View source for Biology:Surfactant

{{Short description |Substance that lowers the surface tension between a liquid and another material}}

[[File:A lipid micelle.png|thumb|[[Schematic|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 [[Physics:Surface tension|surface tension]] or interfacial tension between two [[Physics:Liquid|liquid]]s, a liquid and a [[Physics:Gas|gas]], or a liquid and a [[Physics:Solid|solid]]. The word "surfactant" is a blend of '''''surf'''ace-'''act'''ive '''a'''ge'''nt''''',<ref name="Rosen MJ">
{{Cite book |url=https://books.google.com/books?id=1rCdNIzB78AC |title=Surfactants and Interfacial Phenomena |vauthors=Rosen MJ, Kunjappu JT |publisher=John Wiley & Sons |year=2012 |isbn=978-1-118-22902-6 |edition=4th |location=Hoboken, New Jersey |page=1 |quote=A surfactant (a contraction of '''''surf'''ace-'''act'''ive '''a'''ge'''nt''''') 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). |archive-url=https://web.archive.org/web/20170108051750/https://books.google.com/books?id=1rCdNIzB78AC&printsec=frontcover |archive-date=8 January 2017 |url-status=live |df=dmy-all}}
</ref> coined {{circa | 1950}}.<ref>
{{oed | surfactant}} – "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."
</ref> 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 different industries use them in large quantities as detergents and cleaning agents, but also for example as [[Chemistry:Emulsion#Emulsifiers|emulsifiers]], [[Physics:Wetting|wetting agents]], [[Chemistry:Foaming agent|foaming agent]]s, [[Physics:Antistatic agent|antistatic]] additives, or [[Chemistry:Dispersant|dispersant]]s. 

Surfactants occur naturally in traditional plant based detergents, e.g. [[Biology:Aesculus|horse chestnuts]] or [[Biology:Sapindus|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 [[Chemistry:Petroleum product|petroleum products]]. However, surfactants are (again) increasingly produced in whole or in part from renewable [[Biology:Biomass|biomass]], like sugar, fatty alcohol from vegetable oils, by-products of biofuel production, or other biogenic material.<ref>{{Cite web |title=Biobased Surfactants Market Report: Market Analysis |url=https://ceresana.com/en/produkt/biobased-surfactants-market-report-world |access-date=2024-01-05 |website=Ceresana Market Research |language=en-US}}</ref>

==Classification==
Most surfactants are organic compounds with [[Chemistry:Hydrophile|hydrophilic]] "heads" and [[Chemistry:Hydrophobe|hydrophobic]] "tails." The "heads" of surfactants are polar and may or may not carry an electrical charge. The "tails" of most surfactants are fairly similar, consisting of a [[Chemistry:Hydrocarbon|hydrocarbon]] chain, which can be branched, linear, or aromatic. [[Chemistry:Fluorosurfactant|Fluorosurfactant]]s have [[Chemistry:Fluorocarbon|fluorocarbon]] chains. Siloxane surfactants have [[Chemistry:Siloxane|siloxane]] chains.

Many important surfactants include a polyether chain terminating in a highly [[Chemistry:Chemical polarity|polar]] anionic group. The polyether groups often comprise ethoxylated (polyethylene oxide-like) sequences inserted to increase the hydrophilic character of a surfactant. 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''.

[[File:TensideHyrophilHydrophob.png|thumb|upright=1.2|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 [[Physics:Zwitterion|''zwitterionic'']], or ''amphoteric''.  Commonly encountered surfactants of each type include:

===<span class="anchor" id="Anionic"></span>Anionic: sulfate, sulfonate, and phosphate, carboxylate derivatives===
Anionic surfactants contain anionic functional groups at their head, such as [[Chemistry:Organosulfate|sulfate]], [[Chemistry:Sulfonate|sulfonate]], [[Chemistry:Phosphate|phosphate]], and [[Chemistry:Carboxylic acid|carboxylate]]s.
Prominent alkyl sulfates include [[Chemistry:Ammonium lauryl sulfate|ammonium lauryl sulfate]], sodium lauryl sulfate (sodium dodecyl sulfate, SLS, or SDS), and the related alkyl-ether sulfates [[Chemistry:Sodium laureth sulfate|sodium laureth sulfate]] (sodium lauryl ether sulfate or SLES), and [[Chemistry:Sodium myreth sulfate|sodium myreth sulfate]].

