Surfactants can be classified according to different perspectives such as structure, function, and source. As far as structural classification is concerned, it can be carried out according to the types of hydrophilic and hydrophobic groups and the overall configuration of molecules. In the following, combined with Figure 1, the basic structure of surfactants, the types of common head groups and hydrophobic tail chains, and representative special structures are introduced.

1. Divided by hydrophilic groups
Since the types of hydrophobic groups of surfactants have been relatively single for a long time, the classification according to the types of hydrophilic groups has become the main method for classifying surfactants. According to this method, surfactants can be roughly divided into four categories: anionic surfactants, cationic surfactants, zwitterionic surfactants and nonionic surfactants.

2. According to the hydrophobic tail chain
As mentioned above, for a long time, the types of hydrophobic tail chains of surfactants have been relatively limited. As far as the most common alkyl group is concerned, in addition to the straight chain type, it also includes branched alkyl groups (such as sodium bis(2-ethylhexyl) succinate sulfonate, AOT) and unsaturated alkyl groups (such as sodium oleate) ;

3. Divided by molecular configuration
The above discussion is limited to the case where the hydrophilic/hydrophobic part of the surfactant has a single structure. With the continuous renewal of the surfactant structure, there are diversified combinations of both the hydrophilic head group and the hydrophobic tail chain. As far as the hydrophilic head group is concerned, such as fatty alcohol polyoxyethylene (3) monosodium sulfosuccinate (MES) containing polyoxyethylene, sulfonate and carboxylate at the same time; containing polyoxyethylene (AEO) and Alcohol ether phosphate (AEP) of phosphate, etc. These surfactants containing complex hydrophilic head groups have shown better performance than single surfactants in the fields of infant care formulations, anti-temperature and anti-salt additives, etc. As far as the hydrophobic tail chain is concerned, the combination of alkyl and benzene rings creates sodium dodecylbenzenesulfonate and alkylphenol polyoxyethylene ether which are widely used; the combination of alkyl and fluorocarbon chains creates hydrocarbon - Fluorocarbon hybrid surfactants, etc.

4. Other classification criteria
In addition to the above classification criteria, some surfactants are also named after their sources, such as biosurfactants, which refer to surfactants that are directly extracted from animals and plants, or obtained through biotechnology such as fermentation. The hydrophilic group of some surfactants is a certain type of organic compound, hence the name, such as amino acid surfactants, alkyl glycosides and peptide surfactants. Because of their high biocompatibility, these surfactants are favored by people in life sciences, daily chemicals, washing, skin care, etc. In addition, there are other classification criteria, such as dividing surfactants into small molecule surfactants and polymer surfactants according to molecular weight, and so on.