Surfactants, also known as surfactants, are compounds that can significantly reduce the surface tension or interfacial tension between two liquids, between liquids and gases, and between liquids and solids. The molecular structure of surfactants is amphoteric: hydrophilic group at one end, hydrophobic group at the other end; hydrophilic groups are often polar groups, such as carboxylic acid, sulfonic acid, sulfuric acid, amino or amine groups and their salts, hydroxyl, amide, ether bonds, etc., can also be used as polar hydrophilic groups; and hydrophobic groups are often nonpolar hydrocarbon chains, such as hydrocarbon chains of more than eight carbon atoms. Surfactant are divided into ionic surfactants (including cationic surfactants, anionic surfactants, and amphoteric surfactants), nonionic surfactants, complex surfactants, and other surfactants.
Overview of surfactants
Surfactants are a class of chemical substances with a special molecular structure, which usually contain hydrophilic and hydrophobic groups. This amphiphilic nature enables surfactants to form interfaces between water and other immiscible liquids and reduce interfacial tension, thus playing the roles of wetting, emulsifying, dispersing, solubilizing, foaming, defoaming and so on.
Types of surfactants
Surfactant is a special chemical substance that can significantly reduce the surface tension of the solvent at a very low concentration, thus changing the interfacial state of the system. This substance usually has both hydrophilic and lipophilic properties and can play a bridge role between two immiscible liquids, water and oil, so it is also known as an amphiphilic molecule.
Surfactants have a wide range of applications in many fields, such as daily life, industrial production, and scientific research. According to their different chemical structures and properties, surfactants can be divided into two categories: ionic and nonionic. Ionic surfactants can be further divided into cationic, anionic, and amphoteric types.
Ionic surfactants
Anionic surfactants
Anionic surfactants are the most widely used and most widely produced surfactants. Common anionic surfactants include salts of fatty acids, sulfonates, sulfate salts and phosphate salts. They have good detergency, emulsification, dispersion, solubilization, and other properties and are widely used in detergents, cosmetics, textiles, printing and dyeing, petroleum, pharmaceutical, and other industries.
Cationic surfactants
Cationic surfactants are mostly nitrogen-containing organic amine derivatives with good bactericidal, antistatic and softening properties. Because of their good softness and antistatic properties on fabrics, they are often used as post-treatment agents, softeners, antistatic agents and sterilizers for textiles.
Amphoteric ionic surfactants
Amphoteric ionic surfactants have both positive and negative charge groups in the molecule and show different charge properties at different pH values. These surfactants have excellent foaming, low irritation, good compatibility, and bactericidal properties and are widely used in detergents, cosmetics, medicine, and other fields.
Nonionic surfactants
Nonionic surfactants do not dissociate into ions in water and exist in solution in the form of neutral molecules or micro ions. These surfactants are highly stable, not easily affected by strong electrolytes and, acids and bases, and are compatible with other types of surfactants. Common nonionic surfactants include polyethylene glycol type, polyol type, fluorinated surfactants and silicone type. They are widely used in detergents, emulsifiers, dispersants, wetting agents and so on.
Examples of surfactants:
Ionic surfactants
Anionic surfactants: e.g. sodium fatty acids, alkyl sulfates, etc.
Cationic surfactants: e.g. quaternary ammonium salts, amine salts, etc.
Amphoteric ionic surfactants: e.g. amino acid type, betaine type, etc.
Nonionic surfactants
Polyoxyethylene ether type: such as fatty alcohol polyoxyethylene ether.
Polyol type: e.g. glycerol ester, sorbitol ester, etc.
Amine oxide type: such as dimethylamine oxide, etc.
Special types of surfactants
Polymer surfactants: surfactants with high molecular chain structure.
Bio-surfactants: such as phospholipids, glycolipids and other surfactants of natural biological origin.
What are the main functions of surfactants?
(1) Emulsification: Due to the large surface tension of grease in water, when grease is dripped into the water and stirred vigorously, the grease will be crushed into fine beads and mixed to form an emulsion, but the stirring will stop and re-layering will take place. If you add surfactant and stir hard, it will not be easy to stratify for a long time after stopping, which is the emulsification effect. The reason is that the hydrophobicity of the grease is surrounded by hydrophilic groups of surfactant, forming a directional attraction, reducing the oil in the water dispersion of the work required to make the grease emulsification is very good.
(2) Wetting effect: Parts often adhere to the surface of a layer of wax, grease, or scale-like substances, which are hydrophobic. Due to the pollution of these substances, the surface of the parts is not easy to wet with water. When adding surfactants to the water solution, the water droplets on the parts will be easily dispersed so that the surface tension of the parts is greatly reduced to achieve the purpose of wetting.
(3) solubilizing effect: oil substances in the addition of surfactant in order to dissolve, but this dissolution can only occur when the concentration of surfactant reaches the critical concentration of colloid, the size of the solubility according to solubilizing objects and properties to decide. In terms of solubilization, the long hydrophobic gene hydrocarbon chain is stronger than the short hydrocarbon chain, the saturated hydrocarbon chain is stronger than the unsaturated hydrocarbon chain, and the solubilization effect of nonionic surfactants is generally more significant.
(4) Dispersing effect: Dust, dirt, and other solid particles are easy to gather together and settle in water; surfactant molecules can make solid particle aggregates divided into small particles so that they are dispersed and suspended in the solution and play a role in promoting the uniform dispersion of solid particles.
(5) Foam effect: the formation of foam is mainly the directional adsorption of active agent, is the gas-liquid two-phase surface tension reduction caused by. Generally, the low molecular active agent is easy to foam, high molecular active agent foam less, cardamom acid yellow foam is the highest, sodium stearate foam is the worst, anionic active agent foam and foam stability than nonionic good, such as sodium alkyl benzene sulfonate foam is very strong. Usually used foam stabilizers are fatty alcohol amide, carboxymethyl cellulose, etc. Foam inhibitors are fatty acids, fatty acid esters, polyethers, etc. and other nonionic surfactants.
Application of surfactants
Surfactants have a wide range of applications, almost covering our daily life and various industrial production fields. The following are some of the main applications of surfactants:
Detergents and cosmetics: Surfactants are important ingredients in detergents and cosmetics, such as laundry detergents, liquid detergents, shampoos, shower gels, moisturizing lotions and so on. They reduce the surface tension of water, making it easier for stains to be removed from the surface of objects while providing a rich lather and lubricating sensation.
Textile industry: In the textile industry, surfactants are used as softeners, wetting agents, antistatic agents, dispersants, leveling agents and, color fixing agents, etc., which help to improve the quality of textiles and enhance the uniformity of dyeing and color vividness.
Food industry: Surfactants can be used as emulsifiers, dispersants, wetting agents, defoamers, etc., in the manufacture of dairy products, beverages, confectionery, and other food products to improve their stability and taste.
Agriculture and pesticides: In agriculture, surfactants can improve the wetting and dispersion of pesticides, thus improving their insecticidal effect. They can also be used as soil conditioners to improve soil water retention and permeability.
Petroleum industry: In the process of oil extraction and processing, surfactants can be used as emulsion breakers, oil repellents, anti-waxing agents, and enhancement of recovery, etc., which help to improve the efficiency of oil extraction and processing.
Pharmaceutical industry: In the pharmaceutical industry, surfactants can be used to prepare emulsions, suppositories, aerosols, tablets, injections, etc., playing the role of emulsification, solubilization, wetting, dispersion and penetration.
In addition, surfactants play an important role in many industries, such as construction, paint, paper, leather, and metal processing. Their application in these fields is mainly realized by improving product processing performance, enhancing product quality, and reducing production costs.