Editing Surfactant (section)

==Classification==
Most surfactants are organic compounds with [[Hydrophile|hydrophilic]] "heads" and [[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 [[hydrocarbon]] chain, which can be branched, linear, or aromatic. [[Fluorosurfactant]]s have [[fluorocarbon]] chains. [[Siloxane surfactant]]s have [[siloxane]] chains.

Many important surfactants include a polyether chain terminating in a highly [[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 oxide]]s 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''.<ref>{{cite web |title=Surfactant {{!}} Defination, Classification, Properties & Uses |url=https://www.esteem-india.com/What-makes-a-surfactant.php |website=www.esteem-india.com |language=en}}</ref>

[[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 [[Zwitterion|''zwitterionic'']], or ''amphoteric''.  Commonly encountered surfactants of each type include:

===<span class="anchor" id="Anionic"></span>Anionic: sulfate, sulfonate, and phosphate, carboxylate derivatives===
[[Anion]]ic surfactants contain anionic functional groups at their head, such as [[organosulfate|sulfate]], [[sulfonate]], [[phosphate]], and [[carboxylic acid|carboxylate]]s.
Prominent alkyl sulfates include [[ammonium lauryl sulfate]], [[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:
* [[Alkylbenzene sulfonate]]s
* [[Docusate]] (dioctyl sodium sulfosuccinate)
* [[perfluorooctanesulfonic acid|Perfluorooctanesulfonate]] (PFOS)
* [[Perfluorobutanesulfonic acid|Perfluorobutanesulfonate]]
* Alkyl-aryl ether phosphates
* Alkyl ether phosphates

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 [[perfluorononanoic acid|perfluorononanoate]], [[Perfluorooctanoic acid|perfluorooctanoate]] (PFOA or PFO).

===Cationic head groups===
pH-dependent primary, secondary, or tertiary [[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> [[octenidine dihydrochloride]].

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

===Zwitterionic surfactants===
[[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 [[amine]]s or quaternary ammonium cations.  The anionic part can be more variable and include sulfonates, as in the [[hydroxysultaine|sultaines]] [[CHAPS detergent|CHAPS]] (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) and [[cocamidopropyl hydroxysultaine]]. [[Betaine]]s such as [[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]] [[phosphatidylcholine|phosphatidylserine]], [[phosphatidylethanolamine]], [[phosphatidylcholine]], and [[sphingomyelin]]s.

[[Lauryldimethylamine oxide]] and [[myristamine oxide]] are two commonly used zwitterionic surfactants of the tertiary [[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, [[biodegradation|biodegradability]]) or permission for use in food.<ref name="Ullmann" />

==== Ethoxylates ====

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

===== Alkylphenol ethoxylates (APEs or APEOs) =====
* [[Nonoxynols]]
* [[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 =====
* [[Polyethoxylated tallow amine]]
* [[Cocamide monoethanolamine]]
* [[Cocamide diethanolamine]]

===== Terminally blocked ethoxylates =====
* [[Poloxamer]]s

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

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

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

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

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

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

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

=== Other classifications ===
[[File:Gemini surfactant.png|thumb|Gemini amino acid-based surfactant (based on [[cysteine]])]]
* [[Amino acid-based surfactant]]s are surfactants derived from an [[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=[[Advances in Colloid and Interface Science]] |volume=222 |pages=79–91 |doi=10.1016/j.cis.2014.10.013|pmid=25846628 }}</ref>
* [[Gemini surfactant]]s consist of two surfactant molecules linked together at or near their head groups. Compared to monomeric surfactants, they have much lower [[critical micelle concentration]]s.<ref name="bordes"/>