Spreading of Liquid Drops over Thick Porous Substrates Complete Wetting Case

3 SPREADING OF LIQUID DROPS OVER THICK POROUS SUBSTRATES COMPLETE WETTING CASE 

The spreading of small liquid drops over thin porous layers saturated with the same liquid (Section 4.1) or a dry porous layer (Section 4.2) has been considered by appropriately matching flows in both the spreading drop and the porous substrate. 

In the present section, we extend our study in Section 4.2 to the spreading of small silicone oil drops (capillary spreading regime) over different porous substrates, whose thickness is much bigger than the drop size. A number of similarities with the case of the spreading over thin porous substrates (Section 4.2) is found. 

As already mentioned in the introduction to Chapter 3, at small capillary numbers. 

FIGURE 4.11 Spreading of liquid drops over dry porous substrates (1) spherical drop (2) wetted region inside the porous substrate (modeled by a spherical cap) (3) dry part of the porous substrate L t) — radius of the drop base l t) — radius of the wetted circle on the surface of the porous substrate 0(f) — dynamic contact angle of the spreading drop, and /(f) — effective contact angle inside the porous substrate. 

---