- Laundry detergent reduces the surface tension of water, allowing the water to penetrate and completely wet the fabrics that need to be cleaned. The laundry detergent lowers the interfacial tension between the fabric and the laundry detergent and water solution. At the same time, it also lowers the interfacial tension between the oil and the laundry detergent and water solution, allowing stains on the fabric to be lifted. The surfactant molecules in the laundry detergent are strongly attracted to the water and lift the soil from the fabric that normally would not dissolve in water alone. Because surfactants found in laundry detergent do not have an electrical charge, they are resistant to being deactivated by the hardness of the water.
- As the water and laundry detergent interact with the clothing in the washing machine, they cause the stains to spontaneously dissolve and enter into the laundry detergent and water solution. Once the dirt is dispersed into the solution, the anionic surfactants found in the laundry detergent actually adhere to the surface of the dirt as well as the surface of the fabric being laundered. The result is a negative charge on the surface of the dirt and the fabric, which causes electrostatic repulsion. It is the electrostatic repulsion that actually prevents the dirt and grime from landing back onto the fabric and staying immersed in the water.
- Detergent additives such as enzymes are included in some laundry detergents to help remove stains that are protein based. Bleach additives add to the cleaning power of some detergents as do blue dyes that help prevent whites from turning yellow. The surfactants in the detergents bind the soil and pull it away from the clothes into the soapy water as it swirls around the clothes by the washing machines mechanical action. The rinse cycle then eliminates most of the detergent and soil. Using hot water can help the laundry detergent by melting fats and oils, making it easier for laundry detergent to dissolve them and pull them away into the rinse water.
