Removing Oily Soils
Oily soils are removed in different ways. Some oily soils are light enough to be emulsified in water-based detergents. Other oily soils may be too heavy for detergents to be effective in removing them. These heavier soils can be dissolved with oil-based solvents.
Emulsifying Oily Soils with Detergents
Can we put something into water to help us clean oily soils? Yes - detergents! Water-based detergents are able to dissolve in water, but they are also able to attach to oily soils. Detergents pull the oily soils away from the surface, so we can extract the soils with the detergent.
Detergent molecules are made so that they have a water-loving head and an oil-loving tail.
The makeup of the tail of a detergent molecule is similar to the makeup of oil, gasoline, grease, and animal fats. The detergent's tail will dissolve substances similar to grease and oil. The head of the detergent molecule breaks oily soils apart and the head pulls them into the water, creating an emulsion. An emulsion means that the detergent acts as a connecting link between oil and water molecules, allowing them to be mixed evenly through the cleaning solution. The cleaning solution can then be rinsed out along with the emulsified soils.
Detergents have some drawbacks. If they are not rinsed thoroughly, they leave a sticky residue. Also, when detergents combine with hard water (water that contains minerals, such as calcium or magnesium), they make a salt. These salts will not dissolve in water, so they slow down the cleaning action of the detergent and form a scum.