Others include:
* [[Chemistry:Alkylbenzene sulfonate|Alkylbenzene sulfonate]]s
* [[Chemistry:Docusate|Docusate]] (dioctyl sodium sulfosuccinate)
* [[Chemistry:Perfluorooctanesulfonic acid|Perfluorooctanesulfonate]] (PFOS)
* [[Chemistry:Perfluorobutanesulfonic acid|Perfluorobutanesulfonate]]
* Alkyl-aryl ether phosphates
* Alkyl ether phosphates

Carboxylates are the most common surfactants and comprise the carboxylate salts (soaps), such as [[Chemistry:Sodium stearate|sodium stearate]].  More specialized species include [[Chemistry:Sodium lauroyl sarcosinate|sodium lauroyl sarcosinate]] and carboxylate-based fluorosurfactants such as [[Chemistry:Perfluorononanoic acid|perfluorononanoate]], [[Chemistry:Perfluorooctanoic acid|perfluorooctanoate]] (PFOA or PFO).

===Cationic head groups===
pH-dependent primary, secondary, or tertiary [[Chemistry:Amine|amine]]s; primary and secondary amines become positively charged at pH < 10:<ref>{{Cite web | title = Bordwell pKa Table (Acidity in DMSO) | url = http://www.chem.wisc.edu/areas/reich/pkatable/index.htm | date = 2012 | first = Hans J. | last = Reich | publisher = University of Wisconsin | access-date = 2 April 2013 | archive-date = 27 December 2012 | archive-url = https://web.archive.org/web/20121227045833/http://www.chem.wisc.edu/areas/reich/pkatable/index.htm | url-status = live }}</ref> [[Chemistry:Octenidine dihydrochloride|octenidine dihydrochloride]].

Permanently charged quaternary ammonium salts: [[Chemistry:Cetrimonium bromide|cetrimonium bromide]] (CTAB), [[Chemistry:Cetylpyridinium chloride|cetylpyridinium chloride]] (CPC), [[Chemistry:Benzalkonium chloride|benzalkonium chloride]] (BAC), [[Chemistry:Benzethonium chloride|benzethonium chloride]] (BZT), [[Chemistry:Dimethyldioctadecylammonium chloride|dimethyldioctadecylammonium chloride]], and dioctadecyldimethylammonium bromide (DODAB).

===Zwitterionic surfactants===
[[Physics:Zwitterion|Zwitterion]]ic (ampholytic) surfactants have both cationic and anionic centers attached to the same molecule.  The cationic part is based on primary, secondary, or tertiary [[Chemistry:Amine|amine]]s or quaternary ammonium cations.  The anionic part can be more variable and include sulfonates, as in the [[Chemistry:Hydroxysultaine|sultaines]] [[Chemistry:CHAPS detergent|CHAPS]] (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) and [[Chemistry:Cocamidopropyl hydroxysultaine|cocamidopropyl hydroxysultaine]]. [[Chemistry:Betaine|Betaine]]s such as [[Chemistry:Cocamidopropyl betaine|cocamidopropyl betaine]] have a carboxylate with the ammonium. The most common biological zwitterionic surfactants have a phosphate anion with an amine or ammonium, such as the phospholipids [[Chemistry:Phosphatidylcholine|phosphatidylserine]], [[Biology:Phosphatidylethanolamine|phosphatidylethanolamine]], [[Chemistry:Phosphatidylcholine|phosphatidylcholine]], and [[Biology:Sphingomyelin|sphingomyelin]]s.

[[Chemistry:Lauryldimethylamine oxide|Lauryldimethylamine oxide]] and [[Chemistry:Myristamine oxide|myristamine oxide]] are two commonly used zwitterionic surfactants of the tertiary [[Chemistry:Amine oxide|amine oxide]]s 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.<ref name="Ullmann" />

==== Ethoxylates ====

===== Fatty alcohol ethoxylates =====
* [[Chemistry:Narrow-range ethoxylate|Narrow-range ethoxylate]]
* [[Chemistry:Octaethylene glycol monododecyl ether|Octaethylene glycol monododecyl ether]]
* [[Chemistry:Pentaethylene glycol monododecyl ether|Pentaethylene glycol monododecyl ether]]

===== Alkylphenol ethoxylates (APEs or APEOs) =====
* [[Chemistry:Nonoxynols|Nonoxynols]]
* [[Chemistry:Triton X-100|Triton X-100]]

