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.
