Surfactant
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Surfactants

Surfactants

surfactants

The compounds that lower the surface tension between two phases, like between two liquids, a gas and a liquid, or a liquid and a solid are called surface-active agent or surfactant.

In aqueous solutions surfactants behave like organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their tails) and hydrophilic groups (their heads). The arrangement of the hydrophilic head is at the interface of water and the hydrophobic groups aligns toward oil. Therefore, a surfactant contains both a water-insoluble (or oil-soluble) component and a water-soluble component. Surfactant will diffuse in water and adsorb at interfaces between air and water or at the interface between oil and water, in the case where water is blended with oil. This property allows surfactants to act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.

Many important surfactant include a polyether chain terminating in a polar anionic group. The polyether groups often comprise ethoxylated (polyethylene oxide-like) sequences inserted to increase the hydrophilic character of a surfactant. Polypropylene oxides conversely, may be inserted to increase the lipophilic character of a surfactant. Surfactants molecules have either one tail or two; those with two tails are said to be double-chained. Surfactant classification according to the composition of their head falls under nonionic, anionic, cationic, and amphoteric. A nonionic 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. Zwitterionic or amphoteric surfactants have both cationic and anionic centers attached to the same molecule.

Two major surfactants, are linear alkylbenzene sulfonates (LAS) and the alkyl phenol ethoxylates (APE). Anionic surfactants contain anionic functional groups at their head, such as sulfate, sulfonate, phosphate, and carboxylates. Prominent alkyl sulfates include 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.

Nonionic 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 nonionic surfactants therefore decreases with increasing temperature. The characteristic feature of cloud point (CP) of nonionic surfactants is the temperature at which the surfactant separates out from an aqueous solution due to the weakening of hydrogen bonds between the surfactant and water molecules. Nonionic surfactants are less sensitive to water hardness than anionic surfactants, and they foam less strongly.

Most anionic and nonionic surfactants are nontoxic, having LD50 comparable to sodium chloride. The toxicity of quaternary ammonium compounds, which are antibacterial and antifungal, varies. Prolonged exposure to surfactants can irritate and damage the skin because surfactants disrupt the lipid membrane that protects skin and other cells. Skin irritancy generally increases in the series nonionic, amphoteric, anionic, cationic surfactants.

Surfactants play an important role in personal care products such as cosmetics, shampoos, shower gel, hair conditioners, and toothpastes. Surfactants with different HLB are used in detergents, fabric softeners, soaps, paints, adhesives, inks, emulsions, anti-fogs, ski waxes, snowboard wax, deinking of recycled papers, in flotation, washing and enzymatic processes. Agrochemical formulations such as some herbicides, insecticides, biocides (sanitizers), and spermicides also contain Surfactants. Surfactants find use in firefighting and pipelines as liquid drag reducing agents. Alkali Surfactant polymers are used to mobilize oil in oil wells for exploration.

Nonionic Surfactantsurfactant refers to the Surfactant molecules, which do not undergo ionization when being dissolved in water. The Nonionic Surfactantsurfactant are not in the ionic state in the solution, thereby having high stability and being less susceptible to the effect of strong electrolyte inorganic salts as well as acid and alkalis. Nonionic Surfactantsurfactants have excellent compatibility with other types of surfactants and have excellent solubility (which vary depending on different structures, HLB etc) in both water and organic solvents.

Nonionic surfactants have covalently bonded oxygen-containing hydrophilic groups, which are bonded to hydrophobic parent structures. These Nonionic surfactants, are not ionized in water, and contain both hydrophilic groups (e.g. oxyethylene-CH2CH2O-, ether groups, hydroxyl group -OH or -CONH2 amide group, etc.) and lipophilic group (e.g., hydrocarbons which can be natural fatty alcohols or synthetic alcohols, acids or glyceryl esters/oils). The water-solubility of the oxygen groups is the result of hydrogen bonding. Hydrogen bonding decreases with increasing temperature, and the water solubility of Nonionic surfactants therefore decreases with increasing temperature. This result in formation of a milky/cloudy emulsion called the cloud point of surfactants. This property is very essential for determining the optimum use of Nonionic surfactant in formulations at elevated temperature especially in cleaning formulations like detergents, CIP etc.

As discussed above Nonionic surfactants have a unique property called a cloud point. The cloud point is the temperature at which the Nonionic surfactant begins to separate from the cleaning solution, called phase separation. When this occurs, the cleaning solution becomes cloudy. This cloud point is therefore considered the temperature for optimal detergency. For low foaming cleaners, optimal detergency is at the cloud point; for foaming cleaners optimal detergency is either just below the cloud point or at the start of the cloud point. The agitation of low foaming cleaners is sufficient to prevent phase separation. The temperature of the cloud point depends upon the ratio of the hydrophobic and hydrophilic portions of the Nonionic surfactant. Some cloud points are at room temperature while others are very high. Some Nonionic surfactants don’t have a cloud point because they have a very high ratio of hydrophilic to hydrophobic moieties.



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