Washburn's equation facing Galileo's transformation: some remarks.
Capillary rise is the basis of some methods employed for the determination of contact angles in porous materials. One of them consists of the measuring of the distance the liquid advances into the pores of the solid. Normally, the results are analyzed by a rectilinear fitting to Washburn's equation. However, if it is taken into account that the distance-time measurements can be made under numerous reference systems and that, therefore, Galileo's transformations must be considered, it can be proved that the analysis of the results has to be carried out by parabolic expression of Washburn's equation. Even more, this work demonstrates theoretically that the traditional expression of Washburn's equation is valid only to describe the distance-time measurements got from that place where the initial contact between the porous solid and the liquid is established.
Labajos-Broncano
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L
Department of Physic, University of Extremadura, Av. Elvas s/n, 06071 Badajoz, Spain.
González-Martín
M L
ML
Bruque
J M
JM