Formulating with Surfactant Silicones

Jan 1, 2010 | Contact Author | By: Anthony J. O’Lenick, Jr., Siltech LLC, and Kevin O’Lenick, SurfaTech Corp.
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Title: Formulating with Surfactant Silicones
surfactant siliconesx cushionx playtimex rheologyx
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Keywords: surfactant silicones | cushion | playtime | rheology

Abstract: The authors describe how the use of amphiphilic silicones or surfactant silicones has allowed formulators to efficiently incorporate silicone polymers into personal care products. These materials act by lowering the surface tension in the oil phase of a formulation, allowing for easier spreading on skin and hair.

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AJ O'Lenick, Jr, K O'Lenick, Formulating with surfactant silicones, Cosm & Toil 125(1) 44-49 (Jan 2010)

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Silicone polymers have experienced tremendous growth in the personal care market. Known since the 1860s and commercialized with the pioneering work of Rochow since the 1940s, they are now present in almost every personal care product category. The reason for this expansion is twofold: first, increasing classes of compounds have been developed; and second, the formulator has learned how to incorporate them efficiently into formulations. The continued development and application of silicone compounds for personal care requires the use of amphiphilic silicones—silicones with two or more groups that, in their pure form, are insoluble in one another.

These surface active or surfactant silicones move to the surface of the oil phase in which they are contained, much like sodium laureth sulfate moves to the surface of water, and lower the surface tension, allowing for easier spreading on the skin and hair. For most alkyl silicones, a concentration of 1% w/w lowers the surface tension. This makes them effective in providing a silicone-like feel to oils, most interestingly natural oils such as olive oil. If the concentration is increased to between 5–10% by weight, micelles form, providing a thixotrophic gel and change in aesthetics.


Lab Practical: Silicone Surfactants

  • Silicone surfactants, like all anhydrous products, aqueous products and emulsions—both standard and inverted—should be added to the phase in which they are soluble. 
  • Most formulators think of silicone as an insoluble phase, but in fact it is not. 
  • Silicone fluids are soluble in silicone. 
  • Alkyl silicones are soluble in oil.  
  • PEG/PPG dimethicones are soluble in water. 

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Table 1. Melting point of alkyl dimethicone compounds

Table 1. Melting point of alkyl dimethicone compounds

Waxes based on alkyl groups of 16 or fewer carbon atoms are liquid at room temperature, whereas those with 18 or more carbon atoms are solid; the melting point increases as the carbon length goes up.

Table 2. Alkyl silicone solubility

Table 2. Alkyl silicone solubility

Liquid alkyl dimethicone can be used as an additive to improve the solubility of polar oils in formulations. Shown here are the solubilities of alkyl silicones in a variety of solvents.

Figure 1. Alkyl dimethicone structure

Figure 1. Alkyl dimethicone structure

The structure of a polymer determines its function.

Figure 2. Addition of surfactant silicone to soybean oil

Figure 2. Addition of surfactant silicone to soybean oil

Liquid alkyl dimethicone can be used as an additive to improve the solubility of polar oils in formulations. Here, the addition of behenyl dimethicone to soybean oil is shown.

Figure 3. Behenyl dimethicone gellation of olive oil (5% additive)

Figure 3. Behenyl dimethicone gellation of olive oil (5% additive)

Altering the ratio of alkyl to silicone component in alkyl dimethicone the molecule will change the clarity of the gel and occlusivity of the blend.

Figure 4. Multi-domain silicone structure

Figure 4. Multi-domain silicone structure

A series of alkyl dimethicones have been developed that contain two different alkyl groups—one a liquid at ambient temperatures, and another a solid at ambient temperatures. One such polymer conforms to the structure shown here.

Figure 5. Multi alkyl dimethicone comparison

Figure 5. Multi alkyl dimethicone comparison

Multi alkyl dimethicone comparison;co-reacted di-alkyl dimethicone (left) and blend of two alkyl silicones (right)

Figure 6. Photomicrograph of multi-domain silicone (left) and a blend of two single domain silicones (right)

Figure 6. Photomicrograph of multi-domain silicone (left) and a blend of two single domain silicones (right)

Photomicroscopy of the two materials shows that the multi-domain silicone polymer is highly structured while the blend of the two single domain silicone polymers is random and lacks structure

Footnotes [O'Lenick [125(1)]

a Independent studies were commissioned through Microtrace LLC, Elgin, IL USA.

Cushion and Playtime

The terms cushion and playtime are commonly used to describe the feel of ingredients and formulations on the skin. If one places a compound or formulation on their index finger and rubs it onto the forearm, both cushion and playtime can be evaluated.

Cushion refers to the amount of compound that persists between the finger and forearm—i.e., the greater the “distance” between the finger and the forearm, the greater the cushion. Playtime refers to the length of time that cushion persists. If the cushion is felt for a long period of time, the playtime is said to be long. If the cushion collapses rapidly, the playtime is said to be short.

In most compounds, the cushion and playtime are directly related. Honey, for example, has both a high cushion and a high playtime. There are also materials that have good cushion but a low playtime, such as the multi-domain alkyl silicone compounds described. Many applications require a high level of cushion and a short playtime, such as lipsticks, sun products and lotions. The reason for this is to impart an initial feel that is highly desirable that quickly changes to the final desired property, i.e., a dry, non-greasy feel.

Formulas 1a-c. Sample sunscreen formulations with and without multi-domain silicone

Formula 1. Sample sunscreen formulations with and without  multi-domain silicone

The capability of changing a formula’s properties using alkyl silicones was tested in sample sunscreens.

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