Cationic surfactants are mainly nitrogen-containing organic amine derivatives. The nitrogen atoms in their molecules have lone pair electrons, which can form hydrogen bonds with hydrogen atoms in acid molecules, giving the amino group a positive charge. Therefore, they have good surface activity only in acidic media, and are easily precipitated and lose their surface activity in alkaline media. In addition to nitrogen-containing cationic surfactants, there are also a small number of cationic surfactants containing elements such as sulfur, phosphorus, and arsenic.
The positive charge is similar to the hydrophobic group of anionic surfactants. The hydrophilic group of cationic surfactants contains nitrogen atoms, which can be divided into three types: ammonium salts, quaternary ammonium salts, and heterocyclic types, depending on the position of the nitrogen atom in the molecule.
In practical applications, different situations often require special-effect surfactants with certain characteristics, but in order to facilitate actual use, the variety cannot be too complicated. Therefore, there is a need for "universal" multi-functional surfactants that contain different types of functional groups.
Compatibility research with anionic surfactants
Compatibility is one of the main research and development directions of surfactant science as a whole. Recent research has shown that if used properly, the use of anionic and cationic surfactants in combination can exhibit better surface activity. However, in most cases, anionic and cationic surfactants still cannot be used together, which is a major weakness limiting their application.
Safe and low-toxicity surfactants
Today, the call to eliminate environmental pollution caused by surfactants is becoming increasingly strong, and the pollution caused by surfactants to the environment is mainly eliminated by natural microorganisms breaking them down. It is particularly important to reduce toxicity and facilitate biodegradation for naturally occurring cationic surfactants with high toxicity and poor biodegradability, such as quaternary ammonium salt cationic surfactants.
Cationic surfactants do not have detergent and cleaning functions, but have good bactericidal, algal killing, mildew proofing, softening, antistatic, and conditioning properties, and are used in detergents as fabric softeners, bactericides, antistatic agents, and conditioners. The cationic surfactants commonly used in detergents are alkyl quaternary ammonium salts, ester quaternary ammonium salts, and polymer cationic surfactants. Among them, quaternary ammonium salts are the largest in production and the most widely used type of important cationic surfactant, mainly used as fabric softeners, antistatic agents, bactericides, etc.