Detailed explanation of the action principle and selection method of dispersant


What is dispersant? The surfactant that can make the solid particles in the solid-liquid suspension stably disperse in the medium is called dispersant.


The principle of dispersant - dispersion is the process of evenly distributing solid particles in the dispersion, which has certain stability.


The main performance is as follows:


1. It is adsorbed on the surface of solid particles, so that the surface of condensed solid particles is easy to be wetted.


2. Polymer dispersant forms an adsorption layer on the surface of solid particles, which increases the charge on the surface of solid particles and improves the formation of particles with three-dimensional obstruction






Reaction between particles.


3. Double molecular layer structure is formed on the surface of solid particles. The polar end of outer dispersant has strong affinity with water, which increases the wettability of solid particles by water






Degree. The solid particles are far away from each other due to electrostatic repulsion. 4. Make the system uniform, increase the suspension performance, and do not precipitate, so that the physical and chemical properties of the whole system are the same


As described above, the solid particles in the liquid can be dispersed stably by using the dispersant.


Dispersing mechanism of dispersant


Double layer principle: dispersants used in water-based coatings must be water-soluble, and they are selectively adsorbed on the interface between powder and water. At present, Yin is commonly used






Ionic type, they ionize in water to form anions, and have certain surface activity, adsorbed by the powder surface. Powder particle surface adsorption dispersant






After forming a double electric layer, anions are closely adsorbed on the surface of particles, which is called surface ions. Ions with opposite charges in the medium are called anti ions. it






They are adsorbed by the surface ions through static electricity. Some of the anti ions are closely combined with particles and surface ions. They are called bound anti ions. it






They become a moving whole with negative charge in the medium, and another part of anti ion is surrounded by them. They are called free anti ion, forming a diffusion layer.






In this way, a double electric layer is formed between the surface ion and the anti ion.


Electrokinetic potential - a double layer formed by the negative charge of a particle and the positive charge of a diffusion layer. It is called electrokinetic potential. Thermoelectric potential: the potential of all anions and cations






A double electric layer formed between them, corresponding to the potential.


It is the electrokinetic potential rather than the thermoelectric potential that plays the role of dispersion. The charge of the electrokinetic potential is unbalanced and there is charge repulsion phenomenon, while the thermoelectric potential belongs to the charge level






Heng phenomenon. If the concentration of anti ion increases in the medium, the free anti ion in the diffusion layer will be forced into the bound anti ion layer due to electrostatic repulsion,






In this way, the double electric layer is compressed and the electrokinetic potential drops. When all free anti ions become bound anti ions, the electrokinetic potential is zero, which is called isoelectric point.






There is no charge rejection, and the system is not stable to flocculate.


Steric effect - the formation of a stable dispersion system, in addition to electrostatic repulsion, that is, the negative charges adsorbed on the particle surface repel each other to prevent






In addition to the adsorption / aggregation between particles and the final formation of large particles and delamination / sedimentation, the theory of steric resistance effect should also be used, i.e. in the adsorbed






When the negatively charged particles are close to each other, they slide and stagger with each other. The surfactants that play the role of steric hindrance are generally non-ionic surfactants






Sex agent. A highly stable dispersion system can be formed by using the theory of electrostatic repulsion and steric resistance flexibly.


The polymer adsorption layer has a certain thickness, which can effectively block the mutual adsorption of particles, mainly depends on the solvation layer of polymer, when the powder surface






When the adsorption layer reaches 8-9nm, the repulsive force between them can protect the particles from flocculation. So polymer dispersant is better than common surfactant.


From surfactant platform