The interaction between water, surfactant, and surface is called “surface activity.” In fact, the name surfactant comes from the phrase “SURFace ACTive AgeNT.”
Surfactants are molecules that reduce the surface tension of water, helping it to spread out more uniformly. Basically, surfactants make water “wetter”. They also help penetrate, loosen and trap soil so you’re really cleaning, not just moving dirt and grime from place to place.
Easing the tension – how surfactants work
If you’ve ever seen drops of water form little beads on your kitchen countertops or your shower door, you’ve seen surface tension in action. Plain water doesn’t contain any surfactants, so water molecules do what comes naturally – they stick together. Water’s surface tension causes it to cling to itself and reject other, non-water objects. Adding surfactants to water (or a water-based cleaning product) weakens that tension and allows water to relax a little and cover a larger surface.
Surfactants are molecules made up of two parts. They have heads that are hydrophilic (water-loving) and tails that are hydrophobic (water-hating).
Let’s think about that drop of water on your kitchen counter. Without a surfactant, the water molecules are clinging to each other and the water is still in a round, tight bead. If we add a surfactant to that drop of water, it would start to flatten and spread out as the water-hating tails tried to get far from the water and close to the countertop. The water’s surface tension is broken, and as the bead of water spreads out, more of the counter gets wet.
Rolling up dirt and grime: The cleaning power of surfactants
As the hydrophobic tail of a surfactant tries to cling to a surface, it forces itself underneath layers of soil and grime, loosening and lifting it from your countertop or bathroom sink. This is called roll-up, and it saves you a lot of scrubbing time.
As the cleaning solution rolls up bits of dirt and soil, the surfactant’s hydrophobic tails cling to the particles because they’re not water. The soil is held suspended in the cleaning solution by the power of the surfactant, keeping it from settling back on your countertop. Once the surface is clean, you simply wipe and dry.
The chemistry of effective cleaning
Almost all commercially produced cleaning products contain surfactants. The combination of wetting and roll-up helps to make cleaning easier and more effective. So whether you’re running the dinner plates through the dishwasher or cleaning the mirror in your bathroom, you’ll do less scrubbing with the power of surfactants.