Common emulsions, one phase is water or aqueous solution, and the other phase is organic matter immiscible with water, such as grease, wax, etc. The emulsion formed by water and oil can be divided into two types according to its dispersion: oil dispersed in water to form an oil-in-water emulsion, expressed as O / W (oil / water): water-in-oil type is formed in water-dispersed oil Emulsion, expressed as W / O (water / oil). In addition, complex multi-emulsions of water-in-oil-in-water W / O / W type and oil-in-water-in-oil O / W / O type may be formed.
The emulsifier stabilizes the emulsion by reducing the interfacial tension and forming a monomolecular interface film.
Requirements for emulsifiers in emulsification: a: the emulsifier must be able to adsorb or concentrate on the interface of the two phases, so that the interfacial tension is reduced; b: the emulsifier must give the particles a charge to cause electrostatic repulsion between the particles, or A stable protective film with a particularly high viscosity is formed around the particles. Therefore, the substance used as an emulsifier must have amphiphilic groups for emulsification, and surfactants can meet this requirement.

2. The preparation method of the emulsion and the factors that affect the stability of the emulsion
There are two methods for preparing an emulsion: one is to use a mechanical method to disperse the liquid with tiny particles in another liquid, and the industry mostly uses this method to prepare an emulsion; the other is to dissolve the liquid in a molecular state In another liquid, it is then properly aggregated to form an emulsion.
Emulsion stability refers to the ability to resist phase aggregation due to particle aggregation. The emulsion is a thermodynamically unstable system with a large free energy. Therefore, the so-called emulsion stability actually refers to the time required for the system to reach equilibrium, that is, the time required for a liquid to separate in the system.
When there are polar organic molecules such as fatty alcohols, fatty acids and fatty amines in the interface film, the film strength increases significantly. This is because in the interface adsorption layer, the emulsifier molecules interact with polar molecules such as alcohol, acid, and amine to form a "composite", which increases the strength of the interface film.
An emulsifier composed of two or more surfactants is called a mixed emulsifier. The mixed emulsifier is adsorbed on the water / oil interface, and the interaction between the molecules can form a complex. Due to the strong interaction between molecules, the interfacial tension is significantly reduced, the amount of emulsifier adsorbed on the interface is significantly increased, the density of the formed interfacial film is increased, and the strength is increased.
The charge of the liquid beads has a significant effect on the stability of the emulsion. For stable emulsions, the droplets are generally charged. When an ionic emulsifier is used, the lipophilic group of the emulsifier ions adsorbed on the interface is inserted into the oil phase, and the hydrophilic group is in the water phase, thereby charging the liquid beads. Because the droplets of the emulsion bear the same kind of charge, they repel each other and are not easy to coalesce, which increases the stability. It can be seen that the more emulsifier ions adsorbed on the liquid beads, the greater the charge capacity, the greater the ability to prevent the liquid beads from coalescing, and the more stable the emulsion system.
The viscosity of the emulsion dispersion medium has a certain effect on the stability of the emulsion. Generally, the greater the viscosity of the dispersion medium, the higher the stability of the emulsion. This is because the viscosity of the dispersion medium is large, which has a strong obstructive effect on the Brownian motion of the liquid beads, slows the collision between the liquid beads, and keeps the system stable. Generally, the polymer materials soluble in the emulsion can increase the viscosity of the system and increase the stability of the emulsion. In addition, the polymer can form a strong interface film, making the emulsion system more stable.
In some cases, the addition of solid powder did not stabilize the emulsion. The solid powder is not in water, oil or on the interface, depending on the wetting ability of the oil and water to the solid powder. If the solid powder is not completely wetted by water and can be wetted by oil, it will stay at the water-oil interface on.
The reason why the solid powder does not stabilize the emulsion is that the powder gathered at the interface does not enhance the interface film, which is similar to the interface adsorbed emulsifier molecules, so the closer the solid powder is arranged on the interface, the more stable the emulsion.
Surfactants have the ability to significantly increase the solubility of organic matter that is insoluble or slightly soluble in water after forming micelles in an aqueous solution, and the solution is transparent at this time. This action of micelles is called solubilization. Surfactants that produce solubilization are called solubilizers, and solubilized organic substances are called solubilized substances.