Viscous Flow of Liquids at Constant Volume and Constant Pressure

摘要

The energy of activation for viscous flow at constant volume,Ev,is dependent on the volume of a liquid. For normal liquids at elevated temperatures,Evis only a small fraction of the value of the activation energy at constant pressure,Ep.However, for associated liquids, on account of the presence of hydrogen bonds,Evis almost equivalent toEp.It is suggested that in highly associated liquids like liquid silica and some molten glasses where flow necessitates the rupture of bonds of even greater energy, the difference betweenEvandEpshould be negligible.