Friday, April 23, 2010

Surfactants: Building viscosity - increasing surfactant concentration

We're getting ready to do some formulating, but we need to take a few moments to look at how to thicken our surfactant based creations.

There are three ways to thicken a surfactant based creation - increase the concentration of the surfactants, make the micelles larger, or create a gel. (There's a brief summary about this topic in this post...)

You can increase the surfactant very easily by adding more surfactants and removing the water. But, when you increase the surfactant concentrations above the suggested usage rates, you are asking for irritation, plus you're wasting supplies. 

The other way to increase the surfactant concentration is to use the salt curve.

The salt curve is the concept of adding salt - an electrolyte - to a surfactant mix to make it thicker. It does this in two ways. The first - the electrolyte increases the size of the micelles in the surfactants, so the viscosity increases. The second - the electrolytes compete with the surfactants for water, so as we add more salt, we fool the product into thinking we've increased the concentration of the surfactants, which will increase viscosity.

When we add salt to the mixture, there is a distinct curve (pictured to the left). As we gradually increase the salt, it will thicken nicely and stay that way. But if we add too much salt, we eventually start to thin it out back to the watery state. This is one of the reasons we add it slowly - as you can see, the difference between 3% and 3.5% is huge! This is due to the imbalance of charges between the various ingredients in your creation.

When we see a surfactant can help thicken another - like cocamidopropyl betaine or SMC taurate - this is thanks to the increase of electrolytes in the mix. When we see something like cocamide DEA increase viscosity, we have fooled the system into thinking we've increased the concentration of the surfactants, and it thickens. 

Ideally you'll use between 1% and 3% salt in your creation - remember to add it slowly so you don't end up on the wrong side of that curve! The down side of using salt is that it can make your creations cloudy, so you'll want to bottle those in a non-clear container (like I should have done with this bottle of cocamide DEA thickened bubble bath!) or just accept it!

Join me tomorrow for more fun with thickeners - increasing the micelle size!


Tara said...

My cocamidopropyl betaine is so watery compared to my other surfactants. How can it thicken them?

Anonymous said...

Because you're planning on doing a Hair thing in May, I'd like to add this product for your evaluation:

I hope you don't mind me putting it here for your consideration?

Susan Barclay-Nichols said...

Through the magic of chemistry! Cocamidopropyl betaine is very watery. It thickens by increasing the electroytes in the surfactant mix, which increases the size of the micelles in the surfactant. When we do this, the mixture thickens.

I know it doesn't seem possible given the wateriness of the cocamidopropyl betaine, but think of a micelle as a sponge. If you soak a sponge in water, it soaks up the liquids and gets bigger. If you had 10 sponges in a box and you poured water on them, they'd swell so much they'd start to crowd each other. If you think of the micelle as the sponge and cocamidopropyl betaine as the water, you get a decent enough analogy.

Susan Barclay-Nichols said...

Hi Anonymous. Do you know where I can get some ingredients for this product? And I love suggestions for posts - keep them coming!

Anonymous said...

I'll try to find the ingredients list for you. :)


Anonymous said...

Another, for May hair blog, question I'd love to understand the answer to is:

Mechanical damage, etc defined. For example, how damaging is brushing my hair? How damaging is wind? How damaging is hair color? Blow drying? Heat? Going to the beach? Chlorine from swimming pools? And then what is the best remedy to reduce that kind of damage?

Anonymous said...

Wella Color Touch ingredients?

Anonymous said...

One of my friends gave me this information off of her old box of the Wella Color Touch:

they're recently repackaged CT so i dont know if they changed the ingredients but on my box they are; Water, cetearyl alcohol, ethanolamine, laureth-3 sodium laureth sulfate, Glyceryl stearate SE, toluene-2, 5-diamine sulfate, sodium sulfate, decyltertade-canol, sodium lauryl sulfate, beeswax(cire d'abeille) resorcinol, sodium sulfite, hyrdroxyethyl-3, 4-methylendioxy-aniline hcl, fragrance, m-amminophel, ascorbic acid, editronic, acid, hydrolized keratin, 2-methylresorcinol, hexyl cinnamal

Anonymous said...

I have another May hair question for you. Recently, on the LHC a person proposed that oxides could be used to color your hair. Based on the Himba women in Africa using it in their hair.

Would that be feasible? You'd have to avoid EDTA or it would take it out of your hair. And I'm not sure how you would make it as an application?

It was proposed as possible non damaging hair coloring option.

Anyway, thought I'd run that past you too. :)

Anonymous said...

