(2) Interfacial adsorption

Oversaturated surfactant molecules without being dissolved at a molecular level will aggregate and adsorb at the water/air or water/container interface, representing a minimum free energy state attained by the lipophilic group's hydrophobic property and the hydrophilic group's hydrophilic property.

(3) Micelle formation

Most of the remaining surfactant molecules will aggregate micelles with their hydrophilic head regions in contact with water so that they can minimize the unstable free energy after failing to obtain an adsorption interface. As shown in [Fig.1], micelles are formed in various shapes, such as spherical, layered, rod, and small micelles.
Most of the molecules are found in the form of a micelle in the surfactant solution. In addition, a small amount of surfactant molecules and adsorbed molecules at an interface also exist.
The cleaning mechanism works as follows: Dip a dirty metallic product into a cleaning bath. New interfaces of water-product surface and water-dirt appear in the bath. At that time, the surfactant molecules existed in the solution as micelles start breaking up their micelles to be adsorbed onto new interfaces. A series of processes including disassociation, dispersion and adsorption are the mechanism of cleaning.
If the dispersed hydrophobic dirt is in the liquid or solid form, it will be adsorbed by being emulsified or in the suspended solids respectively. At this time, the dirt particles are present in the solution in a stable state.

(4) Surface tension reduction

The surface tension is the amount of free energy stored between air and solution. The interfacial tension is the amount of free energy stored per unit area between dirt particles and solution. As the amount of surfactant increases, the surface tension decreases (it becomes saturated at a certain point). As a result, it makes the dirt dissolution, emulsification, and suspension easier. [Fig.2] shows the relationship between the surfactant concentration and surface tension.
Reduction of surface tension not only brings about the effect mentioned here but also prevents plating solution from being pumped out or avoids mist generation.