1、 Electrostatic repulsion theory
Pigment particles in aqueous dispersions and even in oily dispersions are charged for different reasons. Since the particles are charged, an equal amount of countercharge will inevitably be adsorbed around their interface to form a double layer structure.
DLVO theory is a theory based on the diffuse double layer. It is the core of the charge repulsion theory. There are two main reasons for the stability of the dispersed system:
(1) The attraction between colloid particles is the van der Waals force. Because colloid particles are composed of many molecules, the attraction between colloid particles is the sum of the attraction of all molecules. This attraction between particles is a long-range van der Waals force, which is inversely proportional to the cube of the distance. This is different from the general attraction between molecules, which is inversely proportional to the sixth power of the distance;
(2) The mutual repulsion between particles is generated by charged particles. When particles approach each other to the point where the ion atmosphere overlaps, the ion concentration in the overlapping area increases, destroying the symmetry of the original charge distribution and causing charge redistribution in the ion atmosphere, that is, ions diffuse outward from the overlapping area with higher concentration. As a result, the positively charged particles generate repulsion, causing nearby particles to separate. Theory has proven that this repulsion is an exponential function of the distance between particles.

2、 Steric hindrance stabilization mechanism
Steric hindrance, the high molecular polymer adsorbed on the surface of the colloidal particles can effectively prevent the aggregation of the colloidal particles and keep the dispersion in a stable state. This stabilization effect is called the steric hindrance effect.
Practice has proved that the dispersant with the best steric hindrance effect should have a pigment anchoring base, which is firmly anchored and adsorbed on the surface of the pigment particles through chemical or physical adsorption to ensure that the dispersant polymer will not desorb when the particles move; it should also have a free stretching chain part that is compatible with the dispersion medium (resin). It forms an adsorption layer of a certain thickness, which can keep a certain distance between particles; once the adsorption layers overlap, the particles can be repelled by the free energy generated in the overlapping area, achieving a long-range repulsion effect.