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Surfactants are
chemical compounds A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
that decrease the
surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) t ...
between two
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, ...
s, between a gas and a liquid, or
interfacial tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) t ...
between a liquid and a
solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
. Surfactants may act as
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
s,
wetting Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. This happens in presence of a gaseous phase or another liquid phase not miscible with ...
agents,
emulsifiers An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...
,
foaming agent A foaming agent is a material such as a surfactant or a blowing agent that facilitates the formation of foam. A surfactant, when present in small amounts, reduces surface tension of a liquid (reduces the work needed to create the foam) or increase ...
s, or
dispersant A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their sett ...
s. The word "surfactant" is a
blend A blend is a mixture of two or more different things or substances; e.g., a product of a mixer or blender. Blend Blend may also refer to: * Blend word, a word formed from parts of other words * ''Blend'' (album), a 1996 album by BoDeans * B ...
of ''surface-active agent'', coined . 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 (also known as salt-induced precipitation, salt fractionation, anti-solvent crystallization, precipitation crystallization, or drowning out) is a purification technique that utilizes the reduced solubility of certain molecules in a s ...
: by adding an inorganic salt to an aqueous solution of a weakly polar substance, the substance will precipitate. The substance may itself be a surfactant – this is one of the reasons why many surfactants are ineffective in sea water.


Composition and structure

Surfactants are usually
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s that are
amphiphilic An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compo ...
, meaning each molecule contains both a
hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are n ...
"water-seeking" group (the ''head''), and a
hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, ...
"water-avoiding" group (the ''tail''). As a result, a surfactant contains both a water-soluble component and a water-insoluble component. Surfactants diffuse in water and get
adsorb Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
ed at
interfaces Interface or interfacing may refer to: Academic journals * ''Interface'' (journal), by the Electrochemical Society * '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics'' * '' Int ...
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 the air or into the oil phase, while the water-soluble head group remains in the water phase. The hydrophobic tail may be either
lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipo ...
("oil-seeking") or lipophobic ("oil-avoiding") depending on its chemistry.
Hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
groups are usually lipophilic, for use in soaps and detergents, while
fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...
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
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are us ...
s. Other surfactants produced on a particularly large scale are linear
alkylbenzene sulfonates Alkylbenzene sulfonates are a class of anionic surfactants, consisting of a hydrophilic sulfonate head-group and a hydrophobic alkylbenzene tail-group. Along with sodium laureth sulfate, they are one of the oldest and most widely used synthetic ...
(1.7 million tons/y),
lignin sulfonate Lignosulfonates (LS) are water-soluble anionic polyelectrolyte polymers: they are byproducts from the production of wood pulp using sulfite pulping. Most delignification in sulfite pulping involves acidic cleavage of ether bonds, which connect m ...
s (600,000 tons/y),
fatty alcohol Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4–6 carbons to as many as 22–26, derived from natural fats and oils. The precise chain length varies ...
ethoxylate Ethoxylation is a chemical reaction in which ethylene oxide adds to a substrate. It is the most widely practiced alkoxylation, which involves the addition of epoxides to substrates. In the usual application, alcohols and phenols are converted i ...
s (700,000 tons/y), and
alkylphenol Alkylphenols are a family of organic compounds obtained by the alkylation of phenols. The term is usually reserved for commercially important propylphenol, butylphenol, amylphenol, heptylphenol, octylphenol, nonylphenol, dodecylphenol and related ...
ethoxylate Ethoxylation is a chemical reaction in which ethylene oxide adds to a substrate. It is the most widely practiced alkoxylation, which involves the addition of epoxides to substrates. In the usual application, alcohols and phenols are converted i ...
s (500,000 tons/y).Kurt Kosswig "Surfactants" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, 2005, Weinheim.


Structure of surfactant phases in water

In the bulk aqueous phase, surfactants form aggregates, such as
micelles A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated coll ...
, 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 bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
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
surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) t ...
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
diffusion coefficient Diffusivity, mass diffusivity or diffusion coefficient is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration of the species (or the driving force for diffusion). Diffusivity is enc ...
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 Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
or electrostatic repulsions. The
surface rheology {{more references, date=November 2011 Surface rheology is a description of the rheological properties of a free surface. When perfectly pure, the interface between fluids usually displays only surface tension. But when surfactants are adsorbed on ...
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 The spinning drop method or rotating drop method is one of the methods used to measure interfacial tension. Measurements are carried out in a rotating horizontal tube which contains a dense fluid. A drop of a less dense liquid or a gas bubble is ...
. 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 Ellipsometry is an optical technique for investigating the dielectric properties (complex refractive index or dielectric function) of thin films. Ellipsometry measures the change of polarization upon reflection or transmission and compares it t ...
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.


