Sunday, April 18, 2010

Surfactants: Betaines

If you read anything about cocamidopropyl betaine, it is usually listed as an amphoteric, meaning it has a positive functional group - the quaternized nitrogen - and a negative functional group - a carboxylate, phosphate, or a sulfate functional group able to carry a negative charge in neutral or alkaline conditions. Believe it or not, there is some dispute about this with some considering it a cationic surfactant. I'm going with the perspective that it is amphoteric, meaning it has a different charge depending upon pH.

Cocamidopropyl betaine (CAPB) may behave as a zwitterion, which is a "chemical compound that carries a total net charge of 0 and is thus electrically neutral, but carries formal charges on different atoms." It has different behaviours depending on the pH. In alkaline solution (over pH 8) it behaves as an anionic surfactant with good foaming and detergency properties. In acidic solution (under pH 6), it behaves as a cationic surfactant that is substantive to our hair and skin that can increase mildness.

CAPB is never used alone in a formulation; you'll always use it as a secondary surfactant. It offers great foam stabilizing and a reduction in the irritant level of the anionic surfactants. It offers a great flash foam and some humectant properties. Because it behaves as a cationic in our products - because our pH should be below 7 - we find an increase in moisturization of our hair or skin and some anti-static properties. CAPB is a great thickener for alkyl sulfates (like SLS) or alkyl ether sulfates (like SLeS and ALeS).

I generally use Amphosol CG as my cocamidopropyl betaine choice, which is about 30% active CAPB. It has a pH of 5 to 7, and at 10% it has a minimal effect on skin and eye irritation (so you need to use about 35% before you reach this amount).

I use CAPB in every single surfactant creation I make because of all the lovely qualities listed above. In shampoos, it behaves as a humectant and a light conditioner. In body washes, it behaves as a humectant and offers some moisturizing to my skin. In bubble baths, it offers good flash foam and stabilization to the bubbles. If you are planning to make any of these types of products, stock up on CAPB!

In very mild or baby type cleansers, CAPB might be used as the primary surfactant with something like decyl glucoside (non-ionic) for a very very mild cleanser without a lot of foaming, a nice feeling of moisturizing, and some conditioning. If you have ridiculously dry skin, consider making a cleansing product using CAPB and decyl glucoside!

CAPB is suitable for all skin types as it is a mild cleanser that makes the other surfactants even more mild. It offers hygroscopic features - which benefits every skin type - and moisturizing through substantivity. In short, as a secondary surfactant, it's fantastic for everyone!

Shampoo bars (without CAPB, but I'd suggest using 10% in place of one or other or both of the surfactants)

Join me tomorrow for fun with non-ionic surfactants!

20 comments:

Anonymous said...

Isn't it actually called cocomiDOpropyl betaine?

Susan Barclay-Nichols said...

Yep, can't really explain why I've written it this way other than my brain hurts from 8 months of headache-y fun!

Susan Barclay-Nichols said...

And I've spelled it wrong again! It's cocamidopropyl betaine! EEK! I usually just write coco betaine, so apparently this made my brain completely stupid!

p said...

I was wondering, are the gentlest surfactants like cocamidopropyl betaine and decyl glucoside able to wash away silicones?

Susan Barclay-Nichols said...

If you aren't using tons and tons of it, yes. (When I say tons, I mean using a conditioner, leave in, anti-frizz, and heat protecting spray - especially the last one! - every single day.) If you're using that much, I'd include 2% cetrimonium chloride in your conditioner, which is a great silicone remover.

Even the most gentle surfactants are effective at removing silicones and other things that can film form. This is one of the reasons we don't see much build up on our hair from conditioners any more - gentle and mild isn't equal to poor cleansing!

Nedeia said...

I would really love a post on Babassuamidopropyl betaine :-)

Soapinatrix said...

