Surfactant

Source: Wikipedia, the free encyclopedia.

Schematic diagram of a micelle of oil in aqueous suspension, such as might occur in an emulsion of oil in water. In this example, the surfactant molecules' oil-soluble tails project into the oil (blue), while the water-soluble ends remain in contact with the water phase (red).

Surfactants are

chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word "surfactant" is a blend of surface-active agent,[1] coined c. 1950.[2]
As they consist of a water-repellent and a water-attracting part, they enable water and oil to mix; they can form foam and facilitate the detachment of dirt.

Surfactants are among the most widespread and commercially important chemicals. Private households as well as many industries use them in large quantities as detergents and cleaning agents, but also for example as emulsifiers, wetting agents, foaming agents, antistatic additives, or dispersants.

Surfactants occur naturally in traditional plant-based detergents, e.g. horse chestnuts or soap nuts; they can also be found in the secretions of some caterpillars. Today the most commonly used surfactants, above all anionic linear alkylbenzene sulfates (LAS), are produced from petroleum products. However, surfactants are (again) increasingly produced in whole or in part from renewable biomass, like sugar, fatty alcohol from vegetable oils, by-products of biofuel production, or other biogenic material.[3]

Classification

Most surfactants are organic compounds with

Fluorosurfactants have fluorocarbon chains. Siloxane surfactants have siloxane
chains.

Many important surfactants include a polyether chain terminating in a highly

Polypropylene oxides
conversely, may be inserted to increase the lipophilic character of a surfactant.

Surfactant molecules have either one tail or two; those with two tails are said to be double-chained.[4]

Surfactant classification according to the composition of their head: non-ionic, anionic, cationic, amphoteric.

Most commonly, surfactants are classified according to polar head group. A non-ionic surfactant has no charged groups in its head. The head of an ionic surfactant carries a net positive, or negative, 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, or amphoteric. Commonly encountered surfactants of each type include:

Anionic: sulfate, sulfonate, and phosphate, carboxylate derivatives

Anionic surfactants contain anionic functional groups at their head, such as sulfate, sulfonate, phosphate, and carboxylates
. Prominent alkyl sulfates include
sodium lauryl sulfate (sodium dodecyl sulfate, SLS, or SDS), and the related alkyl-ether sulfates sodium laureth sulfate (sodium lauryl ether sulfate or SLES), and sodium myreth sulfate
.

Others include:

Carboxylates are the most common surfactants and comprise the carboxylate salts (soaps), such as sodium stearate. More specialized species include sodium lauroyl sarcosinate and carboxylate-based fluorosurfactants such as perfluorononanoate, perfluorooctanoate (PFOA or PFO).

Cationic head groups

pH-dependent primary, secondary, or tertiary amines; primary and secondary amines become positively charged at pH < 10:[5] octenidine dihydrochloride.

Permanently charged

dioctadecyldimethylammonium bromide
(DODAB).

Zwitterionic surfactants

phospholipids phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelins
.

Lauryldimethylamine oxide and myristamine oxide are two commonly used zwitterionic surfactants of the tertiary amine oxides structural type.

Non-ionic

Non-ionic surfactants have covalently bonded oxygen-containing hydrophilic groups, which are bonded to hydrophobic parent structures. The water-solubility of the oxygen groups is the result of

hydrogen bonding
. Hydrogen bonding decreases with increasing temperature, and the water solubility of non-ionic surfactants therefore decreases with increasing temperature.

Non-ionic surfactants are less sensitive to water hardness than anionic surfactants, and they foam less strongly. The differences between the individual types of non-ionic surfactants are slight, and the choice is primarily governed having regard to the costs of special properties (e.g., effectiveness and efficiency, toxicity, dermatological compatibility, biodegradability) or permission for use in food.[6]

Ethoxylates

Fatty alcohol ethoxylates
Alkylphenol ethoxylates (APEs or APEOs)
Fatty acid ethoxylates

Fatty acid ethoxylates are a class of very versatile surfactants, which combine in a single molecule the characteristic of a weakly anionic, pH-responsive head group with the presence of stabilizing and temperature responsive ethyleneoxide units.[7]

Special ethoxylated fatty esters and oils
Ethoxylated amines and/or fatty acid amides
Terminally blocked ethoxylates

Fatty acid esters of polyhydroxy compounds

Fatty acid esters of glycerol
Fatty acid esters of sorbitol

Spans:

Tweens:

  • Tween 20
  • Tween 40
  • Tween 60
  • Tween 80
Fatty acid esters of sucrose
Alkyl polyglucosides
Main article: Alkyl polyglycoside

Other classifications

Gemini amino acid-based surfactant (based on cysteine)

Composition and structure

aprotic solvents such as oil in water, or as protic solvents such as water in oil. When the droplet is aprotic it is sometimes[when?
] known as a reverse micelle.

Surfactants are usually

interfaces
between air and water, or at the interface between oil and water in the case where water is mixed with oil. The water-insoluble hydrophobic group may extend out of the bulk water phase into a non-water phase such as air or oil phase, while the water-soluble head group remains bound in the water phase.

