On the Use of Washburn's Equation in the Analysis of Weight–Time Measurements Obtained from Imbibition Experiments

Influence of the Meniscus at the Bottom of the Solid Plate on Imbibition Experiments

“…However, this straight-line relationship is not observed when the experimental results are analyzed (1,3,5,(10)(11)(12). In a previous paper, we proved that the change of the slope shown by the experimental curves was caused by the superposition of two physical phenomena: the penetration of the liquid and the effect of the liquid surface tension of the liquid on the solid when the solid is put in contact with the free surface of the liquid (14). Both processes were additive, so the experimental increase of weight could be written as…”

“…The liquid employed was formamide (Fluka, purity >98%), since it was used in our previous paper related to the different physical phenomena that take place in this experimental setup (14), and because its features (viscosity, surface tension, and its components) are well known (16). Besides, this liquid is normally used to carry out measurements of contact angle.…”

Comparison of the Use of Washburn's Equation in the Distance–Time and Weight–Time Imbibition Techniques

“…Height and weight penetration experiments for each particular liquid were made simultaneously by means of an automatic device of measurement, similar to those described by other authors (4,(13)(14)(15) and used by us in two previous works (21,22). Before measurements, the silica plates were dried into an oven at 150 • C for 1 h and kept in a dissicator until the moment of their use.…”

“…However, when the experimental data are plotted, the slope of the experimental lines is not a constant in the whole range (4,(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). The changes of slope of the curves obtained from the height method are a consequence of the choice of the distance-time reference system (21), whereas those changes observed in the curves from the weight technique are caused by the superposition of the imbibition and the effect that appears when the contact between solid and liquid is established (22). These facts force us to use parabolic forms of Washburn's equation to analyze the results of the penetration experiments instead of its linear expressions.…”

“…2) reflects that the imbibition experiments are composed of two simultaneous processes in such a way that the collected values of the experimental increase of weight, w exp , have two contributions, the first one due to the force that the liquid surface tension exerts over the porous body because of the contact and the second one caused by the imbibition (22) w exp = w imb + w cont , [3] where w exp is the measured increase of weight, w imb the gained mass due to the imbibition, and w cont the increase of weight caused by the contact. The increase of weight caused by the imbibition of the liquid into the solid is governed by Washburn's equation, which written in term of the mass gained by a rectangular porous layer has the expression (13, 17)…”