New Formulating Options with Silicone Emulsifiers

Isabelle Van ReethMarilena Morè

Dow Corning Europe

Robin HickersonDow Corning USA

In today’s highly competitive skin careand underarm markets, multifunctional,high performance products have thebest chance of success. Consumers ex-pect convenience and superior aesthet-ics. They want long-lasting, highlyefficient moisturizers; effective anti-aging and anti-wrinkle creams; durable,wash-off resistant, protective color cos-metics; and underarm products that goon smoothly, without tackiness or resi-due. Formulators strive for all that andmore: cost-effectiveness, formulatingflexibility and easy processing.

In many cases, the solution to fulfillingthis broad range of requirements pointsto evolving emulsion technologies. Morethan 80 percent of emulsions in today’spersonal care market are oil-in-watersystems. Emulsions of this type are fa-vored for their stability, flexibility, highwater content (and hence, lower cost),their nongreasy and nonoily feel, and theirability to form an extensive array of prov-en systems with predictable stability.

Compared to oil-in-water emulsions,water-in-oil systems are recognized fora different range of benefits. The externaloil phase typically spreads more easilyon skin, formulations generally are longerlasting with improved emolliency andwash-off resistance, and they exhibitenhanced film barrier properties. Despitethese characteristics, conventional water-in-oil systems can be perceived as im-parting a greasy, oily feel, and lackingin formulation flexibility. In addition,they tend to be less cost effective andmore difficult to produce, typically re-quiring a high shear finishing step.

Silicone Emulsifiers for the BestAll-Around

Silicone emulsifiers can help bridge thegap between the two systems, providingthe best characteristics of both: theycan aid in the formulation of stable,aesthetically pleasing cosmetic emul-sions with high water levels, while re-quiring no heat during processing toprovide a positive impact on overallcost. Some silicone emulsifiers suchas cyclopentasiloxane (and) PEG/PPG-18/18 dimethiconea already have earned

a reputation in personal care by makingpossible new product forms, particularlyclear gels for antiperspirant applications.

These materials belong to the dimethi-cone copolyol family of silicones, whichis broadly used in personal care prod-ucts. Combined U.S. and West Europeanconsumption of dimethicone copolyolsfor skin care applications was estimatedat between 2,500 metric tons and 3,000metric tons in 2002. The U.S. accounts for around 65 percent of this total,driven by the large consumption of dimethicone copolyols in antiperspirantsand deodorants, estimated at more than 85 percent of total U.S. dimethicone copolyol consumption for skin careapplications. In contrast, antiperspirantand deodorant applications accountfor only 55 percent of West Europeandimethicone copolyol consumptionfor skin care applications (1).

Silicone emulsifier technology is basedon the ability of these materials to func-tion differently from organic emulsifi-ers. To perform properly, a siliconeemulsifier must satisfy three require-ments: it must be able to migrate to theinterface between the two phases, stayat that interface, and stabilize the repul-sion forces of the two phases. Whiletypical organic emulsifiers are am-phiphilic molecules of type AB, theaction of the silicone emulsifier is the

result of functional groups alongsidethe silicone backbone, which result inlower interfacial tension and a morerobust, flexible film at the interface.This characteristic is exemplified bydimethicone copolyol emulsifiers suchas the previously mentioned material,cyclomethicone (and) PEG/PPG-18/18dimethicone, and also by laurylPEG/PPG-18/18 methicone.b

The graph in Figure 1 compares thedifference in interfacial tension at thewater and oil boundary for two organicemulsifiers and a silicone emulsifier.Notice that a lower concentration oflauryl PEG/PPG-18/18 methicone isrequired to reduce interfacial tensioncompared to the organic materials.

Finally, because of their branched struc-tures and high molecular weights, eachsilicone molecule packs very tightly atthe oil and water interface. Hydrophilicand lipophilic portions of the moleculeare tightly aligned by the flexible sili-cone backbone to provide highly effec-tive steric repulsion.

