Silicone Emulsifiers and Formulation Techniques for Stable, Aesthetic Products

Oct 1, 2011 | Contact Author | By: Isabelle Van Reeth, Xinyan R. Bao, Yasuhiro Kaneta, Cindy Delvallé and Béatrice Sillard-Durand, Dow Corning
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Title: Silicone Emulsifiers and Formulation Techniques for Stable, Aesthetic Products
emulsifierx silicone emulsifierx silicone polyetherx stabilityx w/sx
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Keywords: emulsifier | silicone emulsifier | silicone polyether | stability | w/s

Abstract: Mastering formulating techniques with water-in-silicone emulsifiers can help cosmetic chemists create stable emulsions that combine distinctive aesthetics with improved performance. Here, the authors describe how altering parameters including the water to silicone/oil ratio, mixing processes, emulsifier levels, the nature of the external and internal phases, and the presence or lack of co-emulsifiers affect the characteristics of final formulations.

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I Van Reeth, X Bao, Y Kaneta, C Delvallé and B Sillard-Durand, Silicone Emulsifiers and Formulation Techniques for Stable, Aesthetic Products, Cosm & Toil 126(10) 720 (2011)

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Emulsions form the underpinning of countless personal care products, from lotions, creams and foundations, to sunscreens, hair conditioners and cleansers. However, not only can emulsions provide the very framework of a product, they may also contribute to the more ethereal or subjective attributes that consumers seek. Qualities that capture the attention of consumers—advertised as fresh, weightless, healthy, smooth and protective—may be evoked in part through emulsions with distinctive textures or sensory effects.

To deliver even the most basic benefits, emulsion stability is the key, and emulsifiers based on silicone polyether structure, generally known as PEG/PPG-X/Y dimethicone, provide one versatile solution, as is shown in the present article. While some organic w/o emulsifiers provide similar marketable effects, they are usually limited in their ability to incorporate silicone oils for a weightless feel in formulations. Furthermore, silicone emulsifiers are typically liquid at RT and do not require waxes for emulsion stabilization, which create a heavier feel.

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Table 1. Variable parameter data for the silicone emulsifier PEG-10 dimethicone

Table 1. Variable parameter data for the silicone emulsifier PEG-10 dimethicone

Thus, smaller particle size emulsions have a lower viscosity, whereas combinations of bigger particle sizes change the way in which particles behave; i.e., independent versus clustering, resulting in higher viscosity emulsions.

Table 2. Selecting a silicone emulsifier

Table 2. Selecting a silicone emulsifier

Table 2 can aid in selecting the appropriate emulsifier, depending on the oil phase composition and the desired emulsion viscosity.

Table 3. Emulsion viscosity as a function of oil type

Table 3. Emulsion viscosity as a function of oil type

This difference is illustrated further in Table 3, based on a formulation comprising 2% PEG-10 dimethicone, an oil phase of 20% and the remaining water phase containing 1% sodium chloride.

Table 4. Prototype formulations for viscosity evaluations

Table 4. Prototype formulations for viscosity evaluations

Table 4 summarizes the content of each of the five prototype formulations evaluated.

Table 5. Remaining vitamin C as measured by HPLC

Table 5. Remaining vitamin C as measured by HPLC

After the samples were stored for one month at 50°C, the glycerin-in-silicone anhydrous emulsion with vitamin C was found to perform best visually (see Figure 5), which was confirmed by HPLC data (see Table 5).

Figure 1. Emulsions with a) PEG-10 dimethicone, b) PEG/PPG-18/18 dimethicone and c) bis-isobutyl PEG/PPG-10/7/dimethicone copolymer

Figure 1. Emulsions with a) PEG-10 dimethicone, b) PEG/PPG-18/18 dimethicone and c) bis-isobutyl PEG/PPG-10/7/dimethicone copolymer

First is the rake silicone polyether, in which polyether segments are attached to the silicone backbone, as shown in Figure 1.

Figure 2. Emulsions with a) PEG/PPG 18/18 dimethicone in cyclopentasiloxane, b) PEG/PPG 18/18 dimethicone in dimethicone 2 cSt and c) PEF/PPG-18/18 dimethicone in dimethicone 5 cSt

Figure 2. Emulsions with a) PEG/PPG 18/18 dimethicone in cyclopentasiloxane, b) PEG/PPG 18/18 dimethicone  in dimethicone 2 cSt and c) PEF/PPG-18/18 dimethicone in dimethicone 5 cSt

Next is the (AB)n silicone polyether, in which polyether segments are incorporated within the silicone backbone (see Figure 2).

Figure 3. Evaluating the w/s emulsion process

Figure 3. Evaluating the w/s emulsion process

With the correct level of emulsifier, viscosity is more likely to remain stable. Based on the study results, Figure 3 shows a formulating and troubleshooting flowchart.

Figure 4. Impact of PPG on viscosity of the aqueous phase

Figure 4. Impact of PPG on viscosity of the aqueous phase

Figure 4 illustrates the impact of increasing propylene glycol concentration in the water phase of a w/s emulsion made with PEF/PPG-18/18 dimethicone in cyclopentasiloxane.

Figure 5. Vitamin C visual stability as a function of water content in emulsions at 50°C after 1 month; a) glycerin-in-silicone emulsion, b) (glycerin + water)-in-silicone emulsion and c) w/s emulsion

Figure 5. Vitamin C visual stability as a function of water content in emulsions at 50°C after 1 month; a) glycerin-in-silicone emulsion, b) (glycerin + water)-in-silicone emulsion and c) w/s emulsion

After the samples were stored for one month at 50°C, the glycerin-in-silicone anhydrous emulsion with vitamin C was found to perform best visually (see Figure 5), which was confirmed by HPLC data (see Table 5).

Figure 6. Sensory comparison between (g + w)/s formulation and pure glycerin

Figure 6. Sensory comparison between (g + w)/s formulation and pure glycerin

Figure 6 on Page 728 compares the improvement in sensory characteristics between the (g + w)/s formulation containing silicone elastomer and pure glycerin.

Footnotes (CT1110 VanReeth)

a Dow Corning ES-5226 DM Formulation Aid (INCI: Dimethicone (and) PEG/PPG-18/18 Dimethicone); b Dow Corning ES-5612 Formulation Aid (INCI: PEG-10 Dimethicone);
c Dow Corning BY11-030 and BY25-337 (INCI: PEG/PPG-19/19 Dimethicone);
d Dow Corning 5200 Formulation Aid (INCI: Lauryl PEG/PPG-18/18 Dimethicone); and
e Dow Corning FZ-2233 (INCI: Bis-Isobutyl PEG/PPG-10/7/Dimethicone Copolymer) are products of Dow Corning, Midland, Mich., USA.
f The Zeiss Axioplan microscope is manufactured by Carl Zeiss AG, Oberkochen, Germany.

Formula 1. Glycerin-in-silicone anhydrous emulsion with vitamin C

Formula 1. Glycerin-in-silicone anhydrous emulsion with vitamin C

A glycerin-in-silicone (g/s) anhydrous emulsion with vitamin C was formulated with PEG-10 dimethicone gels (see Formula 1) and compared with two other emulsions containing either a blend of glycerin and water or water in combination with 10% vitamin C.

Formula 2. Low viscosity fluid foundation

Formula 2. Low viscosity fluid foundation

Formula 2 provides another example of a low viscosity fluid formulation in which PEG-10 dimethicone demonstrated good pigment dispersion properties and enabled the formation of low viscosity, stable emulsions (data not shown).

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