I can’t remember who asked it where, but someone asked me: How can we add a positively charged or cationic ingredient like polyquaternium 7 or Honeyquat to a negatively charged or anionic surfactant blend, like a shampoo or body wash?
Great question! Let’s recap a bit of the chemistry for a second. (Check out this new post I put up about electrical charges if you want more information.)
Non-ionic means the ingredient has a neutral electrical charge.
Anionic means the ingredient has a negative electrical charge.
Cationic means the ingredient has a positive electrical charge.
Our hair and skin are negatively charged or anionic. Positively charged or cationic ingredients will adsorb or form a fine layer on your hair or skin in a process called substantivity. This is how hair conditioners work: They form this film to make the cuticle lay flatter, which reduces tangling, increases shine, increases softeness, and reduces static.
Why should we care about the charge? We usually don’t want to mix something anionic with something cationic as it can make things fail. For instance, if you start putting positively charged ingredients into something like a light, cold process lotion using Aristoflex AVC or a nice gel using Sepimax ZEN, you will get a complete fail. If you add cationics into a slightly negatively charged Ritamulse SCG lotion, you could get a fail.
So how can we mix a positively charged or cationic ingredient like polyquaternium 7 or Honeyquat with negatively charged or anionic ingredients like a bunch of foamy, lathery, and bubbly surfactants in a body wash, facial cleanser, or shampoo? The short answer is that cationic polymers like polyquaternium 4, 7, 10, or 44, cationic guar gum, Honeyquat, and more were designed to work with surfactants like this! Cationic ingredients like Incroquat BTMS-50, and Varisoft EQ 65 weren’t designed that way, so you can’t add them to surfactant mixes.
I was wrong about stearamidopropyl dimethylamine, as it’s designed to work with anionic surfactant mixes, and I have a formula planned to test that theory! Thanks for pointing this out, Camirra!
If you find I’ve written something wrong or need to correct something, please don’t hesitate to share your thoughts with me! I can’t learn if I don’t know I’m wrong!
Be careful when you’re adding cationic polymers to cleansers as they can precipitate out or come out of the solution. If this is a concern – and honestly, it’s never happened to me, but I know it can – then thicken with something other than salt and keep your pH in the 6.0 to 7.0 range.
I always say I end up going down rabbit holes every time you ask me a question, and this one was no different! I learned more about coacervation, an interesting way these positively charged and negatively charged ingredients can interact. If you’re interested in learning more about the chemistry of this, please comment below and I can put something together that might interest you!
Handbook of Cosmetic Science & Technology, 4th edition, page 564 to 565