Work of cohesion

According to Dupré, the work of cohesion Wii is the work done per unit area produced in dividing a homogeneous liquid. The units of work of cohesion are J/m2.


As two new surfaces are produced when a quantity of liquid is divided, the work of adhesion is calculated from the surface tension (which is defined as work per unit change in area) in accordance with the following equation:

Wii = 2σ
In a similar way, the work of cohesion specifies the work which must be expended to produce droplets from a volume of liquid when spraying.

When a liquid phase comes into contact with a second, liquid or solid phase the tendency to spread (complete wetting) is given by the ratio between the work of cohesion per phase and the work of adhesion when wetting. If the work of cohesion is larger, the liquid does not spread; if the work of adhesion is larger, the liquid spreads (see also spreading pressure).