Cationic surfactant

What is a cationic surfactant?

A cationic surfactant is a surfactant whose head group is positively charged in water, usually a nitrogen-containing group. The most common are quaternary ammonium compounds, often called quats. Fatty amines are cationic when the pH is low enough for them to carry a charge.

Properties and uses

Most surfaces, including fabrics, hair, skin, many minerals and sandstone rock, carry a negative charge in water. Cationic surfactants are strongly attracted to them and adsorb onto them, often leaving the surface coated with oily tails pointing outward. That behavior drives their uses:

• Fabric softeners and hair conditioners, where the adsorbed layer makes fibers feel softer and reduces static.
• Disinfectants and sanitizers, because many quats disrupt microbial cell membranes.
• Corrosion inhibitors, which form protective films on metal.
• Mineral flotation, where amine collectors float quartz and other silicates, as in reverse flotation of iron ore.

Cationic surfactants are generally poor detergents on their own and are more toxic to aquatic life than many other classes, so their use is targeted.

Compatibility

Cationic surfactants generally cannot be mixed with anionic surfactants, because the opposite charges attract and can form an insoluble complex. They are usually compatible with nonionic surfactants.

Frequently asked questions