MICROSCOPIC DYNAMICS AND VISCOUS-FLOW IN A BOROSILICATE GLASS-FORMINGLIQUID

The connections between microscopic dynamical processes and macroscopi c viscous transport are not well known in multi-component oxide liquid s, despite their importance in the glass industry and in the earth sci ences. Here, rates of exchange among both silicate and berate network species in an alkali borosilicate liquid are derived from high tempera ture boron-ll and silicon-29 magic angle spinning nuclear magnetic res onance spectroscopy. About 80 degrees C above the glass transition, ex change rates of both types of units are close to the shear relaxation time calculated from the bulk viscosity. However, at lower temperature s, the silicon exchange rates decouple from the viscosity curve, possi bly because of the development of intermediate-range compositional het erogeneities. (C) 1998 Elsevier Science B.V.