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What are Surfactants and How They Work

Dec. 21, 2020


Surfactants are the most commonly used products in the chemical industry. Amphiphilic molecules are widely used in various industries, from household detergents to drilling mud, from food to pharmaceuticals.


The term surfactant comes from the term surfactant. They are amphiphilic molecules and therefore are absorbed at the air-water interface. They are aligned at the interface, so the hydrophobic part is in the air and the hydrophilic part is in the water. This leads to reduced surface or interfacial tension.


Nonionic Surfactant

Nonionic Surfactant

Surfactant foundation


As mentioned above, surfactants are amphiphilic molecules with hydrophobic and hydrophilic parts. The hydrophobic tail is a hydrocarbon, fluorocarbon or siloxane. Surfactants are usually classified according to their polar heads because the hydrophobic tails are usually similar. If the head group is not charged, the surfactant is called a Nonionic Surfactant. If the group at the head is negatively or positively charged, it is called an anionic surfactant or cationic surfactant, respectively. If it contains a positive and negative group at the same time, the surfactant is called a zwitterion.


To date, anionic and nonionic surfactants are the most commonly used types of surfactants in the industry. Anionic surfactants are particularly suitable for cleaning products such as washing powders and shampoos. On the other hand, nonionic surfactants are commonly used as wetting agents and in the food industry. Both cationic surfactants and amphoteric surfactants are more specialized because they are more expensive to produce.


Surfactant is absorbed at the interface


Due to its amphiphilic nature, surfactants are absorbed at the air-water or oil-water interface. At the interface, the surfactant arranges itself so that the hydrophobic part is in air (or oil) and the hydrophilic part is in water.


For simplicity, we will only consider the air-water interface. The cohesion between water molecules is very strong, which makes the surface tension of water very high. As surfactants are absorbed, they disrupt these interactions. The intermolecular force between the surfactant and the water molecule is much lower than the intermolecular force between two water molecules, so the surface tension will decrease. When the surfactant concentration is high, they form micelles. The point at which micelles form is called the critical micelle concentration.


The main purpose of surfactants is to reduce surface and interfacial tension and stabilize the interface. Without surfactants, washing clothes will be difficult, and many foods such as mayonnaise and ice cream will disappear. Therefore, it is important to optimize surfactants for different applications, and the measurement of surface and interfacial tension plays a key role in this process.


If you want to know more about the use of surfactants in industry, please click on the content below to read more.


1. The development history of anionic surfactants


2. What are the three application areas of surfactants?


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