Dispersant

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, but may also be gases.

Applications

Automotive

Dispersing agents are added to lubricating oils used in automotive engines to prevent the accumulation of varnishlike deposits on the cylinder walls and to gasoline to prevent the buildup of gummyish residues.

Bio-dispersing

Dispersants can be used to prevent formation of biofouling or biofilms in industrial processes. It is also possible to disperse bacterial slime and increase the efficiency of biocides.

Concrete

Dispersants/plasticizer/superplasticizers are used in the concrete mix (sand, stone, cement and water) to lower the use of water and still keeping the same slump (flow) property. This makes the concrete stronger and more impervious to water penetration^[1]

Detergents

Dispersing agents are the principal applications of detergents for which the liquid bath is water. Detergents also are used as emulsifiers in many applications.

Gypsum wallboard

A dispersant/plasticizer is added to the gypsum wallboard slurry to reduce the amount of water used, while maintaining the same slump as the slurry without dispersant. The lower water usage allows lower energy use to dry the wallboard, since less water is present in the wallboard^[2]

Oil drilling

Dispersants in oil drilling are chemicals that 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.

Oil spill

Dispersants can be used to dissipate oil slicks.^[3] 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. The oil is 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.^[4]

A dispersant was used in an attempt to clean up the Exxon Valdez oil spill^[3] 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 is currently being 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.

Process industry

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.

Surface coating

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.

See also

• Plasticizer
• Deflocculant
• Detergent
• Surfactant
• Superplasticizer
• Solubilization

References

1. ^ Superplasticizers. Fhwa.dot.gov. Retrieved on 2010-10-27.
2. ^ Gypsum wallboard, and method of making same - Patent 5879446. Freepatentsonline.com. Retrieved on 2010-10-27.
3. ^ ^{a b} "Spill Response - Dispersants". International Tanker Operators Pollution Federation Limited. http://www.itopf.com/spill-response/clean-up-and-response/dispersants/. Retrieved 2010-05-03. 
4. ^ "Spill Response - Dispersants Kill Fish Eggs". journal Environmental Toxicology and Chemistry. http://www.msnbc.msn.com/id/30158418/. Retrieved 2010-05-21.