In biology

The human body produces diverse surfactants.
Pulmonary surfactant Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water in ...
is produced in the
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
s in order to facilitate breathing by increasing
total lung capacity Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breath ...
, and
lung compliance Lung compliance, or pulmonary compliance, is a measure of the lung's ability to stretch and expand (distensibility of elastic tissue). In clinical practice it is separated into two different measurements, static compliance and dynamic compliance. ...
. In respiratory distress syndrome or RDS, 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 Beractant, also known by the trade name of Survanta, is a modified bovine pulmonary surfactant containing bovine lung extract (phospholipids, neutral lipids, fatty acids, and bovine surfactant proteins), to which synthetic DPPC, tripalmitin and ...
) or its generic form Beraksurf, produced by
Abbvie AbbVie is an American publicly traded biopharmaceutical company founded in 2013. It originated as a spin-off of Abbott Laboratories. History On October 19, 2011, Abbott Laboratories announced its plan to separate into two publicly traded compani ...
and Tekzima respectively. Bile salts, a surfactant produced in the liver, play an important role in digestion.


Safety and environmental risks

Most anionic and non-ionic surfactants are non-toxic, having
LD50 In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...
comparable to
table salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
. The toxicity of
quaternary ammonium compounds In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cation ...
, which are
antibacterial An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
and
antifungal An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as ...
, varies. Dialkyldimethylammonium chlorides (
DDAC Didecyldimethylammonium chloride (DDAC) is a quaternary ammonium compound used as antiseptic/disinfectant. It causes the disruption of intermolecular interactions and the dissociation of lipid bilayers. The bacteriostatic (prevent growth) or bac ...
,
DSDMAC Dimethyldioctadecylammonium chloride also commonly distearyl dimethyl ammonium chloride is an organic compound classified as quaternary ammonium salt. The nitrogen center substituted with two methyl groups and two stearyl groups. The combinatio ...
) used as
fabric softener A fabric softener (American English) or fabric conditioner (British English) is a conditioner that is applied to laundry during the rinse cycle in a washing machine to reduce harshness in clothes that are dried in air after machine washing. In con ...
s have low LD50 (5 g/kg) and are essentially non-toxic, while the
disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than s ...
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 The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
that protects skin and other cells. Skin irritancy generally increases in the series non-ionic, amphoteric, anionic, cationic surfactants. 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. Anionic surfactants can be found in soils as the result of
sewage sludge Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term " septage" also refers to sludge from simple wastewater treatment but is connected to s ...
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. In the case of the
Deepwater Horizon oil spill The ''Deepwater Horizon'' oil spill (also referred to as the "BP oil spill") was an industrial disaster that began on 20 April 2010 off of the coast of the United States in the Gulf of Mexico on the BP-operated Macondo Prospect, considere ...
, unprecedented amounts of 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), sorbitan monooleate (Span 80), and polyoxyethylenated sorbitan monooleate ( Tween-80).


Biodegradation

Because of the volume of surfactants released into the environment, their biodegradation is of great interest. Strategies to enhance degradation include
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...
treatment and biodegradation. Two major surfactants, linear alkylbenzene sulfonates (LAS) and the alkyl phenol
ethoxylate Ethoxylation is a chemical reaction in which ethylene oxide adds to a substrate. It is the most widely practiced alkoxylation, which involves the addition of epoxides to substrates. In the usual application, alcohols and phenols are converted i ...
s (APE) break down under
aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...
conditions found in
sewage treatment Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding en ...
plants and in soil to nonylphenol, which is thought to be an
endocrine disruptor Endocrine disruptors, sometimes also referred to as hormonally active agents, endocrine disrupting chemicals, or endocrine disrupting compounds are chemicals that can interfere with endocrine (or hormonal) systems. These disruptions can cause ...
.Mergel, Maria. "Nonylphenol and Nonylphenol Ethoxylates." Toxipedia.org. N.p., 1 Nov. 2011. Web. 27 Apr. 2014. Interest in biodegradable surfactants has led to much interest in "biosurfactants" such as those derived from amino acids. Attracting much attention is the non-biodegradability of
fluorosurfactant Per- and polyfluoroalkyl substances (PFASs) are synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. An early definition, from 2011, required that they contain at least one perfluoroalkyl ...
, e.g.
perfluorooctanoic acid Perfluorooctanoic acid (PFOA; conjugate base perfluorooctanoate; also known colloquially as C8, for its 8 carbon chain structure) is a perfluorinated carboxylic acid produced and used worldwide as an industrial surfactant in chemical processes a ...
(PFOA).


