In systems prone to stable foam formation, such as fermentation, wastewater treatment, or chemical reactions, silicone oil is often a core component of high-efficiency defoamers. Its action is not chemical neutralization, but rather physical intervention in the mechanical balance of the gas-liquid interface, triggering spontaneous foam rupture. This process is driven by low surface tension and involves three continuous stages: spreading, penetration, and film drainage.

The stability of foam stems from the elastic film formed by surfactants at the gas-liquid interface, which resists local thinning through the Marangoni effect. After silicone oil defoamer (typically emulsified micro-droplets) enters the system, because its surface tension (approx. 20–21 mN/m) is significantly lower than that of the foaming liquid (e.g., water at 72 mN/m), it possesses a positive spreading coefficient. This enables it to rapidly spread into a lens-shaped oil film on the foam surface.

The introduction of this oil film disrupts the uniformity of the original interface. Since silicone oil is insoluble in the aqueous phase, the surface tension in the covered area drops sharply, while surrounding areas maintain high tension. This gradient triggers a strong Marangoni flow—liquid flows from the low-tension zone (under the oil film) to the high-tension zone (clean liquid film), causing the liquid film beneath the oil film to thin急剧 (sharply). Simultaneously, silicone oil micro-droplets can penetrate between the bilayer liquid films, further weakening the film's mechanical strength.

When the liquid film thickness drops to a critical value (typically tens of nanometers), van der Waals attractive forces become dominant, the film structure becomes unstable, and it ruptures instantly. The entire process requires no chemical reaction, relying solely on fluid dynamics driven by interfacial tension differences. Furthermore, the chemical inertness and thermal stability of silicone oil ensure its sustained effectiveness in wide pH, high-temperature, or saline environments.


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