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Creating a low visc stable colloidal dispersion of zinc oxide in a oil-in-water emulsion
Hi, first of all happy to be here, this is my first post and I’m looking for some advice and hopefully to share my finding on creating colloidal low viscosity serums, perhaps analogous to liquid spray on sun screens
GoalCreate a stable oil in water emulsion where the zinc oxide remains in colloidal form (not settling on the bottom), thin enough to be applied with a dropper. No “shake before use” required.Example simplified recipe5% Zinc oxide (does micro ionized version work better?)5% Vitamin E acetate1% Essential oilRest water.So what emulsification and thickener system could work to achieve this? Perhaps some combination of Schlerotic Gum and Cetyl + Ceteareth-20? Could polyacrylamide work? -
24 Replies
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I think Synthalen w400 and Stabylen 30 of 3V can be helpful.
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I don’t have an answer to the question but 5% vitmain E acetate? What is it supposed to do in the formula?
Carbomer would be a good suspending / thickening system. -
Sclerotium Gum at 2% is suppose to stabilize up to 20% oil load. So with your formula being 11% oil solubles and 89% water, Schlerotium Gum should work.
Here is a link to a supplier from Texas:
http://ingredientstodiefor.com/item/UltraPureGel/1264?category=36
Carbomer, as Perry suggests, is excellent at stabilizing almost anything. There is a product called Pemulen TR-2 -Acrylates/C10-30 alkyl acrylate crosspolymer , which is suitable in stabilizing up to 30% oil load and can be used for sprayable applicaitons - low viscosity formulas. TR-2 is effective at a ph range between 4 - 11. The Personal Formulator, out of the mid-west, distributes it and does not have a minimum order amount.
Here is the link to their website section regarding TR-2:
http://www.personalformulator.com/wvss/product_info.php?cPath=28&products_id=1014
I think Cetyl Alcohol thickener would be unnecessary in terms of wanting only a sprayable consistency.
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Shahbaz: Got any experience with those? Why do you think they would work?
Perry: Thanks for the carbomer req, Vitamin E acetate is more an example of an oil, not sure I’m going to use it, not convinced by the science, but a lot of people like it.Mike: I actually ordered sclerotium gum a few days ago, looks promising. I will def test carbomer and I’ll look into Pemulen. Regarding Cetyl, Cetearyl and their likes, would they not be required to create a robust emulsification if using say 10% oils? Also I’d be concerned about zinc aggregating and the bottom, so wondering what system will give me robust emulsification, stable colloidal dispersion of zinc, and thin enough consistency to be applied by dropper.Thanks a bunch for the feedback, hope to have some data to share next week. -
@Zlink, you can use also 1-2% of Ecogel or Lecigel for stabilization and emulsification.
But in my opinion, you might still need some better high polarity solubilizing oils to keep the ZnO suspended. -
Do you have any specific solubilizing oils in mind or could you point me in the direction of some relevant reading? Not something I’m familiar with. And thank, “stable suspension” was the term I was looking for
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Solvents like Capryl/Caprylic triglyceride, Alkyl Benzoate etc are non- greasy and used often to create stable dispersions…hope this helps in your formulation
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To have a stable colloidal product you’ll need to have the zinc oxide particles at colloid-forming sizes, otherwise gravity works.
Are you going to use a pre-made dispersion, or a colloid mill? -
Grant Industries, out of NJ, with partners worlwide, distributes micronized zinc and micronized titanium dioxide dispersions that might interest you.
http://www.grantinc.com/cosmetics/uv/uv_cut_zno-61.php
They have a product called UV Cut ZnO-61, which is 60% micronized zinc oxide. If you wanted 5% actual zinc in your product, you could use 8.3% of this UV Cut ZnO-61 to get the equivalent.
The INCI of their product is: Zinc Oxide (and) Cyclopentasiloxane (and) PEG-10 Dimethicone.
Cyclopentasiloxane is volatile silicone and will evaporate quickly after it is applied on the skin. It will help with the viscosity, keeping the formula sprayable and easy to rub across the skin.
PEG-10 Dimethicone is a silicone derived surfactant that will help emulsify your formula. It will also provide moisturizing benefits because of the glycerol component. Thirdly, it will increase the SPF of your product.
Dimethicone will be good for your SPF rating as well, and if you wish, you can add Phenyl Trimethicone to increase the SPF rating even more.
Shoot for an SPF rating of 30. That is considered the ideal rating for sunscreen products. By using the Silicones, you can keep the low viscosity you need, but attain the SPF you want.
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In order to have a colloidal dispersion, and not just a suspension, you will need to have all particles below 1 micron in size. The Grant dispersion will work for this.
