Plasma activation. It is done with the intent to alter or improve adhesion

Adhesion

Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....

 properties of surfaces prior to coating, painting, etc. In most cases, the surface in question is surface of a polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 material and weakly ionised oxygen plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 is used.

Surface activation is a result of following processes:

Removal of weak boundary layers. Plasma removes surface layers with the lowest molecular weight, at the same time it oxidises the uppermost atomic layer of the polymer.

Cross-linking of surface molecules. Oxygen radicals (and UV radiation, if present) help break up bonds and promote the three dimensional cross bonding

Chemical bond

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 of molecules

Generation of polar groups. Oxidation of the polymer is responsible for the increase in polar

Chemical polarity

In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...

groups which is directly related to the adhesion properties of the polymer surface.