Now That's Smart

November 29, 2007

A closer look at the growing emphasis on smart, two-faced and nanostructured particles and their many applications in personal care formulations.

Now, That’s Smart!

A closer look at the growing emphasis on smart, two-faced and nanostructured particles and their many applications in personal care formulations.

Robert Y. Lochhead and Vipul Padman
The Institute for Formulation Science and The School of Polymers & High Performance Materials
The University of Southern Mississippi
Hattiesburg, MS

One very noticeable hair care trend is the increasing use of nanostructured or “smart” particles to impart desirable attributes to hair. This drive appears to have been initiated by an emphasis on amphipathic particles that started about a decade ago. The concept of using amphipathic particles as emulsion stabilizers was originally introduced in 1907 by Pickering1 who discovered the stabilization of oil and water emulsion by colloidal particles situated at the interfacial region between dispersed and continuous phases to form a thin film which provides mechanical stabilization.2

The Roman god Janus had two faces looking in opposite directions. Particles having one side which is hydrophilic and the other hydrophobic are, consequently, named Janus particles and they can be used to stabilize the oil-water interface.3 Amphipathicity can be changed by varying the relative surface areas of two regions on a particle.

Particles such as iron oxide, polystyrene, hydroxide, metal sulfates, silica, clay and carbon particles stabilize oil-in-water or water-in-oil emulsions.4  Two mechanisms have been proposed for stabilization of emulsion by particles; firstly, diffusion of particles to the interface and formation of a mono- or multi-layered film covering the dispersed phase, and secondly, formation of particle-particle three dimensional networks surrounding the dispersed phase. Stabilization of water/cyclohexane system by polystyrene particles5 and oil/water by clay6 are examples of the first and second mechanism, respectively.
Silanized glass spheres7 and polystyrene particles8 can stabilize the air-water interface and monodispersed silica9 particles stabilize the air-toluene interface.
Multiple emulsion systems such as water-in-oil-in-water have been achieved by initially stabilizing a water-in-oil emulsion with essentially hydrophobic silica particles and dispersing this in water and then stabilizing it using essentially hydrophilic silica particles. Oil-in-water-in-oil multiple emulsion system can also be prepared.

A market need exists for products that lightly hold the hair but allow the hair to be restyled without the application of heat. Hair can be styled in this way with compositions containing a crosslinked silicone elastomer (preferably dimethicone/vinyl dimethicone crosspolymer; Dow Coming DC 9506), a nonaqueous polar solvent such as a polyol and a styling polymer.10 Particulate adhesives can also be used for this purpose. Thus, restylable hair fixatives and mascaras may be possible with particulate microspheres.11 The microspheres are particles with a diameter between 10 and 250 microns. Although tiny, they are much bigger than the latex particles in normal adhesives. The particles comprising, for example, poly(2- ethylhexyl acrylate) or poly (butyl acrylate), have a glass transition temperature of less than -20°C, making them rubbery and adhesive. However, the large particle size limits the extent of adhesion and allows them to be easily peeled and re-adhered. Suitable microsphere materials are the Gel Tac water-based microsphere adhesives supplied by Advanced Polymers International.12 An example of a micro-sphere-based mousse for reshapable fixation of hair is shown here.


Ingredient                                    % Wt.

Multi-Lok 38-454A13                    2.35
Empicol BSD 52 surfactant          0.19
Deionized water                           91.46
Propellant A-46                               6.00

Multi-Lok 38-454A (National Starch) is added drop-by-drop to the agitated aqueous phase consisting of water and surfactant. This mixture is combined with propellant in an aerosol bottle to make a mousse product that allows hair to be set to a desired style and subsequently reshaped as wished.

