Drop impact on porous media

This experimental study describes a drop of liquid impacting onto a porous substrate. The interest is on the drop behavior above the surface and especially underneath. There are several applications where this phenomenon plays a major role, like inkjet printing or spray coating. There are already several studies available [1-13], looking at the final state of an absorbed droplet, or simulating the process numerical. For the first time it is now possible to observe the liquid motion above and underneath simultaneously. The liquid has the same refraction index as the porous medium. This, and a small porous depth in the light path gives a clear image of the filled volume inside. This parametric study is comparing the penetration with the Washburn equation[14] and is describing general tendencies. It is shown that different wetting regimes exist and influence the penetration.