I'm trying to hunt out information on if Cocamidapropyl Betaine contains or is made from any form of Water? I've been playing with my Bath Bombs to create some bubbles for my kids, and I noticed last night when I added the Coco Bentaine, the mixture started to marshmallow on me. Not a lot, and I was able to salvage 90% of it... but still wanting to know for my own knowledge.

Any insight / help with this?

Susan Barclay-Nichols said...

Hi Soapinatrix! Sorry for the delay in responding, but I missed this comment. Yes, most cocamidopropyl betaine will have at least 50% water, and mine is about 70% water. But on top of it, the actual surfactant is not going to play well with your bath bombs. I suggest using something like SLSa to create foam in your bath bombs!

Anonymous said...
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Michelle D said...

I'm looking for a betaine (that I can afford) to pair with SLSa for my bubble bars. Would you think coco betaine would work in combination with SLSa as a foam booster? I'm trying to counteract the drying tendency of the SLSa a bit.

Anonymous said...

Could you use arrow root powder as a thickening agent in any shampoos?

Susan Barclay-Nichols said...

Hi Anonymous. You can try it, if you want. I'm not sure what will happen, though...

meemz m. said...

Hi! i just came across your blog and let me say i'm in love!! i just have a question about the type of cocamidopropyl, you said it's amphoteric. but in the post about disodium cocoamphodiacetate, you said it works with any combination of anionic or non-ionic surfactants, much like cocamidopropyl betaine" so is it ionic or non-ionic? Thanks!

Susan Barclay-Nichols said...

Hi meemz m! Disodium cocoamphodiacetate and cocamidopropyl betaine are both amphoteric. They are anionic or cationic depending upon the pH of the product in which we find them. In the post on disodium cocoamphodiacetate, the meaning of that sentence is that it works like cocamidopropyl betaine in that it can work with anionic or non-ionic surfactants.

cherise kane said...

Hi Susan ,
Love all the helpful info ive been learning from you!! Ive been trying to figure out how much active matter of surfactant is in my coco betaine it is not listed on their website. Do all coco betaine have the same active matter or do they vary by supplier?

Anna said...

So I have a question about increasing mildness to anionic surfactants.

When shopping for non-ionic surfactants the supplier often write that non-ionic surfactants make the anionic surfactant less irritating.

Does using cocamidopropyl betaine and/or disodium cocoamphodiacetate increase mildness more than to use a non-ionic one such as sucrose cocoate?

Susan Barclay-Nichols said...

Hi Anna. Cocamidopropyl betaine is zwitteronic or amphoteric, not anionic. As for mildness, there really isn't a scale for measuring mildness, so it really is a subjective assessment on your part.

Anna said...

Oh yes, sorry! How I managed to make it in to an anionic surfactant just after reading the blog post is a bit weird. Thanks for the info, I have now ordered some Disodium cocoamphodiacetate so that I can make up my own mind about it´s power of increasing mildness!

Sherri Liska said...

Hi there, my name is Sherri. Thank you for this post!

You've said several times here that coco betaine should be used only in conjunction with another surfactant (if I'm reading correctly!)

I'd like something just ever so slightly more surfactant-y than a typical cleansing lotion. I was thinking of adding this to a light cleansing lotion (which will probably be based on your cleansing lotion recipe!) In that case, if I add only the coco betaine and no other surfactants, will it add any benefits at all (even a very slight amount of cleansing)? If so, what rate of Coco betaine this product do you recommend I start with when trying to formulate?

As always, thank you so much for your help :)
-Sherri

Susan Barclay-Nichols said...

Hi Sherri. It's a secondary surfactant because it's not a very good foamer or lather-er, so you can use it alone in something, but it's not very effective. My suggestion is to try adding it at 5% and see what you think about it. Lotions will suppress lather and foam, so I'd be surprised if you saw any results, but try it out. Then try 10% and see what you think.

Without knowing your exact recipe, it's hard to make suggestions because the emulsifier you use could have a massive impact on the lather, foam, and cleansing power.