Foaming aerosol products are also used for cleansing purposes. In this case, particulate materials are desired for scrubbing and/or deposition on surfaces to change their physical characteristics. However, the attempted delivery of large particles from aerosols can result in clogging of or seeping from the aerosol valve. Aerosol valves have now been developed to eject foaming compositions that contain particles having diameters in excess of 100 microns.14

US Patent Application 2007023135515 is directed toward the use of multiphasic particles in which different parts of the particle surface have distinctly different properties. The authors of this patent contemplate, for example, multiphasic particles having one phase that is substantive to hair and another in which a scalp care ingredient is encapsulated are included in a shampoo formulation. It is expected that the resulting shampoo formulation would be soothing to the scalp. Likewise, it is contemplated that multiphasic particles that include an adhesive phase and a non-adhesive phase could be included in a hair gel formulation that would be expected to have hairstyling properties.

In its pristine state, hair has a hydrophobic surface but oxidation and/or treatment with surfactants causes the hair surface to become hydrophilic. Consequently, hair loses its natural conditioning. It has now been discovered that responsive particles with two contrasting polymers adsorbed to the particle core16 can adsorb to the hydrophilic hair surface and render it hydrophobic, thereby conferring conditioning attributes to the hair. For example, grafting of aminopropyl-terminated dimethicone and polyethylenimine on titanium dioxide particles (Aerosol P25 supplied by Evonik/Degussa) produces responsive particles. These particles form stable dispersions in water and aqueous solutions because they are sterically-stabilized by expansion of the polyethylenimine into the aqueous medium. However, when they are deposited on hair and dried, the polyethylenimine layer collapses and the dimethicone layer expands to render the surface hydrophobic.

The usefulness of these responsive particles is demonstrated by including them in typical conditioning shampoo and conditioner formulations. In the case of the shampoo, inclusion of the responsive particles results in a higher water contact angle on the treated hair and the conditioner with particles causes an increase in the hydrophobicity of the hair.

Uses in Fragrances

Fragrances tend to change their olfactive characteristics with time because the top notes evaporate at a faster rate than the bottom notes. A number of controlled release strategies have been employed to “even out” the rates of evaporation and render them more uniformly consistent for the periods of normal use. Emulsion polymerization in the presence of fragrances can produce nanoparticles, for deposition on hair, that are useful for delivery of olfactive components.17

The latex nanoparticles desirably have high glass transition temperatures in excess of 50°C, and they preferably consist of cross-linked copolymers of styrene or methyl(meth) acrylate with methacrylic acid. These nanoparticle delivery systems can be included in hair conditioners for deposition of consistent fragrance on hair. For typical hair conditioners, of pH 2.5 containing up to 5% cationic surfactants, stable products can be prepared if the zeta-potential of the nanoparticles is about - 35mV. On the other hand, for anionic shampoos, with a pH of 8, the Zeta potential should be around +18 mV.

Encapsulation of perfumes can also be achieved by polymer particles having a hydrophobic core and a hydrophilic surface.18 Examples of these polymer particles are cross-linked copolymers of butyl acrylate and methyl methacrylate which are subsequently hydrolyzed to form an anionic hydrophilic surface, or butyl acrylate, dimethylaminomethylmeth- acrylate which is then quaternized to form a cationic hydrophilic surface. The particles are solvent stripped to remove unreacted monomer and finally they are loaded with fragrance.

There are three main modes of dyeing hair:
    • Permanent oxidative dyeing,
    • Semi-permanent dyeing in which preformed dye molecules are applied to the hair and
    • Direct temporary dyeing in which the dye molecules or pigments are too large to diffuse into the hair and consequently, they adsorb on the surface of the keratin fiber. The oxidative conditions employed in permanent dyeing usually cause some damage to the keratin fibers. Semi-permanent dyes and direct temporary dyes show poor wash-fastness and fade after a few shampoo cycles. The color intensity and wet and dry combing characteristics of dyed hair can be improved by organosilicone/oxyalkylene block copolymers (Silsoft A-553 from OSI).19 

New Ways to Dye Hair

Semiconductive luminescent nano-particles can be used to dye hair over a large range of colors, with good dye-fastness, while avoiding damage to the keratin fibers. Semiconductive luminescent nanoparticles, for example calcium selenide or calcium sulfide, have been used for the biological labeling of cells and now they are being applied to hair. The large range of colors obtainable from these nanoparticles derives from the fact that the color emitted depends on the particle diameter. Therefore a large range of colors can be obtained by blending different sizes of nanoparticles. For example cadmium selenide particles of diameter 4.0nm will dye hair orange.20