A New Option: Low ShearProcessing

In general, most silicone water-in-oilemulsifiers require high shear to makeemulsions with optimized stability.Recent developments in silicone emul-sifier technology have resulted in still

-5 -4 -3 -2 -1 0 1 2 3 40

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Log Emulsifier Concentration (µ mol/1)

Inte

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Polyglycerin-3Diisostearate

Sorbitan Oleate

Lauryl PEG/PPG-18/18Methicone

aDow Corning® 5225C Formulation AidbDow Corning® 5200 Formulation Aid

Figure 1. Comparison of the difference in interfacial tension at the water-oilboundary as a function of the log emulsifier concentration.

newer materials that offer expandedperformance along with cost effective-ness and formulating ease. For next-generation water-in-oil emulsions, anew silicone emulsifier based on sili-cone elastomer technology has beendeveloped. This material allows formu-lators to develop stable water-in-siliconeemulsions without the need for highshear processing equipment. Given theINCI designation cyclopentasiloxane(and) PEG-12 dimethicone crosspoly-merc, the emulsifier provides:

• A broad variety of sensory profilesand textures to offer a sensory ex-perience ranging from very light torich, depending on the oil used.Enhanced aesthetics over dimethi-cone copolyol emulsifiers.

• Formulation flexibility for formingclear emulsions with stability at lowto high viscosities, and accommo-dating a wide range of oil-phaseingredients.

• Processing flexibility for low- tohigh-shear processing and the optionfor cold mixing.

• Cost effectiveness, with the optionfor using high water content (up to82 percent water in the internalphase), low emulsifier levels andcold processing.

• Stability for long shelf life and con-sistent performance. Improved activesuspension in underarm products.

Using the new emulsion, it is also pos-sible to create novel product forms suchas anhydrous systems or multiple emul-sions with two distinct aqueous phases(water-in-oil-in-water). The latter ap-proach results in aesthetics that aredifferent from those associated withtypical water-in-silicone emulsions; theexternal phase is now aqueous, makingthe first impression on the skin verylight. This method also suggests poten-tial use for delivery of active ingredientssuch as emollients, moisturizers, sun-screens, pigments, vitamins and anti-perspirant salts. The ability of thisemulsifier to make stable anhydrouspropylene glycol-in-silicone emulsionsallows formulators to develop systemswhere vitamin C is not degraded duringthe shelf life of the product. This emul-

Formulation 2Water-in-Silicone Foundation

Ingredient Wt. % Trade Name/SupplierPhase A1. Dextrin palmitate 2.10 Rheopearl KL/Miyoshi Kasel2. PEG-12 dimethicone 1.90 XIAMETER® OFX-0193 Fluid3. Tricaprylin 5.00 Trivent OC-G/Trivent4. Cyclopentasiloxane (and) PEG-12 10.00 Dow Corning® 9011 Silicone Elastomer Blend

dimethicone crosspolymerPhase B5. Cyclopentasiloxane & Cyclohexasiloxane 20.00 XIAMETER® PMX-0345 Cyclosiloxane BlendPhase C6. C.I. 77891, Dimethicone 2.75 SAT-T-47-051/US Cosmetics7. C.I. 77492, Dimethicone 0.43 SAT-Y-338073/US Cosmetics8. C.I. 77491, Dimethicone 0.32 SAT-R-33-128/US Cosmetics9. C.I. 77499, Dimethicone 0.01 SAT-B-33134/US CosmeticsPhase D10. Deionized water to 100.00 11.Sodium chloride 1.00 Sodium chloride/Merck

ProcedureHeat Phase A to 80˚C, ensuring that ingredient 1 is fully dissolved. Cool to 50˚C. Combine ingredients of PhaseC. Add Phase C to Phase B and mix. Add Phase B to Phase A with mixing. Combine ingredients of Phase D.Add Phase D to Phase A with high shear mixing. (Formulation developed by S Black Ltd. UK)

Formulation 1Clear Antiperspirant Gel

Ingredient Wt. % Trade Name/SupplierPhase A1. Cyclopentasiloxane (and) PEG-12 10.0 Dow Corning® 9011 Silicone Elastomer Blend

dimethicone crosspolymer2. Dimethicone 3.5 XIAMETER® PMX-200 Silicone Fluid 10 cSt3. Phenyl trimethicone 0.5 Dow Corning® 556 Cosmetic Grade Fluid4. Cyclopentasiloxane 6.0 XIAMETER® PMX-0245 CyclopentasiloxanePhase B5. Aluminum sesquichlorohydrate 42.0 Reach 301 Solution/Reheis Inc.6. Deionized water 17.57. Propylene glycol 12.5 Propylene glycol/The Dow Chemical Company8. Glycerin 6.5 Glycerin/Fisher Chemical Company9. Ethyl alcohol, 200 proof 1.5 Alcohol/Equistar