The hydrophobic tail may be either lipophilic ("oil-seeking") or lipophobic ("oil-avoiding") depending on its chemistry. Hydrocarbon groups are usually lipophilic, for use in soaps and detergents, while fluorocarbon groups are lipophobic, for use in repelling stains or reducing surface tension.

World production of surfactants is estimated at 15 million tons per year, of which about half are

ethoxylates (500,000 tons/y).[6]

Sodium stearate, the most common component of most soap, which comprises about 50% of commercial surfactants
Sodium dodecylbenzenesulfonate
4-(5-Dodecyl) benzenesulfonate, a linear dodecylbenzenesulfonate, one of the most common surfactants

Structure of surfactant phases in water

Main article: Wetting solution

In the bulk aqueous phase, surfactants form aggregates, such as

micelles, where the hydrophobic tails form the core of the aggregate and the hydrophilic heads are in contact with the surrounding liquid. Other types of aggregates can also be formed, such as spherical or cylindrical micelles or lipid bilayers. The shape of the aggregates depends on the chemical structure of the surfactants, namely the balance in size between the hydrophilic head and hydrophobic tail. A measure of this is the hydrophilic-lipophilic balance (HLB). Surfactants reduce the surface tension of water by adsorbing at the liquid-air interface. The relation that links the surface tension and the surface excess is known as the Gibbs isotherm
.

Dynamics of surfactants at interfaces

The dynamics of surfactant adsorption is of great importance for practical applications such as in foaming, emulsifying or coating processes, where bubbles or drops are rapidly generated and need to be stabilized. The dynamics of absorption depend on the

electrostatic repulsions
. The surface rheology of surfactant layers, including the elasticity and viscosity of the layer, play an important role in the stability of foams and emulsions.

Characterization of interfaces and surfactant layers

Interfacial and surface tension can be characterized by classical methods such as the -pendant or spinning drop method. Dynamic surface tensions, i.e. surface tension as a function of time, can be obtained by the maximum bubble pressure apparatus

The structure of surfactant layers can be studied by ellipsometry or X-ray reflectivity.

Surface rheology can be characterized by the oscillating drop method or shear surface rheometers such as double-cone, double-ring or magnetic rod shear surface rheometer.

Applications

Surfactants play an important role as cleaning,

recycled papers, in flotation, washing and enzymatic processes, and laxatives. Also agrochemical formulations such as herbicides (some), insecticides, biocides (sanitizers), and spermicides (nonoxynol-9).[10] Personal care products such as cosmetics, shampoos, shower gel, hair conditioners, and toothpastes. Surfactants are used in firefighting (to make "wet water" that more quickly soaks into flammable materials[11][12]) and pipelines (liquid drag reducing agents). Alkali surfactant polymers are used to mobilize oil in oil wells
.

Surfactants act to cause the displacement of air from the matrix of cotton pads and bandages so that medicinal solutions can be absorbed for application to various body areas. They also act to displace dirt and debris by the use of detergents in the washing of wounds[13] and via the application of medicinal lotions and sprays to surface of skin and mucous membranes.[14] Surfactants enhance remediation via soil washing, bioremediation, and phytoremediation.[15]

Detergents in biochemistry and biotechnology

In solution, detergents help solubilize a variety of chemical species by dissociating aggregates and unfolding proteins. Popular surfactants in the biochemistry laboratory are

molecular weight
.

Detergents have also been used to decellularise organs. This process maintains a matrix of proteins that preserves the structure of the organ and often the microvascular network. The process has been successfully used to prepare organs such as the liver and heart for transplant in rats.

mammals
.

Quantum dot preparation

Surfactants are used with quantum dots in order to manipulate their growth,[17] assembly, and electrical properties, in addition to mediating reactions on their surfaces. Research is ongoing in how surfactants arrange themselves on the surface of the quantum dots.[18]

Surfactants in droplet-based microfluidics

Surfactants play an important role in droplet-based microfluidics in the stabilization of the droplets, and the prevention of the fusion of droplets during incubation.[19]

Heterogeneous catalysis

Janus-type material is used as a surfactant-like heterogeneous catalyst for the synthesis of adipic acid.[20]

Increased surface tension

Agents that increase surface tension are "surface active" in the literal sense but are not called surfactants as their effect is opposite to the common meaning. A common example of surface tension increase is salting out: adding an inorganic salt to an aqueous solution of a weakly polar substance will cause the substance to precipitate. The substance may itself be a surfactant, which is one of the reasons why many surfactants are ineffective in sea water.

In biology

Further information: Pulmonary surfactant
saturated fatty acid
.

The human body produces diverse surfactants.

