Surfactant

A surfactant is a chemical that lowers the surface tension of a liquid. Less surface tension lets the liquid soak into things better, and can also let bubbles form easier. A liquid that bubbles and soaks into things is better at cleaning, so surfactants are used in soap.

Uses

Every year, 15 million tons of surfactants are made. Half of them are used in soap; the rest are used in many different ways including making toothpaste and concrete.

One popular surfactant is sodium laurel sulfate, also called sodium dodecyl sulfate or SDS. SDS is a cheap, commonly used surfactant that is used in almost every toothpaste and many shampoos, body washes, and shaving creams.

Safety and environment

Small amounts of most common surfactants are usually not harmful to people or animals, although if they get into eyes they can be painful. Very large amounts of surfactants can kill animals, but the amount varies depending on the surfactant.

Larger amounts of surfactants can be a problem in the environment, where they let the soil hold more water than usual, but this problem usually goes away in a few days.

Surfactant Media

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  Schematic diagram of a micelle of oil in aqueous suspension, such as might occur in an emulsion of oil in water. In this example, the surfactant molecules' oil-soluble tails project into the oil (blue), while the water-soluble ends remain in contact with the water phase (red).

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  Schematic diagram of a micelle – the lipophilic tails of the surfactant ions remain inside the oil because they interact more strongly with oil than with water. The polar "heads" of the surfactant molecules coating the micelle interact more strongly with water, so they form a hydrophilic outer layer that forms a barrier between micelles.

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  Sodium stearate, the most common component of most soap, which comprises about 50% of commercial surfactants

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  4-(5-Dodecyl) benzenesulfonate, a linear dodecylbenzenesulfonate, one of the most common surfactants

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  Phosphatidylcholine, found in lecithin, is a pervasive biological surfactant. Shown in red – choline and phosphate group; black – glycerol; green – monounsaturated fatty acid; blue – saturated fatty acid.

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  Surfactant classification according to the composition of their head: non-ionic, anionic, cationic, amphoteric.