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Correct way to create an emulsion
Hi Everyone,
So I am trying to learn as much as I can about emulsions. Please excuse me in advance if I do not use the correct terminology or say something completely idiotic.
I am creating a little lotion that is an oil in water emulsion, with 10% oil and 90% water.
I am using an emulsifier that is added to the oil phase (Montanov68 and Sunflower Lecithin). I have read that both the oil and water phases should be heated to 75°C and then mixed together, which is what I am doing. So here is where I need some advice. Basically I have 2 questions:
1) Does it matter if I add the oil phase to the water phase or add the water phase to the oil phase. The way I see it, the emulsifier will be in the mix and the hydrophilic and hydrophobic molecules should do their thing either way, right?
2) Should I add all the ingredients to the water phase BEFORE adding the oil phase or is it ok to add some ingredients after mixing the two together (mainly due to the fact that some ingredients are heat sensitive).
And finally, do the answers depend on what ingredients are being used?
FYI. I am getting varying degrees of success purely by using exactly the same ingredients (and %) and slightly changing up the way I mix the ingredients. Sometimes it will stay in emulsion for days and sometimes only hours - it looks so easy in the youtube videos
Thanks in advance
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7 Replies
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I would suggest to try putting ingredients in the oil phase. Except solubilizers put those in the water phase.
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1) yes it does matter. There are different types of emulsions such as o/w or w/o. They are very different. In the more common emulsions, the oil is added to the water.
2) Many ingredients are commonly added after your emulsion is made. Like you said, some ingredients are heat sensitive and need to be added at a lower temperature. As long as the formulation is stable and the ingredients are compatible, it will hold together.
3) Yes of course it matters what ingredients are used. But if your lotion only stays together for a few days or hours, then your formula is definitely not stable. -
for O/W, it doesn’t matter which way the phases are added to each other - the laws of thermodynamics do the majority of the work, and any preference for one way over another would be purely practical, dictated by a) the relative ratios of the two phases, b) what kind of equipment you’re using to form the emulsion
what else have you got in the formula?
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Emulsions are kinetically stable systems (it means that they are going to separate given enough time, your aim is to keep it together for long enough time to be totally consumed or to meet the expiry date, whichever comes first). The main parameters to control while making an emulsion are:
- The time and speed of the mixing (the higher the speed the smaller the droplets will be, and the longer the time of mixing the more homogeneous the size of the final droplets, your aim is to have small and homogeneous droplets).
- The choice of surfactants, because some surfactants are incompatible with the oils you are trying to disperse.
- The order of addition of the ingredients, usually the name of the emulsion is indicative of the order of addition, (a water-in-oil indicates that you prepare initially the oil phase and you add the surfactants to it, then you add the water or aqueous phase in small quantities while mixing), for an oil-in-water emulsion it is reverse). The speed of addition also plays a role in the stability of the emulsion, the slower you add the better the final emulsion.
- The use of a thickener can improve the stability of the emulsion, as well as make it more aesthetically pleasing.
All in all, it is a trial-and-error based process in order to obtain the best or sometimes acceptable outcome. just keep in mind that you are finding a compromise between all the parameters and what can be economically viable for you (you cannot mix it for 2 days for example, even if the outcome will be better, and you will never be able to try all the surfactants in the world, and so-on).
As for the thermally fragile ingredients, you can cool down the mixture then add it and mix, just take into account that if the ingredients are oil soluble just increase the mixing speed by at least 10% and reduce the mixing time, in order to force the ingredients into the droplets (the time reduction is to avoid temperature increase, so if you see that the ingredients are not totally dissolved, stop the mixing for a while then repeat the process till it is fully dissolved).
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I would add that sometime to produce O/W eulsion, it is better to add the water to the oil to carry out a phase inversion, and to obtain smaller droplet size and lower polydispersity.
In the case of mechanical stirring, at a certain point, adding more energy does not reduce the droplet size. You have to remember that by mechanical techniques more than 99% of the energy input is lost in form of heat because of viscous dissipation. At the end, less than 1% of the energy is used to emulsify the system.
To obtain small droplet size and low polidispersity the best choice is to select a surfactant system that allows to decrease at the minimum the interfacial tension. -
the technique you are mentioning necessitates the presence of a lammellar phase or at least a sponge phase in the middle of the ternary phase diagram. this limits the use of this technique to a few systems. also this technique requires mechanical stirring. you can refer to Solans et al., she has a lot of articles discussing this technique.
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@ChemicalPyros In the case of Phase inversion with TºC, with clasical cosmetics ethoxylated surfactant with HLB between 12-18, you have good chance to find a ME phase or Lamellar crystalline phase (it may be part of multiphase system) in between 20ºC and 80ºC. In the case of inversion under dilution, studying phase behaviour will also show that many system present ME or Lalpha phase in some regions. C.Solans is one of the reference in this field with Salager and Kunieda. I had the honor and the chance to work with them.
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