Thursday, October 31, 2013

Chemistry Thursday: The difference between solubilizers and emulsifiers redux

In this post on solubilizers, someone asked: I still don't get the difference between a solubilizer and a emulsifier. If I mix propylene glycol (in substitution for the surfactant), cetyl alcohol or stearic acid in water, will I be getting a lotion? 

The quick answer is no because there's nothing in your question that is an emulsifier. The longer answer is still no, but there's an explanation.

Let's start with the basics. What is the difference between a solubilizer and an emulsifier? For our purposes, we'll categorize our ingredients as solubilizers and emulsifiers. Solubilizers are generally used to incorporate oil based ingredients into a water based products. Ingredients like polysorbate 20, polysorbate 80, Caprol Micro Express, Cromollient SCE, and caprylyl/capryl glucoside would be considered solubilizers. Ingredients like BTMS-50, Polawax, e-wax, Ritamulse SCG, Sucragel AOF, and HLB based emulsifiers are emulsifiers. And emulsifiers actually combine the water and oil together to create an oil in water or water in oil lotion to create an emulsion.

The big difference is this...Solubilizers allow you to create a water based solution by making something that wouldn't normally dissolve in water - like an oil - dissolve into water and create a mixture. If you mixed your oil with something that allowed that oil to dissolve better - like our solubilizers - you would have a toner with some oil based stuff in it that may or may not be clear but would have oil suspended in it, instead of floating on the top of the water.

Emulsifiers allow you to create a product that is water-in-oil or oil-in-water where it's a whole different product entirely. Adding oil and water together isn't something where you have a toner with globs of oil in it, but a product called a lotion. Solubilizers mix in a small amount of oil, whereas emulsifiers can mix in a lot of oil.

When you want to make a lotion, you need what's called an all-in-one emulsifier or you need to create one using the HLB system (more on this in a moment...)

With regards to your question, without a recipe it's hard for me to figure out what you're doing, but I'll try my best. Propylene glycol isn't a surfactant, so I'm not sure of a situation where you'd be using it in the place of a surfactant - and I'm guessing you mean a foaming and lathery one - will end up being a good substitution.

What's a surfactant? It's something that has a hydrophilic or water loving head and a lipophilic or fat loving tail. The hydrophilic head clings onto watery stuff - say the water phase of our lotion - and the lipophilic tail creates a ball around the oily stuff - the oil phase of our lotion. Our emulsifiers are surfactants. I know we generally only think of things that are lathery and foamy as surfactants, but things that bring oil and water together are surfactants.

Stearic acid is an emollient that has an HLB value, which means it needs to be considered as an oil when we're making a lotion. It isn't an emulsifier and can't be combined with anything to become an emulsifier. It's no more emulsifying than coconut oil or olive oil, which is to say it's a full blown oil with no emulsifying properties. Cetyl alcohol isn't an emulsifier either. It's an emollient that has an HLB value, which is to say it's treated like any other oil. (Both of these can help thicken and stabilize an emulsion, but they aren't emulsifiers or solubilizers in any way.)

So to mix propylene glycol - not a surfactant - with stearic acid or cetyl alcohol - neither of these are surfactants nor emulsifiers - you will end up with the water soluble stuff and oil soluble stuff just sitting there as individual things, not a mixed lotion or other product. If we were to add an emulsifier - let's say Ritamulse SCG - we would be able to bring these two things together!

We can also create our own emulsifiers, which is where I think things can get a bit confusing because things that aren't emulsifiers on their own - say, something like glycol distearate or ceteareth-20 - can be combined with something else to create an emulsifier!

What's an HLB value? There's a system called the hydrophilic-lipophilic balance system that helps us figure out the value of the oil phase of a lotion so we can figure out what emulsifier would work best with it. We don't need to do this with our all-in-one emulsifiers - like Polawax, Ritamulse, Incroquat BTMS-50, e-wax, and so on - because they've done all that work for us. But if you wanted to create your own emulsifier, this is what you'd use. When something has an HLB required value, that means it's part of the oil phase and not an emulsifier. Some things can be combined with other things to create emulsifiers, ingredients that aren't emulsifiers on their own, and those things can be found in the HLB table as potential emulsifiers. You'd combine one low HLB emulsifier with one high HLB emulsifier to create something awesome. For instance, you could combine glycol distearate with polysorbate 80 to create an emulsifier, but glycol distearate on its own isn't an emulsifier, nor is polysorbate 80.

So let's say you wanted to incorporate an oil soluble thing into a water based product. I like my toner, but I want some rice bran oil in there. I'd choose a suitable solubilizer - polysorbate 80 is a good choice - and I'd mix it with the oil based thing, then add it to the product. You'd still have a toner, but now it's a toner with oil dissolved into it.

