Reduce surface tension
Surfactant molecules are arranged between two phases, making the surfaces of the two phases equivalent to transferring into the interior of the molecules, thereby reducing surface tension. For example, at the liquid gas interface, surfactants reduce the surface tension of water through adsorption.
Form aggregates
In the bulk aqueous phase, surfactants will form aggregates, such as micelles. The hydrophobic tail forms the core of the aggregate, while the hydrophilic head comes into contact with the surrounding liquid. The shape of the aggregate depends on the chemical structure of the surfactant, namely the size balance between the hydrophilic head and hydrophobic tail, which is measured by the hydrophilic oleophilic balance (HLB). In addition to micelles, other types of aggregates such as spherical or cylindrical micelles, lipid bilayers, etc. may also form.