With the constant understanding of the stabilizing factor, people's understanding of the defoaming mechanism is also deepening. The foaming factor is varied and the defoaming mechanism is varied.
  
1) The local surface tension of the foam can be lowered to cause the bubbles to burst.

Some people studied the defoaming process of polysiloxane in the oil system. They took photos of the foam system at a speed of 1/1000 sec. The photo was magnified 100 times. The schematic diagram of four photos taken continuously showed that the silicone oil defoamer was small. The droplets reach the bubble film, and the surface of the bubble film is broken and merged into a large bubble. From 1 to 3, the foam is merged into 4 large bubbles, and the bubble film becomes thin. Finally, the gas and liquid are quickly separated, and the large bubbles are eliminated. This also explains objectively why a drop of defoamer goes down and a series of bubbles burst.
When the antifoaming agent adheres to the bubble film, it is immersed in the bubble liquid, which significantly reduces the surface tension at that place. Since the active ingredient of the antifoaming agent has a small solubility in water in the water system, the reduction in surface tension is limited to the local part of the bubble film, and the surface tension around the bubble film hardly changes. The portion with reduced surface tension is strongly pulled and extended to the surroundings, eventually causing the foam to rupture.

2) Defoaming agent can destroy the elasticity of the film and cause the bubble to burst

The surface tension is lowered due to the adsorption of the surfactant on the surface of the bubble film. Therefore, at the time of partial pressure, the film is locally thinned at this point, and the surface tension is increased due to the thinning of the surfactant. It is precisely because of the difference in surface tension between the new surface and the original surface that the film is thinned by external impact, and an elastic restoring force is generated, so that the bubble film can be broken and plays a role of stabilizing the bubble. If we try to break this elasticity, we can destroy the stability of the bubble. Some experts believe that the role of defoamer is to destroy the elasticity of the film. When the antifoaming agent is added to the foam system, it will diffuse to the gas-liquid interface, making it difficult for the surfactant having a stabilizing effect to recover the elasticity of the film.
  
3) Defoamer can promote liquid film drainage and cause bubble burst

A substance (antifoaming agent) that accelerates the discharge of the bubble film is added to defoam. If the bubble film is thick, the process of draining to 30~40nm is long, and the self-healing effect of the bubble film is strong, and the bubble film elasticity is good, so the bubble life of the bubble film is long, and the bubble discharge rate can reflect the foam. Stability. The liquid film discharge rate is fast, and the liquid film is thinned, and the foam is shattered to a certain extent.

  4) Mechanism of action of hydrophobic solid particle defoamer

In the foamed water system, the hydrophobic silica (i.e., hydrophobic white carbon) particles are separately added, i.e., have a defoaming effect. The hydrophobic white carbon black particles attract the hydrophobic end of the surfactant on the surface of the bubble, and the hydrophobic particles become hydrophilic particles and enter the aqueous phase, completing the defoaming effect. The solid particles of hydrophobic silica are generally white carbon black particles treated with methyl silicone oil, silazane or DMC, which are partially immersed in the surface of the bubble to make the local surface tension of the bubble small, and the effect of the solid particles. Insert a bubble like a needle tip to accelerate the bursting of the bubble. Therefore, the defoaming agent generally containing hydrophobic white carbon black has better foam breaking effect.