Surfactants are used in a range of household cleaners and body care products. They help remove dirt and stains from things like your laundry, your skin and most hard household surfaces by breaking up the stains and keeping them dispersed. Without them, dirt and stains would not dissolve in water and could not effectively be removed.
In order for stains to be removed, the individual particles that they are made of must be dispersed in a solvent such as water and washed away. The problem is, many of the substances that cause stains - like oils - don't readily mix with water. This is due to the surface tension (called interfacial tension) between the two different types of substances. Surfactants help to reduce this interfacial tension, allowing the different substances to be mixed together. The name “surfactant” comes from this property, as it is derived from the words “surface active agent”.
Each surfactant molecule is composed of a hydrophilic head that is attracted to water molecules, and a hydrophobic tail that repels water while being attracted to any oil or grease present in stains. They can then pull the stains away and suspend them in a solution to prevent them from being re-deposited.
The 4 main types of surfactants are categorised according to the + or - charge of the molecule's head.
1. Anionic surfactants: The head of the molecule is negatively charged. This is the most widely used type of surfactant for laundry, dishwashing and shampoo because of their excellent cleaning properties and high sudsing potential. They may require help from builders to work properly, especially if used in hard water.
2. Cationic surfactants: The head of the surfactant molecule is positively charged. Most commonly used as a conditioning agent in fabric softener, hair conditioner and aiding the performance of anionic surfactants in laundry detergents.
3. Non-ionic surfactants: The head of the surfactant molecule has no charge. This makes them more resistant to water hardness than anionic and cationic surfactants and means they are used in a variety of detergents because they are great at removing stains.
4. Amphoteric/zwitterionic surfactants: The names 'amphoteric' and 'zwitterionic' are interchangeable and means that the head can be cationic (positively charged), anionic (negatively charged) or non-ionic (not charged), depending on the pH of the solution. These are a better option for personal care products because of their mildness and dermatological profile.