Friday, September 25, 2009

A slightly more in depth look at emulsification

In anticipation of a series of posts on the HLB system and lotions, here's a post on emulsification. I know I've covered emulsions in the past, but I wanted to expand it a little bit here.

What exactly is an emulsion? For the purposes of this discussion, I'm going to work with the oil-in-water lotion, in which droplets of oil are suspended in water. This is generally the type of lotion you'll see, where generally the water phase is much larger than the oil phase.

If you want to know more about water in oil emulsions, please click here for a comparison of o/w and w/o.

An oil-in-water emulsion is defined as an internal lipid phase dispersed in the external or continuous aqueous phase which is stabilized by surfactants. The internal phase is lipophilic or oil loving and the external phase is hydrophilic or water loving. Adding a surfactant creates a film at the interface of the two phases (oil and water), which creates an emulsion.

In other words, the oil is dispersed through the water phase and stabilized by our emulsifiers.

You might see the oil phase called the internal phase or the discontinuous phase - I'm going to call it the "oil phase" to make life easier. Similarly, the water phase can be called the external or continuous phase - I'm going to call it the "water phase". I realize this isn't completely accurate if we're considering all lotions, but since I'll be writing mostly about oil in water emulsions, it works for me.

Oil and water normally don't want to mix, as you can see in salad dressing or failed lotions. Emulsifiers decrease the interfacial tension between these two phases that refuse to mix (they are considered immiscible, meaning in any proportion do not form a solution) and allow them to come together in a lotion-y goodness. Emulsifiers also act as stabilizers for this mixture.

There are three aspects of emulsification - chemical, heat, and mechanical. The chemical is the emulsifier, the heat is the heating and holding we do, and the mechanical is the mixing process. As our emulsifications are based on kinetic (or physical) stability, they will fail eventually. It may take minutes, it may take years, but eventually the emulsification will break down. We want that date to be well after we've finished the bottle! I'm going to be focusing mainly on chemical emulsification, but temperature and mechanical emulsification will be making appearances.

Why did I mention surfactants? Surfactants are SURFace ACTive agENTS (surf-act-ents) with a hydrophilic, or water loving, head and a hydrophobic, or water hating, tail. (Sometimes you'll see the hydrophobic tail listed as lipophilic or fat loving.) Surfactants can be foamy, lathery things like detergents or they can be emulsifiers. (And yes, theoretically foamy surfactants are emulsifiers as well, but let's not get into that right now!) For the purposes of these posts, emulsifiers are surfactants with at least 14 carbons on a chain that enable us to emulsify oil and water together.

How do emulsifiers emulsify? The hydrophilic head is in contact with the water phase while the hydrophobic tail is in contact with the oil phase. The hydrophilic tail connects to the oil and the head protudes into the water connecting the two. You can see why this is so unstable.

What can cause separation in an emulsification? If we don't have enough chemical emulsification or the right kind of chemical emulsification (meaning not enough or the wrong emulsifier), if we don't have adequate heat energy (heating both phases to the same temperature), and if we don't have enough mechanical energy (using a mixer or stick blender) we're going to see separation.

When you think of how much can go wrong, it's almost a miracle a lotion works sometimes!

So what can we do? We can use emulsification systems like Polawax, e-wax, or BTMS to help us create our emulsions or we can create our own emulsification systems using the HLB (hydrophilic-lipophilic balance) system.

We have a topic for tomorrow - the HLB system!


Lomond Soap said...

Hoorah! Looking forward to info on the HLB system, when I've read bits on other sites it's gone right over my head :( Please be gentle with us.
Thanks Susan :D

Anne-Marie said...

Brilliant post - so thorough and such a nice way of describing all the terms. I am excited about your HLB explanations. I've heard a lot of convoluted ways to describe the HLB system and struggle with plain, common sense language for it.

natalia said...

Hi susan! Happy thanksgiving! Have you ever tried using gds and ceteareth 20 as emulsifiers for hair conditioner? Its quite difficult to find polawax and btms in my country. Would you have any other recommendations? Thanks!

Susan Barclay-Nichols said...

Hi Natalia. Neither of these are appropriate for conditioners. A conditioner has to be cationic, which means it is positively charged, and most of the emulsifiers you see are non-ionic, or carry a neutral charge. An emulsifier like BTMS is positively charged and it will adsorb to your hair strand, which is negatively charged.

If you use something like polawax or glycol distearate as the main emulsifier in a conditioner, it won't adsorb to your hair and will just rinse off, which means you might as well not use anything at all because you aren't conditioning your hair.

Click here for more information on adsorption and substantivity!

Olympia Tsimplostefanaki said...

Dear Susan I admire your work!In my search for new things to learn about cosmetic formulation I came across the term multiple lotions (water in oil in water -wow- and owo). The book said we first create a w/o primary emulsion, next water ans hydrophilic emulsifier are combined with the primary emulsion at room temperature. It is supposed to have less greasy feel and ellegant appearance. Have you ever heard about this? Is it worth to give it a try?

Rachel said...

Hello, thanks for such an informative site. My question is regarding the molecular change from oil to lotion after emulsification. Do oils exhibit the same beneficial properties post emulsification? Thanks again.

Anonymous said...

Hello. Is it possibel to use soy lecithin as an emulsifier in lotions? Thank you

Susan Barclay-Nichols said...

Someone who called themselves anonymous asked...Is it possible to use soy lecithin as an emulsifier in lotions?
I deleted the post as I don't allow anonymous posts, but I thought it was a good question.
Yes, you can, but you have to combine it with another HLB value emulsifier in the proper amounts to make it work. You have to know the HLB value of the lecithin as well. In short, it's a long process and it's not one for beginners.