However, in addition to having the zinc oxide stable within the dispersion, you are also going to need to make the dispersion stable as the oil phase of a low viscosity emulsion. This is not a trivial/easy to solve problem. If I were given this as a project, I would estimate at least six months of full-time research to get a stable low-viscosity formula.You’re going to need some heavy-duty emulsifiers at significant levels, in my opinion. Sclerotium gum won’t cut it. One of the Pemulens might work, but I don’t think you’ll be happy with the viscosity. Try it, see what happens. -
I think this sunscreen is similar to what you want to:
Maybe you can use this formula as an initial “model”, although seems a bit complicated formula. -
Thanks for your excellent replies, my initial thought was to use micronized zinc oxide with a ~200 nm particle size to potentially help against acne, not for SPF purposes:
Adding it after emulsification during cool down under high shear mixing (~5000 rpm staff blender or equivalent).I basically want to keep particle size as low as possible and avoid sedimentation. I’m not sure whether that is equivalent to a colloidal dispersion?Requested a sample of UV Cut ZNO-61, looks good! Any other pre-solubilized products out there? -
Hi Zink,
If you are using a pre-dispersion of Zinc Oxide, it might be easier to work with. But if you are using a ZnO powder then for sure you need a suspending agent like polyhydroxy stearic acid to keep ZnO suspended in your oil phase. You need a suspending agent because it is a low viscosity emulsion and needs to be sprayed.I like to use Carbomer / Pemulen but both of them are incompatible with ZnO and will result in a cottage cheese like product. The incompatibility is due to the charges.Regarding emulsifiers I would recommend using potassium cetyl phosphate in combination with low HLB emulsifiers like Sorbitan stearate, Glyceryl Stearate, etc..I Hope this helps!!! -
Thanks @cosmochem , good info about the compatibility issue, any particular particle size you need to suspend ZnO with polyhydroxy stearic acid? Suspending agents are a new field to me, would be curious to read more about them.
I was looking at the Mario Badescu buffering lotion btw: Deionized Water, Isopropyl Alcohol, Sodium Sulfate, Zinc Oxide, Hydrolyzed Serum Protein, Hydrolyzed Yeast Protein, Pyridoxine, Niacinamide, Panthenol, Propylene Glycol, Allantoin, Biotin.
I wonder what form of Zinc oxide they are using, there is some visible sedimentation on their product images, a “shake before use” product, also curious about whether their sulfur is colloidal or not. -
BTW, where to get Polyhydroxystearic Acid? Also, if you just make the lotion thick enough, then sedimentation won’t be a problem, correct?
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Preventing sedimentation has much more to do with yield value than with “thickness”
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But I’m sure there’s a correlation?
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I’ve found gellan gum (available from CP Kelco, tradename Kelcogel) works remarkably well as a suspending agent and gives almost no viscosity - it’s been used to suspend the glitter in Aquafresh Ultimate Sparkling mouthwash, and the bits of jelly in Orbitz soda
if you do use it, make sure you’ve got a good preservative - it’s a polysaccharide and it can sustain microbial growth
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Bwahaha, sparkling mouthwash! Good tip.
So I’ve been playing around with Carbomer, doesn’t seem to play too well with solids, I tried it with colloidal sulfur in Acacia gum + zinc oxide, mixing the solids into the water phase, adjusting the pH and adding Carbomer to “freeze” the solids in place quickly, but had to use an obscene amount, 5-10 grams, to create a gel, and this was even with minimal immersion blending (as it shears the polymers). Keep in mind this solution also had 15% isopropyl alcohol.
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If you are using a powder ZnO, your oil (liquids) phase better be twice as much as ZnO% you have. These need to be your carrier oils (like emollients). Ex. 10% carrier oils for 5% ZnO. But it can change from formulation to formulation. This will ensure that there is sufficient carrier for ZnO to suspend.
Innospec sells Polyhydroxystearic acid.You can put it in while adding ZnO to oil phase under fast homomixing to ensure a better suspension of ZnO.Yield value is much more important than Viscosity to control sedimentation of solids. If you want a thick product with ZnO, you can try using different gums individually or in combination. Typical gums that go well with ZnO are Xanthan gum, Dehydroxanthan gum, Sclerotium gum, Hydroxymethyl cellulose, etc..Better to stay away from Carbomer or pemulen, if possible. If not make sure carbomer/pemulen are completely neutralized before they come into contact with ZnO. -
If I recall correctly, Carbomer and Zinc Oxide do not play well together at all.
(Please note: the ability to do an efficient Google search is getting more and more important in the cosmetic industry, especially since many companies have dumped and/or purged their collections of supplier literature.) -
Difference between yield value (yield stress) and viscosity:
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So I neutralized my water based formula w/solids incl zinc, then added about 5% (yes..) carbomer to make a thin gel, when used with a treatment pump bottle the resulting lotion actually has a really nice consistency with no additional thickeners, but using that much carbomer can leave some dried carbomer powder on the skin. So I’m going to try xantham and sclerotium gum next, others recommended are “Bentone Gel, Veegum, Cellulose types”.
I skimmed through all the links/papers, def good data for optimization, some coated zinc types work with carbomer too it seems. The lubrizol yield paper is particularly good imo.
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@ Robert,
Thanks for the post….What are your thoughts on Zinc Oxide with Polyacrylates??
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