-
Water-in-oil loss of viscosity after slow cool-down
Dear all,
I’ve been working on a water in oil formulation but I can’t work out why it has a lotion-like viscosity after it cools down.
Immediately after homogenising if I take a sample and it cools rapidly it is a rich cream. However after I have left it stirring for an hour to cool down it loses viscosity and ends up soupy.The basic formula is as follows:Phase A
4% Polyglyceryl 3- Polyricinoleate
12% Coco-caprylate
12% Caprylic Capric Triglycerides
1% Candelilla wax
1% Cetearyl AlcoholPhase B
4% Glycerin
1% Magnesium Sulphate
65% WaterMethod:
1. Heat both phases to 75-80C
2. Add phase B to Phase A slowly under stirring at 350rpm
3. Homogenise using ika turrax at 5000rpm for 2.5min
4. Stir gently 100rpm for 1 hour until coolWhat’s going wrong here? I hope you can help! Thank you in advance
-
7 Replies
-
hi there
it is often a Problem with W/O emulsions that they are very much problematic with steering especially while cooling there are two points you need to look at if you Homogenize again after it is cool down dose the viscosity go up again?
if yes then properly you have a problem with getting bigger droplets while stieren and viscosity are dependent on droplet size.The second possibility would be to look if you get a Better Viscosity if you stop Steering at a Higher temperature so that the Wax Crystals have time to form bigger and Better Structures in your system that are hard.
Problematic is the filling Process later on you need to be Shure to not add too much energy then
-
In most cases you need to homogenise after the temperature drops below 50C. I also see two potential issues with your formula:
1) you use very high polarity emollients. Even o/w are more stable with lower polarity oils let alone w/o. I suggest you change at least one of them to hydrocarbons.
2) one emulsifier isn’t usually enough.
I assume the preservative is actually included. -
- From what I found out on the internet (I don’t have a scientific explanation why this should be the case, quite the opposite): fatty alcohols are not your best choice in w/o emulsions.- I have to disagree with @ngarayeva001 : Unlike o/w emulsions, polar oils are an advantage in w/o emulsions. However, yours aren’t that polar (except for the fatty alcohol) and you wouldn’t gain anything with a hydrocarbon.- Where I do agree with her: PGPR as sole emulsifier is not enough. Using a combo of it or an entirely different w/o emulsifier system would allow for a slightly higher water phase which goes along with higher viscosity (and hopefully better stability as well).- w/o emulsions such as yours can fairly easily be broken with excessive (in terms of rpm and time) homogenisation/mixing. Once such an emulsion is broken, it can’t be rescued with more homogenisation. PGPR tends to form double (w/o/w) emulsions which are at your water content and lack of gelling agents rather low viscosity and are, as an educated guess, what happens in your case.- Candelilla wax can stabilise an unstable or even emulsifier-free w/o emulsion… however, such an emulsion has to have a solid oil phase and is likely to feel quite waxy, hard, even brittle, and will be highly susceptible to mixing. It will break if mixed/homogenised below the oil phase’s ‘melting’ point. Gentle stirring after cool down might be okay (as you observed, it does not tolerate mixing throughout the cooling phase and rapid cooling without mixing is henceforth highly advised). Basically, such an emulsion is the same principle as an old school cold cream (several threads about cold creams are available here on the forum). -
another point to mention is that the emulsion is formed at a relatively high temperature - W/O emulsions should be formed at as low a temperature as practically possible (oil phase set point plus 5-10 °C), so there’s little variation in emulsifier solubility with temperature, and less risk of destabilisation on cooling2-3% hydrogenated castor oil (castor wax) will give some thermal stability, and further to @Pharma and @ngarayeva001 ‘s points about emulsifiers, I’d recommend adding a polymeric emulsifier, e.g. PEG-30 dipolyhydroxystearate
-
Thank you so much for taking the time to reply. These comments are really helpful and have given me a lot to consider and I can begin to experiment again in consideration of all these points. I will experiment with a secondary emulsifier, rapid cool down without mixing, lower emulsification temperature if possible, and @Pharma I do agree the fatty alcohol seems to be working against this emulsion type.
Would magnesium stearate be helpful as a stabiliser here? And should I consider gelling the water phase?Thanks again everybody!
-
With magnesium stearate you could likely reduce the amount of candelilla wax. Basically, the two do the same; increase viscosity of the outer oil phase which is a good thing.Gelling the inner water phase may not considerably increase stability but will affect haptics during and after application. If you like it, sure, try it out. I can’t see any drawbacks or serious concerns with a gel in oil emulsion (except that the emulsification process can be difficult with a too viscous water phase).
-
Thank you very much
Log in to reply.