Dispersing Agents (Solid in water):

These are organic compound. A solid material dispersed in a liquid requires an additive to make the dispersion process easier and more stable – this is the role of the dispersing agent, or dispersant. Dispersing Agents function in a manner similar to emulsifying agents. The difference is that solid particulate matter, rather than insoluble oils, is dispersed. The nature of the lyophilic part of the surfactant molecule must be such that it adsorbs onto the particle's surface. These assist the process of dye particles size reduction and help to dissolve dye particles in water. Pigment colour paste one of the most known example in which dispersing agent is used to disperse pigment in water. Disperse dye also contains dispersing agents.

How they work?

When we shake solid (like sand) in water, it seems that solid is dissolved. However after some time solid particles are separated out from water. These solid particles attract each other. That is why they come together and separate out from water. To separate these particles from each other, there is a need of energy. Also, solid particles must be stabilised after they have been separated from each other. The particles will move to each other and glue together again when particle-particle repulsion is insufficient. The spontaneous process of gluing together of solid particles in a liquid is called flocculation. The functionality of a dispersant is to prevent flocculation. Dispersants do their job because the molecules adsorb on the solid-liquid interface and assure repulsion between the particles.