The Chemistry behind Mascara:

What really is in your vanity?

Mascara, the dark pigment inside a tube that one paints across their eyelashes, is not a simple cosmetic. Used to draw attention to the eyes by darkening and thickening eyelashes, mascara enhances and beautifies one’s appearance. Tracing back to ancient Egypt in 4000 B.C. as a dark pigment formed from natural ingredients such as plants, fruits, and animals, mascara can now be found in a liquid, cream, or cake form. Varying chemical compounds dictate the properties of mascara, whether they be hydrophilic or hydrophobic. However, the most basic components, including pigments, oils, waxes and preservatives, are always prevalent.

But what is it that allows mascara to hold these chemical properties? How does it display such beautifying effects? What is the difference between hydrophilic and hydrophobic mascara?

 

Compounds/Ingredients

The main ingredients of mascara include a pigment to darken lashes, such as carbon black or iron oxide, polymers to film the individual lashes and stiffen the mascara (ceresin, gum tragacanth, methyl cellulose), thickening waxes or oils for enhancing lashes, and preservatives to maintain shelf life. Mascara is made of a heavy base of wax (usually beeswax but also paraffin, carnauba or palm wax), oils (mineral, sesame, eucalyptus, or turpentine oil), and lanoil (moisturizer) nylon or rayon microfibers. Therefore, carbon blackand beeswax are among the most prominent ingredients in mascara. Iron oxide is used to add a brownish tint to mascara, while carbon black adds a deep black  pigment.

Electron Microscope image of carbon black

Chemical structure of beeswax

Carbon Black

  • Produced by incomplete combustion of hydrocarbons, carbon black usually exists in pellets or powder form and is used in rubber, plastic products, and pigments. It is made of fine particles, mainly carbon, and carbon black has a complex structure with spherical particles fused together. It has different functional groups like the hydroxyl and carboxyl group found on its surface. The diameter of the particles affects the blackness and how dispersible the substance is once mixed with resins. The smaller the particle size, the darker the compound is. Therefore, the small particle size of carbon black allows it to be prominently dark and black.

Carbon black pigment in a powder form

  • Increasing the size of the structure lessens the blackness of carbon black but makes its dispersibility properties stronger. Since it also has a relatively large structure, carbon black is very conductive. Because of the vast amount of hydroxyl groups in carbon black, it has a strong affinity to inks and paints, and this increases dispersibility.

  • Carbon black is a network solid, which is formed by atoms or molecules held together in large network (lattice structure) by covalent bonds. Network solids are characterized by having high melting points and boiling point temperatures because of their strong bonds. In mascara, carbon black was used as a pigment due to its dark color. Its other properties prove themselves useful in composition of mascara; for example, the high boiling point prevents mascara from evaporating off the lashes.

Beeswax

  • Manufactured naturally by bees, beeswax (approximate chemical formula: C15H31CO2C30H61) is made up of fatty acids, esters, long-chain alcohols, and carbohydrates (fructose, glucose, and sucrose) and it can be used in painting.

  • It is a tough wax made of many compounds, the most prominent ones being palmitate, palmitoleate, and oleate esters with long-chained aliphatic alcohols  (30-32 carbons). It has a melting point of around 62 °C. In mascara, the wax keeps the eyelashes separated, lengthened, and thickened. It keeps the color attached to the lashes because it is the heavy base.

  • Wax-based mascaras are able to lift and bend eyelashes, and they are often preferred over dryer mascaras, as the wax prevents the mascara from crumbling and falling off the lashes. Since wax is a nonpolar substance, its molecules are able to stick together due to London dispersion forces (LDFs). As discussed in our previous post, LDFs create attractions between molecules by creating a dipole between separated electrons and nuclei of atoms. In larger molecules such as fats and waxes, LDFs play a major role in creating intermolecular attractions, since larger molecules contain more electrons and protons for producing a greater dipole. Therefore, the LDFs in wax help to keep the mascara together, preventing it from falling off the lashes.

Polymers

  • A polymer is a large molecule that is made up of repeating monomers, commonly called subunits. One commonly used polymer in mascara is polyvinylpyrrolidone (PVP).

  • Polymers are added to mascaras to create a film to encapsulate each individual lash. Some polymers are able to do this because of their binding and film forming properties. Polymers create a film around eyelashes because of their transport properties. Molecules rapidly move through the polymer matrix with the property of diffusivity. PVP is water soluble and is therefore able to cling on to other polar molecules.

Waterproof vs. Non-waterproof

Mascara can be split into two categories: waterproof and non-waterproof. Non-waterproof mascaras are hydrophilic, making them soluble in water. Meanwhile, waterproof mascaras can be called  hydrophobic. What exactly is the difference between these two?

Water soluble (hydrophilic) mascara contains water, glyceryl stearate, ammonium acrylates copolymer, polyvinyl alcohol, and alcohol. Ammonium acrylates copolymer contains nitrogens bonded to hydrogens. Since nitrogen is very electronegative, the hydrogens attached to nitrogen can form highly polar bonds, and this allows these hydrogen to participate in hydrogen bonding with other molecules. Hydrogen bonding occurs when hydrogens are bonded to an extremely electronegative element like oxygen, fluorine or nitrogen. The hydrogens obtain a high partial positive charge, as their electrons have been pulled far away from them, while the electronegative atom has a much stronger pull on the electrons, giving them a high partial negative charge. Since these charges are relatively large, they can participate in very strong dipole-dipole interactions with other polar molecules, and this is known as hydrogen bonding. Water (H2O) is a polar molecule that can participate in hydrogen bonding. It will easily form hydrogen bonds with the nitrogen-hydrogen bonded atoms in ammonium acrylates copolymer. Since these two compounds attract each other, the mascara can easily become dissolved in water, explaining why non-waterproof mascara can be removed upon contact with water.

Ammonium acrylates copolymer

Meanwhile, waterproof (hydrophobic) mascara contains petroleum distillate, polyethylene, carnauba wax, pentaerythrityl hydrogenated rosinate, and tall oil glycerides. The large presence of waxes and oils automatically indicates that the substance contains nonpolar components, as these waxes and oils consist of only carbon-hydrogen bonds. Since these molecules are nonpolar, they will not be able to dissolve in water, which is polar. Instead, other nonpolar molecules, such as petroleum distillate oil, are required to remove the mascara from the lashes. Often, stores will sell special makeup removers containing these nonpolar oil molecules, and these makeup removers must be bought in order to sufficiently remove waterproof mascara.

The next time you are considering which mascara to purchase, think about how much chemistry influences your decision. What ingredients make up the luscious substance, how mascara forms a film around your eye lashes, and what prevents your tears from running waterproof mascara down your face?

Coming up next: An interview with cosmetic chemist Mr. Stephen Herman!

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