A dispersant or a dispersing agent or a plasticizer or a superplasticizer is either a non-surface active polymer or a surface-active substance added to a suspension, usually a colloid, to improve the separation of particles and to prevent settling or clumping. Dispersants consist normally of one or more surfactants.
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/plasticizers/superplasticizers are used in the concrete mix (sand, stone, cement and water) to lower the use of water and still exhibiting the same slump (flow) property. This makes the concrete stronger and more impervious to water penetration.
Dispersing is the principal goal in the use of detergents, which the liquid bath is water (detergents also are used as emulsifiers in some applications). Laundry detergents encase dirt and grime in miscelles, which naturally disperse.
Dispersants in oil drilling aid in breaking up solids 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 (emulsification) of oil into water (or water into oils), surfactants selected on the basis of hydrophilic-lipophilic balance (HLB) 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.
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 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 (Ixtoc), used over one thousand square miles of sea.
In the process industry dispersing agents or plasticizers 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.
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