Teach Soap

Formulating shampoo is way more tricky than formulating creams, at least for me.
The problem is the salt curve is so steep.
What happens, I believe, is that you need a certain minimum % of surfactant blend to actually get to the point where the salt curve starts to work. Before that point you can do anything you like, add DEA for instance to move the salt curve to the left, but with insufficient surfactants it just stays like water.

However, if you use just a little too much surfactant blend, it pushes so far up the salt curve that the shampoo becomes way too thick - in fact my first ones became almost solid in the bottle.

The big problem is that the usable range of % concentration of the surfactant is really very small. Just a bit too little or a bit too much for any particular blend, and it's no good. The curve is so steep it is almost vertical. To see something very weird just add 50% amphoteric surfactant to an anionic. It turns into a ball of liquid crystal!

I really feel the need for a viscometer but they are too expensive. I am thinking of using a graduated cylinder full of shampoo, drop a marble into it and see how long it takes to reach the bottom. Or something along those lines. Or maybe make myself a viscosity cup?

It's a learning curve that's for sure. Most of mine came out too thick and once diluted, didn't have enough bubbles. The marble sounds like a good idea.

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Irena
Closed minds are like faulty parachutes; they refuse to open.

I just tried one of our little 30mL sample bottles, it has a small outlet almost like a dropper bottle. I attached a handle and cut off the bottom. Filled it with stuff and timed it to reach a mark near the bottom as it pours through. It seems to work.
Times:

1. Caprice shampoo 89s
2. Liquid soap (mine) 9s
3. water 3s

So, while I have no idea about how many centipoises these times might represent, I guess that if I want to make a shampoo as thick as a commercial product I just need to make it as thick as it needs to be to get the same pour-through time

I'm closing in, slowly. My comparison item is Caprice shampoo. That pours through my home made viscosity cup in 63 seconds (water = 3 seconds, pure ALS = 3.8 s)

It's amazing how little surfactant you need to make a really thick liquid. At the moment I have 15g ALS + 5g Dehyton AB-30 in 150mL total, that's a 13% concentration, and using just 1g of NH4Cl was enough to put it right on the curve and get a cup pour time of 103 s! Way thicker than the Caprice. It looks to me as if you only need about 10% surfactant.

Having said that, the combination of the anionic with the amphoteric is essential. I tried it with just 20g ALS instead and under the same conditions could only get a maximum pour time of 14 s. The experimenting takes forever as I have to wait for bubbles to settle, a bubbly mixture won't give the correct viscosity.

If you gently heat it, stir just once or twice, then spritz it with alcohol, then cool off, would that speed up the testing time any?

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Irena
Closed minds are like faulty parachutes; they refuse to open.

I'll try that - the viscosity is very temperature dependent. Maybe the bubbles will escape while hot, then when it cools I can test it.
This morning I encountered another problem. The pH was at 8 so I added 1g/100mL citric acid to get it to pH6 which is where it should be. Unfortunately that knocked it right off the salt curve. Evidently the neutralisation should be done prior to adding the salt.