Review on penetration and transport phenomena in porous media during slot die coating

A distinctive field in the coatings industry is coating of porous media, which has broad applications including paper, textiles, electronics, filtration, and energy sectors. Fluid penetration is an important issue during direct coating of a liquid bead on porous media, which is driven by the pressure from an external flow field and the surface tension in the porous media. Generally, during the coating process, some level of penetration is desirable to obtain specific material properties, but inadequate or excessive penetration is detrimental. To help control the level of penetration, understanding relationships between operating parameters and penetration are highly desirable. In this article, the current state of academic research on modeling penetration in porous media during common coating processes, especially the slot die coating process, is reviewed. Specifically, the challenges, basic ideas, advantages, and disadvantages of macroscale, microscale, and pore-network models on penetration in porous media are discussed. This article concludes with some recommendations for future work.