This conditioning shampoo bar contains Sodium Coco Sulphate to cleanse and BTMS 50 (Behentrimonium Methosulfate, Cetyl Alcohol, Butylene Glycol) and Cocamidopropyl betaine to condition.  It is scented with rose geranium, red mandarin and marjoram essential oils.  For the colour, which is salmon pink, a combination of red clay and sea buckthorn was used.  It's a simple formula that is effective at cleansing and conditioning the hair.  It is also effective and slightly less conditioning with BTMS 25.  The bar is pH adjusted to around pH 6 with a 50% citric acid solution.

You can see from below, it is a very simple formula.  I have only used select ingredients to give functionality: cleansing and conditioning; and to give aesthetics: colour and scent.

Let's take a closer look at the ingredients.

Surfactants

Sodium coco sulphate (SCS) is an anionic surfactant derived from coconut oil.  It is highly water soluble and has a pH of between 8 and 11, so needs help to come down to a more skin and hair optimum level.  Some people often confuse it with sodium lauryl sulphate, and although they are similar, SCS has a larger molecular size, causes less disruption to the skin,  and as such is less of a skin irritant. This is the main surfactant used in the shampoo bar.

BTMS 50 is a quaternary ammonia salt.  Chemically, it has a positively charged head and is classed as a cationic.   It is used as a conditioning emulsifier and will add slip and glide to hair. As a quaternary ammonia salt, it will stay positively charged at neutral, acidic or basic pH.  Cationics are compatible with amphoteric and nonionic surfactants.  They are mostly incompatible with anionic surfactants as there is a risk of precipitation and instability in aqueous solutions.  I used it in the bar as essentially there is no solution; it seemed to work well.  BTMS 50 has a pH of between 5-7 and will help lower the pH of the overall formula when wet. It also acts to bind the surfactant grains together.

Cocamidopropyl betaine - This, like other betaines, is commonly classed as an amphoteric surfactant, however, some scientists have argued this is incorrect because it retains its positive cationic charge, despite changes in pH.  Regardless of this, betaines are known for being mild to the skin and hair and can cut irritation that arises from anionic surfactants like sodium coco sulphate.  They work well in hard and soft water and have good foam stability.  I used it in here for this purpose but also the high water content, about 70%,  helps bind the surfactant pearls.

Essential Oils

Here I used a combination of Rose Geranium, Marjoram and Red mandarin for a floral scent with a citrus/herby undertone.

Colour

To colour, a combination of Sea buckthorn and red clay is used. Sea Buckthorn Co2 is a fixed oil that has been supercritical extracted.  As a result, it has a stronger colour than your standard pressed oil.  As mentioned the orange in the buckthorn is used to morph the pinkness given by the red clay, to give a warmer colour.

Other Ingredients

I used citric acid in a 50% solution.  To make this simply weigh out equal amounts of citric acid and water (I use warm water to help the citric acid dissolve).  If you want to lower the pH further to make it between pH 4-5 then use more citric acid solution. I would estimate another 0.5% would probably do it.

The Formula

Method

1.  Weigh and combine all ingredients in phase A and set aside.

2. Combine all ingredients in stage B and heat until melted.

3. Add stage C to stage B and stir until well combined.

4. Add stage B/C to stage A and stir well

5. Press using a shampoo puck/ mold and leave to harden for 24 hours

N.B You may need to put the combined wax and essential oil back on the heat as the cold essential oils can lower the temperature of the wax, causing it to set.  We need it to be mobile in order to mix in with the surfactants in stage 4.  Don't worry, momentarily heating up the wax will not affect the scent of the essential oil in the final product. Alternately, you could try adding the essential oils after you have combined the wax to the surfactant and see what happens.

So, there it is. A perfectly cleansing and conditioning shampoo bar, that smells awesome and looks ever so pretty. 

References

https://www.sciencedirect.com/topics/chemistry/cocamidopropyl-betaine

https://www.sciencedirect.com/topics/chemistry/cationic-surfactant

https://www.researchgate.net/publication/333324339_Anioniccationic_interactions