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Defoaming Mechanism

Jun 2, 2022

Defoaming mechanism
1. The decrease of the local surface tension of the foam leads to the collapse of the foam
The origin of this mechanism is to sprinkle higher alcohol or vegetable oil on the foam. When it dissolves into the foam liquid, it will significantly reduce the surface tension there. Because these substances are generally less soluble in water, the reduction of surface tension is limited to the part of the foam, and the surface tension around the foam hardly changes. The part with reduced surface tension is pulled and extended to the surroundings, and finally ruptures.

2. The defoamer can destroy the elasticity of the film and cause the bubble to burst
When the defoamer is added to the foam system, it will diffuse to the gas-liquid interface, making it difficult for the foam-stabilizing surfactant to recover the elasticity of the film.

3. The defoamer can promote the drainage of the liquid film, thus causing the bubble to burst
The rate of foam drainage can reflect the stability of the foam. Adding a substance that accelerates the foam drainage can also play a defoaming effect.

4. Adding hydrophobic solid particles can cause bubbles to burst
The hydrophobic solid particles on the surface of the bubbles will attract the hydrophobic end of the surfactant, making the hydrophobic particles hydrophilic and enter the water phase, thereby playing the role of defoaming.

5. Solubilizing and foaming surfactants can cause bubbles to burst
Some low-molecular substances that can be fully mixed with the solution can solubilize the bubble surfactant and make it

The effective concentration is reduced. Low-molecular substances with this effect, such as octanol, ethanol, propanol and other alcohols, can not only reduce the surfactant concentration of the surface layer, but also dissolve into the surfactant adsorption layer to reduce the tightness between the surfactant molecules. Degree, thereby weakening the stability of the foam.

6. The electrolyte collapses the electric double layer of the surfactant and causes the bubble to burst
For the interaction of the electric double layer of the surfactant with the help of foam to produce a stable foaming liquid, the addition of ordinary electrolyte can disintegrate the electric double layer of the surfactant to have a defoaming effect.

1. Active ingredients
Function: Break foam, defoam, reduce surface tension:
Representatives: silicone oil, polyethers, higher alcohols, mineral oil, vegetable oil, etc.
2. Emulsifier
Function: Disperse the active ingredients into small particles, which are easy to disperse in water, and have better defoaming and anti-foaming effects.
Representative: non(octyl) phenol polyoxyethylene ether, soap salt, op series, Tween series, Span series, etc.
3. Carrier.
Function: Contribute to the combination of the carrier and the foaming system, easy to disperse into the foaming system, and combine the two, its own surface tension is low, it helps to inhibit foam and can reduce the cost.
Representative: solvents other than water, such as aliphatic hydrocarbons, aromatic hydrocarbons, oxygenated solvents, etc.
4. Emulsifying additives

Function: make the emulsification effect better.Representative: dispersant: hydrophobic silica, etc.; tackifier: CMC, polyvinyl ether, etc.(1) Wide range of applications: Due to the special chemical structure of silicone oil, it is neither compatible with water or substances containing polar groups, nor with hydrocarbons or organic substances containing hydrocarbon groups. Due to the insolubility of silicone oil to various substances, it has a wide range of applications. It can not only use water system to defoam, but also can be used in oil system.

(2) Low surface tension: The surface capacity of silicone oil is generally 20-21 dyne/cm, which is smaller than that of water (72 dyne/cm) and general foaming liquids, and has good defoaming performance.
(3) Good thermal stability: Taking the commonly used dimethyl silicone oil as an example, it can withstand 150°C for a long time and 300°C for a short time, and its Si-O bond will not decompose. This ensures that the silicone defoamer can be used in a wide temperature range.
(4) Good chemical stability: Since the Si-O bond is relatively stable, the chemical stability of silicone oil is very high, and it is difficult to chemically react with other substances. Therefore, as long as the formulation is reasonable, silicone defoamers are allowed to be used in systems containing acids, alkalis, and salts.
(5) Physiological inertia: Silicone oil has been proven to be non-toxic to humans and animals, and its half-lethal dose is greater than 34 g/kg. Therefore, silicone defoamers (with suitable non-toxic emulsifiers, etc.) can be safely used in food, medical, pharmaceutical and cosmetic industries.
(6) Strong defoaming power: Silicone defoaming agent can not only effectively break the foam that has been generated, but also can significantly inhibit the foam and prevent the formation of foam. Its usage is very small, as long as it is added to one millionth (1ppm) of the weight of the foaming medium, it can produce a defoaming effect. The commonly used range is 1 to 100 ppm. Not only is the cost low, but also does not pollute the defoamed substance.

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