The surfactant that can make the solid particles in the solid-liquid suspension stably disperse in the medium is called dispersant. Dispersion is a process in which solid particles are evenly distributed in the dispersion, and the dispersion has certain stability. A kind of
Principle of action:
Mechanism: 1. Adsorbed on the surface of solid particles, so that the condensed solid particles surface is easy to wet. 2. Macromolecular dispersant forms an adsorption layer on the surface of solid particles, which increases the charge on the surface of solid particles and improves the reaction force between particles that form solid obstacles.   
3. A bimolecular layer structure is formed on the surface of solid particles. The polar end of the outer dispersant has a strong affinity with water, which increases the degree of solid particles being wetted by water
4. Make the system uniform, increase the suspension performance, do not precipitate, so that the physical and chemical properties of the whole system are the same.

Selecting dispersant.
In our paint production process, pigment dispersion is a very important production link, it is directly related to the coating storage, construction, appearance and film performance, so the reasonable selection of dispersant is a very important production link. But the dispersion of coating paste is not only related to dispersant, but also to formulation of coating formulation and selection of raw materials. Dispersant Gu Ming Si Yi, is to disperse all kinds of powder in solvent reasonably, through certain charge repulsion principle or polymer steric effect, make all kinds of solid very stable suspension in solvent (or dispersion liquid).   
Electric double layer principle
Dispersants used in waterborne coatings must be water soluble, and they are selectively adsorbed to the interface between the powder and water. At present, anions are commonly used. They are ionized in water to form anions with certain surface activity and are adsorbed on the surface of powders. The surface of powder particles adsorbs dispersant to form electric double layer. Anions are closely adsorbed on the surface of particles, which are called surface ions. Ions with opposite charges in the medium are called counter ions. They are adsorbed by surface ions through static electricity. Some of the counter ions are closely combined with particles and surface ions. They are called bound counterions. They become a moving whole in the medium, with negative charges, and the other part of the counter ions are surrounded by them. They are called free counter ions and form a diffusion layer. In this way, a double layer is formed between the surface ions and the counter ions.   
Electrokinetic potential: the particle with negative charge and diffusion layer with positive charge to form a double layer, called electrokinetic potential. Thermoelectric potential: the electric double layer formed between all anions and cations
The dynamic potential is not the thermal potential but the dynamic electric potential. The charge of the electrokinetic potential is not balanced and there is charge repulsion phenomenon. The thermoelectric potential belongs to the charge balance phenomenon. If the concentration of counter ions in the medium is increased, the free counter ions in the diffusion layer will be forced to enter the bound anti ion layer due to electrostatic repulsion. Thus, the electric double layer will be compressed and the electrokinetic potential will drop. When all the free counter ions become bound anti ions, the electrokinetic potential will be zero, which is called the isoelectric point. There is no charge repulsion and the system has no stability and flocculation.

Steric effect
The formation of a stable dispersion system not only uses electrostatic repulsion, that is, the negative charges adsorbed on the surface of particles repel each other, so as to prevent the adsorption / aggregation between particles and finally form large particles and delamination / sedimentation, but also uses the theory of steric hindrance effect, that is, when the particles with negative charges are close to each other, they slide and stagger each other Steric hindrance
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The surfactants used are generally nonionic surfactants. By using the theory of electrostatic repulsion and steric hindrance, a highly stable dispersion system can be formed.   
When the adsorption layer on the surface of the powder reaches 8-9nm, the repulsion between them can protect the particles from flocculation. So polymer dispersant is better than common surfactant.