What are the characteristics of cationic surfactants?

Surfactant(surfactant) refers to a substance with fixed hydrophilic and lipophilic groups that can be directionally arranged on the surface of a solution and can significantly reduce the surface tension. The molecular structure of surfactants 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 carboxylic acid, sulfonic acid, sulfuric acid, amino or amine The base and its salt can also be hydroxyl, amide group, ether bond, etc.; while the hydrophobic group is often a non-polar hydrocarbon chain, such as a hydrocarbon chain with more than 8 carbon atoms. Surfactants are divided into ionic surfactants and nonionic surfactants.

（1）Composition

The molecular structure of surfactant is amphiphilic: one end is a hydrophilic group and the other end is a hydrophobic group.

(2)Principle

By molecule The affinity of different parts in the two phases to the two phases makes both phases regard them as components of the original phase. The molecules are arranged between the two phases, so that the surfaces of the two phases are equivalent to being transferred into the interior of the molecules. thereby reducing surface tension. Since both phases regard it as a component of the original phase, it means that the two phases do not form an interface with the surfactant molecules, which means that the interface between the two phases is partially eliminated in this way, which reduces the surface tension and surface free energy.

(3)Adsorption

in solution Positive adsorption: increase wettability, emulsification, foaming; Adsorption on solid surface: single-layer adsorption on non-polar solid surface, Multi-layer adsorption can occur on the surface of polar solids .

(4)Properties

SurfactantReduces the surface tension of water by adsorbing at the gas-liquid interface. It can also reduce the oil-water interfacial tension by adsorbing at the liquid interface. Many surfactants can also aggregate in bulk solution to formfor aggregates. Vesicles and micelles are such aggregates. The concentration at which surfactant begins to form micelles is called the critical micelle concentration orCMC. When micelles form in water, the tails of the micelles form a core that can surround the oil droplets, while their (ionic/polar) heads form a shell that remains in contact with the water. Surfactants aggregate in oil, and the aggregates are referred to as reverse micelles. In reverse micelles, the head is in the core and the tail remains in full contact with the oil. Surfactants are generally divided into four major categories: anionic, cationic, nonionic, and zwitterionic (double electron). The thermodynamics of surfactant systems is important, both theoretically and practically. Because the surfactant system represents a system between ordered and disordered material states. Surfactant solutions may contain ordered phases (micelles) and disordered phases (free surfactant molecules and/or ions).

Micelles – the lipophilic tail ends of surfactant molecules gather in micelles Inside, it avoids contact with polar water molecules; the polar hydrophilic head end of the molecule is exposed to the outside, interacts with polar water molecules, and protects the hydrophobic groups inside the micelle. The compounds that form micelles are generally amphiphilic molecules. Therefore, in addition to being soluble in polar solvents such as water, micelles can also be dissolved in non-polar solvents in the form of reverse micelles. For example, commonly used detergents can improve the penetration of water into the soil, but the effect only lasts for a few days (many standard laundry detergents contain certain amounts of chemicals, such as sodium and bromine, that are not suitable for soil because they damage plants).

Commercial Soil Wetting Agent Association If the effect continues for a period of time, it will eventually be degraded by microorganisms. However, some have an impact on the biological cycle of aquatic life, so care must be taken to prevent these products from entering surface runoff, and excess product should not be decontaminated. Cationic surfactant The The active part of surfactants is cationic, so it is called positive soap. The main part of its molecular structure is a pentavalent nitrogen atom, so it is also called a quaternary ammonium compound. It is characterized by high water solubility, relatively stable in acidic and alkaline solutions, and good surface activity and bactericidal effects. Commonly used varieties include benzalkonium chloride (benzalkonium chloride) and benzalkonium bromide (new benzalkonium chloride).