Applications

The annual global production of surfactants was 13 million tons in 2008. In 2014, the world market for surfactants reached a volume of more than US $33 billion. Market researchers expect annual revenues to increase by 2.5% per year to around $40.4 billion until 2022. The commercially most significant type of surfactants is currently the anionic surfactant LAS, which is widely used in cleaners and detergents. Surfactants play an important role as cleaning,
wetting Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. This happens in presence of a gaseous phase or another liquid phase not miscible with ...
, dispersing,
emulsifying An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...
, foaming and anti-foaming agents in many practical applications and products, including
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
s,
fabric softener A fabric softener (American English) or fabric conditioner (British English) is a conditioner that is applied to laundry during the rinse cycle in a washing machine to reduce harshness in clothes that are dried in air after machine washing. In con ...
s,
motor oil Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, deterg ...
s,
emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Alth ...
s,
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are us ...
s,
paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...
s,
adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...
s, inks,
anti-fog Anti-fog agents, also known as anti-fogging agents and treatments, are chemicals that prevent the condensation of water in the form of small droplets on a surface which resemble fog. Anti-fog treatments were first developed by NASA during Project ...
s,
ski wax Ski wax is a material applied to the bottom of snow runners, including skis, snowboards, and toboggans, to improve their coefficient of friction performance under varying snow conditions. The two main types of wax used on skis are glide waxes and ...
es, snowboard wax,
deinking Deinking is the industrial process of removing printing ink from paperfibers of recycled paper to make deinked pulp. The key in the deinking process is the ability to detach ink from the fibers. This is achieved by a combination of mechanical ac ...
of
recycled paper The recycling of paper is the process by which waste paper is turned into new paper products. It has a number of important benefits: It saves waste paper from occupying homes of people and producing methane as it breaks down. Because paper fib ...
s, in flotation, washing and enzymatic processes, and
laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubri ...
s. Also agrochemical formulations such as
herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
s (some),
insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed t ...
s,
biocide A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a sli ...
s (sanitizers), and
spermicide Spermicide is a contraceptive substance that destroys sperm, inserted vaginally prior to intercourse to prevent pregnancy. As a contraceptive, spermicide may be used alone. However, the pregnancy rate experienced by couples using only spermicid ...
s (
nonoxynol-9 Nonoxynol-9, sometimes abbreviated as N-9, is an organic compound that is used as a surfactant. It is a member of the nonoxynol family of nonionic surfactants. N-9 and related compounds are ingredients in various cleaning and cosmetic products ...
). Personal care products such as
cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protec ...
,
shampoo Shampoo () is a hair care product, typically in the form of a viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in solid bar format. Shampoo is used by applying it to wet hair, massaging the product into the ...
s, shower gel,
hair conditioner Hair conditioner is a hair care cosmetic product used to improve the feel, texture, appearance, and manageability of hair. Its main purpose is to reduce friction between strands of hair to allow smoother brushing or combing, which might otherwise ...
s, and
toothpaste Toothpaste is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from the teeth, ...
s. Surfactants are used in
firefighting Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter. Firefighters typically ...
and pipelines (liquid drag reducing agents). Alkali surfactant polymers are used to mobilize oil in
oil well An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas ma ...
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 and via the application of medicinal lotions and sprays to surface of skin and mucous membranes.