ProcedureCombine Phase A ingredients. In a separate container, combine Phase B ingredients. Match the refractiveindex of Phase A to that of Phase B. If the refractive index of Phase A is higher than that of Phase B, addwater to the aqueous phase to match. If lower, add glycerin to match. With rapid mixing, add Phase B toPhase A very slowly, using a separatory funnel. (Use a 1000 ml tall beaker and 1376 rpm.)

sifier is outside current clear antiperspi-rant patents and therefore allows free-dom to practice.

Formulation 1 illustrates the use of thenew silicone emulsifier in a clear antiper-spirant gel made with a low shear process.

Formulation 2 demonstrates the use ofthe silicone emulsifier in a water-in-silicone foundation.

The Solution for Novel ProductForms

For formulators seeking ways to createhighly differentiated product forms, laurylPEG/PPG-18/18 methicone, a dimethi-cone copolyol emulsifier previously men-tioned, offers unique potential in skincare applications.

cDow Corning® 9011 Silicone Elastomer Blend

This material allows:

• Very stable water-in-oil systems with-out the addition of waxes and up toapproximately 80 percent water phase.

• The ability to accommodate a lowto medium polarity oil phase includ-ing a high level of silicone oils.

• Long-lasting moisturizing, wash-offresistance and superior aesthetics.

• A flexible sensory profile from lightand nongreasy to nourishing andrichly emollient.

• The option for cold processing.• Novel product forms such as water-

in-wax emulsions for potential usein foundation sticks and lipsticks.For example, a prototype water-in-wax base stick containing 60 percentwater imparts a feel of freshness toskin compared to the expected feelfrom an anhydrous stick. In additionto a surprising feel, the presence ofwater offers the possibility of addingwater-soluble actives to the stick, aswell as reducing the overall cost of the formulation.

Figure 2 illustrates the moisturizing per-formance of a water-in-oil emulsionbased on lauryl PEG/PPG-18/18 methi-cone. These data show that an increaseof 40 percent in the hydration level ofthe skin can be maintained for longerthan six hours. Although this formulationcontains 10 percent glycerin, the creamhas a silky, nongreasy and nontacky feelas shown in Figure 3, where it is com-pared to an oil-in-water emulsion.

Based on paired comparisons, the spiderdiagram of Figure 3 compares the sen-sory profiles of an oil-in-water formula-tion and a water-in-oil formulation madewith the lauryl PEG/PPG-18/18 methi-cone emulsifier. Except for the wetnessand spreadability parameters, the water-in-oil formulation demonstrates eitherequivalent or improved sensory perfor-mance over the oil-in-water system. Foran equivalent performance on greasiness(a parameter that is usually a disadvan-tage of water-in-oil systems), the water-in-oil formulation with the silicone emul-sifier has a silky, nontacky and slipperyfeel on the skin.

An Added Advantage: Durabilityand Resistance to Wash-Off

With their external oil phase, water-in-oil systems can form an immediate con-tinuous and homogeneous film on theskin to optimize the film-barrier prop-

erties. In addition, since the emulsifieris water insoluble, wash-off resistancewill be improved because the oil phasecannot be re-emulsified by water. Thedegree of film forming properties andwash-off resistance will be dependenton the types of ingredients present inthe oil phase. Another benefit of water-in-oil emulsions is the protection ofhydrosoluble actives such as vitaminC, which are sensitive to oxidation.

Figure 4 illustrates the wash-off resis-tance of a water-soluble sunscreen ac-tive in an oil-in-water formulation con-taining an organic emulsifier (cetylphosphate) and a water-in-oil systemformulated with lauryl PEG/PPG-18/18methicone. The formulation containing

the silicone emulsifier resists wash-off,while 53 percent of the sunscreen in theformulation containing the organicemulsifier is washed away.

