Betaine Alternatives, Foaming Properties

While searching for betaine alternatives, I came up with sodium cocoamphoacetate and disodium cocoamphodiacetate as possible candidates. Based on my (albeit limited) understanding, betaines are often used in shampoo and body wash for the following benefits:
  1. Improved mildness
  2. Improved foaming
  3. Improved viscosity
As I am still learning about the different properties of surfactants, I decided to do a blender test on all of the ones that I own. I have heard that amphoterics are better at foaming than non-ionics, but less than anionics. This was confirmed in my blender testing. What surprised me, however, was that--at least for sodium cocoamphoacetate and disodium cocoamphodiacetate--this was only true at highly alkaline pH. When I performed blender tests at acidic (<6) and neutral (7) pH, the amphoterics produced less foam than non-ionics. I know that the charge of an amphoteric changes based on pH, but what I didn't know was how that affected foaming characteristics.

Anyway, here are my questions:
  1. Does cocamidopropyl betaine perform any better at the acidic pH that we would normally aim for when formulating shampoo?
  2. Similarly, is there a better alternative to the betaines that serves the same purpose?
  3. Is there some synergy that I'm missing, whereby betaines or amphoterics foam poorly on their own (in acidic conditions), but somehow still manage to boot foaming of other surfactants?
  4. Exactly how do these surfactants thicken? I see that claim for all three in my post, but I'm not sure how it works. Do they adjust the salt curve or is there something else?
Sorry for so many questions; I'm still learning ;)
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Comments

  • thebrain,  I'll be following this with interest!  I had a file that had photos of foam tests on different surfactants but I haven't located it...yet!  Here is a link to a Colonial Chemical file (on the bottom of this page) that compares all of their betaines.  Yes, I know it is from a manufacturer so keep that in mind but they do make comparisons between all their betaine products which I have not often seen from chemical companies!

    http://www.colonialchem.com/fm/search/?query=betaines

    If I find the file with the foam comparison photos I'll post it!

    The best of luck to you!
    David
  • I found it!  Again it is from a chemical company, Stepan but it does show a variety of surfactants foam tests!  For whatever it is worth:

    http://www.stepan.com/Products/General-Literature.aspx

    Click on "personal care" and download "Stepan Sufate Free Cross Reference for Personal Care"

    It shows quite a few pictures of foam testing and you may find it helpful.

    David
  • Thanks David. I've seen those brochures; unfortunately, it doesn't really answer my (many) questions about betaines and their alternatives. I guess I'll just have to do more testing and try to figure it out on my own.

    BTW, I checked out your website. It looks nice! I'd buy your soap ;)
  • chemicalmattchemicalmatt Member, Professional Chemist
    brain, there's too much ground to cover here in your inquiry, so I'll suggest more research into surfactant chemistry. Check out the Allured index for some cues.  Having said that , the amphoterics you mention are best used as hydrotropes, not thickeners or "mildness agents". Hydrotropes keep other materials in harmony with water and polyols. In this fashion, CAPB performs just the same, if not slightly better, in acidic media as in alkaline; though as a surfactant but maybe not as a foaming agent.(Never confuse the two)  Amphos improve viscosity only when used in synergy with anionics and/or builders.  Being zwitterionic, they will behave more like soaps in the alkaline range, more like inert oils (for lack of a better word) in the acid range - thus your foaming difference. As for alternatives to amphos...best start a new thread on that one and follow it.  I don't have the time here. 
  • @chemicalmatt: I'm with you--I'm still reading up on surfactant properties and chemistry. I suppose I was asking for a shortcut to testing and reading, but in any case, your post is really helpful. Thanks!
  • It's hard to generalize a lot of the things you asked about.  For instance, nonionic surfactants encompass classes with vastly different hydrophilic groups, and that act very differently from each other & are typically used for different purposes.  Some nonionics are used as foam stabilizers that make hardly any foam on their own, while others are foaming ingredients that have practically no foam stabilizing property.  Other nonionics are more like foam moderators, producing some foam on their own but destabilizing the foam produced by other film-forming substances.  Betaines have both foaming & foam stabilizing properties.

    How betaines thicken is a combination of effects.  Betaine surfactants are supplied in solutions with considerable amounts of simple salts, typically sodium chloride, and you can also buy low-salt versions; that salt has to be taken into consider'n in the total ionic strength of the solution as affects the viscosity of surfactants in it.  The alkamidopropyl betaines also jell more or less with surfactants containing ethoxylated moieties.  Betaines also have strong buffering capacity around the pH many preparations are adjusted to, so if you want to vary the pH you may find yourself needing more acid or base than you might otherwise, and therefore increasing ionic strength.

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