ABSTRACT
For many years the study of wetting of porous media was concerned only with infinite porous media and infinite liquid reservoirs. However, the development of inkjet printing and need for understanding print quality triggered the realization that systems of limited size (such as tiny ink drops and very thin, porous printing layers) are of interest [2]. As a first-order approximation, systems consisting of a porous medium and a liquid have three characteristic dimensions: the typical size of the porous medium (such as thickness), D, the typical radius of curvature of the liquid reservoir, /?, and the typical dimension of a pore, r. These three dimensions can be grouped into two independent, dimensionless ratios, Rlr and Dlr, which are not necessarily infinite. Their actual, finite values determine the behavior of the system: Rlr is responsible for the criterion for penetration and its rate, while Dlr is responsible for the "re-exposure effect" to be explained below.
