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The dispersion of pigments is actually divided into three processes:

The first step is wetting, which means removing the air on the surface of the pigment to facilitate the anchoring of our dispersant on the surface of the pigment.

The second step is actually the process of dispersion. The process mainly relies on mechanical force to finely grind the pigment, such as the sanding process. We rely on the collision and friction between glass beads to finely grind the particles, which is not related to dispersants.

The third one is that the process is a stable process. Can the particles of finely ground pigments be stable? Mainly relying on the action of dispersants. What are the stable mechanisms? We can discuss.

The first stable mechanism is called electrostatic stability. In liquid coatings, the surface of pigment particles is charged, with both positive and negative charges. It does not exhibit any repulsive effect between particles. Then when the dispersant adsorbs onto the surface of the pigment, it can cause all pigment particles to have the same charge on their surfaces, forming an electrostatic structure of the coating layer. After a charge is formed on the surface of the pigment, charged ions with opposite charges will surround it. When two particles approach each other, the effect of the electric charge is due to their same-sex repulsion, resulting in a repulsive mechanism that allows them to reach a stable state.

The second type is a spatially stable dispersant, usually composed of anchoring groups, such as an anchoring group, which adsorbs onto the surface of the pigment. In addition, there is a spatial main group, also known as a solvation segment. A dispersant for polymers, which adsorbs onto the surface of pigments through anchoring groups, and then solvates the segments or spatial main groups, which extend into the resin and solvent, forming a barrier layer of solvated polymer segments with a certain thickness. When these two particles are compressed close to each other, the density of the adsorbate in the compression zone will be reduced, which will increase the degrees of freedom and decrease the process. It is a process of entropy reduction. We all know in chemistry that entropy cannot decrease, it can only increase. So the trend of the entire system is to prevent the process from happening further. In addition, as the chain segments mix, the solvent inside is discharged, and being excluded between particles can also lead to an uneven distribution of solvent concentration. The solvent outside will permeate into the interior. Osmotic pressure will force the solvent to return to the intersection and maintain the dispersed state of the particles. The comprehensive effect of such a process is called the spatial position master effect.

The stability of dispersants mainly depends on the two types mentioned above, one is electrostatic stability, and the other is spatial stability.

There is a mechanism theory for vacancy stability, and colloidal particles can produce a negative adsorption on high polymers. When the negative adsorption layers overlap, it will also cause an increase in free energy and generate a corresponding repulsive force, thereby stabilizing the system.

For example, in the aqueous phase, the polyoxyethylene ether with molecular weight of 750 can stabilize the vacancy of styrene lotion. Both theory and practice have shown that the molecular weight of polymers, the size of gel particles, and solvents are all factors that affect vacancy stability.