To choose a good and suitable dispersant, there are 3 criteria of dispersant:
Compatibility : the dispersant must compatible with the resin
Low surface tension : surface tension of the dispersant less than surface tension of pigment
Anchoring group : dispersant must have anchoring group to stick with pigment
Pigment is one of the main material in coating. Pigments need to be distributed in coating in order to achieve a bright, clean and attractive color. In order to do that, these pigments have to been stabilizing in small particles when the paint is in the can for long term. Wetting dispersing agent has function to replace air and wetting the solid particle surface, disperse the agglomerate particles to it primary particle size, and then stabilized the solid particle in coating. A good dispersing is needed to prevent flocculated pigment. Flocculated pigment can cause many defect such as loss of gloss, loss of transparency to organic pigment, poor color stability, syneresis, flooding and floating, and reduce in tinting strength. They are 2 types of wetting dispersing agent:

Conventional wetting and dispersing agent

Conventional wetting and dispersing agent are low molecular weight material and usually used in inorganic pigment. Conventional wetting and dispersing agent that has ionic structure mostly used in solvent base. While that has non-ionic structure mostly used in water-base system.

High molecular weight polymeric dispersant

High molecular weight polymeric dispersant is high molecular weight dispersant that needed to separate two pigment particles to a distance where it can reach the critical distance or where the attraction forces between them is near to zero. This type of dispersant usually used with organic pigment.