I got several failures adding Cetrimonium chloride to water first, then SLES and everything else
while I didn't see any precipitate forming, it got disgustingly sticky and stringy, then it bacame water-thin and it couldn't be thickened with salt. It seemed to have little conditioning or cleaning activity too.
In latter experiments adding CTAC as the last thing, it seemed to work.
I thought it was because SLES doesn't react with CTAC when it's diluted
But this study says that CTAC won't react with SLES if CAPB is added first:
Advances in shampoo formulation: synergism of anionic/cationic/zwitterionic surfactant ternary systemAbstractThere is a rule among cosmetic formulators of not mixing an anionic
surfactant with a cationic surfactant in the same formulation, especially
if it’s a clear product, since this interaction will result in the appearance
of turbidity (precipitation). Nevertheless, vast reports show not only the
possible but also synergistic combination of surfactants with opposed
charge, conferring unique properties to the final product. The aim of this
study is to evaluate the use of a co-surfactant as a novel tool for
maintaining high levels of both cationic and anionic surfactants mixed in
the same product, without precipitation. Not only we found this possible
at certain rates, but also attributes of the system such as viscosity,
detergency and foam stability, were improved.http://www.journalbinet.com/uploads/2/1/0/0/21005390/188.8.131.52_advances_in_shampoo_formulation_synergism_of_anionic_cationic_zwitterionic_surfactant_ternary_system.pdf
... Tested samples were prepared by combining variable
amounts of Sodium laureth sulfate (SLES), Cocamidopropyl betaine (CAPB) and Cetrimonium chloride
(CTC)...... When SLES and CTC are mixed at a similar concentration (1 wt%), precipitation occurs as a result of the
formation of a SLES-CTC complex...
... On the contrary, when CAPB is introduced in the mixture before the CTC, instead of precipitation, there is an increase in viscosity which continues as the level of CAPB increases, while maintaining a 1 wt% fixed concentration of SLES and CTC...
... But after a peak in viscosity at 1.5 wt% of CAPB, a
gradual descent is followed with every new addition of surfactant. At this point, micelles become less
polar with every CAPB increase, resulting in chain contraction and relative viscosity decrease...
... In general, it is easy for the SLES-CTC ion pairs to be precipitated from solution. However, the ion pairs have been "solubilized" by forming mixed micelles with CAPB in the present case, resulting in an increase of the could point, similarly to the observed linear increase in the clouding temperature of Triton X-100 on addition of small amounts of Sodium dodecyl sulfate (Valaulikar, 1985)...
Step 3 – Learn the rational behind the formula
Seems to be the hardest part, so far.http://chemistscorner.com/making-cosmetics-the-scientific-way/