Surfactants, also known as wetting agents, lower the surface tension of a liquid, allowing easier spreading, and the interfacial tension between two liquids. The term surfactant is a contraction of "Surface active agent". Surfactants are usually organic compounds that are amphipathic, meaning they contain both hydrophobic groups (their "tails") and hydrophilic groups (their "heads"). Therefore, they are typically sparingly soluble in both organic solvents and water. Surfactants reduce the surface tension of water by adsorbing at the air-water interface. They also reduce the interfacial tension between oil and water by adsorbing at the liquid-liquid interface. Many surfactants can also assemble in the bulk solution into aggregates that are known as micelles. The concentration at which surfactants begin to form micelles is known as the critical micelle concentration or CMC. When micelles form in water, their tails form a core that is like an oil droplet, and their heads form an outer shell, or corona, that maintains favorable contact with water. When surfactants assemble in oil, the aggregate is referred to as a reverse micelle. In a reverse micelle, the heads are in the core and the tails maintain favorable contact with oil.
In Index Medicus and the National Library of Medicine (NLM, USA Dept. of Health and Human Services), "surfactant" is reserved for the meaning pulmonary surfactant (see "alveoli" link below). For the more general meaning, "surface active agent" is the heading.
Surfactants play an important role in many practical applications and products, including:
Surfactant is a complex substance containing phospholipids and a number of apoproteins. This essential fluid is produced by the Type II alveolar cells, and lines the alveoli and smallest bronchioles. Surfactant reduces surface tension throughout the lung, thereby contributing to its general compliance. It is also important because it stabilizes the alveoli. Laplace Law tells us that the pressure within a spherical structure with surface tension, such as the alveolus, is inversely proportional to the radius of the sphere (P=4T/r for a sphere with two liquid-gas interfaces, like a soap bubble, and P=2T/r for a sphere with one liquid-gas interface, like an alveolus: P=pressure, T=surface tension, and r=radius). That is, at a constant surface tension, small alveoli will generate bigger pressures within them than will large alveoli. Smaller alveoli would therefore be expected to empty into larger alveoli as lung volume decreases. This does not occur, however, because surfactant differentiallyreduces surface tension, more at lower volumes and less at higher volumes, leading to alveolar stability and reducing the likelihood of alveolar collapse.
Surfactant is formed relatively late in fetal life; thus premature infants born without adequate amounts experience
The four major classifications of surfactants are: anionic, cationic, nonionic, and amphoteric. Anionic surfactants are water soluble and have a negative charge in aqueous solution. Cationic surfactants have a positive charge in aqueous solution and are considered to be poor cleaners. Nonionic surfactants are the most widely used for surface cleaning and have no charge in aqueous solutions. Amphoteric surfactants develop a negative or positive charge depending on whether the solution is alkaline or acidic.
Anionic surfactants are used in laundry and hand dishwashing detergents; household cleaners; and personal cleansing products. They ionize (are converted to electrically charged particles) in solution, carry a negative charge, have excellent cleaning properties and generally are high sudsing. Linear alkylbenzene sulfonate, alcohol ethoxysulfates, alkyl sulfates and soap are the most common anionic surfactants. Tiagabine
Nonionic surfactants are low sudsing and are typically used in laundry and automatic dishwasher detergents and rinse aids. Because they do not ionize in solution and thus have no electrical charge, they are resistant to water hardness and clean well on most soils. The most widely used are alcohol ethoxylates. Nonionic surfactants are a class of synthetic surfactants. They are prepared by attaching ethylene oxide molecules to a water-insoluble molecule. The ethylene oxide molecules, derived from petroleum, are water-soluble polymers. Depending on the number of ethylene oxides and the number of carbon atoms, the synthetic surfactants can be classified as a wetting agent, a detergent, or an emulsifier.
Cationic surfactants are used in fabric softeners and in fabric-softening laundry detergents. Other cationics are the disinfecting/sanitizing ingredient in some household cleaners. They ionize in solution and have a positive charge. Quaternary ammonium compounds are the principal cationics.
Amphoteric surfactants are used in personal cleansing and household cleaning products for their mildness, sudsing and stability. They have the ability to be anionic (negatively charged), cationic (positively charged) or nonionic (no charge) in solution, depending on the pH (acidity or alkalinity) of the water. Imidazolines and betaines are the major amphoterics.
Surfactants for household and industrial & institutional cleaning applications include many diverse products across several surfactant chemistries. The unique functional and economic characteristics of these materials open the door to innovative surfactant solutions for cleaning product applications ĘC from commercial dishwashing detergents to home floor and carpet care products; and from dairy and food process cleaners to hard surface cleaners for household kitchens and bathrooms.
Surfactants for paints, coatings and inks include many diverse products across several surfactant chemistries. The unique functional and economic characteristics of these materials open the door to innovative surfactant solutions for paints, coatings, and ink formulations ĘC from high performance automotive paints, to waterborne colorant and ink systems for packaging applications.
Surfactants improve performance characteristics during the manufacture of styrene-butadiene latex, vinyl-acrylic, and other copolymer resins systems. Latex manufacturers also rely on them to help achieve the desired mechanical properties and storage stability in final products.
Agrochemicals, As inerts for emulsification or penetration for a wide variety of pesticide formulations. Also used in adjuvants.
Electrowinning, Electroplating and Electroless Plating. Remove soils, provide vapor and mist suppression, modify the cathode film to achieve bright deposits, and prevent gas bubbles from sticking to cathodic surfaces.
Textile Processing. Enhance wetting, dye penetration, emulsification for apparel, floor coverings, home furnishings, automotive, and industrial products; textile processing (sizing, mercerizing, scouring, spinning) and textile finishing (softening, dyeing & printing, flameproofing, anti-soil treatments).
Pulp and Paper. Variety of mill operations including pulping and processing, deinking, defoaming, emulsification, and felt cleaning.
Oil Field Chemicals. Drilling fluids, acidizing and stimulation, drilling cutting and well cleaning, enhanced oil recovery.
Metalworking Fluids and Lubricants. Emulsifiers and wetting agents, and auxiliary features including corrosion inhibition, hard water stability, detergency, lubricity. Solviolence.org