===== 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.<ref>{{Cite journal|last=Chiappisi|first=Leonardo|date=December 2017|title=Polyoxyethylene alkyl ether carboxylic acids: An overview of a neglected class of surfactants with multiresponsive properties|journal=Advances in Colloid and Interface Science|volume=250|pages=79–94|doi=10.1016/j.cis.2017.10.001|pmid=29056232}}</ref>

===== Special ethoxylated fatty esters and oils =====

===== Ethoxylated amines and/or fatty acid amides =====
* [[Chemistry:Polyethoxylated tallow amine|Polyethoxylated tallow amine]]
* Cocamide monoethanolamine
* Cocamide diethanolamine

===== Terminally blocked ethoxylates =====
* [[Chemistry:Poloxamer|Poloxamer]]s

==== Fatty acid esters of polyhydroxy compounds ====

===== Fatty acid esters of glycerol =====
* [[Chemistry:Glycerol monostearate|Glycerol monostearate]]
* Glycerol monolaurate

===== Fatty acid esters of sorbitol =====

[[Chemistry:Sorbitan#Esters|Spans]]:
* [[Chemistry:Sorbitan monolaurate|Sorbitan monolaurate]]
* [[Chemistry:Sorbitan monostearate|Sorbitan monostearate]]
* [[Chemistry:Sorbitan tristearate|Sorbitan tristearate]]

[[Chemistry:Polysorbate|Tweens]]:
* Tween 20
* Tween 40
* Tween 60
* [[Chemistry:Tween 80|Tween 80]]

===== Fatty acid esters of sucrose =====

===== Alkyl polyglucosides =====
{{main|Chemistry:Alkyl polyglycoside}}
* [[Chemistry:Decyl glucoside|Decyl glucoside]]
* [[Chemistry:Lauryl glucoside|Lauryl glucoside]]
* [[Chemistry:Octyl glucoside|Octyl glucoside]]

=== Other classifications ===
[[File:Gemini surfactant.png|thumb|Gemini amino acid-based surfactant (based on [[Chemistry:Cysteine|cysteine]])]]
* Amino acid-based surfactants are surfactants derived from an [[Chemistry:Amino acid|amino acid]]. Their properties vary and can be either anionic, cationic, or zwitterionic, depending on the amino acid used and which part of the amino acid is condensed with the alkyl/aryl chain.<ref name="bordes">{{cite journal |last1=Bordes |first1=Romain |last2=Holmberg |first2=Krister |date=28 March 2015 |title=Amino acid-based surfactants – do they deserve more attention? |journal=[[Chemistry:Advances in Colloid and Interface Science|Advances in Colloid and Interface Science]] |volume=222 |pages=79–91 |doi=10.1016/j.cis.2014.10.013}}</ref>
* Gemini surfactants consist of two surfactant molecules linked together at or near their head groups. Compared to monomeric surfactants, they have much lower [[Chemistry:Critical micelle concentration|critical micelle concentration]]s.<ref name="bordes"/>

==Composition and structure==

[[Image:Micelle scheme-en.svg|thumb|upright=1.35|[[Schematic|Schematic]] diagram of a micelle&nbsp;– the lipophilic tails of the surfactant ions remain inside the oil because they interact more strongly with oil than with water. The polar "heads" of the surfactant molecules coating the micelle interact more strongly with water, so they form a hydrophilic outer layer that forms a barrier between micelles. This inhibits the oil droplets, the hydrophobic cores of micelles, from merging into fewer, larger droplets ("emulsion breaking") of the micelle. The compounds that coat a micelle are typically amphiphilic in nature, meaning that micelles may be stable either as droplets of 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|date= February 2019}} known as a reverse micelle.]]

