Any compound that reduces the surface tension of water when dissolved in water or water solution is called surfactants. It affects interfacial tension between two liquids and increases the wetting and cleaning ability of water.
Types of Surfactants.
“Surfactants” are of the following two types:
Washing action of Surfactants. The cleaning action of both soap and detergent is due to lowering of the surface tension. The Cleaning process consists of :
- Thoroughly wetting the dirt and the surface of the article being washed.
- Removing the dirt/grease from the surface, and
- Maintaining the dirt/grease in a stable solution or suspension (detergent).
Since soap and detergents increase the wetting ability of water, it can more easily penetrate the fabrics and get to the dirt/grease spots. Each molecule of surfactant may be considered as a long chain. One end of the chain is hydrophilic (water-loving), and the other is hydrophobic (water-hating or dirt-loving). The dirt-loving ends are attracted to the solid/dirt particle and surround it. At the same time, the water loving-ends pull the molecules and the dirt particles away from the fabrics and take into the water.
This action enables a soap or detergent to remove dirt/grease particles from fabrics.
Soaps are molecules containing a very long alkyl group that is soluble in oil and an ionic end (the salt of a carboxylic acid) that is soluble in water
In function, the hydrophobic portion dissolves in oils and the hydrophilic end (ionic end) dissolves in water. Droplets of oil are thus emulsified and removed. In addition, soaps lower the surface tension of water and thus making it a better wetting agent.
Synthetic detergent is structurally similar to soaps, differing in primarily in the water-soluble portion. They have the advantage of being able to function in hard water. Some example is giving below:
Anion-active Detergents or Anioinic Detergents.
Cationic-active or Cationic Detergent.
A quaternary ammonium salt
Detergents function like soap since one end of molecules is oil-soluble and the other end is water-soluble.