Classification and application of surfactants Abstract: The application scope of surfactants covers all aspects of people's life and work. In 1990s, people began to study surfactants systematically. It can be said that without surfactants, we would not be clean now. Now our understanding of surfactants only stays on the surface, and there is no further research. The following are some basic understandings of surfactants. Keywords: HLB value, classification, application 1. HLB value-The greater the HLB value, the stronger the hydrophilicity, and the smaller the HLB value, the stronger the lipophilicity. Generally speaking, the range of HLB value is 1 ~ 40. The HLB of hydrophilic and lipophilic turning point is 10. HLB less than 10 is lipophilic and more than 10 is hydrophilic. 1 ~-3 as defoamer 3 ~-6 as w/o emulsifier Span (sorbitan fatty acid ester) is a W/O emulsifier with strong emulsifying, dispersing and lubricating effects, and can be mixed with various surfactants, especially Tween -60, with HLB value of 4.7. 7-9 as wetting agent; 8 ~- 18 as O/W emulsifier, also called Tween emulsifier, is a condensate of Span and ethylene oxide, and is a nonionic detergent of polyoxyethylene sorbitan fatty acid ester; Commonly used as oil-in-water (O/W) type, medicinal: (1) can be used as solubilizing agent for some drugs. (2) It has hemolytic effect, and Tween -80 has the weakest effect. (3) The water solution can be turbid after heating, and clear after cooling, without affecting the quality. (4) In solution, 13~- 18 can interfere with the function of bacteriostatic agent as solubilizing agent. Classification and common use: 1, anionic surfactant: stearic acid, sodium dodecyl benzene sulfonate 2, cationic surfactant: quaternary ammonium compound 3, zwitterionic surfactant: lecithin, amino acid type, betaine type 4, nonionic surfactant: fatty acid glyceride, fatty acid sorbitan (span), polysorbate (Tween) anionic surfactant: 1 Sodium dodecyl sulfate (SDS, sodium lauryl sulfate) 3. Sulfonate: sodium dioctyl succinate (Aloso -OT), sodium dodecyl benzene sulfonate, sodium glycocholate, anionic surfactant, cationic soap. The main part of its molecular structure is a pentavalent nitrogen atom, so it is also called quaternary ammonium compound. It is characterized by high water solubility, stability in acidic and alkaline solutions, good surface activity and sterilization. Commonly used varieties are benzalkonium chloride (bromogeramine) and benzalkonium bromide (bromogeramine). Zwitterionic surfactants have both positive and negative charge groups, which can show the properties of cationic or anionic surfactants in different pH media. 1. lecithin is the main auxiliary material for preparing emulsion for injection and lipid microparticle preparation. 2. Amino acid type and betaine type: amino acid betaine type: it has the properties of anionic surfactant in alkaline aqueous solution and has good foaming and decontamination effects. In acidic solution, it is a cationic surfactant with strong bactericidal ability. Nonionic surfactant 1. Fatty acid glyceride: glycerol monostearate; HLB is 3~4, which is mainly used as auxiliary emulsifier of W/O emulsion. 2. polyol sucrose ester: HLB(5~ 13)O/W emulsifier, dispersant fatty acid sorbitan (span): W/O emulsifier polysorbate (tween): O/W emulsifier 3. Polyethylene oxide type: Myrij (seller, long-chain fatty acid ester); Fatty alcohol ester. Polyoxyethylene-polyoxypropylene * * * polymer: It can withstand hot-pressing sterilization and low-temperature freezing. The emulsifier of intravenous emulsion is generally a low molecular weight dispersant. Surfactant molecules have the function of modification, especially reducing the surface tension between pigment and resin solution. The structure of surfactant contains two groups with opposite solubility or polarity, which increases the surface activity. In aqueous systems, polar groups are hydrophilic groups, while nonpolar groups are hydrophobic or oleophilic. In non-aqueous systems, polar groups are oleophobic and nonpolar groups are oleophilic. Surfactants are classified according to their chemical structures, especially polar groups, including anions, cations, electrically neutral particles and nonionic. The effectiveness of polymer dispersant is determined by the following factors: adsorption of polar groups on the surface of pigment. The anchoring group can be amino, carboxylic acid, sulfonic acid, phosphoric acid and its salts. Behavior of nonpolar fragments around particles in media. Some parts of the molecule (aliphatic or aliphatic-aromatic fragments) must be highly compatible with the adhesive system. The stability mechanism of dispersant similar to surfactant is electrostatic stability: a double-layer charged structure is formed around the polar groups of pigment particles. Due to Brownian motion, pigment particles in liquid