A surfactant is a chemical substance or an organic compound that lowers the surface tension between two liquids. They can also be applied to lower the surface tension between a liquid and a solid. Surfactants are amphiphilic in nature; and this implies that they contain both a hydrophobic tail (water-insoluble group) and a hydrophilic head (water-soluble group). It is a material that can greatly reduce the surface tension of water when used in very low concentrations. Surfactants are secreted by living cells including microbes and animals. They are one of many different compounds that make up a detergent; and surfactants are usually added to remove dirt from skin, clothes and other household articles or materials because of their sole ability to reduce the surface tension of the liquid they come in contact with. Surfactants can also be called surface-active agents; and they include such substances like soap and detergent that, when added to a liquid or water, reduces its surface tension.
Surfactants can act as emulsifiers, wetting agents, dispersants and foaming agents; and they possess great industrial importance in both the medical, pharmaceutical and textile industries. Surfactants concentrate at the interfaces between bodies or droplets of water and those of oil, or lipids, to act as an emulsifying agent, or foaming agent. They help dyes to penetrate evenly into fabrics or textiles; and thus have application in the textile industry. Surfactants are also used in corrosion inhibition, in ore flotation, to promote oil flow in porous rocks, and to produce aerosols. Most household detergents used for laundry purposes such as in washing of clothes, dishes and the toilet and bathroom are composed of surfactants. They are also used in the manufacture of shampoos, shower gels, hair conditioners, fabric softeners and dishwashing tablets and powders. The mechanism of action of surfactants is usually based on their ability to breakdown the interface between water and oils and/or dirt that they come in contact with. They also hold these oils and dirt in suspension, and so allow their removal.
Surfactants are able to do this because they contain a hydrophilic head (water loving group), such as an acid anion (-CO2– or SO3–) and a hydrophobic tail (water hating group), such as an alkyl chain (Figure 1). Molecules of water tend to congregate near the water-loving group while molecules of the water-insoluble material congregate near the water-hating group. Surfactants can also be produced by living organisms including microorganisms even though they can be chemically synthesized. Those surfactants synthesized by living organisms are generally known as biosurfactants.
Surfactants are molecules that concentrate at interfaces and decrease surface and interfacial tension; and they have applications in many areas including but not limited to their use as emulsifying agents, foaming agents, wetting agents, dispersing agents and solubilization agents. Surfactants have applications in a wide variety of commercial sectors including agriculture, pharmacy, medicine, and textile industry. It is noteworthy that these surface active agents are chemically synthesized, and they are mainly derived from hydrocarbons (e.g. petroleum). Surfactants can also increase the surface area of hydrophobic materials, such as pesticides in soil and water environment, thereby increasing their water solubility. Thus, the presence of surfactants may increase microbial degradation of pollutants; and the use of biosurfactants for degradation of pesticides in soil and water environment has gained tremendous importance in agriculture.
Figure 1: Illustration of the action of surfactants. Source: www.essentialchemicalindustry.org
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