Surfactants are usually [[Chemistry:Organic compound|organic compound]]s that are akin to amphiphilic, which means that this molecule, being as double-agent, each contains a [[Chemistry:Hydrophilic|hydrophilic]] "water-seeking" group (the ''head''), and a [[Chemistry:Hydrophobic|hydrophobic]] "water-avoiding" group (the ''tail'').<ref name="The Lipid Chronicles">{{cite web|title=Bubbles, Bubbles, Everywhere, But Not a Drop to Drink|url=http://www.samuelfurse.com/2011/11/bubbles-bubbles-everywhere-but-not-a-drop-to-drink/|work=The Lipid Chronicles|access-date=1 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120426082602/http://www.samuelfurse.com/2011/11/bubbles-bubbles-everywhere-but-not-a-drop-to-drink/|archive-date=26 April 2012|df=dmy-all|date=2011-11-11}}</ref>  As a result, a surfactant contains both a water-soluble component and a water-insoluble component. Surfactants diffuse in water and get [[Chemistry:Adsorption|adsorb]]ed at [[Chemistry:Interface|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 [[Chemistry:Lipophilicity|lipophilic]] ("oil-seeking") or [[Chemistry:Lipophobicity|lipophobic]] ("oil-avoiding") depending on its chemistry. [[Chemistry:Hydrocarbon|Hydrocarbon]] groups are usually lipophilic, for use in soaps and detergents, while [[Chemistry:Fluorocarbon|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 [[Chemistry:Soap|soap]]s.  Other surfactants produced on a particularly large scale are linear [[Chemistry:Alkylbenzene sulfonates|alkylbenzene sulfonates]] (1.7 million tons/y), lignin sulfonates (600,000 tons/y), [[Chemistry:Fatty alcohol|fatty alcohol]] ethoxylates (700,000 tons/y), and [[Chemistry:Alkylphenol|alkylphenol]] ethoxylates (500,000 tons/y).<ref name=Ullmann>Kurt Kosswig "Surfactants" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, 2005, Weinheim. {{doi|10.1002/14356007.a25_747}}</ref>
[[File:sodium stearate.svg|thumb|Sodium stearate, the most common component of most soap, which comprises about 50% of commercial surfactants]]
[[File:Sodium dodecylbenzenesulfonate skeletal.svg|thumb|alt=Sodium dodecylbenzenesulfonate|4-(5-Dodecyl) benzenesulfonate, a linear dodecylbenzenesulfonate, one of the most common surfactants]]

===Structure of surfactant phases in water===
{{main|Chemistry: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 [[Biology:Lipid bilayer|lipid bilayer]]s. 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 [[Physics:Surface tension|surface tension]] of water by [[Chemistry:Adsorption|adsorbing]] at the liquid-air interface. The relation that links the surface tension and the surface excess is known as the [[Physics:Gibbs isotherm|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 diffusion coefficient of the surfactant. As the interface is created, the adsorption is limited by the diffusion of the surfactant to the interface. In some cases, there can exist an energetic barrier to adsorption or desorption of the surfactant. If such a barrier limits the adsorption rate, the dynamics are said to be ‘kinetically limited'. Such energy barriers can be due to steric or electrostatic repulsions.
The [[Physics:Surface rheology|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 [[Physics:Spinning drop method|spinning drop method]].
Dynamic surface tensions, i.e. surface tension as a function of time, can be obtained by the [[Physics:Maximum bubble pressure method|maximum bubble pressure apparatus]]

The structure of surfactant layers can be studied by [[Physics:Ellipsometry|ellipsometry]] or [[Physics:X-ray reflectivity|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, [[Physics:Wetting|wetting]], [[Chemistry:Dispersant|dispersing]], emulsifying, [[Chemistry:Foaming agent|foaming]] and [[Chemistry:Defoamer|anti-foaming]] agents in many practical applications and products, including detergents, fabric softeners, [[Physics:Motor oil|motor oil]]s, [[Chemistry:Emulsion|emulsion]]s, [[Chemistry:Soap|soap]]s, [[Engineering:Paint|paint]]s, [[Chemistry:Adhesive|adhesive]]s, inks, [[Engineering:Anti-fog|anti-fog]]s, [[Chemistry:Ski wax|ski wax]]es, snowboard wax, [[Engineering:Deinking|deinking]] of recycled papers, in flotation, washing and enzymatic processes, and [[Chemistry:Laxative|laxative]]s. Also agrochemical formulations such as [[Biology:Herbicide|herbicide]]s (some), [[Biology:Insecticide|insecticide]]s, [[Biology:Biocide|biocide]]s (sanitizers), and [[Biology:Spermicide|spermicide]]s ([[Chemistry:Nonoxynol-9|nonoxynol-9]]).<ref>{{cite journal|doi=10.1016/j.cis.2007.11.001|title=Surfactant-enhanced remediation of organic contaminated soil and water|year=2008|last1=Paria|first1=Santanu|journal=Advances in Colloid and Interface Science|volume=138|issue=1|pages=24–58|pmid=18154747}}</ref> Personal care products such as cosmetics, [[Medicine:Shampoo|shampoo]]s, shower gel, hair conditioners, and [[Medicine:Toothpaste|toothpaste]]s. Surfactants are used in firefighting and pipelines (liquid drag reducing agents). Alkali surfactant polymers are used to mobilize oil in [[Engineering:Oil well|oil well]]s.