medium often collide together, so there is a strong tendency to re-flocculate during its deceleration. According to its chemical structure (such as low molecular weight) and electrostatic stability theory, surfactants have the following defects: water sensitivity: surfactants usually make the final coating water sensitive and are not suitable for outdoor applications. Foam-prone: Many surface modifiers will produce foam, resulting in defects (such as fisheye, pits, etc.) on the coating. If foam appears in the grinding process, it will lead to a decrease in productivity. Interference of adhesion between coatings. After years of development, special surfactants have been improved, which can minimize coating defects, and some can also make the coating have some other advantages, such as defoaming/corrosion resistance or making the substrate difficult to wet. The most commonly used surfactants for pigment dispersion are fatty acid derivatives, phosphate esters, sodium polyacrylate/polyacrylic acid, acetylene glycol and soybean lecithin. Development direction of surfactant 1. Industrial Manufacture of Alkyl Phosphocarboxylate (AEC) With the rapid development of science and technology and the continuous progress of modern cultural alliance, people have higher and higher requirements for the use of surfactants, which are mild, biodegradable, multifunctional, emphasizing safety, ecological protection and improving efficiency. Alkyl alcohol ether carboxylate (AEC) is a kind of high-quality surfactant actively developed by developed countries since 1980s. Together with alkyl polyglycoside and alcohol ether phosphate monoester, it is called "the green variety of surfactants in the 1990s". Production of alkyl ether carboxylate. AEC and APEC are generally prepared from fatty alcohols or alkylphenols by ethoxylation and carboxymethylation. Alkyl ether carboxylate is similar to soap in chemical structure, and ethylene oxide with a certain addition number is embedded between hydrophobic groups and hydrophilic groups, which makes it have many excellent properties in anionic and nonionic surfactants and become a multifunctional variety. It is superior to the corresponding alcohol (phenol) ether surfactant in metal processing, and has the following characteristics: (1) is less irritating to skin and eyes. (2) The cleaning performance is less affected by pH value and temperature. (3) Stable to acid, alkali and chlorine. (4) Excellent biodegradability. Figure 1 Surfactant Structure Diagram There is still a big gap between the domestic application market of alkyl ether carboxylates and developed countries. With the continuous strengthening of environmental awareness and the continuous improvement of people's material and cultural level, this kind of mild, biodegradable and multifunctional surfactant will play a greater role in the field of metal processing. 2. Gemini, a new generation of surfactants, has synthesized oligomer surfactants such as dimer, trimer and tetramer, among which dimer is the most eye-catching, and the structural diagram is shown in figure 1. Dimer surfactant was first synthesized in 197 1 [4-5], and was named Gemini because of its structural characteristics. Gemini surfactant (or dimer) is composed of two single-chain single-headed Kiptoon surfactants connected by chemical bonds on ionic head groups, thus inhibiting the separation force of head groups in the process of ordered aggregation of surfactants and greatly improving the surface activity. Compared with many attempts to improve surface activity, such as adding salt, raising temperature or mixing anionic surfactant with anionic surfactant, Gemini surfactant is a conceptual breakthrough, so it is known as a new generation of surface inclusion agent. In Gemini surfactants, two ionic heads are connected by chemical bonds through connecting groups, which leads to the close connection of monomer ions of the two surfactants, and it is easier to produce strong interaction between hydrocarbon chains, that is, the hydrophobic binding force between hydrocarbon chains is strengthened, and the repulsion tendency between ionic heads is greatly weakened by the chemical bond force, which is the fundamental reason why Gemlrd surfactant has higher surface inclusion than single-chain single-head surface inclusion agent. On the other hand. The chemical bond between the two ionic heads does not destroy their hydrophilicity, which provides a basis for the wide application of high surface activity C~mini surfactant. Improving the surface activity by chemical bonding is different from the physical methods commonly used in the past, which is a breakthrough in concept. Fig. 2 Excellent performance of alkynol gemini surfactant: Experiments show that ionic gemini surfactant has the following characteristics: (1) is more easily adsorbed on gas/liquid surface, thus reducing the