 Nanoparticles enable cosmetic chemists to create a wide range of hair colors.
Polymeric conditioners have been used with oxidation dyes but the viscosity achieved is often insufficient to allow hairdressers to use highlighting, lowlighting or foiling techniques. This drawback can be overcome by including thickeners such as Polyacrylate-13 or acrylamide/acrylate copolymer.21

Carbon black has been used as a temporary hair dye, especially for white or gray hair. However, carbon black and other temporary hair pigments readily transfer on contact with hands, clothing and pillows, but pigment transfer is reduced by including cationic polymers and an aqueous ethanol carrier in the formulation.22

Carbon nanotubes have been used to volumize hair.23 Now it has been claimed that white or gray hair can be more durably colored black by treating the hair with polymer, then with chemically-functionalized carbon nanotubes, then iterating these steps.24 Carbon nanotubes are hollow cylindrical structures that are 0.5 to 2 nm in diameter and 20 to 4000 nm in length. They can be single-walled (made of a single layer of carbon atoms), or they can be multi-walled nanotubes. The nanotubes can be physically-modified by treatment with surfactants, dispersants, polymers of nanoparticles. They can also be chemically functionalized by oxidation, sulfonation etc., or by radical initiated functionalization or by Diels-Alder reaction between the C-C nanotube bonds and a conjugated molecule. The method of dyeing is exemplified by treating hair with polyallylamine and sulfated multi-walled carbon nanotubes. The sulfated carbon nanotubes are prepared by treating multi-walled carbon nanotubes (from Carbon Nanotechnologies Inc. Houston, TX) with ammonium persulfate and sulfuric acid.

Another approach to increase the durability of dyes and conditioners on hair is to couple the dyes with specific peptide sequences that have high binding affinity to hair.25

An exquisite class of smart pigments enables the preparation of dry water compositions that change color upon application to a keratinous substrate.26 The term “dry water” appears to be an oxymoron, but this “dry” or “powdered water” is made by combining water with hydrophobic, non-wetting solid particles. The particles surround the water droplets and separate them from each other. The result is a composition that can contain large amounts of water but has the characteristics of a powder. Such compositions have been used in cosmetics since the 1960’s and they are usually whitish/beige in the formulation with no color change upon application to the skin or hair. However, smart dry water products have a “resting” color in the package that can change to another visually distinct color upon application to a keratinous substrate. The smart non-wetting particulates can be hydrophobic silicas such as the Aerosil products from Degussa, or Cab-O-Sil TS-530 and TS-720, which consist of silica treated with hexamethyldisilazane and dimethicone, respectively. The color change derives from activatable pigments that are dissolved in the water phase of the dry-water. The pigments can be rendered dispersible in the aqueous phase by chemisorption of polysaccharides. In particular, iron oxide pigments have been rendered activatable and water-dispersible by surface coating with galactoarabinan. These are supplied by Color Techniques as the GA series of pigments. While in the aqueous phase these pigments are white or beige, when they are applied to keratinous surfaces the dyes diffuse out of the dispersed water phase on to the target surface and change color. The color change trigger can be the water or lipids on the surface, temperature, pH or the mechanical work of the application process.


The recent patent literature reveals a distinct trend towards the use of particles that are highly structured, dual-nature and/or nano-sized to alter and enhance the surface, style and color of hair. This looks like the beginning of a whole new formulation approach for personal care products. 


