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Silicone antifoams prevent foam from forming. Silicone defoamers cause existing foam to rapidly collapse. The generic term "antifoam" is often used to describe both types of foam-control products.
Foam is difficult to break down because it is stabilized by the surface elasticity and surface viscosity of its film. Silicones have low surface and interfacial tensions. This enables them to flow easily over the film. They seek out openings between the foam-stabilizing surfactants at the liquid-air interface and occupy them. Silicones’ low surface tension and interfacial properties combined with their lack of foam-stabilization properties cause the foam wall to thin and collapse.
A single drop of silicone antifoam quickly destroys process foam
Controlling foam in nonaqueous vs. aqueous systems
For nonaqueous systems, invading the spaces between the foam-stabilizing surfactants is generally all that is required to collapse the foam. This can be accomplished by a simple silicone fluid, such as polydimethylsiloxane.
For aqueous systems, the addition of finely dispersed hydrophobic solids, such as polydimethylsiloxane-treated silica, is needed. These fluid/solid combinations are called antifoam compounds. The hydrophobic solids help break down the "pseudo-emulsion" film that forms between the antifoam droplet and the surface of the foaming solution. Antifoam compounds are often prepared as emulsions for easy dispersal in water-based systems.
Antifoam and defoaming benefits of silicone
* Lower surface tension, compared to organic antifoams
* Insoluble in most systems
* Tends to react less with process ingredients
* Persistence – generally performs longer
* Can cost less to use due to its effectiveness and persistence at low use levels
Typical silicone antifoam and defoamer applications
Foam reduces processing speed and capacity. It limits the cleaning capability of detergents, limits formulations, and can lead to environmental concerns.
Courtesy: Dowcorning.com
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