Surfactants-with their unique amphiphilic molecular structure, they are close to water and embrace oil. They can not only melt oil and water, but also reduce the surface tension of the liquid. They play a central role in emulsification, decontamination, dispersion, and solubilization.From daily cleansing to high-end skin care, surfactants have long penetrated into all aspects of life, and according to the charged characteristics of molecules in water, they are subdivided into four categories: anionic, cationic, nonionic and amphoteric. Each category has a distinctive personality and exclusive application scenarios.
Anionic Surfactants
Anionic surfactants are currently the most productive and widely used class. After they dissociate in water, the part that exerts surface activity will be negatively charged.The hydrophilic groups of such surfactants are mainly divided into four categories: carboxylates, sulfonates, alkyl sulfates and phosphate salts, while the oleophilic groups are mostly derived from natural oils or petrochemicals, such as straight 0 alkylbenzene, fatty alcohol, etc.
In daily care products, anionic surfactants have become the core ingredients of shampoo, foam shower gel and liquid soap due to their mild irritation and excellent decontamination and foaming ability.Classic varieties such as sodium linear alkylbenzene sulfonate (LAS) and sodium fatty alcohol polyoxyethylene ether sulfate (AES) can not only quickly take away the oil and dirt on the hair and skin, but also produce a dense and delicate foam, which brings a pleasant sense of use.In the industrial field, they are also used as dispersants for textile printing and dyeing, collectors for mining flotation, and even play a role in enhancing fluidity in building materials.
It is worth mentioning that with the popularization of the concept of green chemistry, the raw materials of anionic surfactants are also transforming to a more environmentally friendly direction.From the original petroleum-based raw materials to the increasing use of vegetable oils such as palm oil and coconut oil, not only has the biodegradable properties of the products been improved, but also the impact on the environment has been reduced.In cosmetic formulas, such surfactants are often used in combination with
Emulsifier for cosmetics to ensure cleanliness and maintain the stable texture of the product.
Cationic
In contrast to anionic surfactants, after the caionic surfactants dissociate in water, the active part will be positively charged.The hydrophilic groups of such surfactants are mainly composed of nitrogen atoms. The most common are quaternary ammonium salt types, such as
Behentrimonium chloride,
Cetrimonium chloride and
Stearalkonium chloride. They have a strong adsorption capacity on all kinds of solid surfaces, so they are outstanding in the fields of softness, antistatic, sterilization and disinfection.
In shampoo and hair care products, cationic surfactants are synonymous with suppleness.In the conditioner used after shampoo, it is precisely because of the addition of such ingredients that positively charged molecules will be adsorbed on the negatively charged hair scales, filling the gap between the damaged hair scales, making the hair smooth and soft, while reducing static electricity generation.In textile processing, they are also used as cationic fabric softeners to make clothes feel fluffy and skin-friendly to the touch, and to inhibit the growth of bacteria.
However, cationic surfactants have almost no washing capacity and relatively weak wetting effect. Therefore, they are rarely used alone in cleaning products, and are more used as functional additives in combination with other surfactants.In the field of cosmetics, they are often added to hair care essences, body creams and other products, which can not only improve skin feeling, but also play a certain antibacterial and anticorrosive role.
Nonionic Surfactants
Nonionic surfactants will not dissociate into ions in water, so their chemical stability is extremely high, they are not affected by acids, bases and salts, and their hard water resistance is also excellent.The molecular structure of such surfactants is composed of hydrophobic groups (such as high-carbon fatty alcohols, fatty acids) and hydrophilic groups (such as ethylene oxide, polyols). They are mainly divided into two categories: polyoxyethylene and polyol. The common ones are fatty alcohol polyoxyethylene ether (AEO), dehydrated sorbitol fatty acid esters, etc.
In cosmetic formulas, the advantages of nonionic surfactants are particularly obvious: low toxicity, low irritation to the skin, and good emulsification and decontamination capabilities.They are often used as
Emulsifying wax. In oil-in-water or oil-in-water formulas such as creams and lotions, they can stably combine the oil phase and the water phase to avoid product stratification.Compared with ionic surfactants, nonionic surfactants have slightly weaker foaming properties, but they are better than mild, so they are very suitable for cleansing products and baby care products for sensitive skin.
In addition, nonionic surfactants are not easy to strongly adsorb on solid surfaces and do not bind to proteins, which makes them widely used in the fields of food and medicine.For example, in ointments and injections, they can be used as
Solubilizers to help insoluble drugs disperse evenly.In baked goods, it can also be used as an
Emulsifier to improve the texture of the dough.This versatile characteristic makes nonionic surfactants one of the core additives for cross-disciplinary applications.
Amphoteric Surfactants
The molecular structure of Amphoteric surfactants has both positively and negatively charged groups, and in environments with different pH values, they can exhibit the properties of anionic or catic surfactants.For example, in an acidic environment, it will carry a positive charge, showing a soft and bactericidal effect similar to cationic surfactants.In an alkaline environment, it will be negatively charged, showing the decontamination ability of anionic surfactants.
This strain characteristic makes amphoteric surfactants the mildest class of surfactants.It is resistant to hard water, has minimal skin irritation, and is well compatible with various surfactants. Therefore, it is often added to high-end cleansing products, baby shampoos, and special care products for sensitive skin.In the textile industry, it can give fabrics a soft feel and good antistatic properties.In disinfection products, it can play an efficient bactericidal effect while gently cleaning.
Common amphoteric surfactants are imidazoline type, betaine type and amino acid type. Among them, cocamide propyl betaine (CAPB) is a frequent visitor in care products. It can not only enhance the foam texture of the product, but also reduce the irritation of the overall formula. After compounding with other surfactants, it can achieve a perfect balance of cleanliness and gentleness.
Surfactant
From the original petroleum-based raw materials to today's plant-based and bio-based raw materials, the development of surfactants has always revolved around a milder, more environmentally friendly, and more efficient direction.
Whether it is decontamination and foaming in cleaning and care, or emulsifying and moisturizing in cosmetics, surfactants are supporting our pursuit of a better life in a low-key way.Understanding the characteristics of these four types of surfactants can help us choose daily chemical products more rationally.
Hubei Mingya New Material Technology Co., Ltd.