    1. Pickering S., J. Chem. Soc., 91, 1907, 2001
    2. Fuller G., Langmuir, 21, 2005, 2158
    3. Binks B. et al., Langmuir, 17, 2001, 4708
    4. Binks B. et al., Advances in Colloid and Interface Science, 100, 2003, 503
    5. Binks B. et al., Langmuir, 17, 2001, 4540
    6. Binks B. et al., Langmuir, 17, 2001, 4540
    7. Horvolgyi Z. et al., Colloids Surf A, 156, 1999, 501
    8. Ghezzi F.et al., J. Colloid Interface Sci., 238, 2001, 433
    9. Hansen P. et al., J. Colloid Interface Sci., 218, 1999, 77
    10. Singer, J.M.;Baek, J.; Hair styling compositions containing a silicone elastomer and a non-aqueous polar solvent, U.S. Patent Application 20070204871, Sept. 6, 2007: assigned to  L’Oréal.
    11. Quadir, M.; Burakov, D.; Rollat-Corvol, I.; Cosmetic and dermatologic compositions containing mesosphere. U.S. Patent Application 20070224140, Sept. 27,2007, assigned to  L’Oréal.
    12. http://www.msphere.com/AboutAPI/tabid/
53/ Default.aspx
    13. Smith, D. E.; Conover, M. A.; ‘Microsphere adhesive formulations,’ United States Patent Application 20030109630 June 12, 2003, assigned to National Starch.
    14. Kuhlman, D. E.; Coffindafer,T .W.; ‘Aerosol Product comprising a foaming concentrate composition comprising particulate materials,’ United States Patent Application 20070225196, Sept. 27, 2007; assigned to the Procter & Gamble Company.
    15. Quadir, M.; Mathonneau, E.; Cosmetic composition comprising multiphasic particles, United States Patent Application 20070231355, Oct.4, 2007: assigned to L’Oréal.
    16. Constantinides, I.C.; Willicut, R.J.; Baker. E.S.; Hutton, H.D.; Felts, T.J.; Schechtman, L.A.; Minko, S.; Motornov, M.; Personal care compositions comprising responsive particles, United States Patent Application 20070196299, Aug. 13, 2007; The Procter & Gamble Company.
    17. Quellet, C.; Hotz, J.; Balmer, M.; Polymeric nanoparticles including olfactive components, United States Patent Application 20070201052, Sept. 6, 2007; assigned to Givaudan SA.
    18. Quali, L.; Latreche, D.; Polymeric particles and fragrance delivery systems, United States Patent 7,279,542; Oct. 9, 2007 ; assigned to Firmenich SA.
    19. Kleen,A.; Rohland,C.; Schwartz,S.; Weishaupt , S.; Hair dye agent comprising organo silicon copolymers with amino groups and polyoxyalkylene groups and use thereof. United States Patent Application 20070226917, Oct. 4, 2007, assigned to Henkel.
    20. Gourlaouen , L.,; Lee, K.; Composition and method of dyeing keratin fibers comprising luminescent semiconductive nanoparticles , United States Patent Application 20070231940, Oct. 4, 2007: assigned to L’0real,
    21. Schmenger, J.; Aeby, J.; Kujawa, J.; Colorants for keratin fibers; United States Patent Application 20070192968, Aug. 23, 2007; The Procter & Gamble Company.
    22. Bogaty, H.; Brown, K.; Loveless, N.P.; Wolfram, L.J.; Process and composition for coloring hair with pigments, U.S. Patent 4,559,057; Dec. 17, 1985, assigned to Clairol.
    23. Giroud, F; Favreau V.; Composition for volumizing keratin fibers and cosmetic use of nanotubes for volumizing keratin fibers, United States Patent Application 20040115232 A1
    24. Huang, X.; Kobos, R.K.; Xu. G.; Hair coloring and cosmetic compositions comprising carbon nanotubes, United States Patent 7,276,088; Oct. 2, 2007; assigned to E. I. du Pont de Nemours and Company.
    25. Wang, H.; Wu, Y; O’Brien, J.P.; Method for identifying hair conditioner-resistant hair-binding peptides and hair benefit agents, United States Patent Application 20070196305, Aug. 23, 2007, E.I. Du Pont de Nemours.
    26. Zamyatin, T.;Sandewicz, I.M.;Russ, J.G.; Jabush, S.K.; United States Patent Application 2007021804, Sept. 20, 2007. Revlon.