Abstract: Discusses the functions of surfactants, such as wetting, dispersing, emulsifying, solubilizing, foaming, defoaming, washing and decontamination, etc., introducing the classification of surfactants, and introducing several commonly used surface activities Agent. And the role in cosmetics, detergents, medicine, food. The development trend of surfactants is described.

1. Classification of surfactants

There are many ways to classify surfactants, which are classified according to the source of surfactants. Surfactants are usually divided into three categories: synthetic surfactants, natural surfactants and biological surfactants.

Surfactants can be divided into four categories: anionic, cationic, zwitterionic and nonionic according to the type of ions generated by the hydrophilic group. Commonly used surfactants, whose hydrophobic base is a hydrocarbon group, may also contain elements such as oxygen, nitrogen, sulfur, chlorine, bromine, and iodine in the molecule, and are called hydrocarbon surfactants or ordinary surfactants. Surfactants containing fluorine, silicon, phosphorus and boron are called special surfactants. The introduction of fluorine, silicon, phosphorus, boron and other elements gives surfactants more unique and excellent performance. Fluorine-containing surfactants are one of the most important varieties of special surfactants.

2. The main role of surfactants

(1) Emulsification: Due to the high surface tension of the oil in the water, when the oil is dripped into the water, stir vigorously, the oil is crushed into fine beads and mixed into an emulsion, but the stirring stops and re-layers. If you add a surfactant and stir vigorously, it will not be easy to separate for a long time after stopping, which is emulsification. The reason is that the hydrophobicity of the oil is surrounded by the hydrophilic group of the active agent, forming a directional attraction, reducing the work required for oil dispersion in water, and making the oil well emulsified. To

(2) Wetting effect: There is often a layer of wax, grease or scaly material attached to the surface of the part, which is hydrophobic. Due to the pollution of these substances, the surface of the parts is not easy to be wetted by water. When surfactants are added to the aqueous solution, the water droplets on the parts are easily dispersed, which greatly reduces the surface tension of the parts and achieves the purpose of wetting. To

(3) Solubilization: oily substances can be “dissolved” after adding surfactants, but this dissolution can only occur when the concentration of the surfactant reaches the critical concentration of the colloid. The solubility is based on the solubilization object and It depends on the nature. 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. To

(4) Dispersion effect: solid particles such as dust and dirt particles are relatively easy to aggregate together, and they are easy to settle in water. The molecules of surfactants can divide the solid particle aggregates into fine particles, which are dispersed and suspended in the solution. Play a role in promoting the uniform dispersion of solid particles. (5) Foam effect: The formation of foam is mainly the directional adsorption of the active agent, which is caused by the decrease of the surface tension between the gas and liquid phases. Generally, low-molecular-weight active agents are easy to foam, high-molecular-weight active agents have less foam, myristic acid yellow has the highest foaming properties, and sodium stearate has the worst foaming properties. Anionic active agents have better foaming properties and foam stability than non-ionic ones. For example, sodium alkylbenzene sulfonate has strong foaming properties. Commonly used foam stabilizers include fatty alcohol amides, carboxymethyl cellulose, etc., and foam inhibitors include fatty acids, fatty acid esters, polyethers, etc. and other nonionic surfactants.

3 Application of Surfactant

The application of surfactants can be divided into civil and industrial applications. According to data, two-thirds of civilian surfactants are used in personal protection products; synthetic detergents are one of the largest consumer markets for surfactants. Products include washing powder, liquid detergents, dishwashing detergents and various household products. Cleaning products and personal protection products such as: shampoo, conditioner, hair cream, hair gel, lotion, toner, facial cleanser, etc. Industrial surfactants are the sum of surfactants used in various industrial fields other than civil surfactants. Its application fields include textile industry, metal industry, paint, paint, pigment industry, plastic resin industry, food industry, paper industry, leather Industry, petroleum exploration, building materials industry, mining industry, energy industry, etc. Several aspects are described below.

3.1.1 Surfactant in cosmetics

Surfactants are widely used in various cosmetics as emulsifiers, penetrants, detergents, softeners, wetting agents, bactericides, dispersants, solubilizers, antistatic agents, hair dyes, etc. Non-ionic surfactants are most commonly used in cosmetics because they are not irritating and are easily compatible with other components. Generally, they are fatty acid esters and polyethers.

3.1.2 The requirements of cosmetics for surfactants

The composition of cosmetic formulations is diverse and complex. In addition to oil and water raw materials, there are also various functional surfactants, preservatives, flavors and pigments, etc., which belong to a multi-phase dispersion system. With more and more cosmetic formulations and functional requirements, the variety of surfactants used in cosmetics is also increasing. Surfactants used in cosmetics should have no skin irritation, no toxic side effects, and also meet the requirements of colorlessness, no unpleasant odor and high stability.

