[Terminology] Surfactant / Surface active agent
Also known as interface active agent.
Definition: the substance having the following properties: strongly reduce surface tension or interfacial tension of the system; at certain concentration can form organized molecular assembly; change surface state or interface state of the system, and further bring a series of abilities, such as: cleansing, emulsifying, dispersing, wetting, foaming, antifoaming, demulsifying, flocculating, solubilizing abilities.
This is a traditional definition of surfactant. The definition mainly describes the role of surface tension or interface tension.
Parts of substances (such as: polyelectrolytes) do not strongly reduce surface tension or interfacial tension of the system; however, can strongly change surface state or interface state of the system.
Therefore, surfactants can be understood: the substance acting on the interface and significantly changing the interface state.
Surfactant is amphiphilic molecule. It includes two structural units: hydrophilic unit and lipophilic unit.
Depending on distinction of charge, surfactant can be divided into four categories:
(1), anionic surfactant, such as: soap.
(2), cationic surfactant, such as: quaternary ammonium salt.
(3), zwitterionic surfactant, such as: betaine.
(4), non-ionic surfactant, such as: fatty alcohol polyoxyethylene ether.
Usually, special surfactant be classified separately. Such as:
(1), fluorine surfactant;
(2), silicon surfactant;
(3), polymer surfactant.