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<ref>{{Cite journal|last1=Percival|first1=S.l.|last2=Mayer|first2=D.|last3=Malone|first3=M.|last4=Swanson|first4=T|last5=Gibson|first5=D.|last6=Schultz|first6=G.|date=2017-11-02|title=Surfactants and their role in wound cleansing and biofilm management|journal=Journal of Wound Care|volume=26|issue=11|pages=680–690|doi=10.12968/jowc.2017.26.11.680|pmid=29131752|issn=0969-0700}}</ref> and via the application of medicinal lotions and sprays to surface of skin and mucous membranes.<ref>{{Cite journal|last1=Mc Callion|first1=O. N. M.|last2=Taylor|first2=K. M. G.|last3=Thomas|first3=M.|last4=Taylor|first4=A. J.|date=1996-03-08|title=The influence of surface tension on aerosols produced by medical nebulisers|journal=International Journal of Pharmaceutics|volume=129|issue=1|pages=123–136|doi=10.1016/0378-5173(95)04279-2|issn=0378-5173}}</ref> Surfactants enhance remediation via soil washing, bioremediation, and phytoremediation.<ref>{{Cite journal |last=Bolan |first=Shiv |last2=Padhye |first2=Lokesh P. |last3=Mulligan |first3=Catherine N. |last4=Alonso |first4=Emilio Ritore |last5=Saint-Fort |first5=Roger |last6=Jasemizad |first6=Tahereh |last7=Wang |first7=Chensi |last8=Zhang |first8=Tao |last9=Rinklebe |first9=Jörg |last10=Wang |first10=Hailong |last11=Siddique |first11=Kadambot H. M. |last12=Kirkham |first12=M. B. |last13=Bolan |first13=Nanthi |date=2023-02-05 |title=Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences |url=https://www.sciencedirect.com/science/article/pii/S0304389422019835 |journal=Journal of Hazardous Materials |volume=443 |pages=130189 |doi=10.1016/j.jhazmat.2022.130189 |issn=0304-3894}}</ref>

===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 sodium lauryl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB). Detergents are key reagents to extract protein by lysis of the cells and tissues: They disorganize the membrane's [[Biology:Lipid bilayer|lipid bilayer]] (SDS, [[Chemistry:Triton X-100|Triton X-100]], X-114, [[Chemistry:CHAPS detergent|CHAPS]], DOC, and [[Chemistry:NP-40|NP-40]]), and solubilize proteins. Milder detergents such as [[Chemistry:N-Octyl beta-D-thioglucopyranoside|octyl thioglucoside]], [[Chemistry:Octyl glucoside|octyl glucoside]] or [[Chemistry:Maltosides|dodecyl maltoside]] are used to solubilize membrane proteins such as [[Biology:Enzymes|enzymes]] and [[Biology:Receptor (biochemistry)|receptors]] without [[Biology:Denaturation (biochemistry)|denaturing]] them. Non-solubilized material is harvested by centrifugation or other means. For [[Biology:Electrophoresis|electrophoresis]], for example, proteins are classically treated with SDS to denature the native [[Biology:Protein structure|tertiary and quaternary structures]], allowing the separation of proteins according to their [[Physics:Molecular weight|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.<ref>{{cite web|url=http://www.nih.gov/researchmatters/june2010/06282010liver.htm|title=Progress Toward an Artificial Liver Transplant&nbsp;– NIH Research Matters|last=Wein|first=Harrison|date=28 June 2010|publisher=National Institutes of Health (NIH)|url-status=dead|archive-url=https://archive.today/20120805083144/http://www.nih.gov/researchmatters/june2010/06282010liver.htm|archive-date=5 August 2012|df=dmy-all}}</ref> [[Biology:Pulmonary surfactant|Pulmonary surfactant]]s are also naturally secreted by type II cells of the lung alveoli in mammals.

===Quantum dot preparation===
Surfactants are used with [[Physics:Quantum dot|quantum dot]]s in order to manipulate their growth,<ref>{{cite journal |title=Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies |journal=[[Physics:Annual Review of Materials Research|Annual Review of Materials Research]] |volume=30 |issue=1 |pages=545–610 |year=2000 |doi=10.1146/annurev.matsci.30.1.545|bibcode = 2000AnRMS..30..545M |last1=Murray |first1=C. B. |last2=Kagan |first2=C. R. |last3=Bawendi |first3=M. G. }}</ref> 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.<ref name="pmid24876347">{{cite journal | vauthors = Zherebetskyy D, Scheele M, Zhang Y, Bronstein N, Thompson C, Britt D, Salmeron M, Alivisatos P, Wang LW | title = Hydroxylation of the surface of PbS nanocrystals passivated with oleic acid | journal = Science | volume = 344 | issue = 6190 | pages = 1380–4 | date = June 2014 | pmid = 24876347 | doi = 10.1126/science.1252727 | bibcode = 2014Sci...344.1380Z | s2cid = 206556385 | url = https://escholarship.org/uc/item/6p2408jt | access-date = 24 June 2019 | archive-date = 26 March 2020 | archive-url = https://web.archive.org/web/20200326084747/https://escholarship.org/uc/item/6p2408jt | url-status = live }}</ref>

