Dear Valerie: Can pickering emulsions realistically work in commercial-scale production? —Picky Peggy

Dear Picky, 

One could say I went through a brief obsession with Pickering emulsions. It coincided with the time I couldn’t get enough of Evonik’s Aerosil fumed silicas. I was using them in everything I could. Once in a while, I still stop and stare at the oversized, teetering jars perched on top of my raw material cabinet and wish I did even more with them in my prior years. My favorite was always R 812 S. Most used? 200.

My favorite thing to do with fumed silicas is to make Pickering emulsions. You may note I’m capitalizing the “P” in Pickering. This emulsion is eponymous for Percival Spencer Umfreville Pickering, who is credited with describing the stabilization of emulsions by solid particles in 1907. Pickering’s name is almost as magnificently excessive as Philippus Aureolus Theophrastus Bombastus von Hohenheim, the father of toxicology and a name I was required to memorize during my initiation into the Alpha Chi Sigma chemistry fraternity during my collegiate years.

The premise behind a Pickering emulsion is that when physical particles are combined with oil and water (in an oil-in-water emulsion, for example), the physical particles orient themselves onto the oil-water interface. This essentially creates a physical barricade around the oil droplet, which prevents the oil droplets from destabilizing and coalescing with other oil droplets. As you can imagine, this isn’t spontaneous.

Most fumed silicas don’t wet very easily so a decent amount of shear stress is required to disperse your water, oil, and Pickering emulsifier. This means high speed and an appropriate batch size that allows the silica to be broken up and properly dispersed. You might have noticed this is quite easy to do in the lab, given the smaller batch size and dispersion impellers (or blenders) at your fingertips. Scale up? Not as easy given—in my experience—most facilities lack appropriate dispersion equipment, and the tanks are too large for this process. I recall we had to overcome the large learning curve to get the process right, make it replicable and ensure the formulation was scalable through various batch sizes. We ended up not going to market.

There are plant-based Pickering emulsifiers, such as PickMulse by Lucas Meyer. The material is nice (less grabby than fumed silica and can make fun textures) but I was not as effusive as other chemists about its launch. Perhaps I know the grim reality of trying to scale up Pickering emulsions, to which my knowledgeable sales representative acknowledged can be a challenge. However, there is one aspect of PickMulse that has me excited because I believe almost any facility can work with it in this way: it can encapsulate sensitive actives and become an ingredient in your formulation.

If you are serious about using materials that can form Pickering emulsions, my recommendation is to start figuring out scale up before you even finish your formulation work. Show your production processing team how to make it in the lab and see what their thoughts are for a production process. Make sure everyone is aligned on batch sizes as the process is quite sensitive and there is a cap on how large you can go and how much you can store, particularly of dry water. Engage the raw material suppliers in your scale up conversations. It is in their best interest to make your scale up work and the Evonik Aerosil and Lucas Meyer teams are quite knowledgeable in this area. Lastly, connect with purchasing. All fumed silicas are a little different in chemistry and they shouldn’t be swapped.

Valerie George

askvalerie@icloud.com

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