Surfactant

Surfactant

Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids.

Etymology

The term 'surfactant' is a blend of "surface acting agent". Surfactants are usually organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their "tails") and hydrophilic groups (their "heads"). Therefore, they are soluble in both organic solvents and water. The term surfactant was coined by Antara Products in 1950.

In Index Medicus and the United States National Library of Medicine, "surfactant" is reserved for the meaning "pulmonary" surfactant (see "alveoli" link below). For the more general meaning, "surface active agent" is the heading.

Surfactants reduce the surface tension of water by adsorbing at the liquid-gas interface. They also reduce the interfacial tension between oil and water by adsorbing at the liquid-liquid interface. Many surfactants can also assemble in the bulk solution into s. Examples of such aggregates are vesicles and micelles. The concentration at which surfactants begin to form micelles is known as the critical micelle concentration or CMC. When micelles form in water, their tails form a core that can encapsulate an oil droplet, and their (ionic/polar) heads form an outer shell that maintains favorable contact with water. When surfactants assemble in oil, the aggregate is referred to as a reverse micelle. In a reverse micelle, the heads are in the core and the tails maintain favorable contact with oil. Surfactants are also often classified into four primary groups; anionic, cationic, non-ionic, and zwitterionic (dual charge).

Thermodynamics of the surfactant systems are of great importance, theoretically and practically. This is because surfactant systems represent systems between ordered and disordered states of matter. Surfactant solutions may contain an ordered phase (micelles) and a disordered phase (free surfactant molecules and/or ions in the solution).

Ordinary washing up (dishwashing) detergent, for example, will promote water penetration in soil, but the effect would only last a few days. However, many standard laundry detergent powders contain levels of chemicals such as sodium and boron, which can be damaging to plants and should not be applied to soils. Commercial soil wetting agents will continue to work for a considerable period, but they will eventually be degraded by soil micro-organisms. Some can, however, interfere with the life-cycles of some aquatic organisms, so care should be taken to prevent run-off of these products into streams, and excess product should not be washed down.

Applications and sources

Surfactants play an important role in many practical applications and products, including:
* Detergents
* Fabric softener
* Emulsifiers
* Paints
* Adhesives
* Inks
* Anti-fogging
* Soil remediation
* Wetting
* Ski wax, snowboard wax
* Deinking (particularly during the enzymatic deinking of used paper during the recycling and repulping process)
* Foaming agents
* Defoaming agents
* Laxatives
* Agrochemical formulations
** Herbicides
** Insecticides
* Quantum dot coating
* Biocides (sanitizers)
* Hair conditioners (after shampoo)
* Spermicide (nonoxynol-9)
* Used as an additive in 2.5 gallon fire extinguishers
* Pipeline, Liquid drag reducing agent
* Alkali Surfactant Polymers (used to mobilize oil in oil wells)

Pulmonary surfactants are also naturally secreted by type II cells of the lung alveoli in mammals.

Classification

A surfactant can be classified by the presence of formally charged groups in its head. A non-ionic surfactant has no charge groups in its head. The head of an ionic surfactant carries a net charge. If the charge is negative, the surfactant is more specifically called anionic; if the charge is positive, it is called cationic. If a surfactant contains a head with two oppositely charged groups, it is termed zwitterionic.

Some commonly encountered surfactants of each type include:

* Ionic
** Anionic (based on sulfate, sulfonate or carboxylate anions)
*** Sodium dodecyl sulfate (SDS), ammonium lauryl sulfate, and other alkyl sulfate salts
*** Sodium laureth sulfate, also known as sodium lauryl ether sulfate (SLES)
*** Alkyl benzene sulfonate
*** Soaps, or fatty acid salts
** Cationic (based on quaternary ammonium cations)
*** Cetyl trimethylammonium bromide (CTAB) a.k.a. hexadecyl trimethyl ammonium bromide, and other alkyltrimethylammonium salts
*** Cetylpyridinium chloride (CPC)
*** Polyethoxylated tallow amine (POEA)
*** Benzalkonium chloride (BAC)
*** Benzethonium chloride (BZT)
** Zwitterionic (amphoteric)
*** Dodecyl betaine
*** Cocamidopropyl betaine
*** Coco ampho glycinate
* Nonionic
** Alkyl poly(ethylene oxide)
** Copolymers of poly(ethylene oxide) and poly(propylene oxide) (commercially called Poloxamers or Poloxamines)
** Alkyl polyglucosides, including:
*** Octyl glucoside
*** Decyl maltoside
** Fatty alcohols
*** Cetyl alcohol
*** Oleyl alcohol
** Cocamide MEA, cocamide DEA
** Polysorbates: Tween 20, Tween 80
*** Dodecyl dimethylamine oxide

Health and Environmental Controversy

Some surfactants are known to be toxic to animals, ecosystems and humans, and can increase the diffusion of other environmental contaminants [http://www.ncbi.nlm.nih.gov/pubmed/18333674 Detecting the transport of toxic pesticides from g... [Environ Toxicol Chem. 2008 - PubMed Result ] ] [http://www.ncbi.nlm.nih.gov/pubmed/15734192 Fate of glutaraldehyde in hospital wastewater and ... [Environ Int. 2005 - PubMed Result ] ] [http://dx.doi.org/10.1016/j.chemosphere.2004.11.084] ] . Despite this, they are routinely deposited in numerous ways on land and into water systems, whether as part of an intended process or as industrial and household waste.

References

External links

* [http://www.curoservice.com/parents_visitors/surfactant/action.asp Surfactants explained for Parents]
* [http://www2.sigmaaldrich.com/Area_of_Interest/Biochemicals/BioUltra/Detergents_Surfactants.html?cm_mmc=wiki-_-social-_-surfactants-_-Surfactants Sigma-Aldrich: Surfactants - structures, information, and applications]

See also

* Anti-fog
* Cleavable detergent
* Niosomes


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  • surfactant — [sʉr fak′tənt] n. [surf(ace) act(ive) a(ge)nt] any substance that is SURFACE ACTIVE …   English World dictionary

  • Surfactant — A fluid secreted by the cells of the alveoli (the tiny air sacs in the lungs) that serves to reduce the surface tension of pulmonary fluids; surfactant contributes to the elastic properties of pulmonary tissue. In more technical terms, a… …   Medical dictionary

  • Surfactant — Sur|fac|tant [sə faektənt; engl. Kurzw. aus surface active agent = grenzflächenaktiver Stoff], das; s, s: 1) im dt. Sprachgebrauch unübliches Syn. für ↑ Tensid 2) in der Med. Bez. für ein die Innenfläche der Lunge auskleidendes System aus… …   Universal-Lexikon

  • surfactant — A surface active compound; the best known example of which is the lung surfactant that renders the alveolar surfaces hydrophobic and prevents the lung filling with water by capillary action. The lung surfactant is produced just at parturition,… …   Dictionary of molecular biology

  • Surfactant — Tensioactif Un tensioactif ou agent de surface est un composé qui modifie la tension superficielle entre deux surfaces. Les composés tensioactifs sont des molécules amphiphiles, c est à dire qu elles présentent deux parties de polarité différente …   Wikipédia en Français

  • surfactant — noun Etymology: surface active + ant Date: 1950 a surface active substance (as a detergent) • surfactant adjective …   New Collegiate Dictionary

  • surfactant — n. a wetting agent. Pulmonary surfactant, secreted by type II pneumocytes, is a complex mixture of compounds (including lipids, protein, and carbohydrates) that prevents the air sacs (alveoli) of the lungs from collapsing by reducing surface… …   The new mediacal dictionary

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