=== Surfactants in droplet-based microfluidics ===
Surfactants play an important role in [[Physics:Droplet-based microfluidics|droplet-based microfluidics]] in the stabilization of the droplets, and the prevention of the fusion of droplets during incubation.<ref>{{Cite journal|last=Baret|first=Jean-Christophe|date=2012-01-10|title=Surfactants in droplet-based microfluidics|url=https://pubs.rsc.org/en/content/articlelanding/2012/lc/c1lc20582j|journal=Lab on a Chip|language=en|volume=12|issue=3|pages=422–433|doi=10.1039/C1LC20582J|pmid=22011791|issn=1473-0189|access-date=18 April 2020|archive-date=14 February 2020|archive-url=https://web.archive.org/web/20200214151429/https://pubs.rsc.org/en/content/articlelanding/2012/LC/C1LC20582J|url-status=live}}</ref>

=== Heterogeneous catalysis ===
Janus-type material is used as a surfactant-like heterogeneous catalyst for the synthesis of adipic acid.<ref>{{Cite journal |last1=Vafaeezadeh |first1=Majid |last2=Wilhelm |first2=Christian |last3=Breuninger |first3=Paul |last4=Ernst |first4=Stefan |last5=Antonyuk |first5=Sergiy |last6=Thiel |first6=Werner R. |date=2020-05-20 |title=A Janus‐type Heterogeneous Surfactant for Adipic Acid Synthesis |journal=ChemCatChem |language=en |volume=12 |issue=10 |pages=2695–2701 |doi=10.1002/cctc.202000140 |issn=1867-3880|doi-access=free }}</ref>

=== 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|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|Biology:Pulmonary surfactant}}
[[Image:1-Oleoyl-2-almitoyl-phosphatidylcholine Structural Formulae V.1.png|thumb|300px|[[Chemistry:Phosphatidylcholine|Phosphatidylcholine]], found in lecithin, is a pervasive biological surfactant. Shown in {{color|#800000|red}} – choline and phosphate group; {{color|#000000|black}} – glycerol; {{color|#008000|green}} – monounsaturated fatty acid; {{color|#000080|blue}} – saturated fatty acid.]]

The human body produces diverse surfactants. [[Biology:Pulmonary surfactant|Pulmonary surfactant]] is produced in the [[Medicine:Lung|lung]]s in order to facilitate breathing by increasing total lung capacity, and [[Medicine:Lung compliance|lung compliance]]. In respiratory distress syndrome or RDS, [[Medicine:Pulmonary surfactant (medication)|surfactant replacement]] therapy helps patients have normal respiration by using pharmaceutical forms of the surfactants. One example of a pharmaceutical pulmonary surfactant is Survanta (beractant) or its generic form Beraksurf, produced by [[Company:AbbVie Inc.|Abbvie]] and Tekzima respectively. Bile salts, a surfactant produced in the liver, play an important role in digestion.<ref>{{cite journal|doi=10.1016/j.cis.2010.12.002|pmid=21236400|title=The role of bile salts in digestion|journal=Advances in Colloid and Interface Science|volume=165|issue=1|pages=36–46|year=2011|last1=Maldonado-Valderrama|first1=Julia|last2=Wilde|first2=Pete|last3=MacIerzanka|first3=Adam|last4=MacKie|first4=Alan}}</ref>

== Safety and environmental risks ==
Most anionic and non-ionic surfactants are non-toxic, having LD50 comparable to table salt. The toxicity of [[Chemistry:Quaternary ammonium cation|quaternary ammonium compounds]], which are antibacterial and [[Chemistry:Antifungal|antifungal]], varies. Dialkyldimethylammonium chlorides (DDAC, DSDMAC) used as fabric softeners have high LD50 (5 g/kg) and are essentially non-toxic, while the [[Chemistry:Disinfectant|disinfectant]] alkylbenzyldimethylammonium chloride has an LD50 of 0.35 g/kg. Prolonged exposure to surfactants can irritate and damage the skin because surfactants disrupt the lipid membrane that protects skin and other cells. Skin irritancy generally increases in the series non-ionic, amphoteric, anionic, cationic surfactants.<ref name=Ullmann/>

