Capillarity

Capillarity is defined as the degree to which a material or object containing minute openings or passages, when immersed in a liquid, will draw the surface of the liquid above the hydrostatic level.
We can use the concepts of capillarity to predict the equilibrium shape of an interface.
Consider a bubble (Fig. 2.4).

Figure 2.4. A bubble in equilibrium with its surroundings

is the pressure in the dispersed phase

is the pressure in the surrounding medium and,

is the radius of the bubble

At the interface, the pressures ( and ) on two sides are equal only for flat surfaces, i.e. when goes to infinity. For a curved surface, these will not be equal.