Influence of Paper Morphology on Short Term Wetting and Sorption Phenomena

Abstract

Lucas Washburn theory has been used for many gears to model the penetration of liquids into paper where the rate of penetration is a function of the balance between surface tension forces and viscous drag. Interfacial contact angle is assumed to be constant and the pore morphology is reduced to an’ equivalent cylindrical pore radius. In reality, the pore morphology in paper is extremely complex. The interactions of liquids with paper are largely determine by local variation in Young-Laplace equilibria. Thus, the rate-determining factors for penetration of liquids in paper may be the distribution of divergence and convergence in pore wall geometry and the presence of discontinuities. In this paper, the penetration of liquids into paper coatings is examined as a function of pore morphology, pigment shape, and packing order. Sorption phenomena such as the “wetting delay” observed in uncoated but sized papers is explained in terms of the difference in morphology of surface and bulk pores. Fractal assembly rules are applied to morphological subunits in pigment coatings such that the rate of liquid penetration in a continuous coating could be predicted.