Bile salts, a surfactant produced in the liver, play an important role in digestion.[21]

Safety and environmental risks

Most anionic and non-ionic surfactants are non-toxic, having

lipid membrane that protects skin and other cells. Skin irritancy generally increases in the series non-ionic, amphoteric, anionic, cationic surfactants.[6]

Surfactants 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.[22][23][24]

Anionic surfactants can be found in soils as the result of sewage sludge application, wastewater irrigation, and remediation processes. Relatively high concentrations of surfactants together with multimetals can represent an environmental risk. At low concentrations, surfactant application is unlikely to have a significant effect on trace metal mobility.[25][26]

In the case of the

dioctyl sodium sulfosuccinate (DOSS), sorbitan monooleate (Span 80), and polyoxyethylenated sorbitan monooleate (Tween-80).[27][28]

Biodegradation

Because of the volume of surfactants released into the environment, for example laundry detergents in waters, their biodegradation is of great interest. Attracting much attention is the non-biodegradability and extreme persistence of

ethoxylates (APE) break down under aerobic conditions found in sewage treatment plants and in soil to nonylphenol, which is thought to be an endocrine disruptor.[32][33] Interest in biodegradable surfactants has led to much interest in "biosurfactants" such as those derived from amino acids.[34] Biobased surfactants can offer improved biodegradation. However, whether surfactants damage the cells of fish or cause foam mountains on bodies of water depends primarily on their chemical structure and not on whether the carbon originally used came from fossil sources, carbon dioxide or biomass.[3]

See also

Look up surfactant in Wiktionary, the free dictionary.
  • Anti-fog – Chemicals that prevent the condensation of water as small droplets on a surface
  • Cleavable detergent – class of chemical compounds
  • Disodium cocoamphodiacetate – mixture of chemicals used as a surfactant
  • Emulsion – Mixture of two or more immiscible liquids
  • Hydrotrope – chemical substance
  • MBAS assay – Scientific testing method, an assay that indicates anionic surfactants in water with a bluing reaction.
  • Niosome – Non-ionic surfactant-based vesicle
  • Oil dispersants
     – Mixture of emulsifiers and solvents used to treat oil spills
  • Surfactants in paint
  • Surfactant leaching

References

  1. ^ Rosen MJ, Kunjappu JT (2012). Surfactants and Interfacial Phenomena (4th ed.). Hoboken, New Jersey: John Wiley & Sons. p. 1.
    ISBN 978-1-118-22902-6. Archived
    from the original on 8 January 2017. A surfactant (a contraction of surface-active agent) is a substance that, when present at low concentration in a system, has the property of adsorbing onto the surfaces or interfaces of the system and of altering to a marked degree the surface or interfacial free energies of those surfaces (or interfaces).
  2. ^ "surfactant". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.) – "A new word, Surfactants, has been coined by Antara Products, General Aniline & Film Corporation, and has been presented to the chemical industry to cover all materials that have surface activity, including wetting agents, dispersants, emulsifiers, detergents and foaming agents."
  3. ^ a b "Biobased Surfactants Market Report: Market Analysis". Ceresana Market Research. Retrieved 5 January 2024.
  4. ^ "Surfactant | Defination, Classification, Properties & Uses". www.esteem-india.com.
  5. ^ Reich, Hans J. (2012). "Bordwell pKa Table (Acidity in DMSO)". University of Wisconsin. Archived from the original on 27 December 2012. Retrieved 2 April 2013.
  6. ^
    doi:10.1002/14356007.a25_747
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  9. ^ "Bubbles, Bubbles, Everywhere, But Not a Drop to Drink". The Lipid Chronicles. 11 November 2011. Archived from the original on 26 April 2012. Retrieved 1 August 2012.
  10. PMID 18154747
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  11. ^ Better Than Water? How Wet Water Outperforms Regular Water in Firefighting
  12. ^ Firefighters Turn to "Wet Water" to Fight Larger, More Complex Fires
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  16. ^ Wein, Harrison (28 June 2010). "Progress Toward an Artificial Liver Transplant – NIH Research Matters". National Institutes of Health (NIH). Archived from the original on 5 August 2012.
  17. doi:10.1146/annurev.matsci.30.1.545
    .
  18. S2CID 206556385. Archived
    from the original on 26 March 2020. Retrieved 24 June 2019.
  19. PMID 22011791. Archived
    from the original on 14 February 2020. Retrieved 18 April 2020.
  20. ISSN 1867-3880
    .
  21. PMID 21236400
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  23. ^ "Simultaneous analysis of cationic, anionic and neutral surfactants from different matrices using LC/MS/MS | SHIMADZU (Shimadzu Corporation)". www.shimadzu.com. Archived from the original on 14 November 2021. Retrieved 14 November 2021.
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  27. ^ "European Maritime Safety Agency. Manual on the Applicability of Oil Dispersants; Version 2; 2009". Archived from the original on 5 July 2011. Retrieved 19 May 2017.
  28. ISBN 978-0-309-03889-8. Archived
    from the original on 3 January 2019. Retrieved 31 October 2015.
  29. ^ USEPA: "2010/15 PFOA Stewardship Program" Archived 27 October 2008 at the Wayback Machine Accessed October 26, 2008.
  30. S2CID 96787489
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  31. PMID 16125241
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  32. ^ Mergel, Maria. "Nonylphenol and Nonylphenol Ethoxylates." Toxipedia.org. N.p., 1 Nov. 2011. Web. 27 Apr. 2014.
  33. PMID 11090828
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  34. S2CID 3017826
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External links
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