Nonionic Surfactants


Nonionic surfactants differ from both cationic and anionic surfactants in that the molecules are actually uncharged. The hydrophilic group is made up of some other very water soluble moeity, (e.g. a short, water-soluble polymer chain) rather than a charged species. Traditionally, nonionic surfactants have used poly(ethylene oxide) chains as the hydrophilic group. Poly(ethylene oxide) is a water soluble polymer; the polymers used in nonionic surfactants are typically 10 to 100 units long.

The two common classes of surfactant that use poly(ethylene oxide) chains as their hydrophilic group are the alcohol ethoxylates and the alkylphenol ethoxylates.

An alcohol ethoxylate and an alkylphenol ethoxylate. The poly(ethylene oxide) chain forms the water soluble surfactant "head".

Another class of nonionic surfactants are the alkyl polyglycosides. For at least the last 20 years these have been dubbed the "new generation nonionic surfactants". In these molecules, the hydrophilic group is sugar - in this case they are just polysaccharides, but they can be made from disaccharides, trisaccharides, maltose and various other sugars.

Examples of alkyl polyglycosides: an alkyl glucoside and a glucose ester.

Although they are called polyglycosides, they generally only have one or two sugar groups in the chain.

Sorbitan ester surfactants are commercially signicant surfactants. Fairly harsh conditions are required to synthesise them: 225-250 °C in the presence of an acid catalyst.

"Tween 85" (sorbitan trioleate poly(ethylene oxide)) is one of the sorbitan ester surfactants

Uses of Nonionic Surfactants

The predominant use of these surfacants is in foods and drinks, pharmaceuticals and skin-care products. It is thought that these surfactants are mild on the skin even at high loadings and long-term exposure (although they can lead to a weakening of the skin barrier by helping the transport of molecules.