CHARACTERIZATION OF POROUS-MEDIA BY THE KINETICS OF LIQUID PENETRATION - THE VERTICAL CAPILLARIES MODEL

the kinetics of vertical capillary penetration is demonstrated. The ad vantage of vertical over horizontal penetration experiments lies in th e possibility of independently characterizing the equivalent pore radi us and contact angle, Methods for analyzing the experimental data are discussed in terms of two models: a modified presentation of the well- known equation for penetration into a single vertical cylindrical capi llary, and a simple new model for penetration into an assembly of vert ical cylindrical capillaries with a radius distribution. It is shown t hat presenting the data in the form of the cube of the height of rise over time vs time is useful for deciding which model is more suitable and for elucidating the equivalent radii and contact angle. The presen t approach is demonstrated by discussing two experimental examples: ca pillary rise in filter paper and in sand, The former is well described by the single capillary model, while the latter requires the capillar y assembly model. A striking common result of the analysis of the two cases is that the equivalent contact angle comes out to be very far fr om zero, although the intrinsic contact angle may be expected to be cl ose to zero. (C) 1997 Academic Press.