Emulsifiers or surfactants

are molecules that have special properties. They contain two parts. One that can dissolve in water and one that can dissolve in oil.

Emulsifiers reduce the tendency of oil and water to separate into layers by forming an emulsion. An emulsion is formed when tiny droplets of one liquid are suspended in another liquid.

Two types of emulsions can be formed oil-in-water and water-in-oil. Oil-in water emulsions feel cool on the skin while water-in-oil feel greasy.

These molecules change the surface properties of liquids. The hydrophobic (water hating) or lipophilic tail (oil loving) of these molecules burrows into the oil leaving exposed the hydrophilic (water loving)or lipophobic (oil hating) head. When the oil and water mixture is agitated micelles form.

 

 
Mayonnaise is an example of an oil-in-water emulsion. Tiny droplets of oil are suspended in the water by the action of emulsifiers, as shown on the right.

 
Micelles float freely in the water as they carry the trapped oil with them.

 

Substance X is most likely to be

Substance Y is most likely to be

This is a in emulsion.

Egg contains lecithin. Lecithin is an additive in foods that acts as an emulsifier. What should a lecithin molecule have in order to behave as an emulsifier?
Lecithin is used in chocolate, ice-cream and margarine to name a few. What is it about these foods that makes lecithin useful?
Mayonnaise is formed by shaking oil, water and egg together. What would happen if egg was omitted from the mixture? Explain why.