Surfactant Classes: Cationic, Anionic, and Non-ionic Quiz

Anionic surfactants possess a hydrophilic head with a negative net charge. Because most dirt and fabric surfaces also carry a slight negative charge these surfactants create electrostatic repulsion that helps lift dirt away.

Cationic surfactants have a positive charge. Since many surfaces are negatively charged these molecules tend to stick to the surface rather than lift dirt. Therefore they are better used as fabric softeners to reduce static.

Nonionic surfactants use polar groups that interact with water through hydrogen bonding rather than ionic attraction. Because they lack a charge they do not react with calcium or magnesium ions in hard water.

Because of their positive charge cationic surfactants attach to surfaces to reduce friction or disrupt the negatively charged cell membranes of bacteria.

In hard water positively charged ions like Calcium can bond with the negatively charged heads of anionic surfactants causing them to precipitate as scum. Builders neutralize these ions to protect the surfactant.

Nonionic surfactants are generally low sudsing or low foam. This makes them ideal for use in automatic dishwashers where excessive foam can interfere with the mechanical subsystem.

Depending on the pH of the solution these surfactants can act as either anionic or cationic. They are often very mild and are frequently used in no tear baby shampoos.

These groups are all negatively charged ions that define the anionic class. Ammonium groups conversely are positively charged and characterize cationic surfactants.

Even without a formal charge the hydrophilic heads of nonionic surfactants are highly polar. They contain oxygen atoms that form hydrogen bonds with water providing the necessary solubility.

Due to their high efficiency at removing oily stains and their relatively low production cost anionic surfactants form the backbone of most domestic cleaning systems.

Static occurs when surfaces rub together and exchange electrons. The positively charged heads of the cationic surfactant bond to the negatively charged fibers creating a neutral lubricated layer.

Nonionic surfactants are versatile because their lack of charge makes them chemically quiet they do not react with minerals and their solubility is less dependent on ionic strength.

Quaternary ammonium compounds feature a nitrogen atom bonded to four organic groups resulting in a permanent positive charge. This allows them to stick to surfaces.

While there is an optimal concentration increasing surfactant levels generally increases cleaning power up to a point. The primary limitation is the ability of the system to rinse the surfactants away.

Because anionic surfactants can be harsh and strip natural oils from the skin gentle cleansers use nonionic or amphoteric molecules. These interact more mildly with the skin.