1. Wetting effect

When the solid is in contact with the liquid, the original solid/gas and liquid/gas interfaces disappear and a new solid/liquid interface is formed. This process is called wetting. For example, textile fiber is a porous material with a huge surface. When the solution spreads along the fiber, it will enter the gap between the fibers and drive out the air, turning the original air/fiber interface into a liquid/fiber interface. It is a typical wetting process; while the solution will enter the fiber at the same time, this process is called penetration. Surfactants that help wetting and penetration are called wetting agents and penetrants.

2. Emulsification

Emulsification refers to two immiscible liquids (such as oil and water), one of which is formed by evenly dispersing very small particles (particle size 10-8~10-5m) into the other liquid The role of emulsion. Oil droplets dispersed in water are called oil-in-water emulsions (O/W), and water droplets dispersed in oils are called water-in-oil emulsions (W/O). Surfactants that can help emulsification are called emulsifiers. Surfactants used as emulsifiers have two functions: stabilization and protection.

 

(1) Stabilization

The emulsifier has the effect of reducing the interfacial tension between the two liquids to stabilize the mixed system. This is because when oil (or water) is dispersed into many tiny particles in water (or oil), the contact area between them is enlarged, resulting in an increase in the energy potential of the system and an unstable state. When an emulsifier is added, the lipophilic group of the emulsifier molecule is adsorbed on the surface of the oil droplet particles while the hydrophilic group extends into the water, and is aligned on the surface of the oil droplet to form a hydrophilic molecular film, which reduces the oil/water interfacial tension , Which reduces the energy level of the system and reduces the attraction between oil droplets, preventing the oil droplets from accumulating and re-dividing into two layers.

(2) Protection

The oriented molecular film formed by the surfactant on the surface of the oil droplets is a strong protective film that can prevent the oil droplets from colliding and gathering. If it is an oriented molecular film formed by an ionic surfactant, the oil droplets will also be charged with the same kind of charge, which will increase the mutual repulsion and prevent the oil droplets from gathering during frequent collisions.

 

3.washing decontamination effect

Due to the emulsification effect of the surfactant, the grease and dirt particles detached from the solid surface can be stably emulsified and dispersed in the aqueous solution, and will no longer be deposited on the cleaned surface to form re-contamination.

The process of removing liquid oil from the surface is described below to illustrate the role of surfactants. Liquid oil stains originally spread on the solid surface. When surfactants are added, due to its low surface tension, the surfactant aqueous solution quickly spreads on the solid surface and wets the solids, and gradually replaces the oil stains. The oil stains spread on the solid surface gradually curl into oil droplets (the contact angle gradually increases, changing from wetting to non-wetting).

 

4.suspension dispersion

The process of dispersing insoluble solids into a solution with very small particles to form a suspension is called dispersion. The surfactant that promotes the dispersion of solids and forms a stable suspension is called a dispersant. In fact, when semi-solid oil is emulsified and dispersed in a solution, it is difficult to distinguish whether a certain process is emulsification or dispersion, and emulsifier and dispersant are usually the same substance, so put the two together in actual use. Emulsifying and dispersing agent.

The principle of action of dispersants is basically the same as that of emulsifiers. The difference is that the dispersed solid particles are generally less stable than the emulsified droplets.

 

5.foaming effect

The state of gas dispersed in liquid is called bubble. If a certain liquid is easy to form a film and is not easy to break, the liquid will produce a lot of bubbles when it is stirred. After the foam is generated, the gas/liquid surface area in the system is greatly increased, making the system unstable, so the foam is easy to burst. When the surfactant is added to the solution, the surfactant molecules are adsorbed on the gas/liquid interface, which not only reduces the surface tension between the gas/liquid phases, but also forms a monomolecular film with a certain mechanical strength to make the foam difficult to burst.

Surfactant aqueous solutions have different degrees of foaming effect. Generally, anionic surfactants have stronger foaming properties, while nonionic surfactants have weaker foaming properties, especially when used above the cloud point.

Because the foam surface has a strong adsorption effect on dirt, the durability of washing is improved, and it can also prevent dirt from re-depositing on the surface of the object. Therefore, people always think that detergents with good foaming properties have strong decontamination ability. Therefore, many liquid detergents will reduce the pressure of the jet pump and are not conducive to rinsing. Therefore, low-foaming non-ionic types should be used in this case. Surfactant.