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.<ref name="pmid18333674">{{cite journal | vauthors = Metcalfe TL, Dillon PJ, Metcalfe CD | title = Detecting the transport of toxic pesticides from golf courses into watersheds in the Precambrian Shield region of Ontario, Canada | journal = Environ. Toxicol. Chem. | volume = 27 | issue = 4 | pages = 811–8 | date = April 2008 | pmid = 18333674 | doi = 10.1897/07-216.1 | s2cid = 39914076 }}</ref><ref name="pmid15734192">{{Cite web|title=Simultaneous analysis of cationic, anionic and neutral surfactants from different matrices using LC/MS/MS {{!}} SHIMADZU (Shimadzu Corporation)|url=https://www.shimadzu.com/an/literature/lcms/apo112145.html|access-date=2021-11-14|website=www.shimadzu.com|language=en|archive-date=14 November 2021|archive-url=https://web.archive.org/web/20211114134903/https://www.shimadzu.com/an/literature/lcms/apo112145.html|url-status=live}}</ref><ref name="pmid15722095">{{cite journal | vauthors = Murphy MG, Al-Khalidi M, Crocker JF, Lee SH, O'Regan P, Acott PD | title = Two formulations of the industrial surfactant, Toximul, differentially reduce mouse weight gain and hepatic glycogen in vivo during early development: effects of exposure to Influenza B Virus | journal = Chemosphere | volume = 59 | issue = 2 | pages = 235–46 | date = April 2005 | pmid = 15722095 | doi = 10.1016/j.chemosphere.2004.11.084 |bibcode=2005Chmsp..59..235M}}</ref>

Anionic surfactants can be found in soils as the result of [[Engineering:Sewage sludge|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.<ref name="pmid21163562">{{cite journal | vauthors = Hernández-Soriano Mdel C, Degryse F, Smolders E | title = Mechanisms of enhanced mobilisation of trace metals by anionic surfactants in soil | journal = Environ. Pollut. | volume = 159 | issue = 3 | pages = 809–16 | date = March 2011 | pmid = 21163562 | doi = 10.1016/j.envpol.2010.11.009 }}</ref><ref name="pmid20830918">{{cite journal | vauthors = Hernández-Soriano Mdel C, Peña A, Dolores Mingorance M | title = Release of metals from metal-amended soil treated with a sulfosuccinamate surfactant: effects of surfactant concentration, soil/solution ratio, and pH | journal = J. Environ. Qual. | volume = 39 | issue = 4 | pages = 1298–305 | date = 2010 | pmid = 20830918 | doi = 10.2134/jeq2009.0242 }}</ref>

In the case of the Deepwater Horizon oil spill, unprecedented amounts of [[Chemistry:Corexit|Corexit]] were sprayed directly into the ocean at the leak and on the sea-water's surface.  The apparent theory was that the surfactants isolate droplets of oil, making it easier for petroleum-consuming microbes to digest the oil.  The active ingredient in Corexit is dioctyl sodium sulfosuccinate (DOSS), [[Chemistry:Sorbitan monooleate|sorbitan monooleate]] (Span 80), and polyoxyethylenated sorbitan monooleate ([[Chemistry:Polysorbate 80|Tween-80]]).<ref>{{cite web |url=http://emsa.europa.eu/opr-documents/opr-manual-a-guidelines/download/1166/719/23.html |title=European Maritime Safety Agency. Manual on the Applicability of Oil Dispersants; Version 2; 2009. |access-date=2017-05-19 |url-status=live |archive-url=https://web.archive.org/web/20110705151503/http://www.emsa.europa.eu/opr-documents/opr-manual-a-guidelines/download/1166/719/23.html |archive-date=5 July 2011 |df=dmy-all }}</ref><ref>{{cite book |url= https://www.nap.edu/read/736/chapter/1 |title= Using Oil Spill Dispersants on the Sea |vauthors= ((Committee on Effectiveness of Oil Spill Dispersants (National Research Council Marine Board))) |year= 1989 |publisher= National Academies Press |doi= 10.17226/736 |isbn= 978-0-309-03889-8 |access-date= October 31, 2015 |archive-date= 3 January 2019 |archive-url= https://web.archive.org/web/20190103110128/https://www.nap.edu/read/736/chapter/1 |url-status= live }}</ref>

