When the system contains two or more phases, one of them is continuous phase be called Dispersion medium At least one other phase is good dispersed Become in continuous phase Discontinuous phase or dispersed phase Medium. The dispersed system has a large Phase interface and Interfacial energy Therefore, there is a tendency to automatically reduce the coalescence of interface and particles, which is a thermodynamic unstable system. [2] one grind and stir It can enhance and accelerate dispersion. The gas, liquid or solid is dispersed in the liquid medium by stirring to increase the area of the phase medium and speed up the heat and mass transfer rate. In the reactor design, according to the characteristics of a certain polymerization reaction, the stirring effect can be strengthened by changing the paddle and rotating speed of the agitator. If a high viscosity bulk polymerization process, it is required to highlight the mixing and stirring role to achieve good stirring effect. [2]
2. Stable dispersion systems are usually prepared by Dispersion method 、 Coagulation method And add dispersant. In order to obtain a good dispersion system, it is necessary to take appropriate methods to disperse the objects into particles and make them have good wettability to improve the stability of the dispersion system. The usual method is to use dispersants. Dispersants can be divided into inorganic dispersants, low relative molecular mass Organic dispersants and Polymer compound In general, low molecular weight organic dispersants and some macromolecular compounds belong to surface active agent 。 Surfactant is a good dispersant, which can promote grinding effect, improve wetting ability and prevent condensation effect. Generally, insoluble solids such as dust, soot and dirt are easy to sink in water. When surfactant is added to water, solid particles can be separated into very fine particles and dispersed in solution. In a narrow sense, the action of promoting solid particles to be crushed and evenly dispersed in liquid is called dispersion. [3] The dispersal effect of surfactant is in calcium soap dispersion, pigment dispersion Nanoparticles Dispersion, pesticide and other aspects are more and more widely used, and their advantages are more and more prominent. The following is a brief overview of their principles and applications in the above aspects. Fatty acid potassium Fatty acid sodium It has rich foam and good washing ability in soft water, but forms insoluble calcium soap and magnesium soap with Can and Mg in hard water, which not only reduces the washing ability, but also deposits on the washing material, and is difficult to rinse and remove. Therefore, a small amount is added in the production of soap Calcium soap dispersant , such as sodium fatty acid methyl ester sulfonate (MES), dodecyl polyglycerol ether and other surfactants, can significantly improve the solubility and decontamination ability of soap in cold water, and do not produce calcium soap scale. [3] Colored substances are insoluble in water and in the medium used, but they are colored by colored substances in the state of highly dispersed particles. They are called pigments. The system formed by pigment in dispersion medium is thermodynamically unstable. Due to the Brownian motion and the relative density difference between pigment and dispersion medium, pigment molecules will naturally settle and cause the system to be destroyed, which will have a serious impact on the application performance of pigment, such as coloring strength, hiding power, transparency, etc. Therefore, it is very important to improve the stability of pigment dispersion system. [4]
The addition of surfactants plays an important role in the wetting, dispersion and stability of pigments. In order to obtain an ideal effect, the type and amount of surfactant added must be determined according to the performance of pigment, dispersion medium and surfactant.
Nanoparticles have surface effect and volume effect, and show special properties different from large particles. Nanoparticles are easy to agglomerate due to their special surface structure. In order to prepare nano materials with good dispersion and stable performance, the newly generated particle surface must be quickly wetted by the medium, that is, isolated by the dispersed medium. In the process of preparation of nanoparticles, solving the dispersion problem of nanoparticles has always been a concern.
Adding surfactant in the preparation process of nano materials can not only be used as Template And can quickly adsorb on the surface of newly formed nanocrystals, thereby effectively preventing the agglomeration of nanoparticles. [1] Generally, pesticides cannot be directly used for the prevention and control of diseases and pests, but need to be processed into pesticide dispersion systems with various specific physical and chemical properties, namely pesticide formulations. Surfactants play a role in wetting, dispersing, emulsifying and solubilizing in pesticide processing, and have become Pesticide preparation It is an indispensable component in pesticide formulation and plays an important role in giving efficacy to active ingredients. The addition of surfactant can greatly reduce the surface tension of the solution, enhance the wetting, spreading and adhesion of the agent on the surface of plants or pests, increase the retention amount of pesticides on the surface of plants, extend the retention time and improve the Plant epidermis To improve the efficacy. [1] The dispersion of surfactants is also widely used in pharmaceutical, textile printing and dyeing, food industry and other fields. In the pharmaceutical industry, suspension refers to the heterogeneous dispersion system formed by the dispersion of insoluble solid drugs in the form of particles in the liquid medium. Surfactants can be used as suspension aids because of their excellent dispersion performance, and are one of the important excipients to maintain the physical stability of suspension. The surfactant forms a solvated film and the same charge at the interface of the two phases to stabilize the suspension particles; At the same time, it can also reduce the interaction between dispersed phase and solvent interfacial tension , which is conducive to the wetting and dispersion of hydrophobic drugs. [5] In the textile printing and dyeing industry, dispersants are indispensable auxiliaries in dye processing and dye application. They mainly play the role of removing the aggregation ions for deflocculation and maintaining the stability of dispersed particles. Widely used dispersants Anionic surfactant Mainly, such as Lignosulfonate And naphthalene sulfonate formaldehyde condensate; Second, right and wrong Ionic surfactant as Nonylphenol ethoxylate It is often used in combination with other types of surfactants; Cationic and amphoteric surfactants have some limitations in application. [6] In the food industry, surfactants are mainly used as emulsifiers, thickeners, defoamers, etc. In addition, it can also be used as a wetting agent and dispersant to improve the hydrophilicity and dispersion of powdered foods such as milk powder and cocoa powder. Cocoa powder particles are fine and covered with an oily film, which is difficult to disperse. The dispersion ability can be improved by sucrose ester. Add 0.2%~0.3% Soybean phospholipid It can be quickly dissolved without agglomeration during mixing. In the production of cakes, ice cream, etc., the addition of fatty acid monoglyceride can improve the dispersion of fat, produce a fine pore structure, and improve product quality. [7] 