 

6.solubilization

Solubilization refers to the effect of surfactants to increase the solubility of poorly soluble or insoluble substances in water. For example, the solubility of benzene in water is 0.09% (volume fraction). If surfactants (such as sodium oleate) are added, the solubility of benzene It can be increased to 10%.

The solubilization effect is inseparable from the micelles formed by surfactants in water. Micelles are micelles formed by the hydrocarbon chains in the surfactant molecules moving closer together in the aqueous solution due to hydrophobic interaction. The inside of the micelle is actually a liquid hydrocarbon, so non-polar organic solutes such as benzene and mineral oil that are insoluble in water are easier to dissolve in the micelle. Solubilization is the process of micelles dissolving lipophilic substances. It is a special effect of surfactants. Therefore, only when the concentration of surfactant in the solution is above the critical micelle concentration, there are more large micelles in the solution. Solubilization occurs only when the time, and the larger the micelle volume, the greater the solubilization capacity.

Solubilization is different from emulsification. Emulsification is a discontinuous and unstable multi-phase system obtained by dispersing a liquid phase into water (or another liquid phase), while solubilization results in that the solubilized solution and the solubilized substance are in the same Single-phase homogeneous and stable system in one phase. Sometimes the same surfactant has both emulsification and solubilization effects, but only when its concentration is above the critical micelle concentration can it have solubilization effects.

 

7.soft and smooth

When the surfactant molecules are aligned on the surface of the fabric, the relative static friction coefficient of the fabric can be reduced. Such as linear alkyl polyol polyoxyethylene ether, linear alkyl fatty acid polyoxyethylene ether and other nonionic surfactants and a variety of cationic surfactants have the effect of reducing the static friction coefficient of the fabric, so it can be used Used as fabric softener. Surfactants with branched alkyl or aromatic groups cannot form a neat directional arrangement on the surface of the fabric, so they are not suitable for use as a softener.

 

8.Antistatic effect

Certain anionic surfactants and quaternary ammonium salt cationic surfactants are easy to absorb water and form a conductive solution layer on the surface of the fabric, so they have antistatic effects and are used as antistatic agents for chemical fiber fabrics.9. bactericidal effect

Quaternary ammonium bactericides have the properties of ionic compounds. They are easily soluble in water but not in non-polar solvents, and have stable chemical properties. The mechanism of action of this kind of bactericides is mainly through electrostatic force, hydrogen bonding force and hydrophobic binding between surfactant molecules and protein molecules, etc., to adsorb negatively charged bacteria and cause them to gather on the cell wall, causing lysis and production. The room obstructive effect causes the growth of bacteria to be inhibited and death. At the same time, its hydrophobic alkyl group can also interact with the hydrophilic group of bacteria to change the permeability of the membrane, and then undergo lysis, destroy the cell structure, and cause cell dissolution and death. This kind of fungicides has high efficiency, low toxicity, no accumulation, moderate toxicity to fish, is not easily affected by pH changes, is convenient to use, has a strong peeling effect on the mucus layer, and has stable chemical properties, dispersion and corrosion inhibition Good function and other characteristics.

Since the discovery of the bactericidal effect of cationic surfactants in 1935, 4 to 6-generation quaternary ammonium salt bactericide products have been developed so far. The first generation is alkyl dimethyl benzyl ammonium chloride, cetyl trimethyl ammonium chloride, etc.; the second generation is the first generation derivative, which is carried out on the benzene ring or quaternary nitrogen of the quaternary ammonium salt Obtained by substitution reaction: the third generation product is dialkyl dimethyl ammonium chloride, such as didecyl dimethyl ammonium chloride, etc.; the fourth generation is a compound product of the first and third generations; Substituted as double quaternary ammonium salts such as: ethylene bis (dodecyl dimethyl ammonium bromide), they belong to gemini or dimer type surfactants.

The quaternary ammonium bactericide not only has a bactericidal effect, but also has a strong peeling effect on the slime. It can kill the sulfate-reducing bacteria that grow under the slime. It also has a corrosion-inhibiting and synergistic effect when used with other agents. Common ones are 1227 (dodecyl dimethyl benzyl ammonium chloride), 1231 (dodecyl trimethyl ammonium chloride), dodecyl dimethyl benzyl ammonium bromide, 1427 (fourteen Alkyl dimethyl benzyl ammonium chloride), dodecyl dimethyl ammonium bromide, tetradecyl dimethyl ammonium chloride, etc.