Detailed Explanation of the Defoaming Mechanism of Organosilicon Defoamers

I. Root Causes of Stable Foam

The persistence of foam in wastewater systems is primarily caused by the presence of various surfactants in the water. These substances form a double-layered elastic liquid film around bubbles. This film possesses self-healing properties that firmly encapsulate air, making spontaneous bubble rupture difficult. As a result, foam accumulates, floats, and builds up, leading to problems such as overflow and wall adhesion. The surface tension of ordinary aqueous solutions generally ranges from 30 to 45 mN/m, resulting in a stable bubble structure that is difficult to eliminate rapidly using conventional methods.

II. Basic Components of Organosilicon Defoamers

Common industrial organosilicon defoamers are compound systems consisting of three core components, each serving a specific function:

1. Polydimethylsiloxane (silicone oil): The primary active ingredient, possessing extremely low surface tension and playing a crucial role in defoaming;

2. Hydrophobic silica: Helps penetrate the foam liquid film, enhances foam-breaking efficiency, and improves the persistence of foam suppression;

3. Emulsifier: Ensures that the hydrophobic silicone oil is uniformly dispersed throughout the aqueous phase, preventing agglomeration and phase separation and making the formulation suitable for water treatment applications.

   

III. The Complete Three-Step Defoaming Process

1. Infiltration and Spreading

Polydimethylsiloxane has a surface tension of only 18–21 mN/m, which is significantly lower than that of the foaming liquid film. In addition, it is hydrophobic and only slightly soluble in water. When a defoamer droplet comes into contact with the foam, it does not dissolve in the aqueous phase but instead rapidly spreads across and penetrates the foam surface, forcibly embedding itself into the double-layer structure of the liquid film. It gradually replaces the surfactants originally adsorbed on the film, enabling a small amount of defoamer to cover a large foam area.

2. Surface Tension Imbalance and Foam Rupture

Once the defoamer is embedded in the liquid film, the local surface tension at that point decreases significantly, while the surrounding foam film retains a higher surface tension. This imbalance generates unequal forces that continuously stretch and thin the liquid film. Meanwhile, the hydrophobic silicone segments disrupt the orderly arrangement of surfactant molecules, causing the film to lose its elasticity and self-healing capability. Consequently, the liquid film ruptures, allowing the trapped air to escape rapidly. As a result, the foam collapses and dissipates quickly over a large area, corresponding to the instantaneous disappearance of foam observed in graduated-cylinder experiments after the addition of the defoamer.

3. Long-Lasting Foam Suppression

Silicone components remain stably dispersed in the aqueous phase and continuously adsorb newly generated surfactants, preventing them from reconstructing resilient bubble films. Consequently, even under continuous stirring and aeration, the formation of new foam is greatly inhibited. This enables long-lasting foam suppression with a single application, unlike short-acting defoamers that merely eliminate existing foam.

IV. Core Advantages of Organosilicon Defoamers

1. Low dosage and rapid action, with no significant increase in water treatment chemical costs;

2. Excellent chemical inertness, providing resistance to acids, alkalis, and both high and low temperatures, making these defoamers suitable for a wide range of industrial wastewater conditions;

3. No adverse effects on microbial activity in biological treatment tanks, ensuring that the overall wastewater treatment process remains unaffected;

4. Low water solubility and minimal loss, allowing the product to combine effective defoaming with long-lasting foam suppression, thereby offering superior overall cost-effectiveness.