But a comment from this post from Anonymous got me thinking yet again! Hi Susan, what I understand from reading the Dr. Z explanation you linked is that the oil phase can be added to the water phase and phase inversion will still occur. Dr. Z described adding the oil phase to the water phase and having an initial w/o emulsion form because of the lack of H-bonding and low HLB of the heated emulsifier. It then said that at the Phase Inversion Temperature the emulsion changes to o/w. It did not mention anything about adding the oil to the water or the water to the oil and any effect of either on phase inversion occurring so I don't understand why you say the water phase must be added to the oil phase.
To get some context, either visit the linked post or read these two documents - Dr Z link and a paper on choosing emulsifiers.
Great question! So I went off to find stuff to show this reader why I wrote what I wrote. But I couldn't find anything! Everything I found was silent on the issue, or stated something like "add phase B (oil phase) to phase A (water phase) after heating". Hmm. I checked my textbooks - no luck. I checked a ton of data sheets from various companies - including the data sheet on Polawax - and found nothing indicating we should be adding the water to the oil.
But I know I read it somewhere or at least heard it from a very reputable source, because it would have to be on good authority to get me to change what is a lot easier - pouring the oil into the water, which means I'm only using two containers - to something more annoying that required further cleaning! I was about to give up for the day, when I thought I'd check the Dish forum for posts that happened around the day I wrote this post because obviously I had seen something interesting there from Liz. I followed the trail and found this from the mighty LabRat...(I really hope it's okay to post this from the forum because I think it's such valuable information!)
What are the adverse effects if any of mixing the water into the oil?
I suppose technically, adding water to the oil could make a better emulsion. When you add the first few drops of your water phase to the oil phase, you are forming a water-in-oil (W/O) emulsion. As you add more water, your emulsion changes from a water-in-oil (W/O) emulsion to an oil-in-water (O/W) emulsion. This is called a phase inversion. Emulsions that go through a phase inversion are supposed to be better emulsions. This has been supported in the technical literature,
Most cosmetic emulsions are O/W emulsions. There is more water than oil in the formula. It's easier to add a small amount of oil to a large amount of water. When large batches are being made, due to the physical configurations of the main mixing vessel and the stirrer, most often, the stirrer does not reach down far enough to stir the oils as the water is being added.
And these are Liz's comments from the thread that started my brain working!
In an O/W emulsion you add the oil phase to the water phase. For a W/O emulsion you add the water phase to the oil phase. That is because the emulsifiers for each type O/W or W/O is designed to make that particular type of emulsion. Phase Inversion as it is called is reversing these phases which can result in a more stable or unstable product. These methods usually use PIT ( Phase Inversion Temperatures) along with certain types of emulsifers that would offer more stability. I have done it with success a few times. Many other times I ended up with messy separated emulsions.
Very true as well as the addition rate (how fast or slow) will influence the phase to volume ratio for "catastrophic" inversion to take place. Non-ionic O/W emulsifiers typically will go through phase inversion as heating occurs anyway and then settle to the most stable morphology. I think this is what people experience with their varied methods here. Lab Rat mentions heating to the same temp kills bugs but it also will allow for phase inversion to take place or not depending again on temperature, surfactants used, which phase is added first, how much and at what rate (how fast etc.) cooling temp and rate, shear etc.. However this is not to say inversion always takes place to produce a more stable emulsion. Many things can influence stability of emulsions, not just phase to volume ratios. The problem with "catastrophic" inversion and why I personally don't do this method more often is you really don't know the precise time of inversion nor the actual physical conditions you end up with. So I follow the more conventional methods for now.
Uncontrolled phase inversion is typically what we do and it is a hit or miss for stability. The plus to a controlled and hopefully in our uncontrolled phase inversion the end result is a finer and more stable emulsion. At least this has been my understanding how it should be. Ideally in making any emulsions you want to use the least amount of time, energy and emulsifier to produce the best possible emulsion.
So the gist of it all is this: Although adding water to the oil phase can result in a more stable emulsion (and is backed up by science), for us as homecrafters, we seem to have just as much of a chance of messing it up as getting it right because we really don't know when that phase inversion might happen. As both Liz and LabRat are suggesting that the homecrafter should be adding the oil phase to the water phase, I am going to go with this suggestion from now on!
We can add the oil phase to the water phase when making a lotion and still get a great lotion.
Thank you to Anonymous for posing these questions! You've really made me think and change my mind on the topic. I will be updating the various posts on water into oil or oil into water over the next few days!
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