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 Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula . It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium s ...
(SDS) and cetyl trimethylammonium bromide (CTAB). Detergents are key reagents to
extract An extract is a substance made by extracting a part of a raw material, often by using a solvent such as ethanol, oil or water. Extracts may be sold as tinctures, absolutes or in powder form. The aromatic principles of many spices, nuts ...
protein by lysis of the cells and tissues: They disorganize the membrane's
lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
(SDS, Triton X-100, X-114,
CHAPS Chaps ( or ) are sturdy coverings for the legs consisting of leggings and a belt. They are buckled on over trousers with the chaps' integrated belt, but unlike trousers, they have no seat (the term "assless chaps" is a tautology) and are not jo ...
, DOC, and NP-40), and solubilize proteins. Milder detergents such as octyl thioglucoside,
octyl glucoside Octyl glucoside (''n''-octyl-β--glucoside) is a nonionic surfactant frequently used to solubilise integral membrane proteins for studies in biochemistry. Structurally, it is a glycoside derived from glucose and octanol. Like Genapol X-100 and Tr ...
or dodecyl maltoside are used to solubilize membrane proteins such as
enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
and
receptors Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...
without denaturing them. Non-solubilized material is harvested by centrifugation or other means. For
electrophoresis Electrophoresis, from Ancient Greek ἤλεκτρον (ḗlektron, "amber") and φόρησις (phórēsis, "the act of bearing"), is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric fi ...
, for example, proteins are classically treated with SDS to denature the native tertiary and quaternary structures, allowing the separation of proteins according to their
molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...
. 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.
Pulmonary surfactant Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water in ...
s are also naturally secreted by type II cells of the lung
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...
in
mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...
.


Quantum dot preparation

Surfactants are used with
quantum dot Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the ...
s in order to manipulate the growth, assembly, and electrical properties of quantum dots, in addition to mediating reactions on their surfaces. Research is ongoing in how surfactants arrange on the surface of the quantum dots.


Surfactants in droplet-based microfluidics

Surfactants play an important role in
droplet-based microfluidics Droplet-based microfluidics manipulate discrete volumes of fluids in immiscible phases with low Reynolds number and laminar flow regimes. Interest in droplet-based microfluidics systems has been growing substantially in past decades. Microdroplet ...
in the stabilization of the droplets, and the prevention of the fusion of droplets during incubation.


Heterogeneous catalysis

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


Classification

The "tails" of most surfactants are fairly similar, consisting of a
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
chain, which can be branched, linear, or aromatic.
Fluorosurfactant Per- and polyfluoroalkyl substances (PFASs) are synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. An early definition, from 2011, required that they contain at least one perfluoroalkyl ...
s have
fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...
chains. Siloxane surfactants have
siloxane A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compound ...
chains. Many important surfactants include a polyether chain terminating in a highly
polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...
anionic group. The polyether groups often comprise ethoxylated (
polyethylene oxide Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...
-like) sequences inserted to increase the hydrophilic character of a surfactant.
Polypropylene oxide Polypropylene glycol or polypropylene oxide is the polymer (or macromolecule) of propylene glycol. Chemically it is a polyether, and, more generally speaking, it's a polyalkylene glycol (PAG) H S Code 3907.2000. The term polypropylene glycol or PPG ...
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''. 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. Commonly encountered surfactants of each type include:


Anionic: sulfate, sulfonate, and phosphate, carboxylate derivatives

Anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
ic surfactants contain anionic functional groups at their head, such as
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
, sulfonate,
phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
, and
carboxylate In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, (or ). It is an ion with negative charge. Carboxylate salts are salts that have the general formula , where M is a metal and ''n'' is 1, 2,...; ''carboxylat ...
s. Prominent alkyl sulfates include ammonium lauryl sulfate,
sodium lauryl sulfate Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes written sodium laurilsulfate, is an organic compound with the formula . It is an anionic surfactant used in many cleaning and hygiene products. This compound is the sodium s ...
(sodium dodecyl sulfate, SLS, or SDS), and the related alkyl-ether sulfates
sodium laureth sulfate Sodium laureth sulfate (SLES), an accepted contraction of sodium lauryl ether sulfate (SLES), also called sodium alkylethersulfate, is an anionic detergent and surfactant found in many personal care products (soaps, shampoos, toothpaste, etc.) an ...
(sodium lauryl ether sulfate or SLES), and
sodium myreth sulfate Sodium myreth sulfate is a mixture of organic compounds with both detergent and surfactant properties. It is found in many personal care products such as soaps, shampoos, and toothpaste. It is an inexpensive and effective foaming agent. Typic ...
. Others include: *
Docusate Docusate is the common chemical and pharmaceutical name of the anion bis(2-ethylhexyl) sulfosuccinate, also commonly called dioctyl sulfosuccinate (DOSS). It is on the World Health Organization's List of Essential Medicines. Salts of this anio ...
(dioctyl sodium sulfosuccinate) * Perfluorooctanesulfonate (PFOS) * 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 Sodium lauroyl sarcosinate (INCI), also known as sarcosyl, is an anionic surfactant derived from sarcosine used as a foaming and cleansing agent in shampoo, shaving foam, toothpaste, and foam wash products. This surfactant is amphiphilic due to ...
and carboxylate-based fluorosurfactants such as perfluorononanoate, perfluorooctanoate (PFOA or PFO).


