Dispersant
- Also known as
- dispersing agent
A dispersant is a substance that keeps solid particles or droplets evenly separated in a liquid and prevents them from clumping together or settling out. It works by adsorbing on particle surfaces and creating electrical or physical repulsion between them.
What is a dispersant?
Fine particles in a liquid tend to attract one another and form clumps, called agglomerates or flocs, which then settle or stick to surfaces. A dispersant, or dispersing agent, prevents that. It coats the particles and keeps them apart, so they stay evenly distributed through the liquid.
How dispersants work
- Wetting. A dispersant helps the liquid wet the particle surface and displace trapped air, the first step in breaking up a powder.
- Electrostatic stabilization. Charged dispersants give particles the same electrical charge, so they repel one another.
- Steric stabilization. Polymeric dispersants adsorb with long chains extending into the liquid, forming a physical barrier that stops particles from getting close enough to stick.
Many dispersants use both mechanisms. Low-molecular-weight surfactants often act as wetting and dispersing agents, while polymers provide long-term stability.
Where dispersants are used
- Paints and coatings, for pigment dispersion: even color, gloss and stability in the can.
- Water treatment, where dispersants keep suspended solids and scale-forming crystals from depositing on surfaces, as part of deposit and fouling control.
- Oil production, where dispersants break up deposits of paraffin and asphaltenes and keep them suspended in the oil.
- Cleaning, where dispersing loosened soil prevents soil redeposition.
- Mineral processing, where dispersants control fine clays and slimes.
Dispersion vs. flocculation
Dispersion is the opposite of flocculation. In some processes, such as tailings thickening, particles are deliberately flocculated so they settle; in others, such as coatings, they must stay dispersed. The same plant can need both at different stages.
Frequently asked questions
A dispersant keeps solid particles apart in a liquid. An emulsifier keeps liquid droplets apart in another liquid. Some products do both, and the term dispersant is sometimes also used for chemicals that break oil into droplets.
Individual fine particles settle much more slowly than large clumps. By preventing clumping, dispersants keep particles small and suspended.
Sources
- dispersing agent, IUPAC Compendium of Chemical Terminology (Gold Book)
- Surfactants and Interfacial Phenomena, 4th edition, M. J. Rosen and J. T. Kunjappu, Wiley, 2012