If I wanted to make this product into a lotion, I'd use an emulsifier to incorporate a larger amount of oil into the water based product and end up with a completely different product, a lotion instead of a toner with rice bran oil dissolved in it.

Now here's a question - why are lotions white when the initial ingredients are generally clear? That's a question for another Chemistry Thursday!


Anonymous said...

thanks you for ur answer susan, i was trying to understand the chemical reaction behind the mix instead the importance of the recipe, thats what i found too, that the diference is the quantity of oil that u wanna add, i love the science behind all that n simplifying like i did (just putting oil, water n a "substitute" for the surfactant) helps me understant the importance of one by one the ingredients, thank you again :)

DU KOKO said...

Thank you Susan. I can now grab the concept. Many Sites listed these ingredients as Emulsifiers! Thanks a lot.

suelorrimer said...

Hi Susan
This is a great site - really useful. I am trying to make a natural emulsifier that also thickens. Cetyl alcohol is no good for my skin. I was thinking of using sucragel and xanthan gum. Also, I noticed on miessence site that they have used soy letchin, xanthan gum and another gum (but no emulsifier, so I am assuming these are their emulsifiers). Looking at soy letchin, there are many sites where you can buy it in health food shops - is this the same type used for cosmetics?
Thanks very much. Sue

Susan Barclay-Nichols said...

Hi Sue. I've answered your question in today's Weekend Wonderings. The short answer is that it could be the same lecithin, there's no way to know, and gums aren't emulsifiers!

Keisha said...

I'm late on this post, but wanted to ask…You mention that stearic acid can't be combined with anything to make an emulsifier. Looking at's-Argan-Body-Conditioner/03590,en_US,pd.html it appears that Lush uses triethanolamine and stearic acid as an emulsifier. How do they make this happen?

Susan Barclay-Nichols said...

Hi Keisha! You're completely right, combining stearic acid and TEA creates a soap based emulsifier. I'll write up more about this shortly as it's really interesting. I confess to being more elementary than I should have been in writing that stearic acid isn't an emulsifier, but for 99.5% of the people reading this, it really isn't as they want to use it without TEA. My bad...

Lexi said...

Apologies in advance for the long post, hope my explanations are clear.

I understand the difference between emulsifiers and solubilizers, how to calculate the required HLB and blend 2 emulsifiers to satisfy said rHLB.

In reading the ingredients listings of some lotions I noticed that some of them contain 3 or even 4 ingredients that are categorized as emulsifiers. I assume that in some instances ingredient might actually be serving as a solubilizer but how does that work?

Let's say we have glyceryl stearate (HLB3.8), ceteareth-20 (HLB 15.2) and polysorbate-20 (HLB 16.7).

If I assume the polysorbate-20 is a solubilizer for the essential oils, how would that work? Since it is water soluble (like glycerin) do they just put it in the water phase and disregard the HLB?

Is it as simple as putting the emulsifier into the water-phase of the lotion to get it to act as a solubilizer? Or do we assume that this is a 3/4 component emulsion blend? If the latter how would those calculations work.

Thanks in advance.


Susan Barclay-Nichols said...

If we look at the three you're using as example, I would think the glyceryl stearate and the ceteareth-20 are the emulsifiers and the polysorbate 20 is the solubilizer for the fragrance/essential oil (as you rightly state). The way I would do this is this... I would work out the HLB using the ceteareth-20 and the glyceryl stearate as the emulsifiers that go into the heated oil phase. I would mix the fragrance oil with the polysorbate 20 - you need to mix the two together before adding - and add it to the cool down phase of the product. You don't really need to consider the HLB of the polysorbate as it isn't working as an emulsifier for the whole product but just for the fragrance/essential oil. I wouldn't put it into the heated water phase as fragrance doesn't handle heat.

Just my thoughts...

Lexi said...

Thanks Susan, that clears things up a lot.

Part of my confusion came from envisioning these three emulsifiers in the oil phase. How would the glyceryl stearate "know" that the ceteareth-20 was the co-emulsifier? Adding the polysorbate 20 in the cool down phase is good for the essential oils and it means that the emulsifiers have already "paired up" to do their job :)

I tried a fragrance free lotion which came out great. I then repeated the procedure but added' 1% lavender oil, after a few weeks I saw "seepage" presumably from the fragrance.

I figured this occurred because I did not consider the HLB of the lavender, prepared again still got seepage. I figured then that the HLB I had was incorrect, so set out to determine it experimentally. Tried a range HLBs based on the emulsifiers used in the fragrance free lotion, all were similarly unstable separating after an hour. Maybe this lavender oil just doesn't like this product?

I am going to repeat but this time I will use the polysorbate to incorporate the lavender into the lotion. Hopefully this should work as the system is much more stable (no separation at 6 hours) than my emulsification systems.


Great explanation. Thank you!