Wetting agents and dispersants are both additives used in the dispersion process but have different functions. Wetting agents lower the surface tension of liquids to allow solid particles to be wet, which is the first step of dispersion. Dispersants adsorb to particle surfaces and provide repulsion between particles to prevent them from flocculating after separation. Wetting agents work by adsorbing to liquid-air interfaces while dispersants adsorb to solid-liquid interfaces and can provide electrostatic or steric stabilization between particles. Both are important interface additives but have distinct roles in the dispersion process.

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The Differences Between Wetting Agents and
Dispersants
Posted on April 10, 2015 by Jochum Beetsma
Introduction
Several types of additives can be used in the dispersion process in which solid particles, like pigments
and fillers, are distributed and stabilised in a liquid.
The three steps in the dispersion process.
Often two categories of additives, wetting agent (EU) and dispersants (EU), are mentioned in one
breath. However, the two materials differ strongly with respect to the role they play in the system and
with respect to chemical composition and morphology of the molecules they are composed of.
Functionality
It is important to have a clear view on what each raw material that is used in a paint or ink should do.
The job a raw material, like an additive, must do in a system is called functionality. It describes in a few
words what the system developer would like the additive to do. A check question that can be asked in
case you are not sure about the functionality of a component: What will happen when I remove the
additive from the formulation?
Wetting agents
Wetting is the first step in the dispersion process. The air that surrounds the solid particles in an
agglomerate must be substituted by liquid. Wetting will take place when the surface tension of the liquid
is low compared to the surface energy of the solid particles. Wetting will not occur when the surface
tension of the liquid is too high. In that case, the surface tension of the liquid can be lowered by adding a
wetting agent. A wetting agent does its job because the molecules adsorb and orient on the liquid-air
interface.

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Wetting agent molecules adsorbed and oriented on a liquid-air interface.
Dispersants
Solid particles attract each other. For this reason, energy is needed to separate the particles from each
other in the second step of the dispersion process. 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.
Dispersant molecules adsorbed on the interface of a solid particle and
liquid.
Repulsion can result from two mechanisms that may either be used separately or in combination:
Electrostatic stabilisation: all particles carry a charge of the same sign.
Steric stabilisation: all particles are covered with tails dissolving in the liquid that surrounds the
particles.
Overview
Wetting agents and dispersants are additives that are used in dispersion processes. Both are interface
additives but there are fundamental differences between the two types of raw materials.

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Key differences between wetting agents and dispersants.
System developers want to predict the behaviour of the additives they use. The behaviour of wetting
agents and dispersants depends upon their chemical composition and molecular morphology. Useful
information can be obtained by studying the documentation of the additives, like TDS (technical data
sheets) and SDS (safety data sheets). The surface composition of the solid particles and the
composition of the continuous liquid phase must also be known in order to be able to select the right
additives.
Search wetting agents in Prospector… (EU)
Search dispersants in Prospector… (EU)
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Filed Under: Paint & Coatings
Tagged With: Category Overview, dispersants, wetting agents
About Jochum Beetsma
With 25 years of experience in the coatings and ink industries, Drs.
Jochum Beetsma brings expertise in physical chemistry, product
development, innovation implementation and problem solving to his role as
a paint and coatings industry expert at Prospector. A credentialed physical
chemist and PDMA-certified New Product Development Professional,
Jochum Beetsma authors in-depth technical articles for Knowledge.ULProspector.com.

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