WHAT ARE SURFACTANTS AND HOW DO THEY WORK?
Surfactants are some of the most versatile products in the chemical industry. They are used in every industry, from household detergents to drilling mud, from food to pharmaceuticals.
Basics of surfactants
Surfactants are amphiphilic molecules with hydrophobic and hydrophilic parts. The hydrophobic tails are hydrocarbons, fluorocarbons or siloxanes. Surfactants are usually classified according to their polar heads, since the hydrophobic tails are usually similar. If the head group has no charge, the surfactant is referred to as a Nonionic Surfactant. If the head group has a negative or positive charge, it is referred to as anionic or cationic, respectively. If it contains both positive and negative charges, the surfactant is called amphoteric.
By far, nonionic and Anionic Surfactants are the most used surfactant types in industry. Anionic surfactants are particularly suitable for cleaning products such as laundry detergents and shampoos. On the other hand, nonionic surfactants are often used as wetting agents and in the food industry. Cationic and amphoteric surfactants are more often used for special applications because they are more expensive to produce.
Surfactant absorption at the interface
Due to their amphiphilic nature, surfactants are absorbed at the air-water or oil-water interface. At the interface, the surfactants are arranged neatly so that the hydrophobic part is in air and the hydrophilic part is in water.
For the sake of simplicity, we will consider only the air-water interface. The cohesion between water molecules is very strong, making the surface tension of water very high. With the absorption of surfactants, they break these interactions. The intermolecular forces between the surfactant and water molecules are much lower than the forces between two water molecules, so the surface tension decreases. When surfactant concentrations are high, they form micelles. The point at which micelles are formed is called the critical micelle concentration.
The main purpose of surfactants is to reduce surface and interfacial tension and stabilize the interface. Without surfactants, laundry would be difficult and many foods such as mayonnaise and ice cream would not exist. Therefore, it is very important to optimize surfactants for different applications, where the measurement of surface and interfacial tension plays a key role.
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