Both bottles contain the same liquid - my toner recipe - but I added a ton of extracts to bottle 2. When I made the product and added the extracts at cool down (below 45˚C), it looked great. But when it cooled to room temperature (around 20˚C or 70˚F-ish), I saw this mass of stuff at the bottom of the mister. That's a precipitate! And as I mentioned in part one of this post - why don't oil and water mix? - it's all about the solubility.
There are a few reasons we care about solubility...
- We don't want to use more ingredient than will be soluble in our product and end up with precipitate.
- We want to know with which solvents - oil or water - our ingredients will work and into which phase we should add them.
- We want to know how temperature affects solubility and homogeneity of our products, for instance, with lotions being emulsified well.
- We also like to know why the world works the way it does, and why oil and water won't mix without an emulsifier!
In this data bulletin for Amaze XT, it reports that "AMAZE XT polymer is soluble in water and ethanol (< 30%)." What this means is that the ingredient is water and alcohol soluble.
Or look at this data bulletin for Cosmocil CQ, which notes its solubility as "Soluble in water, ethanol, glycerine and propylene glycol. Insoluble in hydrocarbons, vegetable and animal oils, and aromatic solvents." Again, this ingredient is water soluble.
The suggested usage rate of an ingredient could be based upon the solubility or it could be based on another thing, such as safe as used rates, tested rates of efficacy, or even how badly something might smell in a product. Always stay in the suggested usage range of your ingredient!
You know what I noticed in researching this post? Very few suppliers have suggested usage information and solubility on their pages. They don't mention if the ingredient is heat sensitive or not, so we're left trying to figure out how to use the ingredient. That seems ridiculous to me!
Solubility tends to go up as temperature goes up for liquids and solids. When I mixed in 1 gram or 1% powdered extract into the toner at 45˚C (cool down), it dissolved nicely, but when the mixture reached room temperature, the extract precipitated or solidified out of the mixture. If I heat it up again, it will return to its lovely dissolved state. There isn't a rule for how much more you can incorporate into a product at a higher temperature - those solubilities are figured out experimentally.
As an aside, it tends to go up for gases in lower temperatures. That's why we put pop in the fridge! The solubility of carbon dioxide goes up as the temperature goes down, so cold pop is fizzier than warm pop!
And as a further aside, this is why we wash our hands, clothes, dishes, and stuff in warmer water because it means the solubility of the stuff on the plates, clothes, and hands increases and washing becomes easier!
Allantoin has a solubility of 0.57 g/100 mL (25 °C) or 4.0 g/100 mL (75 °C). This means I can get 4.0 grams of allantoin to dissolve in 100 ml of 75˚C water (a little warmer than our heated water phase), but only 0.57 grams will remain dissolved at room temperature. So 3.43 grams of allantoin will end up at the bottom of the container as a precipitate. And allantoin can be like little shards on your skin!
If you see something listed as mixing in water and having a solubility in water of 1% at 25˚C, you know you should only use maximum 1 gram in 100 grams of product in the water phase. If you see something listed as having a solubility of 10% in oil, you know that you should use maximum 10 grams in 100 grams of product and it should go into the oil phase. How to know if it should go into the heated or cool down phase? Check out this post on that topic, as well as this post on how to know how much to add (that is about solubility and safe usage rates). That depends upon heat sensitivity, not solubility.
What does this mean for adding a bit of this and a bit of that? Will the solubility of one ingredient affect another? Possibly. Again, these things are determined experimentally, so you might have to play around to figure out if using MSM with allantoin will change the solubility of one or the other. It probably won't, but if you include things with a common ion, it can change the solubility big time!
Things that look mixed well at higher temperatures might fall apart at lower temperatures because the solubility of solids and liquids tend to be higher when the temperature is warmer. This is really evident in lotions - something that looked well emulsified at 70˚C or 45˚C has separated by room temperature. It's amazing what heat and mixing can do - it can make water and oil stay emulsified without emulsifiers for a short period of time, but that mixture won't be stable once we get to room temperature!
This is why heating and holding is so vital! If you can get everything to the right temperature and mix it well, the chemical emulsification doesn't have to do as much work because its solubility in water is higher. If we get it right, it means it will stay stable when it cools down when the solubility goes to a lower percentage.
Isn't chemistry awesome? Join me tomorrow for more fun with stuff and things and...I have no idea what I'm going to write about tomorrow, so we'll both be surprised, eh?