Work of adhesion
The work of adhesion W12 is the work which must be done to separate two adjacent phases 1 and 2 of a liquid-liquid or liquid-solid phase boundary from one another. Conversely, it is the energy which is released in the process of wetting. The units of work of adhesion are J/m2.
When one phase is wetted by another, the two previously existing surfaces disappear, as a result of which energy is released due to the respective surface tensions σ1 and σ2. At the same time, work, which is referred to as interfacial tension σ12, must be done in order to form the interface. The work of adhesion is given by the following equation:
Wls = σ1 + σ2 - σ12
For a liquid-solid phase boundary, the work of adhesion Wls (l for liquid; s for solid) can be calculated from the contact angle θ using the Young-Dupré equation:
Wls = σl(1 + cosθ)
The work of adhesion is a measure of the strength of the contact between two phases. Its knowledge is therefore important for processes such as coating, painting, cleaning, printing, hydrophobic or hydrophilic coating, bonding, dispersion etc.