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W/O Emulsion tips please
I’ve been trying to keep an emulsion stable yet unsuccessful. I am relatively new to W/O but have been doing O/W for a while. The product I am trying to develop is a thicker creme. The problem I have been getting is the water coalescing during cooldown while stirring at a low speed. My water is around 73% (including little aloe, prop glycol, etc), my oil at 27% including my emulsifier is around 6% with co-emulsifier (cetyl OH) at 14%. Any help/tips would be appreciated, thank you.
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16 Replies
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What is your primary emulsifier? And are you SURE that you want 73% water suspended in 27% oil? Do you believe that this promotes stability? I know that current thought is that 60-80% water (or less than 74%) is stable but I have always found this to be a difficult and advanced problem to crack;
http://www.cosmeticsandtoiletries.com/research/methodsprocesses/4418977.html
Use that to do more research and you may get the problem solved. -
Hi thanks for responding, my primary is ABIL® WE 09. I’m not sure I want 73%, I just want a high viscosity lotion ~30k cps. Should I be high sheer mixing for longer than 5 min before I switch to paddle mixer? This is just a lot different than o/w
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Here is a sample Formulation from the distributor. Usually they have better documentation. I would suggest reaching out to your rep. I think you are on the right track;
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Ive always thought the continuous phase is the one with the most volume. So looking at your formulation suggests its a o/w one? Im interested in being corrected. I haven’t seen formulations or made any w/o with these input percentages. If such a high volume of water can be suspended in oil, the only hypothetical theory I can suggest is to make sure you use a water compatible thickener and that the emulsifiers are a mixture of low HLB values to suspend it?
Interested in hearing what you come up with :
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Looks like you have most of the tips in the following article covered but just in case…. http://knowledge.ulprospector.com/306/pcc-ask-expert-water-oil-emulsion-unstable-can/
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@becsmith that’s a very common misconception; the nature of the emulsion depends entirely on the nature of the emulsifiers, and the relative volumes of the two phases is irrelevant
or, to put it another way: there is no way that the system can in itself ‘determine’ the relative volumes of the two phases
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yeah put together another go at it flipping the oil phase emulsifiers with the primary being the higher percentage at 11% and the co emu at 8%, fell apart around 40C.
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They are some of the most difficult emulsions to achieve. Keep at it.
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creating W/O emulsions is very much a question of technique as well as materials - you want to form your emulsion at as low a temperature as possible (so there’s little variation in emulsifier solubility as it cools, hence, less chance of the water phase separating), but you also want to form it above the drop point of your oil phase, so the two phases are still fluid
you also need a high-shear mixer with a fine screen on the stator head, e.g. 1 mm; the larger the screen, the higher the probability of failure
on the formulation side, you can help improve stability by using hydrogenated castor oil to gel the oil phase, and a polymeric co-emulsifier (e.g. PEG-30 dipolyhydroxystearate; Cithrol DPHS from Croda, Dehymuls LE from BASF)
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@becsmith, think of the two phase names this way: The “continuous” phase, also called the “external” phase, is called continuous because it’s unbroken - there’s at least a continuous film around each of the individual droplets of the “internal” phase. The relative volume of the two phases is not considered at all.
In a O/W (oil in water) emulsion, the continuous/external phase is always the water, and the internal/droplet phase is the oil. In a W/O (water in oil) emulsion, the continuous/external phase is always the oil, and the internal/droplet phase is the water.
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Alright took another stab at it. I’m using cetyl OH so i have to heat this up to around 75°C. My homogenizer right now is a propeller blade that is bent up real extreme. I pumped that up really high poured the water in the oil and continued to aggressively mix till it got down to ~35°C (no force cool). Then I noticed it starting to floccuate a little bit (breakdown) so stopped it and paddle mixed it and it magically went from a matte finish to a nice glossy shine. so weird. anyway got down to ambient temp and in a jar so hopefully i dont get any coalescing, we’ll see. I’m a little scared to put it in stability at 45° or in the centrifuge. Thoughts? Primary - Abil WE 09 ~10% CoEm- cetyl OH ~5% …. water ~70%~ I’m thinking I can raise HOH and lower Primary and still get a large visc without breakdown … Thoughts?
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@chickenskin if you want to create this kind of emulsion consistently and successfully, you really need a proper rotor/stator homogeniser, and a stator head with a fine screen
the screen size is critical; when I first started trying to make W/O emulsions in the lab I had no end of trouble using a 6mm screen, but it became much easier, and my products stayed stable for much longer, after we bought and fitted a head with a 1mm screen
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@Bill_Toge hey thanks for the info! my lab will soon be getting a homogeniser so I am stuck using a “chopper” blade till then.
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Here’s more relevant advice, regarding this Evonik formula: you must always add the water phase (internal) to the oil phase (external) slowly drip-wise for at least the first 65% of your phase addition, and only at very low shear. Also, double the amount of salt in this formula - better yet triple it. They always short the salt ( like some food recipes) in inverse-phase emulsions; and the electrolyte is critical to stability. Finally, do NOT over-homogenize at the end or you’ll lose it and ruin everything you just successfully achieved. Try this and you may find much better results with that formula.
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@chemicalmatt thanks! yeah my salt is around 2.5% right now, are you saying I can bump that up quite a bit? I don’t have a homogenizer yet so I’m relying on a high sheer blade and high rpm. Also at “the end” are you talking about the cool down from the 50° to ambient?
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IF you keep your mixer speed/shear rate low while adding your water phase, you shouldn’t need to homogenize much; and I did mean after both phases are combined and your batch is at ambient temperature by “at the end”. That’s enough NaCl by the way.
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