Dimethicone

Silicones are manufactured from quartz, which contains silicon in the form of SiO2. Through a number of processing steps a variety silicone entities may be synthesized including silicone polymers, such as dimethicone. Silicones have been used in cosmetic products for more than half a century. They are commonly found in personal care formulations that are applied to skin and hair due to their ease of spreadibilty as well as many other characteristics. Their unique surface properties arise from their low surface energy (surface tension). Some applications of silicones in cosmetics consist of: skin lotions (desoaping, rub-out, protection, feel), skin cleanser (lubricity and wetting), antiperspirant (anti-whitening and detackification), pre-shave lotion (lubricity), aftershave lotion (feel), makeup (water resistance), hair care (conditioning), and shaving cream (reduce razor drag).

The low surface energy of silicones may be explained by their structural characteristics. For example, dimethicone contains a siloxane backbone (high surface energy) with pendant methyl groups (low surface energy). It is believed that the methyl groups are the predominant species present at interfaces (or the surface), allowing the low surface energy portion of the molecule to dominate its interactions. Further, it should be noted that methyl groups contribute to lower surface energy than methylene groups. This would explain why most oils (dominated by methylene groups) are higher in surface tension than silicones, such as a dimethicone, which contain mostly methyl groups.

From a structural standpoint, dimethicone is one of the simplest molecules of the silicones, yet it still remains a very popular molecule that is utilized in a variety of cosmetic formulations. The backbone of dimethicone is very flexible due to the freedom of the pendant methyl groups to rotate about the Si-O bonds. As a result, it has a relatively low glass transition temperatura (Tg).2

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Dimethicone