Surfactants, due to their wetting or anti-adhesive, emulsifying or demulsifying, foaming or defoaming, and solubilizing, dispersing, washing, antiseptic, antistatic, and other series of physicochemical effects and corresponding practical applications, have become a flexible and versatile class of fine chemical products with wide applications. Besides their use as detergents in daily life, surfactants are used in almost all areas of fine chemicals.

● Solubilization    

Requirement: C>CMC (HLB 13~18)

Critical Micelle Concentration (CMC): The lowest concentration at which surfactant molecules associate to form micelles. When the concentration is higher than the CMC value, the surfactants arrange themselves into spherical, rod-like, bundle-like, layered, or plate-like structures.

The lower the CMC and the larger the aggregation number, the higher the solubilization capacity (MAC);

Effect of temperature on solubilization: Temperature affects micelle formation, the dissolution of the solubilizate, and the solubility of the surfactant.

Krafft point: For ionic surfactants, the temperature at which the solubility increases sharply with increasing temperature is called the Krafft point. The higher the Krafft point, the lower the critical micelle concentration.

Cloud point: For polyoxyethylene-type non-ionic surfactants, when the temperature is increased to a certain extent, the solubility decreases sharply and precipitates, and the solution becomes cloudy. This temperature is called the cloud point. This is because the hydrogen bonds between polyoxyethylene and water are broken. When the temperature rises to a certain temperature, polyoxyethylene can undergo strong dehydration and contraction, reducing the solubilization space and decreasing the solubilization capacity. With the same polyoxyethylene chain, the longer the hydrocarbon chain, the lower the cloud point; with the same hydrocarbon chain, the longer the polyoxyethylene chain, the higher the cloud point.

● Emulsification

HLB value between 3-8 is used for W/O emulsifiers

HLB value between 8-16 is used for O/W emulsifiers

● Wetting

Requirement: HLB: 7-9.

Surfactants can be used to control the degree of wetting between liquids and solids. In the pesticide industry, some granular and dusting powders also contain a certain amount of surfactants to improve the adhesion and deposition of the pesticide on the treated surface, increase the release rate and expansion area of the active ingredient under moist conditions, and improve disease prevention and control effects.

In the cosmetics industry, emulsifiers are indispensable components in creams, lotions, cleansers, and makeup removers.

● Suspension

In the pesticide industry, wettable powders, emulsifiable oils, and concentrated emulsions require a certain amount of surfactants. For example, in wettable powders, the active ingredient is mostly an organic compound with hydrophobicity. Only in the presence of surfactants, which reduce the surface tension of water, can the pesticide particles be wetted by water to form an aqueous suspension;

● Foaming and Defoaming

Surfactants are also widely used in the pharmaceutical industry. In pharmaceuticals, many poorly soluble drugs, such as volatile oils, fat-soluble cellulose, and steroid hormones, can be made into clear solutions and their concentrations increased using the solubilizing action of surfactants; during pharmaceutical preparation, they are indispensable emulsifiers, wetting agents, suspending agents, foaming agents, and defoaming agents.

● Disinfection and Sterilization

The surfactants used for disinfection and sterilization are mainly cationic surfactants, such as benzalkonium bromide, whose chemical name is dodecyldimethylbenzylammonium bromide, and whose trade name is "New Jie Er Mie". In the pharmaceutical industry, it can be used as a bactericide and disinfectant. Its bactericidal and disinfecting effects are attributed to their strong interaction with bacterial biofilm proteins, causing them to denature or lose function. These disinfectants have relatively high solubility in water and, depending on the concentration used, can be used for preoperative skin disinfection, wound or mucous membrane disinfection, instrument disinfection, and environmental disinfection.

● Hard Water Resistance

Betaine surfactants exhibit excellent stability to calcium and magnesium ions, i.e., their own tolerance to calcium and magnesium hard ions and their dispersing power for calcium soaps. During use, they prevent the precipitation of calcium soaps and improve the effectiveness.

● Viscosity and Foaming Enhancement

Surfactants have an effect on changing the solution system, increasing the viscosity and thickening, or increasing the foam of the system. They have wide applications in some special cleaning and mining industries.

● Degreasing and Washing

Removing oil and dirt is a complex process that is related to the wetting, foaming, and other actions mentioned above.

Finally, it should be noted that surfactants do not act solely due to one aspect; in many cases, multiple factors work together. For example, in the paper industry, they can be used as cooking agents, deinking agents for waste paper, sizing agents, resin barrier control agents, defoamers, softeners, antistatic agents, scale inhibitors, softeners, degreasing agents, bactericides and algicides, and corrosion inhibitors, etc.

Surfactants are used as performance additives in many industry formulations, such as personal and home care, and countless industrial applications: metal treatment, industrial cleaning, oil extraction, pesticides, etc.