Explore the principle of defoaming agent
Bubbles and foams often accompany people’s lives and production. Sometimes they need to be used, such as flotation, fire extinguishing, dust removal, washing, making foam ceramics and plastics, etc.; sometimes they need to be eliminated, such as fermentation, coating, papermaking, printing and dyeing, eliminating flatulence in body organs, boiler water, wastewater treatment and prism (or glass) manufacturing, etc. The so-called “bubbles” or “bubbles” refer to insoluble gases existing in liquids or solids, or existing in independent bubbles surrounded by their thin films. The accumulation state of many bubbles gathered together and separated from each other by thin films is called foam. Bubbles are a dispersed system with gas/liquid, gas/solid, and gas/liquid/solid interfaces. The latter is commonly seen in bubbles in mineral processing and oil field systems.
Generally speaking, pure water and pure surfactants do not foam because their surfaces and interiors are uniform, and it is difficult to form an elastic film. Even if it is formed, it is unstable and will disappear instantly. However, there are surfactants in the solution. After the bubbles are formed, due to the intermolecular force, the hydrophilic and hydrophobic groups in the molecules are adsorbed by the bubble wall to form a regular arrangement, with the hydrophilic groups facing the water phase and the hydrophobic groups facing the inside of the bubble, thus forming an elastic film on the bubble interface, which is very stable and not easy to break under normal conditions. The stability of foam is related to factors such as surface viscosity and elasticity, electrical repulsion, movement of the surface film, temperature, and evaporation. Furthermore, the surface tension of bubbles and liquids is inversely related. The smaller the tension, the easier it is to foam. In life and production, the appearance of foam sometimes brings many inconveniences to people, so defoaming is necessary.
Any factor that can destroy the stability of foam can be used for defoaming. Defoaming covers two factors: “foam suppression” and “foam breaking”. Silicone defoaming agent has this function. It can reduce the surface tension of water, solution, suspension, etc., prevent the formation of foam, or reduce the original foam, and usually has a selective effect. Generally, physical defoaming methods are difficult to defoam instantly, while chemical and interfacial defoaming methods are very quick, convenient and efficient.
In general, defoaming agents refer to agents with chemical and interfacial chemical defoaming effects. As defoaming agents, there are low-carbon alcohols, mineral oils, organic polar compounds and silicone resins. Its forms include oil type, solution type, emulsion type and foam type. As defoaming agents, they all have the characteristics of strong defoaming power, chemical stability, physiological inertness, heat resistance, oxygen resistance, corrosion resistance, gas dissolution, breathability, easy diffusion, easy penetration, difficult to dissolve in the defoaming system and no physical and chemical effects, small amount of defoaming agent, and high efficiency.
Defoaming agents are of various types and widely used. The process of “foam suppression” and “foam breaking” of defoaming agents is: when the defoaming agent is added to the system, its molecules are randomly distributed on the surface of the liquid, inhibiting the formation of an elastic film, that is, terminating the generation of foam. When a large amount of foam is generated in the system, defoamer is added, and its molecules are immediately spread on the foam surface, spreading rapidly to form a very thin double film layer, which further diffuses, penetrates, and invades in layers, thus replacing the original thin wall of the foam film. Due to its low surface tension, it flows to the liquid with high surface tension that generates the foam. In this way, the defoamer molecules with low surface tension continue to diffuse and penetrate between the gas-liquid interface, making its film wall thinner rapidly. At the same time, the foam is strongly pulled by the surrounding film layer with high surface tension, thus causing the stress around the foam to be unbalanced, resulting in its “bubble breaking”. The defoamer molecules that are insoluble in the system re-enter the surface of another foam film, and this is repeated until all the foams are completely destroyed.