Cationic head groups

pH-dependent primary, secondary, or tertiary
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s; primary and secondary amines become positively charged at pH < 10: octenidine dihydrochloride. Permanently charged
quaternary ammonium salts In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cations ...
: cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC),
benzalkonium chloride Benzalkonium chloride (BZK, BKC, BAK, BAC), also known as alkyldimethylbenzylammonium chloride (ADBAC) and by the trade name Zephiran, is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs ha ...
(BAC), benzethonium chloride (BZT),
dimethyldioctadecylammonium chloride Dimethyldioctadecylammonium chloride also commonly distearyl dimethyl ammonium chloride is an organic compound classified as quaternary ammonium salt. The nitrogen center substituted with two methyl groups and two stearyl groups. The combinatio ...
, and dioctadecyldimethylammonium bromide (DODAB).


Zwitterionic surfactants

Zwitterion In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively- and negatively-charged functional groups. : With amino acids, for example, in solution a chemical equilibrium wil ...
ic (
amphoteric In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used. One type of amphoteric species are amphipro ...
) surfactants have both cationic and anionic centers attached to the same molecule. The cationic part is based on primary, secondary, or tertiary
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s or quaternary ammonium cations. The anionic part can be more variable and include sulfonates, as in the sultaines
CHAPS Chaps ( or ) are sturdy coverings for the legs consisting of leggings and a belt. They are buckled on over trousers with the chaps' integrated belt, but unlike trousers, they have no seat (the term "assless chaps" is a tautology) and are not jo ...
(3- 3-cholamidopropyl)dimethylammonio1-propanesulfonate) and
cocamidopropyl hydroxysultaine Cocamidopropyl hydroxysultaine (CAHS) is a synthetic amphoteric surfactant from the hydroxysultaine group. It is found in personal care products (soaps, shampoos, lotions etc.). It has uses as a foam booster, viscosity builder, and an antistatic ...
. Betaines such as
cocamidopropyl betaine Cocamidopropyl betaine (CAPB) is a mixture of closely related organic compounds derived from coconut oil and dimethylaminopropylamine. CAPB is available as a viscous pale yellow solution and it is used as a surfactant in personal care products an ...
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 Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids ...
phosphatidylserine Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid and is a component of the cell membrane. It plays a key role in cell cycle signaling, specifically in relation to apoptosis. It is a key pathway for viruses to enter cells via ap ...
, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelins. Lauryldimethylamine oxide and
myristamine oxide Myristamine oxide is an amine oxide based zwitterionic surfactant with a C14 (tetradecyl) alkyl tail. It is used as a foam stabilizer and hair conditioning agent in some shampoos and conditioners. Like other amine oxide based surfactants it is an ...
are two commonly used zwitterionic surfactants of the tertiary
amine oxide In chemistry, an amine oxide, also known as an amine ''N''-oxide or simply ''N''-oxide, is a chemical compound that contains the functional group , a nitrogen-oxygen coordinate covalent bond with three additional hydrogen and/or substituent-grou ...
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 In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
. 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 Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...
) or permission for use in food.


Ethoxylates


= Fatty alcohol ethoxylates

= * Narrow-range ethoxylate * Octaethylene glycol monododecyl ether * Pentaethylene glycol monododecyl ether


= Alkylphenol ethoxylates (APEs or APEOs)

= *
Nonoxynols Nonoxynols also known as nonaethylene glycol or polyethylene glycol nonyl phenyl ether are mixtures of nonionic surfactants used as detergents, emulsifiers, wetting agents or defoaming agents. The most commonly discussed compound nonoxynol-9 is a ...
* 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.


