Adhesion refers to the attractive forces that exist between two materials. Questions that are based on these attraction forces, e.g: surface tension, contact angle, capillary rise, should use this tag. use with the tag: [surface-chemistry]

Adhesion is the tendency of dissimilar particles or surfaces to cling to one another. The forces that cause adhesion and cohesion can be divided into several types. The intermolecular forces responsible for the function of various kinds of stickers and sticky tape fall into the categories of chemical adhesion, dispersive adhesion, and diffusive adhesion. In addition to the cumulative magnitudes of these intermolecular forces, there are certain emergent mechanical effects.

Surface energy:

Surface energy is conventionally defined as the work that is required to build an area of a particular surface. Another way to view the surface energy is to relate it to the work required to cleave a bulk sample, creating two surfaces. If the new surfaces are identical, the surface energy γ of each surface is equal to half the work of cleavage, $W: γ = (1/2)W_{11}$. If the surfaces are unequal, the Young-Dupré equation applies:

$W_{12} = γ_1 + γ_2 – γ_{12}$

where $γ_1$ and $γ_2$ are the surface energies of the two new surfaces, and $γ_{12}$ is the interfacial energy. This methodology can also be used to discuss cleavage that happens in another medium:

$γ_{12} = (1/2)W_{121} = (1/2)W_{212}$.

These two energy quantities refer to the energy that is needed to cleave one species into two pieces while it is contained in a medium of the other species. Likewise for a three species system:

$γ_{13} + γ_{23} – γ_{12} = W_{12} + W_{33} – W_{13} – W_{23} = W_{132}$

where $W_{132}$ is the energy of cleaving species 1 from species 2 in a medium of species 3. A basic understanding of the terminology of cleavage energy, surface energy, and surface tension is very helpful for understanding the physical state and the events that happen at a given surface, but as discussed below, the theory of these variables also yields some interesting effects that concern the practicality of adhesive surfaces in relation to their surroundings.