Yet another May hair question. :)

What is the best way/ingredients to keep your color after you dye your hair?

What shampoo ingredients are strong enough to clean oily hair, but not make scalp itchy? I always need a strong cleanser to cut the scalp oil, but often make my scalp itchy afterward.

After hair dye, is it a good idea to use a mordant like vinegar to close the cuticle?

Anonymous said...

How to choose a hair safe hair spray? I know that if you stick your hair together and then pull it out with a brush you do a lot of mechanical damage to your hair. So is there a simple diy hair spray recipe that would help to hold your hair, but still make it brush-able?

kontakt said...

The salt curve should be dependent om general ionic strenght, I guess, not just the prescence of Na+ and Cl-. Do you know of other stuff that affects it? Exchanging some of the water for propylene glycol? (If you don't know, just tell me to go to the Dish. I'll start posting there after I've done some more reading in the forums.)

Susan Barclay-Nichols said...

Hi kontakt! My understanding is that it is the presence of electrolytes in the solution, so you could use other salts or other ingredients containing electrolytes (for example, aloe vera) to get the same effect. The electrolytes increase the effective size of the micelles, so the viscosity increases, and compete with the surfactants for water.

I'm not sure if you've seen this post - increasing micelle size - but it does go into some detail about using other ingredients to increase the micelle size. Is this the information you seek? If not, let me know!

C.P.3O said...

I am loving this blog. Every time I am researching an ingredient on the web, I invariably end up here in the end. This is a growing online community of home formulators of varying degrees of experience. This is the first time I have posted here, so there is no way I could do so without commenting on how awesome I think it is. I have become a dedicated reader. And I found that Hans in carbonite soap mold on a will be mine.
Got that out of the way.
I was looking around for some info on how dead sea salt would work with the salt curve. At first I wasn't sure if it was the NaCl that made it work, and I know that dead sea salt contains a low-ish amount of NaCl.
But since the thickening can actually can result from the presence of any electrolyte... Now I wonder how much of dead sea salt is made up of electrolytes.
I found a tiny smidgeon of info floating around out there. I was wondering what you might know about it...and its potential interactions.
I bought some to make a salt bar and found out last minute that it is not a good idea to use it for that. But talk about label appeal- so I am looking for a useful way to incorporate it.
Thanks again for the free exchange of information and ideas.

Michelle Squyars said...

I'm wondering if you could use sodium lactate in a similar way; to increase viscosity. Also, how does NaCl change (or does it) the pH of the final product? I have read using NaCl to increase viscosity of shampoo, but would you use this in lotions or conditioners as well? Would you NOT use it in leave-on products? Thanks!

Susan Barclay-Nichols said...

Hi Michelle. No, sodium lactate won't thicken your surfactant based products. And salt doesn't nothing to the pH - it isn't an acid or base. No, you can't thicken a lotion or conditioner with a salt, just the surfactants. If you look at the way salt thickens, it simply wouldn't do those things in an emulsified product. I wouldn't use salt in a leave on product, but I would use sodium lactate in a leave on because of its awesome humectant properties!

Jonica Renee said...

I have chemical sensitivities and I am trying to make a very basic dish soap with SLS and salt. It is not thickening at all. Any suggestions?

30% SLS
3% sodium chloride
Water to 100%

Susan Barclay-Nichols said...

Hi Jonica. You can increase the concentraton of the SLS or add a secondary surfactant like cocamidopropyl betaine to increase viscosity. I have written quite a few posts about this topic, which you can find if you hit "newer post" or "older post" or visit the surfactant section of the blog.

A few thoughts...
Consider including other ingredients that will thicken this product.
Consider you may have used 3.5% salt and it's starting to thin out.
Consider using another thickener, like Crothix.

You can handle straight SLS on your hands? Just curious...

San Pedro Soapworks said...

Hi Susan! Love the blog!! I have been using xanthan as a thickener, but don't like the sometimes slimy results. Can you tell me how exactly the thicken cocamidopropyl betaine with salt? Is it a 20% salt solution, similar to thickening castille soap? I've googled everywhere, and can't seem to find any instructions on this.


Matt said...


It is my understanding that Cocamidopropyl Betaine cannot thickened with salt. Rather, CocoBetaine is used to thicken formulations with anionic surfactants such as the sulfates or sulfonates.

If your only surfactant is CocoBetaine, then you should consider xanthan gum (as you have), other gums, the carbomers (Ultrez 10, Ultrez 20, Acrylates/C10-30 Acrylates Crosspolymer), Crothix (pastilles or liquid) or PEG-150 Distearate to thicken your formula.

Hope that helps.