Fumed silica (pyrogenic silicon dioxide) acts as both a carrier and a liquid control agent in antifoaming agents, with a highly synergistic mechanism of action, making it a core component of high-efficiency silicone oil-based antifoaming agents.

Carrier Mechanism
Fumed silica acts as a dispersion carrier for silicone oil.  Through its high specific surface area (typically >200 m²/g) and surface chemical properties, it forms a stable "silicone paste" complex with dimethyl silicone oil, significantly improving the wettability and dispersion efficiency of silicone oil in the liquid phase.
Hydrophobic fumed silica, after surface modification, has reduced Si–OH groups and lower interfacial tension with silicone oil, allowing the silicone oil to be more easily adsorbed and evenly coated onto the surface of the silica particles, preventing the aggregation of silicone oil droplets.
This composite structure allows the silicone oil to spread rapidly when in contact with the foam liquid film, overcoming the problem of delayed defoaming caused by the low dispersibility of traditional silicone oil, achieving a "pinpoint" defoaming effect.

Liquid Control Capabilities
Surface Tension Regulation: Fumed silica particles adsorb at the gas-liquid interface, disrupting the cohesive forces between liquid molecules, reducing local surface tension, and inhibiting bubble nucleation and stable growth.
Liquid Film Destruction Mechanism: Its nano-sized particles form physical "stress concentration points" in the foam liquid film, working synergistically with low-surface-tension silicone oil to induce local thinning and rupture of the liquid film, achieving efficient defoaming.
Thickening and Anti-Settling: Fumed silica forms a three-dimensional hydrogen bond network in the system, increasing the system viscosity and preventing the settling of silicone oil or active components, significantly enhancing the storage stability and long-term effectiveness of the antifoaming agent. Synergistic Effects Summary

Functional Dimension | Mechanism of Action | Key Physicochemical Basis
Carrier Function | Silicone oil dispersion and encapsulation | High specific surface area, hydrophobic surface modification, low interfacial tension
Liquid Control | Surface tension reduction, liquid film disruption | Nanoparticle adsorption, stress concentration, three-dimensional network structure
System Stability | Anti-settling, homogenization | Hydrogen bond network formation, viscosity regulation

Fumed silica is not an independent defoaming agent, but rather achieves performance enhancement through its composite synergy with silicone oil.  Its "carrier-impact-stabilization" three-in-one mechanism makes it an indispensable functional component in industrial-grade defoaming agents (such as those used in food, pharmaceuticals, and chemicals).