Basic Introduction of surfactant
Surfactant comes from English surfactant. It's actually a contraction of the phrase surface active agent. It also has a name called tenside. A small amount of substances which can significantly reduce the surface tension of the liquid is collectively referred to as surfactants. Their surface activity is for a particular liquid, usually water. The end of the surfactant is a non-polar hydrocarbon chain (hydrocarbon base), which has little affinity with water and is often called hydrophobic base. On the other end were polar groups (e.g., OH, COOH, NH nitrogenh, SO benzene H, etc.), which had a strong affinity with water. Therefore, they were called hydrophilic groups, and they were collectively called "amphiphilic molecules" (hydrophilic molecules). To achieve stability, surfactants can be dissolved in water in two ways:
1、A monomolecular membrane is formed at the liquid level.
Leave the hydrophilic base in the water and thrust the hydrophobic base into the air to reduce repulsion. And the repulsive force between hydrophobic base and water molecule is equivalent to make the water molecule on the surface receive an outward thrust, counteracting the originally drawn force on the water molecule on the surface, even if the surface tension of water decreases. This is the basic principle of foaming, emulsifying and wetting of surfactants. In an oil-water system, surfactant molecules are adsorbed at the oil-water interface, while polar groups are inserted into the water and non-polar groups enter the oil and are aligned at the interface. This creates tension between the oil-water phase, reducing the oil-water interfacial tension. This property has important influence on the wide application of surfactant.
2、Form "micelle".
Micelles can be spherical or stratified, with hydrophobic base hidden within the micelle and hydrophilic base exposed. Monomolecular membranes and micelles, where a spherical polar base is represented and a columnar non-polar base is represented as hydrophobic. If there is an insoluble oil in the solution (a generic term for insoluble organic liquid), it can be dissolved in the interlayer between the spherical micelle center and the laminated micelle. This is called surfactant solubilization.
Surfactant can play a variety of roles, such as washing, emulsification, foaming, wetting, soaking and dispersing, and the dosage of surfactant is low (generally several per cent to several thousandths). It is easy to operate, non-toxic and non-corrosive. Therefore, it is an ideal chemical product and has important application in production and scientific research. At the same concentration, the surfactant has high non-polar components and strong surface activity. That is, in the homolog, the surface activity of carbon atom is larger. However, if the carbon chain is too long, the solubility in water is too low and it has no practical value.
