An Experimental Study of the Radial Penetration of Non-Newtonian Fluids in Thin Porous Substrates

We present the results of an experimental study of the radial capillary penetration of non-Newtonian fluids in thin porous substrates. The porous substrates included paper and thin packed beds of spherical glass beads. The porous substrates were sufficiently thin that the liquid completely penetrated across the porous substrate in all cases, leading to the formation of identical nearly circular liquid stains on both sides of the substrate. Measurements of the time-evolution of stain area were used to characterize the spreading rate. For fixed porous substrate, the spreading rates for non-Newtonian fluids were compared to those for Newtonian fluids. The effect of the size of the liquid reservoir on the rate of the radial spreading was also examined by considering both infinite liquid reservoirs and finite drops.