Applied Cosmetic Science and Technology Applied Cosmetic Science and Technology

Shampoos contain key ingredients such as cationic polymers, anionic surfactants, and amphoteric surfactants. These components are known to undergo liquid–liquid phase separation, called coacervation, at specific relative concentrations during dilution with water when used. Recently, non-sulfate shampoos have become increasingly popular, but there are insufficient research reports on coacervation in this system. In previous work, the authors investigated coacervation and the properties of the coacervates generated during dilution using commercial non-sulfate shampoos. However, due to the lack of detailed information on the ingredients in commercial products, it was difficult to manipulate the factors influencing coacervation. Therefore, model shampoos were developed using cationic polymers, anionic/amphoteric surfactants, and salts with known compositions. In this study, the model shampoos were analyzed using turbidity, dynamic light scattering, ζ-potential, rheological measurements, and microscopy to observe coacervation and the structure of the coacervates formed during dilution. The results showed that the model shampoos underwent coacervation during the dilution process, and the coacervates exhibited more elastic properties at lower relative concentrations. Additionally, their structure transitioned from a hexagonal liquid crystalline to a lamellar one. These findings suggest that the dilution process in non-sulfate shampoos leads to distinct structural changes in the coacervates, offering insights into the formulation design for improved product performance.