Defoamers can disrupt membrane elasticity and cause bubble collapse
Due to the adsorption of surfactants on the surface of the bubble film, the surface tension is reduced. So when subjected to local pressure, the foam film thins locally at that location, and at the same time, the surface tension increases due to the thinning of the surfactant. It is precisely because of the difference in surface tension between the newly formed surface and the original surface that when the bubble film becomes thinner under external impact, it generates elastic recovery force, which prevents the bubble film from breaking and plays a stabilizing role. If we try to break the elasticity, we can break the stability of foam. Some experts believe that the function of defoamers is to destroy the elasticity of the foam film. When defoamer is added to the foam system, it will diffuse to the gas-liquid interface, making it difficult for the surfactant with foam stabilizing effect to recover the membrane elasticity. Defoamers can promote the discharge of liquid film, resulting in the collapse of bubbles
Adding substances (defoamers) to accelerate the discharge of foam film can defoaming. If the foam film is thick, the process of liquid discharge to 30~40nm will be long. Moreover, the self-healing effect of the foam film is strong and the elasticity of the foam film is good, so the life of foam with thick foam film will be long. The liquid discharge rate of the foam film can reflect the stability of the foam. The liquid film has a fast discharge rate, which makes the liquid film thin, and when it is thin to a certain extent, the foam will burst.
Adding hydrophobic solid particles can cause bubble collapse
In a foaming water system, the addition of hydrophobic silica (i.e. hydrophobic silica) particles alone has a defoaming effect. 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. They are locally immersed on the surface of bubbles, reducing the surface tension of the bubbles. In addition, the effect of solid particles, such as needle tips inserted into bubbles, accelerates the rupture of bubbles. So generally, defoamers containing hydrophobic silica have better defoaming effects.
Solubilizing and foaming surfactants can cause bubble collapse
Some low molecular substances that can be fully mixed with the solution can increase the solubility of bubble surfactants and reduce their effective concentration. Low molecular substances with this effect, such as octanol, ethanol, propanol and other alcohols, can not only reduce the surfactant concentration in the surface layer, but also dissolve into the surfactant adsorption layer, reducing the compactness of surfactant molecules, thus weakening the stability of foam.
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