= Special ethoxylated fatty esters and oils

=


= Ethoxylated amines and/or fatty acid amides

= *
Polyethoxylated tallow amine Polyethoxylated tallow amine (also polyoxyethylene tallowamine, POE-tallowamine) refers to a range of non-ionic surfactants derived from animal fats (tallow). They are a class of polyethoxylated amines (POEAs). The abbreviation 'POEA' is often er ...
*
Cocamide monoethanolamine Cocamide MEA, or cocamide monoethanolamine, is a solid, off-white to tan compound, often sold in flaked form. The solid melts to yield a pale yellow viscous clear liquid. It is a mixture of fatty acid amides which is produced from the fatty acids ...
* Cocamide diethanolamine


= Terminally blocked ethoxylates

= *
Poloxamer Poloxamers are nonionic triblock copolymers composed of a central hydrophobic chain of polyoxypropylene (poly(propylene oxide)) flanked by two hydrophilic chains of polyoxyethylene (poly(ethylene oxide)). The word was coined by BASF inventor, I ...
s


Fatty acid esters of polyhydroxy compounds


= Fatty acid esters of glycerol

= *
Glycerol monostearate Glycerol monostearate, commonly known as GMS, is a monoglyceride commonly used as an emulsifier in foods. It takes the form of a white, odorless, and sweet-tasting flaky powder that is hygroscopic. Chemically it is the glycerol ester of stearic ...
*
Glycerol monolaurate Monolaurin (abbreviated GML; also called glycerol monolaurate, glyceryl laurate, and 1-lauroyl-glycerol) is a monoglyceride. It is the mono-ester formed from glycerol and lauric acid. Its chemical formula is C15H30O4. Uses Monolaurin is most comm ...


= Fatty acid esters of sorbitol

= Spans: *
Sorbitan monolaurate Sorbitan monolaurate is a mixture of esters formed from the fatty acid lauric acid and polyols derived from sorbitol, including sorbitan and isosorbide. As a food additive, it is designated with the E number E493. See also * Sorbitan monostearat ...
*
Sorbitan monostearate Sorbitan monostearate is an ester of sorbitan (a sorbitol derivative) and stearic acid and is sometimes referred to as a synthetic wax.
*
Sorbitan tristearate Sorbitan tristearate is a nonionic surfactant. It is variously used as a dispersing agent, emulsifier, and stabilizer, in food and in aerosol sprays. As a food additive, it has the E number E numbers ("E" stands for "Europe") are codes fo ...
Tweens: *
Tween 20 Polysorbate 20 (common commercial brand names include Kolliphor PS 20, Scattics, Alkest TW 20, Tween 20, and Kotilen-20) is a polysorbate-type nonionic surfactant formed by the ethoxylation of sorbitan monolaurate. Its stability and relative non ...
*
Tween 40 Polysorbates are a class of emulsifiers used in some pharmaceuticals and food preparation. They are commonly used in oral and topical pharmaceutical dosage forms. They are also often used in cosmetics to solubilize essential oils into water-based ...
*
Tween 60 Polysorbates are a class of emulsifiers used in some pharmaceuticals and food preparation. They are commonly used in oral and topical pharmaceutical dosage forms. They are also often used in cosmetics to solubilize essential oils into water-based ...
*
Tween 80 Preadolescence is a stage of human development following middle childhood and preceding adolescence.New Oxford American Dictionary. 2nd Edition. 2005. Oxford University Press. It commonly ends with the beginning of puberty. Preadolescence is c ...


= Fatty acid esters of sucrose

=


= Alkyl polyglucosides

= *
Decyl glucoside Decyl glucoside is a mild non-ionic surfactant used in cosmetic formularies,Fiume MM, Heldreth B, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler D, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Andersen FA. Safety assessment of decyl gluco ...
*
Lauryl glucoside Lauryl glucoside is a surfactant used in cosmetics and laundry detergents. It is a glycoside produced from glucose and lauryl alcohol. See also * Decyl glucoside Decyl glucoside is a mild non-ionic surfactant used in cosmetic formularies,F ...
*
Octyl glucoside Octyl glucoside (''n''-octyl-β--glucoside) is a nonionic surfactant frequently used to solubilise integral membrane proteins for studies in biochemistry. Structurally, it is a glycoside derived from glucose and octanol. Like Genapol X-100 and Tr ...


See also

* * * * * * , an
assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of ...
that indicates
anionic An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
surfactants in water with a bluing reaction. * * * *
Surfactant leaching Surfactant leaching of acrylic (latex) paints, also known as exudate staining, streak staining, streaking, weeping, exudation, etc., occurs when the freshly painted surface becomes wet and water-soluble components of the paint ( dispersants, sur ...


References


External links

* {{authority control Bioremediation Biotechnology Cleaning product components Colloidal chemistry Environmental terminology Underwater diving physics