There have been a multitude of approaches to the formulation of hair care products that provide multifunctional benefits. This partially is because the various functions expected from products do not coexist well in one formulation. Consumers demand cleansing, viscosity, foam, wet conditioning (antistat and wet comb) and longer-term conditioning (dry-property conditioning). It would be ideal if a universal surfactant existed that had just the right amount of each property so formulation would be easy, but there is none. Any step toward increasing the level of understanding related to the interaction of surfactants and providing optimized properties in formulation is desirable.
One major area in which interactions are critical is the anionic/cationic interaction. Most formulators of 2-in-1 shampoos understand that indiscriminate mixing of anionic and cationic materials can result in undesired insoluble “gunky” solids. Anionic and cationic materials that are incompatible when mixed together have been classifi ed as hard complexes. As the expression implies, the cationic and anionic compounds possess properties that when added together form insoluble complexes such as salts. In contrast, anionic and cationic compounds that can be mixed over a wide range of ratios and provide a clear, viscous, high-foaming complex are defi ned as soft complexes. Optimized soft complexes have many desirable properties including high levels of foam, viscosity build without alkanolamides, conditioning properties, and low levels of eye and skin irritation.