Clo said...

Hello Susan,

I love your blog and your e-books! I was hoping you might be able to suggest a good emulsifier that would emulsify 20% Olive Oil in 80% Ethanol (95% pure) without thickening it. Any suggestions?

Thank you and happy holidays!

sawnjuh said...

Hello! I am struggling with a fragrance spray. the first 3 attempts, perfectly clear. The second 2 - super cloudy and had to add just waaaaaay too much poly20 to get it clear. I don't like a soupy spray. I have read on your blog that heat helps, so my plan in the future is to heat water then mix. I have also been using alcohol in the recipe. For the sake of the best possible experiments, I am wondering: does alcohol help with the solubilizing of essential oils+poly20 in water?

My basic recipe looked like this:
1.5 part alcohol
1 part h20
1oz essential oil
1.5 oz poly 20

Again, the first 3 attempts were perfectly clear! I used the same oils for a second go and cloudy muck ensued. :-( I am mostly just wondering if I should nix the alcohol. Thank you!!

Susan Barclay-Nichols said...

Hi sawnjuh. I recommend doing a search for solubilizers or clicking on that label because I have written quite a lot of about working with these ingredients. Do a search for polysorbates for more about these specific solubilizers.

glamaris said...

Hi Susan, I have an emulsifier question. I'm thinking about trying to recreate a discontinued conditioner that I really liked, and I'm having trouble identifying how it is emulsified from the ingredients (listed below)! The only thing I see in there that could be an emulsifier on its own is stearamidopropyl dimethylamine (trade name CleanLocks); it's available from Ingredients to Die For, but they list it as a "co-emulsifier", so I figured there should be something else in there too. I'm not an HLB expert, but I don't see any other ingredients that combine to make an emulsifier. Maybe you can offer some insight on this. Thanks a lot!

Water; Stearyl Alcohol; Cyclopentasiloxane; Cetyl Alcohol; Stearamidopropyl Dimethylamine; Dimethicone; Lavandula Angustifolia (Lavender) Flower/Leaf Stem Extract; Jade Plant (Crassula Argentea) Extract; Fragrance; Glutamic Acid; Benzyl Alcohol; EDTA; Methylchloroisothiazolinone; Methylisothiazolinone; Citric Acid; Ext Violet 2

Kostas Tsimenidis said...

Hi susan, I have all of your e-books and I have learned so much, but I am facing a serious problem in lotion making. This is the air bubbles that either are external or from internal formation. I change 3-4 mixers but I cant get away with this. Does the emulsifier percentage effect on the formation of air bubbles? I first dissolve xanthan gum in glycerin and then I add water.

d.i.water 71%
Humectants 11%
Xantan gum 0.2%

oils 4%
esters 4%
Glyceryl stearate-PEG.100 5%
Stearic acid 3%

Opthiphen 1%

Susan Barclay-Nichols said...

Hi Kostas! What's your method? Did you heat and hold? When did you bottle your products?

Kostas Tsimenidis said...

yes i heat and hold at 70-75 celcius for 20 min. I keep the lotion in pyrex jar for 24 to check if there are bubbles.

Kostas Tsimenidis said...

so I heat and hold at 70 for 20 min. Then I add water to oil phase and mix with a mixer that lotion crafter promotes. Then I mix periodically until cooling. In cool down phase I add only the preservative because it is a testing batch. I have been using also emulsifing wax and facing the same problem

Thank you for your time

Susan Barclay-Nichols said...

Holy moly, you have a lot of glycerin in that. Glycerin promotes bubbles, so that could be the issue. When you check it at 24 hours, and it has bubbles, what do you do? My suggestion is to mix it again to get rid of them. I regularly get bubbles in my lotions, but a quick mix with a spoon or even a mixer is enough to make them go down.

Try this. If it doesn't work, can you write to me with pictures of your product and the bubbles and maybe I can figure out something else?

Kostas Tsimenidis said...

I didnt know that glycerin promotes bubbles!!!! So I will dissolve xantan in Propylene glycol or may I put it in the oil phase?? After 24h I mix it with spatula but doesnt make a change.
Does xanthan gum also promotes bubbles? Also I would like your opinion about carbomer 940 and how to use it. I use to make stock solution of 1% carbomer 940 in order to avoid long term hyrdration stage. Am I use it in right way?

glamaris said...

Okay, now, after 6 failed - and one successful - attempts, I think I am prepared to answer my own question, above.

Stearamidopropyl dimethylamine does work fine as a stand-alone emulsifier. The most important thing I have found working with this product is using adequate acid to neutralize it... it is quite an alkaline substance as it comes from the supplier, and must be neutralized into a salt using an acid (I use citric acid) both before it can act as an emulsifier, and before it will act as a substantive conditioner (the lower the pH, the more attracted it will be to hair). The ratio given by my supplier of 1 part citric acid to 5.88 parts SD was not adequate to form a stable and thick emulsion in my recipe. I ended using closer to 1 part citric acid to 3 parts SD. The pH of the finished conditioner was about 5.5.

Stearamidopropyl dimethylamine is apparently often used for no build-up conditioners, and is supposed to be able to remove silicones and quaternary compounds. My conditioner doesn't feel like much when applied to the hair (unlike the lubricating feel of BTMS), but thanks to the inclusion of dimethicone and cyclomethicone, it feels amazingly smooth and slick when rinsing. I like it! :)