Surfactant

Surfactant is a kind of substance that can significantly change the liquid surface tension or interfacial tension between two phases. It is a class of novel chemical product that had emerged together with plastics, synthetics rubber and synthetic fibers with the development of petrochemical industry. Its molecule contains hydrophilic polar group (such as hydroxyl, sulfate, sulfonate) and hydrophobic or lipophilic, atmophile non-polar group (such as a hydrocarbon group, being a long chain hydrocarbon) two parts. It gathers in the interface between the liquid and the other phase, forming a thin layer of molecule membrane, making the concentration of the surface layer of the solution much greater than that of the internal solution, further greatly reducing its surface tension and causing many effects such as wetting, emulsifying, dispersion and bubbling. There are many types of surfactants. They are generally divided into anionic type (e.g., alkylbenzene sulfonate), cationic type (e.g. octadecylamine hydrochloride, etc.), nonionic (e.g. glyceryl stearate, etc.), and amphoteric surfactant.

This product has a wide range of applications. In daily life, the most commonly used surfactant is detergent. The detergent take advantages of its lipophilic group to make the oil staining in the clothing gradually rolled into oil beads and leave the surface of the substance, further being dispersed, suspended in the medium and removed after rinsing.

Besides being used in family life for washing, in the field of industrial and agricultural production, it is often used as wetting agents, emulsifying agents, dispersing agents, penetrating agents, foaming agents and microbicides.

In the field of environmental protection, it can be used for sea oil pollution treatment, wastewater treatment, flotation separation, anti-dust, fire distinguishing and so on.

Photographic emulsions mostly take anionic surfactants such as nekal and diisooctyl ester sulfonate. They can make the emulsion coating be uniformly, and also has various kinds of effects such as antiseptic, anti-foaming and preventing the occurrence of defects such as comet spots and dots. It can also used to stabilizing solution for developing.

During the process of galena flotation, the surfactants (such as sodium xanthan) in the flotation agent can be adsorbed on the surface of galena, generating lead xanthan. Acid group can bound to the metal on the solid surface. The hydrocarbon tails can be outwardly arranged so the wettability of the galena is reduced wettability, attaching to the bubble and floating up to achieve the purpose of being separated from the surface to be enriched.

In agriculture, the leaf fertilizer containing surfactants can be applied to the leaves of crops with property of fast fertilizing effect, low cost and significant efficacy of increasing the yield. It has been widely used in crops such as tea, watermelon and grapes. Since there is a layer of wax contained in the crop leaf surface, it is not easy for water droplets to spread. Adding this foliar fertilizer can enable to rapid spread of the droplet on the leaf surface so that the nutrients in the water can be absorbed by crops.

Artificially synthetic surfactants can enter into coastal water areas together with sewage, and is a type of marine pollutants. The situation is particularly severe in the coastal zone of industrial countries. Such contaminants can gather on the ocean surface and can not only affect the sea - air interface process but also cause the deterioration of oxygen-containing condition of the coastal waters, thereby threatening the marine ecosystems.

There are some kinds of naturally existing organic substances in seawater that have surface activity such as fatty acids, long chain alcohols, proteinoids and some kinds of water humus. They tend to be absorbed in the sea - air and sea - particles interfaces in the seawater, further forming surface membrane on the ocean surface. This kind of membrane can have direct impact on the physical and chemical properties, interfacial properties, material exchange in sea - air interface and the formation of the marine aerosols.

In the ground water, the surfactants can be degraded by organisms. However, upon a concentration exceeding 4 mg/mL, it is toxic to the aquatic creatures and fishes. Moreover, it can even cause eutrophication of the water. Sodium alkyl benzene sulfonate (ABS) has teratogenic effects on animals. Upon a concentration of 10 mg/L in water, the fish can hardly survive; in a concentration of 45mg / L, the growth of rice will be severely affected.

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