxide liquids, despite their importance in the glass industry and in the earth sciences. Here, rates of exchange among both silicate and borate network species in an alkali borosilicate liquid are derived from high temperature boron-11 and silicon-29 magic angle spinning nuclear magnetic resonance spectroscopy. About 80°C above the glass transition, exchange rates of both types of units are close to the shear relaxation time calculated from the bulk viscosity. However, at lower temperatures, the silicon exchange rates decouple from the viscosity curve, possibly because of the development of intermediate-range compositional heterogeneities.