On the evaluation of the surface free energy of porous and powdered solids from imbibition experiments: equivalence between height-time and weight-time techniques.

A study of the equivalence between the height-time and weight-time experimental techniques, based on the imbibition of liquids into porous or powdered solids, has been carried out, determining under what conditions the deductions about the surface free energy of these solids made from the analysis of the experimental results obtained as weight versus time are similar to those deduced from the analysis of height versus time. Concretely, we have proved that only if the particular values of the porosity of the solid determined from the proper technique of imbibition, named the effective porosity, are taken into account, the analysis of both type of experimental measurements leads to the same conclusions about the surface free energy of the porous and powdered solids. In order to exemplify this, capillary rise measurements have been carried out by means of these two techniques with different liquids on silica gel layers.