New theory of water activity in heterogeneous systems

Abstract

A new theory of water activity in heterogeneous porous systems has been proposed in which the observed activity is calculated as the volume average of a local, spatially varying activity determined by the amount of bulk, surface or structural water at each location in the system. The new theory accounts quantitatively for the sorption isotherms in a variety of model porous systems and provides a consistent explanation of freezing point depression and hysteresis during adsorption and desorption.