The use of quats in two-in-one hair care products can be problematic since many quats are not compatible with anionic materials. This incompatibility can be manifested as a precipitate or as cloudiness in a formulation. Formulators understand that the interaction between anionic and cationic materials can be quite problematic—for example, the combination of stearalkonium chloride and sodium lauryl sulfate together results in a white, pasty mess.
The two types of quats are described in Surfactants: Strategic Personal Care Ingredients: hard quats and soft quats. Hard quats are products that are incompatible with anionic surfactants. Soft quats, on the other hand, form thick, clear, high-foaming complexes with anionic surfactants.
Hardness or softness is tested by first preparing a 10% active soln. of SLS and SLES-3, followed by a 10% active soln. of quat. The 10% quat is then titrated into 100 g of the 10% anionic. Hard quats will become cloudy or precipitate but soft quats will gel in a clear manner when a stoichiometric amount is added.
While there are many soft quats, the basic cocamidopropyl trimethyl ammonium chloride was found to be excellent in anionic systems, producing a thick, translucent gel with a viscosity well over 10,000 cps for both SLS and SLES when added at equal concentrations of anionic and cationic in a 10% soln. This quat also produced excellent foam and outstanding conditioning when evaluated instrumentally.