Development and present situation of organosilicon defoamers
Quincke, a German experimental physicist, first proposed chemical methods for defoaming, such as eliminating soap bubbles with ether vapor. J. Plateau, a colloidal chemist in the 19th century, had delighted in encouraging the study of foamability of liquids, proposing that foamability with low surface tension and high viscosity was strong. Sasaki Kota, a Japanese colloid chemist, began to study the bubble before the two World War. After the war, he published many articles and became an expert on defoaming. During World War II, S. Ross, an American colloidal chemist, studied the defoaming of lubricants. After World War II, he published many studies on defoaming, which made outstanding contributions to the mechanism of defoaming agents.
In 1952, C.C. Currie of Dow Corning Company of the United States made a large-scale collation of the defoamer literature at that time, and made a comprehensive and systematic study of defoaming technology in papermaking, fermentation, boilers, etc. In 1954, Wangnd-ott Company first put into production polyether defoamer in the United States, which has developed rapidly. However, extensive application and research began with the development of polyether industry in recent years.
In the 1950s, China began to explore the defoaming problem in the fermentation and paper industry. In the early 1960s, China began to systematically study the defoaming problem of lubricating oil and transmission oil, which is helpful to the development of aircraft, diesel locomotives, warships and cars. Later, papermaking, printing and dyeing, fermentation, natural gas desulfurization, concrete and other aspects were studied.






In the late 1960s, China began to study polyether defoamers. Since the 1970s, polyether defoamers have been produced. They were first used in antibiotic fermentation and gradually extended to other fields. The varieties of glycerol polyether GP developed from single glycerol polyether GP at that time to GPE, PPE, BAPE and so on. In the 1980s, a variety of defoamers emerged, defoaming technology has also been widely used in all walks of life in China. Foam is a dispersed system with a large number of bubbles dispersed in the liquid. Its dispersed phase is gas and continuous phase is liquid. When surfactant is added to the system, a layer of surfactant molecules are adsorbed on the surface of the bubbles. When the concentration of surfactant reaches a certain level, a solid film is formed on the wall of the bubbles. Surfactants are adsorbed on the gas-liquid interface, resulting in a decrease in surface tension, thus increasing the gas-liquid interface, so that bubbles are not easy to merge. The relative density of bubbles is much smaller than that of water. When rising bubbles pass through the liquid surface, a layer of surfactant molecules on the liquid surface are adsorbed.






Therefore, the bubble membrane adsorbed surfactant in the air is different from that in the solution. It contains two layers of surfactant molecules, forming a bilayer membrane. The adsorbed surfactant has a protective effect on the liquid membrane. Defoamer is to destroy and inhibit the formation of the film. The defoamer enters the bimolecular oriented film of foam and destroys the mechanical balance of the oriented film to achieve bubble breaking. Defoamer must be a liquid that is easy to spread on the surface of the solution. When the liquid is spread on the surface of the solution, it will take away a layer of solution near the surface and make the liquid film partial thinner, so the liquid film ruptures and the foam is destroyed. In general, the faster the defoaming agent spreads on the surface of the solution, the thinner the liquid film becomes, the faster the critical thickness is attained, the faster the foam damage is, the stronger the defoaming effect is. Generally refers to the surface spreading, defoaming liquid, its surface tension is reduced (that is, the surface pressure is increased), the phenomenon of imbalance occurs. So spreading occurs locally, and at the same time, it will take away a layer of adjacent liquid on the surface, resulting in thinning of the liquid film, thus destroying the bubble film. Therefore, the reason for defoaming is on the one hand that it is easy to spread. The adsorbent defoamer molecules replace the foaming agent molecules, forming a film with poor strength. At the same time, during the spreading process, some of the solution near the surface layer is taken away, so that the thin film of the foam liquid becomes thinner, which reduces the stability of the foam and makes it easy to destroy. An excellent defoamer must take into account both the elimination and the foam suppression. That is, not only should the foam be destroyed quickly, but also the foam can be prevented for a long time. It is often found that some defoamers lose their effectiveness after a certain time in the solution. To prevent froth formation, some defoamer should be added. The reason for this may be whether the critical micelle concentration of foaming agent (surfactant) in solution exceeds cmc. In solutions over cmc, defoamers (usually organic liquids) may be solubilized, resulting in loss of surface spreading effect and greatly reduced defoaming effectiveness. When the defoamer is added, its spreading speed on the surface is faster than the solubilizing speed, showing a better defoaming effect; after a period of time, with the defoamer being gradually solubilized, the defoaming effect is correspondingly weakened.