Forming Stable Emulsions

Stable emulsions can exist only whenthe internal phase “droplets” remainseparated from one another over a peri-od of time. Several factors affect thisstate, such as particle size, distribution

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Absorbancy

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Silkiness 99.9%

Tackiness after absorption 99.9%

Slipperiness 99.9%

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Figure 2. Corneometer measurements of moisturization effect from a water-in-oil formulation containing lauryl PEG/PPG-18/18 methicone emulsifier.

Figure 3. Sensory profiles of oil-in-water and water-in-oil formulations, basedon paired comparisons.

Moisturization with Corneometer.

of particle sizes, formulation compo-nents and phase ratio. A homogeneousparticle size is key to developing a stableemulsion. A bi- or multi-modal particlesize distribution can significantly reducestability by increasing coalescencethrough the collisions of the particlesamong themselves. Uniformity is morecritical to stability than size becauselarge particles have a greater mass, andwhen collisions with smaller particlesoccur, large particles will incorporatethe smaller particles. Drop in viscosityis often the first sign that coalescence isoccurring. When a multi-modal particlesize distribution occurs, both formulationand process should be investigated.

Emulsifier level. Too much emulsifiercan result in as much difficulty as too

little. Excess emulsifier may surrounditself or attract other droplets. For thatreason, the recommended approach isto formulate with the minimum andmaximum amount of emulsifier untilinstability is noted.

Phase ratio. A phase ratio of 80:20(water to oil) can be achieved with thethree silicone emulsifiers discussed inthis article. Increasing the internal phaseincreases viscosity. Phase ratios signif-icantly below 65 percent internal phasemay require either additional emulsifier,thickener or a reduced particle size toavoid settling. For example, the oil(external) phase can be thickened by

the use of waxes, bentonite gels or sil-icone elastomers.

Aqueous phase. In the formulation ofunderarm products, small changes inactive ingredients (e.g., switching fromACH to AlZr salts) should have littleimpact on the system. However, anyelement in either phase that changesthe solubility of the emulsifier will havean impact on the system. Some fra-grance components may have this effect,as can high levels of antiperspirant saltsin combination with lauryl PEG/PPG-18/18 methicone.

Oil Phase. Some emulsifiers are moreeffective in certain types of oil systems,such as cyclic versus linear siloxanesor low viscosity versus high viscosity.

In addition, the resulting polarity of theoil phase should be considered. LaurylPEG/PPG-18/18 methicone is most ef-ficient with low to medium polarity. Itis important to thoroughly investigatethe formulation on a laboratory scaleprior to production.

Inorganic electrolytes and polyols. Theuse of an inorganic electrolyte (e.g.,sodium citrate, magnesium sulfate, so-dium chloride or sodium tetraborate) atapproximately 1-2 percent by weighthas been shown to reduce even furtherthe interfacial tension as well as improvefreeze-thaw stability. The addition ofsmall quantities of polyols with their

humectancy properties decreases thewater loss; however, high levels mightdestabilize the emulsion.

Co-emulsifiers. The use of co-emulsifiers(e.g., polysorbate-20, C12-15 pareth-9,laureth-7) should be limited. These in-gredients should be used at levels lowerthan their critical micelle concentrationto avoid depletion flocculation.

Table 1 compares the levels of formu-lation components for forming stablewater-in-oil or water-in silicone systemswith silicone emulsifiers.

Processing. The following general pro-cessing guidelines are recommended forformulating with silicone emulsifiers:Combine the ingredients of Phase A andPhase B in separate containers and mixeach until uniform. Add the water PhaseB to the silicone or oil Phase A veryslowly, using a high turbulence mechan-ical blade mixer set at high speed (900ft/min tip speed). This addition shouldtake from 10 to 30 minutes. Becausethe aqueous phase typically has a higherdensity than the oil phase, it gravitatesto the bottom of the mixing container.Adding the aqueous phase from the topenhances mixing efficiency.

