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Silicone Antifoam Compounds

Silicone Antifoam Compounds

Silicone compounds are effective in lowering the surface tension of water from 72 dynes/cm2 to 20 dynes/cm2. This surface activity is one of the reasons why silicones are used commonly in various applications. The effect achieved once surface tension is lowered by the silicone is related directly to the structure of the silicone. Silicone molecules on the surface of water can enhance or destroy foam depending upon how it interacts with other materials on the surface of the water. Hydrophobic silica can disrupt the interface between foam and water, causing pronounced defoaming. In many applications this is not desired but in some it is. For example in cosmetic industry, Most cosmetic formulations contain surfactants. They provide foam, emulsification, wetting and other desired properties. In some formulations, wetting may be desired, but foam may be a problem. Wetting a surface is an example in which foam generated from this process may interfere, resulting in defects in film uniformity. The first step is to change the surfactant by looking for a lower foam and better wetting. When surfactant selection offers minimal relief, antifoam compounds can be added to many process. 


Foam

Foam refers to a frothy material that is formed by trapping gas bubbles in water. A bubble exists because the surface layer of the water has a surface tension low enough to create a layer that acts like an elastic sheet. The spherical shape of the bubbles is also caused by surface tension. The tension causes the bubble to form a sphere, as a sphere has the smallest possible surface area for a given volume. Ordinary aqueous forms, like suds in a sink, are mostly gas (95%) and a little bit of liquid (5%). The gas subdivides the liquid into a matraix of tiny bubbles. Despite the high concentration of air, foam is a springy material that is quite different from air. 
    Foam is a direct consequence of surface tension reduction. Not all materials that have low surface tension form foam, but all foaming materials lower surface tension. Since most aqueous cosmetic products contain materials that lower surface tension in order to work in the desired application, foam occurs. Sometimes foam is desired. Shampoos without foam do not receive consumer acceptance, despite the fact that foam and detergency are two different phenomenon. Foam is a very beautiful, complicated structure. 
    There are many instances in which foam is a detriment to the intended application. The application of a film can be disrupted by foam. The foam can cause "fish eyes," areas in which the substrate is not fully covered. The first line of defense in controlling foam is to formulate using surface active agents that maximize the desired effect, like wetting or conditioning, while minimizing the undesired effect, like foam. This requires selection of the proper material. In the world of silicon surfactants, molecular weight plays a major role in determining which material foams and which does not. 
    The term defoamer and antifoam have different meanings, though the differences have been blurred over the years. The term antifoam is generally used to denote a compound with the ability to prevent foam from forming. In contrast, the term defoamer generally denotes a material that will knock down existing foam. While some types of compounds are more effective in antifoaming applications and some compounds are more effective in defoaming applications, most compounds have properties that make them useful in both applications.
    Since most silicone compounds are water-insoluble, they simply float on water as oily liquids. This behavior makes them useful in destroying or inhibiting foam.

Citation

Anthony J.O'Lenick Jr., Anthony. Silicones for personal care. 2. Carol, IL, USA: Allured, 2008. 55-61. Print.










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