surface tension of aqueous solution more effectively while keeping the number of carbon atoms connected to each hydrophilic group equal. (2) It is easier to aggregate to form micelles. (3)3) The tendency of Gemini to reduce the surface tension of aqueous solution is much greater than that of aggregation to form micelles, and the efficiency of reducing the surface tension of aqueous solution is quite outstanding. (4) It has a very low Krat~ (2+) phase transition point. (5) The combination of Gemini surfactants and common surfactants, especially nonionic surfactants, can produce a greater synergistic effect on the ability and efficiency of reducing the surface tension of aqueous solution. (6) It has good dispersion performance of calcium soap. (7) It is an excellent wetting agent in many fields. Theoretically, the chemical bonding platform of polar head group region inhibits the separation force between the original single-chain single-head surfactant and its head group, so it is bound to strengthen the bonding between carbon chains. Experiments show that this is an important breakthrough in improving surface activity and opens up a new way for practical application. On the other hand, due to the change of the geometry of new molecules generated by the bond table, some new forms of molecular aggregates have been brought, which greatly enriched the self-organization phenomenon of amphiphilic molecules. Revealing the relationship between new molecular structure and self-organization behavior is helpful to understand the self-organization mechanism of amphiphilic molecules. Therefore, Gemini surfactants are becoming the research direction of major groups in the field of colloid and interface science in the world. 3. Inorganic dispersants such as polyphosphates, silicates and carbonates, traditional small-molecule surfactants and polymer compounds such as polycarboxylates and polypropionates have been used in 3. AB block polymer surfactant coating. Polymer compounds mainly use steric hindrance to stabilize pigments and filler particles, which is better than electrostatic repulsion of small molecular surfactants. The research shows that among many types of polymer dispersants, AB block polymer surfactant has the best effect and the highest efficiency. In terms of molecular structure, AB block polymer is a super-large surfactant, and A block and B block are similar to hydrophilic head group and hydrophobic tail chain of surfactant respectively. AB block polymer surfactant exists on the surface of pigments and fillers in the form of tail adsorption. The A block is the anchor group of the pigment, and the B block is the solvated tail chain. Block A can be a functional group, such as acid, amine, alcohol, phenol, etc. It is adsorbed on the surface of particles through ionic bonds, valence bonds, coordination bonds, hydrogen bonds and van der Waals forces. Because it contains multiple adsorption points, it can effectively prevent the dispersant molecules from desorbing and make the adsorption tight and lasting. B block can be polyether, polyester, polyolefin, polyacrylate and other groups, which are suitable for polar and nonpolar solvents respectively. The typical AB block polymer surfactant structure is shown in Figure 3. The stable particles mainly depend on the steric hindrance of the adsorption layer formed by the B block, so the length and uniformity of the B block as a solvated tail chain are extremely high. It is desirable to form an adsorption layer with a moderate thickness. If the B block is too long, it may play a bridging role, leading to an increase in viscosity of the dispersion system or even flocculation and precipitation. It is generally believed that the best stabilization effect can be obtained when the thickness of the steric barrier layer is 20nm. Figure 3 AB block polymer surfactant Synthesis AB block polymer surfactant with clear molecular structure and controllable relative molecular weight is the development direction of coating dispersion additives, which requires controlled polymerization technology. Group transfer polymerization (GTP), atom transfer radical polymerization (ATRP), nitroxyl polymerization (NMP) and reversible addition-fragmentation chain transfer polymerization (RAFT) are the most commonly used controllable polymerization technologies. By using these technologies, the required polymer structure can be obtained by selecting appropriate methods and equipment. Different monomers can be selected and arranged according to the designed order, and finally a polymer with specific structure, narrow relative molecular weight distribution and close to monodispersion can be synthesized. At present, only a few companies such as BYK, Ciba and Rhodia have controllable polymerization technology. The new dispersant being developed by Shenzhen Haichuan Company is also AB block polymer surfactant.