What Is an Ionic Surfactant?

Cationic surfactants are mainly nitrogen-containing organic amine derivatives. Because the nitrogen atom in the molecule contains a lone pair of electrons, it can combine with the hydrogen in the acid molecule by hydrogen bonding to make the amino group bear a positive charge. Therefore, they have good surface activity in acidic media; they easily precipitate in alkaline media and lose surface activity. In addition to nitrogen-containing cationic surfactants, there are a small number of cationic surfactants containing sulfur, phosphorus, arsenic and other elements.

Cationic surfactants have not been used extensively in the industry for a long time, and the demand has been increasing rapidly year by year. However, because their main uses are special applications such as fungicides, fiber softeners and antistatic agents,

Most of the cationic surfactants with commercial value are derivatives of organic nitrogen compounds. The positive ion charge is carried by nitrogen atoms. There are also some new cationic surfactants carried by phosphorus, sulfur, iodine, and arsenic atoms. According to the chemical structure of cationic surfactants, they can be divided into four types: amine salt type, quaternary ammonium salt type, heterocyclic type and phosphonium salt type.

The main reaction for the synthesis of cationic surfactants is the N-alkylation reaction, in which a tertiary amine reacts with an alkylating agent to form a quaternary ammonium salt.

Alkyl quaternary ammonium salt

Alkyl quaternary ammonium salts are one of the important varieties of quaternary ammonium salt type cationic surfactants, and have been widely used as bactericides, fiber softeners, mineral flotation agents, emulsifiers and the like. Its structure is characterized by four alkyl groups attached to the nitrogen atom, namely ammonium ion

All four of the hydrogen atoms are replaced by alkyl groups, usually only one or two of the alkyl groups are long-chain hydrocarbon alkyl groups, and the remaining alkyl groups have one or two carbon atoms. According to its structural characteristics, there are three main methods for synthesizing alkyl quaternary ammonium salts, which are obtained by reacting higher haloalkanes with lower tertiary amines, by reacting higher alkylamines with lower haloalkanes, and by formaldehyde-formic acid method.

Heteroatom-containing quaternary ammonium salts

The so-called heteroatom-containing quaternary ammonium salt generally refers to a hydrophobic hydrocarbon chain containing O, N, S and other heteroatoms.

Cationic surfactants have good bactericidal, soft, antistatic, anti-corrosive effects and certain emulsification and wetting properties. They are also often used as phase transfer catalysts. However, such surfactants are rarely used alone as detergents, because the surface of many substrates is usually negatively charged in aqueous solutions, especially in alkaline aqueous solutions. In the application process, positively charged surfactants can be used in The matrix surface forms an arrangement of hydrophilic groups inward and hydrophobic groups outward, making the surface of the substrate hydrophobic, which is not conducive to washing, and even has a negative effect. In addition, the main application area of this type of surfactant is not like other surfactants, which are used to reduce surface tension, but uses its structural characteristics for other special aspects. ^[1]