I have some vague recollection of first learning about chemical bonds and hydrophobicity and hydrophilicity of molecules sometime in high school. Important chemistry concepts indeed. My curiosity about mascara (which is one of two MUST HAVES for me in the make-up department, the other is more crucial: under eye concealer) and especially my new affection for L'Oreal's Beauty Tubes Extend Lash provoked me to make a demonstration video about three different types of mascara: water soluble, water proof and the new Beauty Tubes. It's sort of long, but it is a real time demo/discussion. I wish I could say I was a polymer chemist, but I'm not...I know just enough to be dangerous!
Without turning this into a full-fledged chemistry tutorial, I will quickly quickly discuss various type of chemical bonds as this plays a part in how the various mascaras work. We can divide chemical bonding into two types: covalent and non-covalent. Non-covalent then can be further subdivided into three different types: ionic, hydrogen and van der Waals. Overall, covalent is a very strong type of bond formed primarily by sharing electrons (there can be single or double bonds, but we won't worry about that here).
Before we go onto weaker types of bonding, let's quickly talk about polar vs. non-polar molecules: In a polar covalent bond, electrons are shared unequally, usually between two different atoms such as -O-H (oxygen and hydrogen) and -N-H (nitrogen and hydrogen) resulting inpartial negative charge on one side of the molecule and a partial positve charge on the other. We most certainly see this in water, and this sets up an opportunity for spontaneous electrical attraction and bonding.
On the other hand, the bond between carbon and hydrogen -C-H has the electrons attracted more equally by both atoms and is fairly non-polar. We will see the importance of carbon-hydrogen bonding in the formation of oils, waxes, lipids and plastics in a bit.
Above is an image from Essential Cell Biology by Alberts, et al about Water as a solvent. When a substance dissolves in a liquid, the mixture is termed a solution. The sugar in this image is the solute and the liquid that does the dissolving is the solvent.
For our discussion of mascara, we will focus on non-polar covalent bonding and the weaker hydrogen bonding.
Water is held together by hydrogen bonds. In each molecule of water, the two H atoms are linked to the O atom by covalent bonds. Again, without all the details, water is highly polar because of the imbalance of electrons between the O and the Hs. Two water molecules, when in close proximity to each other can establish a weak bond called a hydrogen bond. These can be broken by random thermal motions and each bond lasts only a short time.
Molecules such as alcohols or urea (see above image) that contain polar bonds and can form hydrogen bonds mix well with water. (molecules that carry positive or negative charges-ions-also dissolve readily in water). These molecules are termed hydrophilic, meaning that they are "water-loving"
Hydrophobic molecules are generally uncharged, form few hydrogen bonds and do not dissolve in water. In these molecules, the H atoms are covalently linked to C atoms by nonpolar bonds.
Let's look at a few molecules from the water soluble (hydrophilic) mascara: (water, glyceryl stearate, ammonium acrylates copolymer, polyvinyl alchohol, alcohol)
The fact that the first molecule listed on the ingredients is water gives a clue that the next items are water soluble. The ammonium (contains Nitrogen) indicates that we have a molecule with a potential to be hydrophilic because it will most likely be in a polar molecule. Alcohol has the ability to dissolve both polar and non polar substances--a very good solvent. Polyvinyl alchohol has many purposes, one being that it is a good adhesive to the lash.
And from the waterproof (hydrophobic) mascara (petrolum distillate, polyethylene, caranuba wax, pentaerythrityl hydrogenated rosinate, tall oil glycerides)
If you see the word wax, or oil or fat, then you know you are dealing with hydrophobic molecules (all cell membranes have a long hydrophobic portion). These all are long hydrocarbons and must be dissolved in an oily substance (petroleum distillate) to be able to be in liquid/gel form in order to be applied to the lashes. The only way to dissolve these from the eyes is an oily make-up remover or a harsher solvent that can break the covalent bonds. We follow the rule "like dissolves like".
When looking at the formulation list for the Beauty tubes, I sense a more sophisticated polymerization (forming of long chains of molecules from smaller parts) and plasticizing process occuring there. This doesn't surprise me as I've never had flaking or smudging at all. The point of weak bonding is clearly between the polymerized mascara and the lash, hence when water is added, any bonding breaks at that point and the mascara comes off in a tube or string. I was looking at the list of step one and saw several waxes that melt easily in the presence of warm water. I can see this being able to support hydrophobic, non-polar polymers of the actual mascara, but allowing the interface to be weak enough to not require a solvent to remove, and warm water being sufficient to loosen the formed polymer.
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