resonance (NMR) relaxation analysis. A model is developed in which the effective capillary di?usion coe?cient is dependent on the instantaneous pore
size distribution. This and earlier data show changes in pore size distribution resultant from changes in saturation that do not occur instantaneously
with changes in degree of saturation. Therefore, it is assumed that the pore size distribution is always relaxing exponentially towards a (saturation de
pendent) equilibrium. It follows that the di?usivity is sample history (i.e.time) dependent as well as saturation dependent. This is su?cient to ex
plain anomalies in rapid capillary water sorption. The same concepts are applied to slow drying. In this case, porosity changes occur on a timescale
much shorter than drying so the system is always in dynamic equilibrium and anomalies are therefore not seen.