What are surfactants?

Different kinds of surfactants have different functions. Some dissolve and remove dirt. Others are added to shampoos due to their abilities as emulsifying agents, antifoaming agents or anti-static agents.

The molecule of a surfactant consists of two parts: a water-loving part and a fat/oil-loving part. The substances can therefore appear in the interface between water and fat/oil (dirt). The molecule can "grab a hold of" the dirt so it can be rinsed off by the water.

The fat/oil-loving part of the surfactant consists of a carbon chain, which is often extracted from natural fatty acids (so called fatty acid chains). The water-loving part of the molecule consists of different chemical groups, which can carry an electronic charge. It is this part which is decisive for the different functions of surfactants and their classification:

amphoteric + / -
non-ionic none
anionic -
cationic +

Cationic surfactants, like anti-static agents, don't function as soaps (washing agents).

They are used in shampoos, conditioners and softeners to reduce the static electricity in hair and clothes (especially synthetic textiles).

Not all substances are soluble and mixable with water. It is crucial that the substances are mixable with water in order to be active during the hair washing process. Emulsifying agents are substances which make water-insoluble substances mixable with water.

When oil and water are mixed together an emulsion is created. In a microscope it is possible to see tiny drops of oil floating in the water.

In cooking eggs are often used to make the ingredients stick together: as the egg yolk contains a natural emulsifying agent named lecithin. Known emulsions in the kitchen are mayonnaise, ice cream, butter and margarine.

Why are creams and lotions white?

Oil and water are colourless. Nevertheless the lotion becomes white. The reason for this is the tiny drops of oil in the emulsion, which reflect most of the light that falls on them. Milk is also white because tiny drops of fat scattered around the milk reflect the light. For the same reason clouds and snow are also white. The drops of water in clouds and snow crystals reflect the major part of the light that falls on them.

Back to Teachers