Capillary Force and Surface Wettability

Definition

Capillary force and surface wettability are related phenomena happening at the interfaces of solid, liquid, and air phases, and are highly dependent upon the interaction between liquids and solid surfaces.

Scientific Fundamental

Surface Wettability

When a liquid is in contact with a solid surface in air, in general, a droplet of the liquid will be formed. The shape of the droplet depends upon the interaction between the liquid and the solid surface. If the interaction is strong, i.e., the liquid “likes” the surface, the liquid drop will be “flat.” On the contrary, if the interaction is weak, i.e., the liquid “hates” the surface, it will “bead up.” Scientifically, such a property is described quantitatively by the concept of contact angle, which demonstrates the angle (θ) at which the air-liquid and solid-liquid interfaces meet (see Fig. 1). Such a situation is the result of the force balance at the location where air, liquid, and solid phase meet, the so-called “three phase...