Valerie George, Simply Formulas05.01.24
—Emulsions for the Masses
Dear Emulsion:
I’m sure there are sophisticated instruments and formal measures for establishing whether your batch has fully emulsified after combining the water and oil phases; I don’t have them. I’m a simple formulator and I like to do as much as possible with as few resources as possible in the lab. This mentality has served me well, and I have yet to face significant challenges in stability or production with my emulsions.
The first resource I use are my own eyes. I simply look through the glass beaker’s walls and see if the consistency looks good. A well-emulsified batch should be opaque and look like 2% or whole milk (cow’s milk, not fancy almond or oat varieties). If the batch is slightly translucent or opalescent, I would suspect the oil hasn’t incorporated into tight little droplets inside the external phase. If encountering this, I simply increase sheer or give the batch a little buzz with a standard emulsion screen using my trusty 1962 Silverson homogenizer. The batch opacifies instantly.
I also check for particulate floating within the batch. Emulsifiers that have free fatty acid impurities, such as stearic acid, will not incorporate on their own. One must use an alkali such as sodium hydroxide or aminopropanol to saponify the free fatty acids and convert them to their emulsifier form. It’s good practice to review any impurities in your emulsifier blend, before working with it, to understand any potential challenges that may occur.
This holds true if you’re using a stearic acid or palmitic acid as an emulsifier. If your emulsion doesn’t appear to come together, you may not be saponifying enough or using an appropriate alkali. Make sure you have done the correct stoichiometry to ensure you’re using the right quantity of alkali.
I also check the emulsion on a metal spatula. I sort of sweep the emulsion around with the spatula, avoiding the propellers (it’s not fun when you hit them!). After I have sufficiently coated the spatula with the emulsified liquid, I pull the spatula out of the beaker and look for droplets. If you can see droplets with your own naked eyes, you either haven’t mixed long enough or well enough. Or, the polarities of your oil phase are not appropriate for the emulsifier. Or, your oil-to-water ratios are not correct.
If the emulsion appears to be homogenous through cooling the batch down to 35ºC, I place one drop of the emulsified product onto a glass microscope slide using a tiny 1.87ml transfer pipette. (There is nothing specific or special about this size of pipette, other than I accidentally bought 1,000 of them and have discovered no other use. I’ll mail one pack of them to the first person who emails me regarding this article!)
I press a slide cover over the drop, smashing it down as thin as possible using the bulbous end of the pipette. I evaluate the sample under the 10x objective lens of a simple microscope, for a total 100x magnification. If the droplets appear tiny and uniformly distributed, I’m happy. If there are large droplets, or the droplets are migrating across the slide before your very eyes, you either have a significant case of floaters or your emulsion has not formed a tight droplet distribution and could be improved either through processing (start here!) or reformulation.
Tricks of the Trade
Another trick to assess emulsion quality (not necessarily whether your emulsion has fully formed) is one I learned from another colleague. Place a sheet of aluminum foil on your lab bench and place a blob of your emulsion onto it. Pick up the aluminum foil so it is perpendicular to your lab bench. The emulsion should drip down the sheet, leaving a trail behind it. If the emulsion slides as a whole glob, or leaves globs behind as it slides down the sheet of foil, this could be an indication of premature stability failure or an improper oil-to-water ratio. Your emulsion should look as good as the one in the photo on p. 38.
Valerie George
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Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com