Pore Space Characterization of Coating Layers, 2000 Coating Conference Proceedings

M. Toivakka, K. Nyfors--Although coating and pore structures are commonly discussed in context of paper coating performance, the actual microscopic geometry of the void space still remains largely unknown. This paper presents a technique to partition a void space of porous material into unambiguously defined collection of individual pores. The characterization technique is based on three-dimensional image analysis and it can be applied to both experimental and model packing data. The technique produces useful new information of microscopic properties of pore spaces including distributions of pore size, surface area, pore connectivity, pore surface-to-volume ratio, throat-to-surface area ratio as well as fractal structural parameters. Additionally, the technique creates a topological model of the pore space that can be used as a starting point for predictions of transport processes in porous structures, e.g. short time absorption of printing inks. Basic ideas and accuracy of the characterization technique are demonstrated by analyzing ordered lattice packings of cubic and hexagonal arrangements. Pore spaces in random packings of mono- and polydisperse spherical particles are characterized. The results quantify differences in pore structures caused by changes in particle size distributions. An understanding of microscopic pore structures in coating layers enables papermaker to improve and optimize coating formulations by using, e.g. pigment-blending.