Zwitterionic Surfactants


A zwitterionic surfactant is a zwitterion that has surface-active properties. (A zwitterion is also known as an internal salt, having an anion and a cation in the one molecule chemically joined together. You may have come across zwitterions when talking about amino acids.) Zwitterionic surfactants are also called amphoteric surfactants as they often comprise a base coupled to an acid.

Three zwitterionic surfactants: an ammonium carboxylate, an ammonium sulfate and an amine oxide.

A couple of very simple zwitterionic surfactants are shown above. Industrially useful zwitterionic surfactants often have rings or other functional groups on them.

Uses of Zwitterionic Surfactants

Zwitterionic surfactants are considered to be specialty surfactants as their use is fairly limited. The 1993 US consumption of zwitterionic surfactants consisted of only 2.8% (by value) of the total surfactant trade.

The one area where these surfactants have become very popular is in skin-care products. This is because they have a good "skin feel". They do not irritate the skin or eyes, and have good surfactant properties over a wide pH range. They are also said to have a favourable "safety profile", apart from not irritating the skin, they also do not assist in the transportation of other substances across the skin-barrier by solublising them.

[Source: Bartolo, R.G., Soap, in Encyclopedia of Chemical Technology, 4th ed, J.I. Kroschwitz, Editor. 1993, Wiley Interscience. p. 297-326.]