What are the types of surfactant? | Detailed Explanation

In the beginning of this essay, we will introduce what surfactant is, then will talk about types of surfactant. A surfactant is a substance that can change the interface situation of the surface of the target solution significantly. There is a settled hydrophilic oil-philic group, which is oriented on the surface of the solution. It has an amphoteric molecular structure: a hydrophilic group is at one end, and a hydrophobic group is at the other end.

Hydrophilic groups are often polar groups, such as carboxylic acid, amino or amine groups, and their salts, and ether bonds can also be used as polar hydrophilic groups. The hydrophobic groups are usually non-polar hydrocarbon chains, such as hydrocarbon chains with more than 8 carbon atoms.

Types of surfactant

According to the characteristics of molecular composition and the dissociation properties of polar groups, surfactants are divided into ionic surfactants and non-ionic surfactants. According to the charge carried by ionic surfactants, they can be divided into cationic surfactants, anionic surfactants, and zwitterionic surfactants. The following are specific descriptions of these surfactants and their uses.

1. Anionic surfactants 

This type of surfactant that plays a surface active role is anion, and the following are several common anionic surfactants.

a. Advanced fatty acid salt: Soap, stearic acid, oleic acid, and lauric acid belong to this kind of surfactant. It can be divided into alkali metal soap, alkali earth metal soap, and organic amine soap. And it is used only in topical preparations.

b. Sulfates: It mainly refers to sulfated oils and higher fatty alcohol sulfates. The representative of sulfated oil is sulfated castor oil, commonly known as Turkish red oil. Higher fatty alcohol sulfate is commonly used sodium dodecyl sulfate, sodium cetyl sulfate, sodium octadecyl sulfate, and so on. It is mainly used as an emulsifier for external ointments, and sometimes as a wetting agent or solubilizer for solid preparations such as tablets.

c. Sulfonic acid: This kind of surfactant usually refers to aliphatic sulfonates alkyl aryl sulfonates and so on. Sodium dioctyl succinate and sodium dodecyl benzene sulfonate are the common varieties. The latter is currently widely used in detergents.

2. Cationic surfactants 

The active part of this type of surfactant is cationic, also known as positive soap. The main part of its molecular structure is a pentavalent nitrogen atom, so it is also called quaternary ammonium, which is characterized by large water solubility, stable in acidic and alkaline solutions, and has good surface activity and bactericidal effect. Benzalkonium chloride and benzalkonium bromide are commonly used.

3. Zwitterionic surfactants

It is a surfactant with anion and cationic groups in the molecule. According to the change of acidity and alkalinity of the solution, it shows the properties of negative or cation. Amphoteric surfactants foaming, penetration is also small, anti-static and fabric soft performance is good, irritation and toxicity to the skin, so in shampoo, personal protection products and many industrial fields. It has a unique and wide range of uses. For example, lecithin is a natural zwitterionic surfactant. It is the main auxiliary material for preparing emulsion and lipid particle preparation for injection.

4. Nonionic surfactants

Nonionic surfactants do not separate in water. The molecules that constitute hydrophilic groups are glycerol, polyethylene glycol sorbitol, and other polyols. And the formation of oil-philic groups are long-chain fatty acids or long-chain fatty alcohols, and alkyl or aryl groups. They are ester or ether bonds with hydrophilic groups. There are many varieties of them and widely used in external use, such as oral preparations, and injections. Some kinds are also used in intravenous injections.

Application of different types of surfactant

Surfactants can be used for wetting or anti-sticking, foaming or defoaming, dispersion, corrosion prevention, and other applications because they have many physical and chemical effects. In addition to daily life as detergents, surfactants are needed in most fine chemical fields.

Conclusion: 

In the end, we want to sum up the topic of "types of surfactant". It is difficult to classify surfactants properly without any overlap in conceptual connotations. Most scholars think that it is more suitable to classify it according to its chemical structure. When the surfactant is dissolved in water, according to whether ions are generated and their electrical properties, they are divided into ionic surfactants and non-ionic surfactants.