3.2 Application of surfactants in detergents

Surfactants have efficient cleaning and disinfection functions, and have long become the most important part of cleaning products. Surfactant is the main component of detergent. It interacts with dirt and between dirt and solid surface (such as wetting, permeating, emulsifying, solubilizing, dispersing, foaming, etc.) and taking advantage of Mechanical stirring obtains the washing effect. The most widely used and most widely used are anionic and nonionic surfactants. Cationic and amphoteric surfactants are only used in the production of certain special types and functions of detergents. The main varieties are LAS (referring to alkyl benzene sulfonate), AES (fatty alcohol polyoxyethylene ether sulfate), MES (α-sulfonic acid fatty acid salt), AOS (α-alkenyl sulfonate), Alkyl polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid diethanolamine, amino acid type, betaine type, etc.

3.3 Application of surfactants in the food industry

3.3.1 Food emulsifiers and thickeners The most important role of surfactants in the food industry is to act as emulsifiers and thickeners. Phospholipids are the most commonly used emulsifiers and stabilizers. In addition to phospholipids, commonly used emulsifiers are fatty acid glycerides S, mainly monoglyceride T, fatty acid sucrose esters, fatty acid sorbitan esters, fatty acid propylene glycol esters, soybean phospholipids, gum arabic, alginic acid, sodium caseinate, Gelatin and egg yolk etc. Thickeners are divided into two categories: natural and chemically synthesized. Natural thickeners include starch, gum arabic, guar gum, carrageenan, pectin, agar, and alginic acid made from plants and seaweeds. There are also gelatin, casein and sodium caseinate made from protein-containing animals and plants. And xanthan gum made from microorganisms. The most commonly used synthetic thickeners are sodium carboxymethyl cellulose: @:, propylene glycol alginate, cellulose glycolic acid and sodium polyacrylate, sodium starch glycolate, sodium starch phosphate, methyl cellulose and polyacrylic acid Sodium etc.

3.3.2 Food preservatives Rhamnose esters have certain antibacterial, antiviral and anti-mycoplasma properties. Sucrose esters also have a greater inhibitory effect on microorganisms, especially spore-forming Gram-positive bacteria.

3.3.3 Food dispersants, foaming agents, etc. In addition to being used as emulsifiers and thickeners in food production, surfactants can also be used as dispersants, wetting agents, foaming agents, defoamers, crystallization control agents, Sterilize and prolong food preservation period. For example, adding 0.2-0.3% soy phospholipids when granulating whole milk powder can improve its hydrophilicity and dispersibility, and it can be dissolved quickly without agglomeration during preparation. When making cakes and ice cream, adding glycerol fatty acid and sucrose fat can have a foaming effect, which is conducive to the production of a large number of bubbles. In the production of condensed milk and soy products, adding glycerol fatty acid has a defoaming effect.

3.3.4 Application in the extraction and separation of pigments, fragrance components, biologically active components and fermented products

In recent years, surfactants have also been widely used in the extraction and separation of natural ingredients in food such as pigments, flavor ingredients, biologically active ingredients and fermented products.

3.4 Application of surfactants in the field of medicine

Surfactants have the functions of wetting, emulsifying, solubilizing, etc., so they are widely used as pharmaceutical excipients, especially in the pharmaceutical microemulsion technology that has been developed in recent years. In drug synthesis, surfactants can be used as phase transfer catalysts, which can change the degree of solvation of ions, thereby increasing the reactivity of ions, making the reaction proceed in a heterogeneous system, and greatly improving the reaction efficiency. Surfactants are often used as solubilizers and sensitizers in analysis, especially in pharmaceutical fluorescence spectroscopy. In terms of skin disinfection, wound or mucous membrane disinfection, instrument disinfection and environmental disinfection before surgery in the pharmaceutical industry, surfactants can strongly interact with bacterial biofilm proteins to denature or lose their function, and are used as bactericides and disinfectants being widely used.

4. The development trend of surfactants

The development direction of surfactants will be manifested in the following aspects:

4.1 Return to nature;

4.2 Replace harmful chemicals;

4.3 Wash and use at room temperature;

4.4 Use in hard water without additives;

4.5 Environmental protection that can effectively treat waste liquid, waste water, dust, etc. Surfactants;

4.6 Surfactants that can effectively improve the utilization of minerals, fuels, and production;

4.7  Multifunctional surfactants;

4.8  Surfactants prepared from industrial or urban waste based on bioengineering;

4.9 Reuse High-efficiency surfactant with synergistic effect produced by formulation technology.