Surfactants have two domains within the one molecule: a polar, or hydrophilic (“water-loving”) head group, and a non-polar, “fatty” or hydrophobic (“water-hating”) tail. The basic principle at work is that polar substances interact well with other polar substances, and non-polar substances interact well with other non-polar substances. |
When a detergent is added, surfactant molecules accumulate near the surface of the water because the non-polar (hydrophobic) tail of the surfactant wants to get away from the water. Since the surfactant disrupts the bonding of water molecules, the water distorts and more surfactant molecules fit near the surface. Because the water now has reduced surface tension it can permeate previously non-wettable surfaces, such as fabrics .
Oil and water do not usually mix. Oil is a non-polar substance and water is a polar substance. However, in the presence of a high enough concentration of surfactant molecules, oil can effectively be emulsified (suspended evenly) in water.
So, the polar (hydrophilic) part of the surfactant molecule is attracted to water, and the non-polar (hydrophobic) part is attracted to the oil. Surfactant molecules accumulate around the oil, and once there are enough molecules a spherical micelle forms. The portion of oil in the micelle is effectively suspended in water. The laundry process can repeat as long as there are available surfactant molecules to interact with the oil deposit.
Surfactants are either derived from petrochemicals, vegetable oils or animal fats, or combinations of these sources. There are three main types of surfactants used in laundry detergents : anionic, non- ionic and cationic.
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