Coating processes employed in several applications involve substrates that are not truly smooth, rigid and impermeable. They could possess inherent surface porosity and permeability that can influence the dynamics of transport of liquids, particulate suspensions, and polymers. Such effects are relevant to applications such as protective wall coatings, paper and textile-based electronics, porous contact lens, and clinical sensors. In this work, a set of fundamental problems on this topic is investigated.

First, liquid film entrainment during dip coating on a saturated porous substrate is modelled as an extension of the classical Landau-Levich problem. The results suggest that the classical 2/3rd power law relation between the limiting film thickness and capillary number (Ca) may deviate into a distorted power law relation or a Ca-independent regime for porous substrates. Insights from these studies are used to understand morphology of silica suspension coatings dip coated onto porous alumina membranes. A coating regime map showing the variation of morphologies is formulated under different operating parameter spaces. Along similar lines, the stability of thin polymer films coated onto permeable surfaces is studied as function of the time of annealing the polymer.

Finally, instabilities at the interface between a Newtonian and viscoelastic fluid in a Hele Shaw cell is investigated, which leads to complex patterns of intrusion of the former into the latter. The results of this work has implications for improving the transportation of fluids in pipelines especially in the food processing and personal care products industries, like chocolates, lotions, sauces by tuning the viscosity and elasticity of fluids during processing.