Detergent chemicals called Sufactants which are in all common cleaning solutions. What are they and how do they work?
One group of chemicals that are without doubt “everyday chemicals” are the surfactants. They are one of the main components of detergents and are used for many different applications around the house. Soap contains surfactants, so does washing up liquid, so do many of the other cleaning products which are freely dispersed around our kitchens, bathrooms and other parts of our houses.
Head and Tail
What are surfactants and how do they work? Surfactants are literally “Surface Acting Agents”. They are called this because they act to reduce the surface tension of a liquid, especially water. They are large molecules with two distinct parts. First there is a head which is hydrophilic. This means that it is attracted to water and soluble in water, usually because it has a positive or negative charge. The other part of the surfactant is the tail which is hydrophobic, meaning it is repelled by water. The tail is also “lipophilic” which means that it is soluble in organic solvents particularly oils and fats or lipids.
Surface Tension
It is this mixed structure which gives a surfactant its properties. When added to water the surface tension of water is reduced. The surface tension of water is caused by the hydrogen bonds which form between the slight charges on different parts of the water molecule (for further information see the water article). Surfactants break up these hydrogen bonds by remaining at the surface, their heads dissolved in the water but their tails extending out of the water, repelled by it. When the surfactant concentration increases sufficiently, micelles are formed. These are spheres of surfactant with all the heads on the outside protecting all the tails within.
Dissolving Oils
Surfactants are active in detergent by allowing oil and grease to be emulsified and dissolved in water. When there is greasy dirt on the skin or on clothes, the best way to remove it is to immerse it in a solution of surfactant (soapy water or washing liquid in water). The oil does not mix with water and so would be unaffected by water on its own.
Emulsion
Surfactant molecules, however, have tails that are attracted to oil and grease. When these tails become embedded in the oil, the hydrophilic heads remain on the surface. This means that the water can dissolve the oil, forming an emulsion with oil droplets covered in the surfactant molecules, tails in the oil and heads towards the water. The dirt that is held by the grease is then released and can be washed away by the water.
Applications
There are many types of surfactant used in many different applications. They differ in the charges on their hydrophilic heads and the length and make-up of their hydrophobic tails. They are used in fabric softeners, paints, adhesives, inks, herbicides, insecticides and even snow-board wax.
