Surfactant refers to a substance which is added in a small amount to cause a significant change in the interface state of the solution system. It has a fixed hydrophilic lipophilic group and can be aligned on the surface of the solution. The molecular structure of the surfactant is amphiphilic: one end is a hydrophilic group and the other end is a hydrophobic group; the hydrophilic group is often a polar group such as a carboxylic acid, a sulfonic acid, a sulfuric acid, an amino group or an amine group; The salt, hydroxyl group, amide group, ether bond and the like may also serve as a polar hydrophilic group; and the hydrophobic group is often a non-polar hydrocarbon chain, such as a hydrocarbon chain of 8 or more carbon atoms. Surfactants are classified into ionic surfactants (including cationic surfactants and anionic surfactants), nonionic surfactants, amphoteric surfactants, complex surfactants, other surfactants, and the like.
Surfactant molecules have a unique amphiphilicity: one end is a hydrophilic polar group, referred to as a hydrophilic group, also known as an oleophobic or oleyl group, sometimes referred to as a hydrophilic head, such as -OH, -COOH, -SO3H, -NH2; the other end is a lipophilic non-polar group, referred to as a lipophilic group, also known as a hydrophobic or hydrophobic group, such as R-(alkyl), Ar-(aryl) . Two types of molecular fragments or groups with opposite structures and properties are at the opposite ends of the same molecule and are joined by chemical bonds to form an asymmetric, polar structure, thus giving the particular molecule a hydrophilic It is also lipophilic, but it is not a characteristic of overall hydrophilicity or lipophilicity. This unique structure of surfactants is often referred to as the "amphiphilic structure", and surfactant molecules are therefore often referred to as "parental molecules." 
For convenience, a common symbol rectangle plus a circle indicates the surfactant molecule, as shown in the right figure. Wherein the rectangle represents a lipophilic group and the circle represents a hydrophilic group.
Surfactants reduce the surface tension of water by adsorbing at the gas-liquid two-phase interface, and can also reduce the oil-water interfacial tension by adsorbing between liquid interfaces. Many surfactants can also aggregate into aggregates in bulk solutions.
Both vesicles and micelles are such aggregates. The concentration at which the surfactant begins to form micelles is called the critical micelle concentration or CMC. When the micelles are formed in water, the tails of the micelles form a core that can wrap oil droplets, and their (ion/polar) heads can form an outer shell that remains in contact with water. Surfactants accumulate in oil, and aggregates refer to reverse micelles. In the reverse micelle, the head remains in full contact with the oil at the core and tail. Surfactants are generally classified into four broad categories: anionic, cationic, nonionic, and zwitterionic (dual electron). The thermodynamics of a surfactant system is important, both theoretically and in practice. Because the surfactant system represents a system between ordered and disordered material states. The surfactant solution may contain an ordered phase (micelle) and a disordered phase (free surfactant molecules and/or ions). Micelle - The lipophilic tail of the surfactant molecule accumulates inside the micelle to avoid contact with polar water molecules; the polar hydrophilic head of the molecule is exposed to the outside and interacts with polar water molecules. It also protects the hydrophobic groups inside the micelles. The micelle-forming compound is generally an amphiphilic molecule, and therefore the micelle is generally soluble in a non-polar solvent in the form of a reverse micelle in addition to being soluble in a polar solvent such as water.
For example, commonly used detergents can increase the penetration of water in the soil, but the effect lasts only a few days (many standard detergents contain a certain amount of chemicals, such as sodium and bromine, which are not suitable for soil because they destroy plants). Commercial soil wetting agents will continue to work for a period of time and eventually will be degraded by microorganisms. However, some have an impact on the biological cycle of aquatic organisms, so care must be taken to prevent these products from flowing into surface runoff and excess product should not be depleted.
Positive adsorption in solution: increase wettability, emulsifying property, foaming property;
Adsorption of solid surfaces: single layer adsorption on non-polar solid surfaces,
Multilayer adsorption on polar solid surface
By the affinity of different parts of the molecule for the two phases, the two phases are regarded as the components of the phase, and the molecules are arranged between the two phases, so that the surface of the two phases is equivalent to the inside of the molecule. Thereby reducing the surface tension. Since both phases regard it as a component of the phase, it is equivalent to the fact that the two phases do not form an interface with the surfactant molecules, which is equivalent to partially eliminating the interface of the two phases in this way, thereby reducing Surface tension and surface free energy.
Surfactants become a kind of flexible and diverse due to a series of physical and chemical effects such as wetting or anti-sticking, emulsification or demulsification, foaming or defoaming, solubilization, dispersion, washing, anti-corrosion, anti-static and the corresponding practical application. , a wide range of fine chemical products. Surfactants can be used as a detergent in daily life, and other applications can cover almost all fine chemical fields.
