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Improve W/O emulsion stability without increasing viscosity
Hi all!
Lately I’ve been finding myself developing a lot o W/O emulsions, specially sunscreens and color cosmetics (basically foundations). However, I’m struggling with their stability. Sometimes increasing the viscosity helps, but with this specific formula I wouldn’t like to do so, as the benchmark is really fluid and this is one of the differential that we want to highlight in this formula. Please see formula below:
Oil phase:
- ABIL EM 90 (Cetyl PEG/PPG-10/1 Dimethicone) - 2.5%
- BENTONE GEL ISD V (Isododecane (and) Disteardimonium Hectorite (and) Propylene Carbonate) - 4.5%
- Dimethicone 1.5CS - 10%
- Dimethicone 350CS - 2%
- Cetiol ABV (C12-15 Alkyl Benzoate) - 5%
- Cetiol Sensoft (Propylheptyl Caprylate) - 10%
- Nomcort HK-G (Glyceryl Behenate (and) Glyceryl Behenate/Eicosadioate) - 0.7%
- Surface treated Titanium Dioxide powder (Sun filter grade) - 14%
- Neo Heliopan 354 (Diethylamino Hydroxybenzoyl Hexyl Benzoate) - 6%
- Neo Heliopan 303 (Octocrylene) - 7%
- Sunscreen booster (Argania Spinosa Kernel Oil (and) Tocopheryl Acetate (and) Bisabolol) - 4%
- Plandool LG-2 (Phytosteryl/Behenyl/Octyldodecyl Lauroyl Glutamate) - 2%
- Film former resin dispersed in volatile emolient - 2%
- Surface treated iron oxides - 8%
Water Phase:
- Propanediol - 2%
- Sodium Chloride - 1%
- Polysorbate 80 - 1%
Phase 3:
- Blend of microspheres (such as silica, boron nitride and cellulose) - 8%
Phase 4:
- Symdiol 68 (1,2-Hexanediol (and) Caprylyl Glycol) - 1%
It is a fluid sunscreen/foundation with estimated SPF 50 and medium coverage. The thing is, this version separeted after 15 days ate 45ºC. The previous version (more viscous) is stable after one month, but as I said, our main goal is to keep the low viscosity.
Does anyone know what I can do to improve this formula stability without changing the viscosity? Is there anything I can add that will help with the stability but won’t increase the viscosity? I’ll definetely run some tests with other emulsifiers, but If anyone has some suggestion it would help me a lot!
Thanks so much (:
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1 Reply
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@LabGuy It must be restated here that virtually ALL invert emulsions are entropically unstable. You will generally find thermodynamic instability at 45C sooner or later with these creations, so don’t feel bad when it happens. Having said that, you were wise to include that BENTONE Gel to stabilize the continuous phase. The issue appears mainly in your water phase. Add much more NaCl, 3.0% will do, and reduce that Tween 80 in half. This may help but your chief problem here is the low level of water in there! Doing the math here and excluding the metal insolubles there is ~16% water and ~60% oils. Not good. You will need much more to keep this viable so some of that oil phase has to go. You may try increasing the Abil EM90, as higher the ratio of oil: water inside, the greater level of w/o emulsifier required. Honestly at this rate I would just forego a water phase entirely and go to an anhydrous system serum. Q.s. with esters and get on with your day.
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