After addition is complete continue mixingfor another 10 to 30 minutes. This stepnarrows the particle size distribution. Tofinish the emulsion, homogenize the sys-tem with a high shear mixing device. Thisstep reduces the mean particle size andincreases emulsion viscosity. The finalhigh shear step is optional when usingcyclopentasiloxane (and) PEG-12 dime-thicone crosspolymer. Without the finalshear step, particle diameters will typicallybe in the 1 to 3 micron range. With a finalhigh shear pass, diameters will be lessthan 1 micron. Additional details relatedto processing and stability assessmentsare available in separate publications (2,3).

Table 2 compares some of the physicaland formulating characteristics thatdistinguish three silicone emulsifiers.

By comparing the requirements and prop-erties of various formulation types, it ispossible to determine which siliconeemulsifier is most appropriate for a par-ticular application. Table 3 provides some

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Figure 4. Comparison of wash-off resistance between a water-soluble sunscreenactive in a water-in-oil formulation containing a silicone emulsifier, versus anoil-in-water formulation containing an organic emulsifier.

general guidelines. Additional details areavailable in a separate publication (4).

Conclusions

New developments in silicone emulsifiertechnology provide expanded optionsfor creating stable water-in-oil and water-in-silicone emulsions with a broad rangeof sensory characteristics. In skin andunderarm products, these ingredientsgive formulators flexibility for develop-ing clear products with superior aestheticsand novel forms such as anhydrous sys-tems, multiple emulsions or water-in-wax sticks. In addition, benefits of water-in-oil systems such as good sensoryprofiles, improved wash-off resistanceand excellent moisturization have beendemonstrated. Silicone emulsifiers offerversatility for low or high shear optionsas well as cold processing, presentingnew opportunities for cost-effective andhighly innovative skin care and underarmproducts.

References

1. Personal Communication, GillianMorris, Group Director, Chemicals,Minerals, Polymers, Kline & Com-pany (2003).

2. Kasprzak, K., “A guide to formulatingWater-in-Silicone emulsions withDow Corning® 3225C formulationaid,” Dow Corning Internal Docu-ment, Form no. 25-713-01 (1995).

3. Dahms, G., and Zombeck, A., “Newformulation possibilities offered bysilicone copolyols,” Cosmetics &Toiletries, Vol 110 number 3, p 91+(1995). Also available as Dow CorningInternal Document, Form no.25-710-01 (1995).

4. Hickerson, R. and Van Reeth, I.,“Silicone Emulsifiers Guide,” Dow Corning Internal Document,Form no. 27-1063-01 (2002).

Table 1. Critical Factors for Stable Emulsions

Table 2. Overview of Silicone Emulsifier Characteristics

Table 3. Selection Criteria for Silicone Emulsifiers

X

X

X

X

Dow Corning®

5225C

XMultiple emulsions W/O/W

XXNew product forms / new sensory

XEmulsions containing AP salts

XWater-in-wax (W/W) systems

XMultiple emulsions W/Si/W

XMoisturizing, wash-offresistant, long lasting creams

XClear systems

XAnhydrous Systems (PPG/S)XW/O Systems

XW/Si Systems

Dow Corning®

5200Dow Corning®

9011System Type

Water-in-oil,Water-in-wax

Water-in-silicone,multiple emulsions,anhydrous emulsions

Water-in-silicone,multiple emulsionsEmulsion Type

High shearLow to high shearHigh shearShear /

Processingrequirements

2-3%

100%

Lauryl PEG/PPG-18/18 Methicone

(Dow Corning®

5200)

12.5%10%% Actives

6-14%7-15%Use Levels

INCI Name

Cyclopentasiloxaneand PEG-12Dimethicone

Crosspolymer

(Dow Corning® 9011)

Cyclopentasiloxaneand PEG/PPG-18/18

Dimethicone

(Dow Corning® 5225C)

Level (%) Water-in-Oil Emulsions(Dow Corning® 5200*)

Emulsifier 7 - 20 1 - 3

Oil phase 20 - 50 20 - 35Water phase 50 - 82 65 - 80

Electrolyte(NaCl preferred)

1 - 2 1 - 2

Co-emulsifier 0.5 0.5

Water-in-Silicone Emulsions(Dow Corning® 5225C* and 9011)

* Dispersion of approximately 10% active emulsifier

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