Requirements: C>CMC ( HLB13~18)
Critical micelle concentration (CMC): The lowest concentration of surfactant molecules associated to form micelles. When the concentration is higher than the CMC value, the surfactant is arranged in a spherical shape, a rod shape, a bundle shape, a layer shape/plate shape, or the like.
The solubilization system is a thermodynamic equilibrium system;
The lower the CMC and the greater the number of associations, the higher the amount of solubilization (MAC);
Effect of temperature on solubilization: temperature affects the formation of micelles, affects the dissolution of solubilizing substances, and affects the solubility of surfactants.
Krafft point: The solubility of ionic surfactant increases sharply with increasing temperature. This temperature is called Krafft point. The higher the Krafft point, the smaller the critical micelle concentration.
Cloud point: For polyoxyethylene type nonionic surfactants, when the temperature rises to a certain extent, the solubility drops sharply and precipitates, and the solution appears turbid. This phenomenon is called Cloud, and this temperature is called Cloud point. This is because the hydrogen bond between the polyoxyethylene and the water is broken. When the temperature rises to a certain temperature, the polyoxyethylene can undergo strong dehydration and shrinkage, so that the solubilization space is reduced and the solubilization ability is lowered.  When the polyoxyethylene chain is the same, the longer the hydrocarbon chain, the lower the cloud point; when the hydrocarbon chain is the same, the longer the polyoxyethylene chain, the higher the cloud point.
Hydrophilic-lipophilic balance (HLB): The combined affinity of hydrophilic and lipophilic groups in a surfactant molecule for oil or water. According to experience, the HLB value range of the surfactant is limited to 0-40, and the non-ionic HLB value is 0-20.
Mixed additivity: HLB = (HLBa Wa + HLBb / Wb) / (Wa + Wb)
Theoretical calculation: HLB = ∑ (hydrophilic group HLB value) + ∑ (lipophilic group HLB)-7
HLB: 3-8 W / O type emulsifier: Span; divalent soap
HLB: 8-16 O/W emulsifier: Tween; monovalent soap
- Wetting effect
Requirements: HLB: 7-9.
The degree of wetting between the liquid and the solid can be controlled by using a surfactant. In the pesticide industry, some of the granules and powders for dusting also contain a certain amount of surfactant, the purpose of which is to improve the adhesion and deposition of the agent on the surface of the drug, and to improve the active ingredients in the water condition. The release speed and extended area are improved to prevent disease and cure diseases.
In the cosmetics industry, as an emulsifier, it is an indispensable ingredient in skin care products such as creams, lotions, cleansers and make-up removers.
In the pesticide industry, wettable powders, emulsifiable concentrates and concentrated emulsions all require a certain amount of surfactants. For example, the wettable powders are mostly organic compounds, which are hydrophobic and only reduce the surface of water in the presence of surfactants. Tension, the granules may be wetted by water to form an aqueous suspension;
- Foaming and defoaming
Surfactants are also widely used in the pharmaceutical industry. In the medicament, some volatile oil-soluble cellulose, steroid hormones and many other insoluble drugs can form a transparent solution and increase the concentration by the solubilization of the surfactant; it is an indispensable emulsifier and moisturizing during the preparation of the medicament. Agents, suspending agents, foaming agents and defoaming agents.
- Disinfection, sterilization
It can be used as a fungicide and disinfectant in the pharmaceutical industry. Its sterilization and disinfection are attributed to their strong interaction with bacterial biofilm proteins to denature or lose their function. These disinfectants have a relatively large solubility in water, according to The concentration can be used for pre-operative skin disinfection, wound or mucosal disinfection, instrument disinfection and environmental disinfection;
- Anti-hard water
Betaine surfactants show very good stability to calcium and magnesium ions, namely their tolerance to calcium and magnesium hard ions and the dispersion of calcium soap. Prevent the precipitation of calcium soap during use and improve the use effect.
- Viscosity and foaming
Surfactants have a role in changing the solution system, increasing the viscosity to thicken or increasing the foam of the system, and are widely used in some special cleaning and mining industries.
- Descaling and washing
The removal of grease and dirt is a relatively complicated process, which is related to the above-mentioned effects of wetting, foaming and the like.
Finally, it should be noted that surfactants work not only because of the role of one aspect, but in many cases multiple factors work together. For example, it can be used as cooking agent, waste paper deinking agent, sizing agent, resin barrier control agent, defoaming agent, softener, antistatic agent, scale inhibitor, softener, degreaser, sterilization in the paper industry. Algae, corrosion inhibitor, etc.
Surfactants are used as performance additives in many industry formulations, such as personal and home care, and in countless industrial applications: metal processing, industrial cleaning, oil extraction, pesticides, and more.
Dongguan Defond defoamer Co, Ltd is specialized in manufacturing of industrial grade surfactants, including the defoamer, emulsifiers, penetrants, dispersants, flatting agents, antistatic agents and other chemical products.
This article is from Defond Surfactant (https://www.defond-surfactant.com/newsList.html), please indicate the source.