A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid to improve the separation of the particles and to prevent their settling or clumping. Dispersants are widely used to stabilize all kinds of industrial and artisanal products, such as paints, ferrofluids, and salad dressings. The plasticizers or superplasticizers, used to improve the workability of pastes like concrete and clay, are typically dispersants. The concept also largely overlaps with that of detergent, used to bring oily contamination into water suspension, and of emulsifier, used to create homogeneous mixtures of non-miscible liquids like water and oil. Natural suspensions like milk and latex contain substances that act as dispersants.
Applications
Automotive
Automotive engine oils contain both detergents and dispersants. Metallic-based detergents prevent the accumulation of varnish like deposits on the cylinder walls. They also neutralize acids. Dispersants maintain contaminants in suspension. Dispersants added to gasoline prevent the buildup of gummy residues.
Dispersants are used as plasticizers or superplasticizers in concrete formulations to lower the use of water while retaining the needed slump property. A lower water contents makes the concrete stronger and more impervious to water penetration. Similarly, dispersants are used as plasticizers in the gypsum slurry during wallboard manufacture, to reduce the amount of water used. The lower water usage allows lower energy use to dry the wallboard.
Detergents
Dispersing is the principal goal in the use of detergents, which the liquid bath is water. Laundry detergents encase dirt and grime in miscelles, which naturally disperse.
Oil drilling
Dispersants in oil drilling aid in breaking upsolids or liquids as fine particles or droplets into another medium. This term is often applied incorrectly to clay deflocculants. Clay dispersants prevent formation of "fish-eye" globules. For dispersing of oil into water, surfactants selected on the basis of hydrophilic-lipophilic balance number can be used. For foam drilling fluids, synthetic detergents and soaps are used, along with polymers, to disperse foam bubbles into the air or gas.
Oil spill
Dispersants can be used to dissipate oil slicks. They may rapidly disperse large amounts of certain oil types from the sea surface by transferring it into the water column. They will cause the oil slick to break up and form water-soluble micelles that are rapidly :wikt:dilute|diluted. Then effectively spread throughout a larger volume of water than the surface from where the oil was dispersed. They can also delay the formation of persistent oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs. Dispersant was used in an attempt to clean up the Exxon Valdez oil spill though its use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water. Dispersant Corexit 9500 was used on the Deepwater Horizon oil spill. Dispersant Corexit 9527 was used to disperse an oil slick in the Gulf of Mexico in 1979, used over one thousandsquare miles of sea.
Process industry
In the process industry dispersing agents are added to process liquids to prevent unwanted deposits by keeping them finely dispersed. They function in both aqueous and nonaqueous media.
In order to provide optimal performance, pigment particles must act independently of each other in the coating film and thus must remain well dispersed throughout manufacture, storage, application, and film formation. Unfortunately, colloidal dispersions such as the pigment dispersions in liquid coatings are inherently unstable, and they must be stabilized against the flocculation that might occur.
