Experimental Investigation of Droplet Spreading on Porous Media

The phenomena of wetting and spreading on solid surfaces and in porous media are being studied for a wide range of applications. Two processes interact to cause drop motion over a porous layer: (a) the spreading of the drop over already saturated parts of the porous layer, which causes the drop base to expand; and (b) the imbibition of the liquid from the drop into the porous substrate, which causes the drop base to shrink and the wetted region inside the porous layer to expand. This study presented an experimental investigation of various size droplets spreading over a thin porous layer. Ink and silicone oil droplets are used to determine drop-spreading behaviour. A drop spreading on porous media increases its contact diameter initially and then decreases. Conversely, the size of the wetted region increases monotonically. Although overall behaviour for silicon oil and ink was comparable, there were qualitative and quantitative variances. Furthermore, it is demonstrated that the initial drop size affects how long it takes for a drop to imbibe into a porous medium.