There are a few ways to create a gel that will thicken our surfactant mix. We can use polysaccharides, carbomers, or something like Amaze XT.
Polysaccharides like agar, carageenan, guar gum, gum arabic, locust bean gum, pectin, xanthan gum (anionic), carboxymethocellulose and variations on the methocellulose (non-ionic), and modified starches are great options for forming gels. (Since I'm still experimenting with carageenan, I won't comment on it just yet!) Because these are botanical in nature, make sure you preserve these well with the maximum preservative allowable!
Xanthan gum is made from saccharide monomer units d-glucose, d-mannose, and d-glucoronic acid. It dissolves in most acidic solutions (less than pH 7) and shows great stability in presence of most organic acids (like vinegar, lactic acid, AHA, and so on). It also shows good compatibility with many basic compounds, but something that is very alkaline like lye (pH around 12), you might see some precipitation of xanthan gum and salts. It is also unusually good with salts, but solubility is an issue. There is an incompatibility of xanthan gum and metal ions in solution with high pH, so addition of EDTA is a good idea if you're using some high pH ingredients like lye (although I can't see a good reason to make a really high pH product...)
Xanthan gum shows good compatibility with non-ionic surfactants in high concentrations, but low concentrations of anionic and amphoteric surfactants. It's not compatible with quaternary compounds, or you want to avoid using something like BTMS, honeyquat or polyquat 7, or Tinosan as your preservative.
You can use xanthan gum in your lotions in the oil phase of the lotions and in your surfactant mixes in the heated water and surfactant phase to create a rich creamy lather. But remember, if you're making a shampoo, leave the honeyquat and polyquat 7 out!
Make sure you're using 0.1% to 0.3% because at lower levels in a lotion, it can actually enhance flocculation and creaming (otherwise known as an epic lotion fail)! EEEK!
You can use a polymer like Carbomer or ETD 2020 to create a lovely gel that will thicken our mixture and suspend things like jojoba beads or pumice for a scrub. (Click on the link as I've already covered this...)
You can use a product like Amaze XT (INCI: Dehydroxanthan gum), which is a modified form of xanthan gum. Use it at 1% to 2% to create a gel without neutralization (unlike the carbomers) in the heated water part of the product. It is soluble in water and alcohol for creating gels. You can't use paraben based preservatives with Amaze XT based gels, which means Phenonip and Germaben II are right out. You can use liquid Germall Plus, Optiphen ND, and Tinosan SDC without problems.
Amaze XT is anionic, and it is compatible with silicones, propylene glycol, hydrolyzed proteins, EDTA, sodium phosphate, and low levels of Flexan II, a polymer used in hair styling products (3:1 ratio of Amaze to Flexan II). In emulsions, you can use carbopol, Structure XL starch, xanthan gum, and hydroxyethyl cellulose as well.
The ideal pH for products containing Amaze XT is between 4.5 and 6, which is right where we want our skin care products. Below 4.5, you'll see a decrease in clarity, so you can add a little salt at 0.1% to make it a little more viscous.
I have been playing with Amaze XT - these recipes from Voyageur - and I just love it. It's great for a suspending type of cleanser and really nice in a very light lotion. The moisturizing sorbet I've linked to would be fabulous for a light lotion for the summer time for oily skinned people (low oils, high humectants).
All right! Let's get making some surfactant based creations for our various skin types!