What is an anionic surfactant? (with photos)

Biosurfactants are anionic surfactants that can be used to break up oil stains.

An anionic surfactant is a macromolecule, usually in the sulfonate or sulfate group of chemicals, such as sodium laureth sulfate, that acts as a surfactant to reduce the surface tension of liquids. This allows them to bind to impurities and suspended particles in the liquid, which makes them effective as cleaning agents in water. In small concentrations, they can also cause compounds to foam in water, creating large numbers of tiny gas bubbles, which makes them effective in cosmetics such as shampoo, toothpaste, and in fire-suppressing agents.

Anionic surfactants are often used in dishwashing detergents to remove oil and grease.

Basic soap used to clean the human body is also a type of surfactant or detergent made from natural fatty acids of plant or animal origin. The difference with an anionic surfactant is that it is primarily a synthetic chemical and is designed to act not only as a surfactant that binds to oils and particles in water, but also as a protein denaturing chemical. As anionic surfactants break down proteins attached to clothes in water, they are not recommended for common soap use as human skin is also a type of protein.

Chemical engineering has been perfecting synthetic anionic surfactant detergents since the late 1940s, when they began to replace common soap for use in washing machines. The negative electrical charge of their ionic nature causes them to bond to minerals dissolved in hard water. Ordinary soap leaves an insoluble gray film on materials that are washed in hard water. The first detergent surfactants were based on alkylated compounds, and the disadvantage of their use was that they are transported to natural waterways in city wastewater systems, where their foaming ability prevents degradation by natural microorganisms. These compounds were made illegal in 1965 in most nations, and a switch to alkylbenzene sulfonate (LAS) chemicals alleviated some of the problems with water pollution.

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LAS surfactants now have a wide variety of uses. They are essential for the emulsion polymerization of many plastics such as polystyrene, are used to protect agricultural seeds from mold and fungus, and are included in a wide variety of emulsified paints. Industrial cleaning supplies also rely on LAS compounds and about 50% of all LAS production goes to household cleaning products.

Non-ionic surfactants are less aggressive than their counterparts and have some similarities to regular soap, making them suitable for widespread use in dishwashing liquids and other household cleaners where contact with human skin is frequent. They are more effective at breaking down the grease produced in the kitchen. This is because they are related to grease molecules and are derived from fatty alcohols made from ethylene, paraffin and so on. The compounds have natural and petroleum-based sources. About 5% of all world oil production in 2003 was for the manufacture of non-ionic fatty alcohol surfactants, accounting for 212 million metric tons of the compound produced globally.

Special types of anionic surfactant compounds known as biosurfactants are also used in oil spill remediation. They are derived from natural compounds and have oleophilic molecular ends for cleaning oil and hydrophilic ends for binding to water molecules. Like a typical anionic surfactant, they reduce the surface tension in water to break large oil droplets into small ones that can disperse and biodegrade naturally. Biosurfactants allow oil cleaning operations to channel polluted water directly to wastewater treatment plants, or they break down the oil slick enough that natural bacteria in the water can further degrade the dispersed oil droplets.

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