===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 [[Chemistry:Fluorosurfactant|fluorosurfactant]], e.g. [[Chemistry:Perfluorooctanoic acid|perfluorooctanoic acid]] (PFOA).<ref>USEPA: [http://www.epa.gov/opptintr/pfoa/pubs/pfoastewardship.htm "2010/15 PFOA Stewardship Program"] {{webarchive|url=https://web.archive.org/web/20081027061359/http://www.epa.gov/opptintr/pfoa/pubs/pfoastewardship.htm|date=27 October 2008}} Accessed October 26, 2008.</ref> Strategies to enhance degradation include [[Chemistry:Ozone|ozone]] treatment and biodegradation.<ref>{{cite journal|doi=10.1007/s10311-014-0466-2|title=Surfactants: Toxicity, remediation and green surfactants|year=2014|last1=Rebello|first1=Sharrel|last2=Asok|first2=Aju K.|last3=Mundayoor|first3=Sathish|last4=Jisha|first4=M. S.|journal=Environmental Chemistry Letters|volume=12|issue=2|pages=275–287|s2cid=96787489 }}</ref><ref>{{cite journal|doi=10.1016/j.envint.2005.07.004|title=Fate, behavior and effects of surfactants and their degradation products in the environment|year=2006|last1=Ying|first1=Guang-Guo|journal=Environment International|volume=32|issue=3|pages=417–431|pmid=16125241}}</ref> Two major surfactants, linear alkylbenzene sulfonates (LAS) and the alkyl phenol ethoxylates (APE) break down under aerobic conditions found in [[Earth:Sewage treatment|sewage treatment]] plants and in soil to [[Chemistry:Nonylphenol|nonylphenol]], which is thought to be an [[Chemistry:Endocrine disruptor|endocrine disruptor]].<ref name="maria">Mergel, Maria. "Nonylphenol and Nonylphenol Ethoxylates." Toxipedia.org. N.p., 1 Nov. 2011. Web. 27 Apr. 2014.</ref><ref name="Scott2000">{{cite journal | vauthors = Scott MJ, Jones MN | title = The biodegradation of surfactants in the environment | journal = Biochim. Biophys. Acta | volume = 1508 | issue = 1–2 | pages = 235–51 | date = November 2000 | pmid = 11090828 | doi = 10.1016/S0304-4157(00)00013-7| doi-access = free }}</ref>  Interest in biodegradable surfactants has led to much interest in "biosurfactants" such as those derived from amino acids.<ref name="pmid20094712">{{cite journal | vauthors = Reznik GO, Vishwanath P, Pynn MA, Sitnik JM, Todd JJ, Wu J, Jiang Y, Keenan BG, Castle AB, Haskell RF, Smith TF, Somasundaran P, Jarrell KA |display-authors = 6| title = Use of sustainable chemistry to produce an acyl amino acid surfactant | journal = Appl. Microbiol. Biotechnol. | volume = 86 | issue = 5 | pages = 1387–97 | date = May 2010 | pmid = 20094712 | doi = 10.1007/s00253-009-2431-8 |s2cid = 3017826}}</ref> 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.<ref>{{Cite web |title=Biobased Surfactants Market Report: Market Analysis |url=https://ceresana.com/en/produkt/biobased-surfactants-market-report-world |access-date=2024-01-05 |website=Ceresana Market Research |language=en-US}}</ref>

==See also==
{{Wikt}}
* {{annotated link|Engineering:Anti-fog}}
* {{annotated link|Biology:Cleavable detergent}}
* {{annotated link|Chemistry:Disodium cocoamphodiacetate}}
* {{annotated link|Chemistry:Emulsion}}
* {{annotated link|Chemistry:Hydrotrope}}
* {{annotated link|Chemistry:MBAS assay}}, an [[Biology:Assay|assay]] that indicates [[Physics:Ion#Anions and cations|anionic]] surfactants in water with a bluing reaction.
* {{annotated link|Biology:Niosome}}
* {{annotated link|Chemistry:Oil dispersants}}
* Surfactant leaching

==References==
{{Reflist|35em}}

==External links==

{{Foam scales and properties}}

[[Category:Bioremediation]]
[[Category:Biotechnology]]
[[Category:Colloidal chemistry]]
[[Category:Environmental terminology]]
[[Category:Underwater diving physics]]

{{Sourceattribution|Surfactant}}