Foam is often accompanied by people's lives and production, sometimes using foam and foam, like flotation, fire fighting, dusting, washing, making foam ceramics and plastics; but in some cases it is necessary to eliminate foam and foam, such as fermentation, paint, Papermaking, printing and dyeing, removal of body flatulence, boiler water, wastewater treatment and the manufacture of prisms (or glass). When drinking beer in general, the beer is turned into a gaseous state due to the vibration of the carbon dioxide in the beer, which causes a large amount of foam in the beer. This is a dehydration by adding a drop of oil to the beer bottle. This is actually the principle of using the defoaming agent.
In general, pure water and pure surfactants do not blister because their surfaces and interior are uniform, and it is difficult to form an elastic film, which is unstable even if it is formed, and disappears instantaneously. However, when there is a surfactant in the solution, after the bubble is formed, the hydrophilic group and the hydrophobic group in the molecule are adsorbed by the bubble wall due to the intermolecular force, forming a regular arrangement, and the hydrophilic group faces the water phase, and is hydrophobic. The base faces the inside of the bubble, thereby forming an elastic film at the bubble interface, and the stability is strong, and it is not easily broken under normal conditions. The stability of the foam is related to surface tack and elasticity, electrical repellency, movement of the surface film, temperature, evaporation and the like.
Furthermore, the bubble is inversely related to the surface tension of the liquid, and the smaller the tension, the easier it is to foam. In the life and production, many times the appearance of the bubble brings a lot of inconvenience to people, so it must be defoamed. Any factor that can destroy the stability of the foam can be used for defoaming. Defoaming covers the two factors of "bubbling" and "breaking". Silicone defoamers have the function of reducing the surface tension of water, solutions, suspensions, etc., preventing the formation of foam, or reducing the original foam, usually with selective action.
The general physical defoaming method is difficult to defoam instantaneously, while the chemical and interface defoaming is very fast, convenient and efficient. In summary, an antifoaming agent refers to an agent having chemical and interfacial chemical defoaming action. Examples of the antifoaming agent include low alcohols, mineral oils, organic polar compounds, and silicone resins. The form is oil type, solution type, emulsion type, foam type. As antifoaming agent, it has strong defoaming ability, stable chemical property, physiological inertness, heat resistance, oxygen resistance, corrosion resistance, dissolved gas, gas permeability, easy diffusion, easy to penetrate, insoluble in defoaming system and irrational influence. The foaming agent is used in a small amount and high efficiency.
Defoamers are available in a wide variety of applications. The antifoaming agent "bubble" and "breaking foam" process is: when the system is added with antifoaming agent, its molecules are disorderly spread on the surface of the liquid, inhibiting the formation of elastic film, that is, terminating the generation of foam. When the system produces a large amount of foam, the defoaming agent is added, and the molecules are immediately dispersed on the surface of the foam, rapidly spreading, forming a very thin double film layer, further diffusing, infiltrating, and layering intrusion, thereby replacing the thin wall of the original bubble film. Because of its low surface tension, it flows to the liquid with high surface tension of foam, so that the low surface tension defoamer molecules diffuse and penetrate between the gas-liquid interface, and the membrane wall is rapidly thinned, and the foam is simultaneously affected by the surrounding surface. The film with a large tension is strongly drawn, so that the stress around the foam is unbalanced, causing it to "break". The defoamer molecules that are insoluble in the system re-enter the surface of the other foam film, and so on, all the foams are completely destroyed.
Shaoxing Shangyu Simo Research institute of organic Chemistry
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