A surfactant or surface active agent is a substance that, when dissolved in water, gives a product the ability to remove dirt from surfaces such as the human skin, textiles, and other solids.

In more technical terms: * they enable the cleaning solution to fully wet the surface being cleaned so that dirt can be readily loosened and removed. * they clean greasy, oily, particulate-, protein-, and carbohydrate-based stains. * they are instrumental in removing dirt and in keeping them emulsified, suspended, and dispersed so they don't settle back onto the surface being cleaned.

Each surfactant molecule has a hydrophilic (water-loving) head that is attracted to water molecules AND a hydrophobic (water-hating) tail that repels water and simultaneously attaches itself to oil and grease in dirt. These opposing forces loosen the dirt and suspend it in the water. The mechanical agitation of the washing machine helps pull the dirt free.

Surfactants are one of the major components of cleaning products and can be regarded as the 'workhorses': they do the basic work of breaking up stains and keeping the dirt in the water solution to prevent re-deposition of the dirt onto the surface from which it has just been removed. Surfactants disperse dirt that normally does not dissolve in water.

As anyone who uses oil based dressings in the kitchen knows, oil and water do not mix unless shaken vigorously in the bottle. They separate almost immediately afterwards. The same is true when washing your dishes or clothes. With the addition of surfactants, oil, which normally does not dissolve in water, becomes dispersible and can be removed with the wash water.

What does a surfactant actually do?

Surfactants are also referred to as wetting agents and foamers. Surfactants lower the surface tension of the medium in which it is dissolved. By lowering this interfacial tension between two media or interfaces (e.g. air/water, water/stain, stain/fabric) the surfactant plays a key role in the removal and suspension of dirt. The lower surface tension of the water makes it easier to lift dirt and grease off of dirty dishes, clothes and other surfaces, and help to keep them suspended in the dirty water. The water-loving or hydrophilic head remains in the water and it pulls the stains towards the water, away from the fabric. The surfactant molecules surround the stain particles, break them up and force them away from the surface of the fabric. They then suspend the stain particles in the wash water to remove them.

More in-depth understanding of Surface tension:

What does a surfactant "look like"?

A tadpole! A surfactant consists of a hydrophobic (non-polar) hydrocarbon "tail" and a hydrophilic (polar) "head" group.

This appearance is key to its behaviour. The dirt-loving or hydrophobic tail absorbs to the oil and grease in dirt and stains.

Are surfactants of natural or synthetic origin ?

They can be either. Surfactants from natural origin (vegetable or animal) are known as oleo-chemicals and are derived from sources such as palm oil or tallow. Surfactants from synthetic origin are known as petro-chemicals and are derived from petroleum.

Having the flexibility to use both oleochemical and petrochemical surfactants allows our formulators to create products that maximize the value in the bottle of detergent, so to speak, by optimizing cleaning ability under a variety of laundry conditions while keeping the price low in the current market. These days, our formulation scientists focus quite a lot on developing detergents that perform well at lower wash temperatures. This approach will continue to yield energy savings during the consumer use phase, hence a reduction of CO2 emissions.

Surfactants also have an important role in our body, where they are used to reduce surface tension in the lungs. The human body does not start to produce lung surfactants until late in foetal development. Therefore, premature babies are often unable to breathe properly, a condition called Respiratory Distress Syndrome. Untreated, this is a serious illness and is often fatal, but administration of artificial surfactants virtually eliminates this health problem.

Want to read more on oleo - versus petro-chemicals?

Are there different types of surfactants?

There is a broad range of different surfactant types, each with unique properties and characteristics: the type of dirt and fabric on which they work best, how they can cope with water hardness. Detergents use a combination of various surfactants to provide the best possible cleaning results. There are four main types of surfactants used in laundry and cleaning products. Depending on the type of the charge of the head, a surfactant belongs to the anionic, cationic, non-ionic or amphoteric/zwitterionic family.

Anionic surfactants

In solution, the head is negatively charged. This is the most widely used type of surfactant for laundering, dishwashing liquids and shampoos because of its excellent cleaning properties and high . The surfactant is particularly good at keeping the dirt away from fabrics, and removing residues of fabric softener from fabrics.

Anionic surfactants are particularly effective at oily soil cleaning and oil/clay soil suspension. Still, they can react in the wash water with the positively charged water hardness ions (calcium and magnesium) , which can lead to partial deactivation. The more calcium and magnesium molecules in the water, the more the anionic surfactant system suffers from deactivation. To prevent this, the anionic surfactants need help from other ingredients such as builders (Ca/Mg sequestrants) and more detergent should be dosed in hard water.

The most commonly used anionic surfactants are alkyl sulphates, alkyl ethoxylate sulphates and soaps.

Cationic surfactants

In solution, the head is positively charged. There are 3 different categories of cationics each with their specific application: * In fabric softeners and in detergents with built-in fabric softener, cationic surfactants provide softness. Their main use in laundry products is in rinse added fabric softeners, such as esterquats, one of the most widely used cationic surfactants in rinse added fabric softeners.

An example of cationic surfactants is the esterquat.

* In laundry detergents, cationic surfactants (positive charge) improve the packing of anionic surfactant molecules (negative charge) at the stain/water interface. This helps to reduce the dirtl/water interfacial tension in a very efficient way, leading to a more robust dirt removal system. They are especially efficient at removing greasy stains.

An example of a cationic surfactant used in this category is the mono alkyl quaternary system.

* In household and bathroom cleaners, cationic surfactants contribute to the disinfecting/sanitizing properties.

Non-ionic surfactants

These surfactants do not have an electrical charge, which makes them resistant to water hardness deactivation. They are excellent grease removers that are used in laundry products, household cleaners and hand dishwashing liquids.

Most laundry detergents contain both non-ionic and anionic surfactants as they complement each other's cleaning action. Non-ionic surfactants contribute to making the surfactant system less hardness sensitive.

The most commonly used non-ionic surfactants are ethers of fatty alcohols

Amphoteric/zwitterionic surfactants

These surfactants are very mild, making them particularly suited for use in personal care and household cleaning products. They can be anionic (negatively charged), cationic (positively charged) or non-ionic (no charge) in solution, depending on the acidity or pH of the water.

They are compatible with all other classes of surfactants and are soluble and effective in the presence of high concentrations of electrolytes, acids and alkalis.

These surfactants may contain two charged groups of different sign. Whereas the positive charge is almost always ammonium, the source of the negative charge may vary (carboxylate, sulphate, sulphonate). These surfactants have excellent dermatological properties. They are frequently used in shampoos and other cosmetic products, and also in hand dishwashing liquids because of their high foaming properties.

An example of an amphoteric/zwitterionic surfactant is alkyl betaine.

How do surfactants work in detail?

Surfactants can work in three different ways: roll-up, emulsification, and solubilization.

Roll-up mechanism

The surfactant lowers the oil/solution and fabric/solution interfacial tensions and in this way lifts the stain of the fabric.

Emulsification

The surfactant lowers the oil-solution interfacial tension and makes easy emulsification of the oily soils possible.

Solubilization

Through interaction with the micelles of a surfactant in a solvent (water), a substance spontaneously dissolves to form a stable and clear solution.

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