What are the classifications of surfactants?

What are the classifications of surfactants?


1. Anionic surfactant; 2. Cationic surfactant; 3. Zwitterionic surfactant; 4. Nonionic surfactant. Surfactant is a substance that can significantly reduce the surface tension of the target solution.


1. Anion

1. Soaps:

Department of higher fatty acid salt, general formula: (RCOO) nM. Fatty acid R are generally long chains of 11 to 17 carbons, and commonly include stearic acid, oleic acid, and lauric acid. According to the different substances represented by M, it can be divided into alkali metal soaps, alkaline earth metal soaps and organic amine soaps. They all have good emulsifying properties and ability to disperse oil. But it is easy to be destroyed, alkali metal soaps can also be destroyed by calcium and magnesium salts, and electrolytes can also make them salt out.

2. Sulfate, RO-SO3-M.

Mainly sulfated oils and higher fatty alcohol sulfates. The aliphatic hydrocarbon chain R is between 12 and 18 carbons. The representative of sulfated oil is sulfated castor oil, commonly known as Turkish red oil. Higher fatty alcohol sulfates include sodium dodecyl sulfate (SDS, sodium lauryl sulfate), which have strong emulsifying properties, are more stable, and are more resistant to acid and calcium and magnesium salts. In pharmacy, it can produce precipitation with some polymer cationic drugs, which is irritating to mucous membranes.

3. Sulfonate, R-SO3-M.

Included in this category are aliphatic sulfonates, alkylarylsulfonates and alkylnaphthalenesulfonates. Their water solubility and acid resistance, calcium and magnesium salt resistance are slightly worse than sulfates, but they are not easily in acidic solutions.


2. Cation

The part where this type of surfactant works is cationic, so it is called positive soap. The main part of its molecular structure is a pentavalent nitrogen atom, so it is also called a quaternary ammonium compound. It is characterized by high water solubility, stable in acidic and alkaline solutions, and good surface activity and bactericidal effect.


3. Zwitterion

The molecular structure of these surfactants has both positive and negative charge groups, and can exhibit the properties of cationic or anionic surfactants in media with different pH values.

1. Lecithin: It is the main excipient for the preparation of emulsions and lipid microparticles for injection.

2. Amino acid type and betaine type:

Amino acid type: R-NH+CH2CH2COO-.

Betaine type: R-N+2-(CH3)2COO-.

In alkaline aqueous solution, it has the properties of anionic surfactant and has good foaming and decontamination effects; in acidic solution, it has the properties of cationic surfactant and has strong bactericidal ability.


4. Nonionic surfactants

1. Alkyl glucoside:

A new type of non-ionic surfactant, commonly known as coco-glucoside, lauryl-glucoside, cetearyl-glucoside, etc.

2. Fatty acid glycerides:

Glyceryl monostearate; HLB is 3~4, mainly used as auxiliary emulsifier for W/O type emulsion.

3. Polyol:

Sucrose ester: HLB (5~13) O/W emulsifier and dispersant.

Fatty acid sorbitan (Span): W/O emulsifier.

Polysorbate (Tween): O/W emulsifier.