interfacial tension

Their adsorption on the hydrophilic surface reduces the solid–gas interfacial tension and thereby increases the contact angle.

The problem is to make the sum of the interfacial tensions a minimum, each tension being proportional to the square of the difference of densities of the two contiguous liquids in question.

At equilibrium, the contact angle adjusts itself in such a way that the difference between the solid–liquid and solid–gas interfacial tensions is balanced by the horizontal component of the liquid–gas interfacial tension.

The difference between these tensions is balanced by the horizontal component of the liquid–gas interfacial tension.

The solid–liquid interfacial tension is smaller than the solid–gas interfacial tension and the contact angle is small.