Water in glass has a disproportionately large influence on glass properties. In particular, chemical and mechanical degradation of glasses are mainly caused by water in glass surface. The reason that water influences these properties may be related to composition fluctuations induced by water. Glasses, in general, have both density and composition fluctuations. All glasses have density fluctuations, originating from the liquid structure in which constituent molecules are actively moving. The magnitude of the density fluctuation is known to scale with the fictive temperature, with a greater density fluctuation being observed for glasses with a higher fictive temperature. Composition fluctuations are usually observed in multi-component glasses. By measuring the x-ray small angle scattering intensity of SiO2 glasses as a function fictive temperature and water content, the extent of density and composition fluctuations was evaluated. Water in glass accelerates the stress relaxation process. The magnitude of relaxation or relaxation strength is expected to increase with increasing composition fluctuation. A large composition fluctuation appears to be responsible for the disproportionately large influence of water on glass properties.
