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What are the causes and mechanisms of deactivation in silicone-based defoamers?
Release Date:
2023-09-15
Deactivation of silicone‑based defoamers is a very common phenomenon, not limited to silicone gel‑type defoamers. Other types of silicone defoamers also frequently experience deactivation; however, I will use silicone gel‑based defoamers as an example to discuss the causes and mechanisms of their deactivation, in the hope that this will be helpful. There are many reasons why silicone‑based defoamers become deactivated.
Deactivation of silicone‑based defoamers is a very common phenomenon, not limited to silica‑gel‑based silicone defoamers. Other types of silicone defoamers also frequently experience deactivation; however, I will use silica‑gel‑based silicone defoamers as an example to discuss the causes and mechanisms of their deactivation, in the hope that this will be helpful. There are many reasons why silicone‑based defoamers become deactivated.
For example, the type of silicone oil and its concentration can influence the performance of silicone‑based defoamers. In such systems, when hydrophobic solid particles—serving as active ingredients—are in prolonged contact with a surfactant solution, they gradually separate from the silicone‑defoamer dispersion and dissolve into the liquid phase. These non‑silicone‑containing particles, due to excessive insertion resistance, do not penetrate the foam film; however, some silicone‑oil molecules that do enter the foam film will adsorb onto the particle surfaces and subsequently migrate into the bulk solution. As a result, the hydrophobic character of the silicone‑defoamer dispersion on the foam film diminishes, its hydrophilicity increases, and its defoaming efficacy is lost.
Understanding the deactivation process of silicone‑based antifoaming agents is straightforward. Deactivation occurs when a layer of silicone oil spreads across the foam film, forming oil bridges that lead to emulsification. Initially, as the silicone oil layer first penetrates the foam film surface, its spreading rate increases; however, over time and with continued defoaming, the silicone oil continues to emulsify, causing the spreading rate to decline and thereby reducing the formation of additional silicone oil. Silicone‑based antifoaming agents do not become deactivated until they have diffused into the oil film.
In general, the underlying principle of silicone‑based defoamers is to form a silicone‑oil layer on the foam film; however, during the defoaming process, this silicone‑oil layer gradually emulsifies into the liquid phase, diminishing its defoaming performance until it becomes ineffective. The above represents my perspective on the deactivation of silicone‑based defoamers.
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