Here's the basic formula, I only had a hand immersion blender as my overhead mixer is being repaired so for this first atempt so I was not able to do low speed mixing during cool down and after adding the final phase which could have lead to inadequate formation of lamellar phases - BTMS is AFAIK a liquid crystal emulsifier. I've wanted to test how it feels in a moisturizer formula for some time now.
1. Heat phase A to 70C
2. Mix B1 and B2 separately until homogenous. Add B1 to B2 under high shear mixing. Heat to 70C.
3. Add A to B under stirring and mix with high shear mixing for 3 minutes.
4. Cool to 40C, add phase C under high shear mixing for 1 minute. Bottle.
Final pH 3.8
|Behentrimonium Methosulfate, Cetearyl Alcohol (BTMS 25)||A||5.0|
|Salicylic Acid ||A||2.0|
|Hyaluronic Acid (Low MW)||B2||0.2|
|Phenoxyethanol, Caprylyl Glycol||C2||1.0|
Salicylic Acid did not entirely solubilize in the oil phase, possibly at least in part due to lack of stirring. Not entirely unexpected.
The end formula formula was watery, too thing for a lotion - likely used too little BTMS, Glyceryl Stearate, Cetyl Alcohol and Xanthan Gum to make a cream. That said, skin feel and effects are good. After a few hours a water phase separated out on the bottom.Let me know what you think are the culprit(s) for the curdling and separation
, I'm thinking of increasing what I mentioned above, along with low shear stirring during cool-down and after adding phase C. There could also be some ionic interference going on with the BTMS but I'm not experienced enough with it to know what it could be. It's been a while since I've formulated myself so a bit rusty, also I'm lacking experience with silicone and I'm not sure It needs anything extra to stably incorporate Dimethicone.
HLB values shouldn't matter too much with BTMS, but they shouldn't be too far off a classic calculation.
Lastly if you have experience with Niacinamide stability at relatively low pH I'd be curious to know about it. It's optimum solution stability is around pH 6. It can hydrolyze and form nicotinic acid at higher or lower PH, but not sure if at a significant enough rate to worry about esp if making a (eventually) thick cream.