Applied Cosmetic Science and Technology Applied Cosmetic Science and Technology

Shampoos are commonly formulated with cationic polymers, anionic surfactants, and amphoteric surfactants. When diluted with water, these components can undergo liquid–liquid phase separation, or coacervation, at specific relative concentrations. Traditionally, shampoos have used sulfate-based surfactants such as sodium lauryl sulfate (LS) and lauryl ether sulfate (LES). However, due to increasing concerns about skin sensitivity and environmental impact, non-sulfate surfactants, such as those derived from amino acids, have become more popular. Despite this shift in formulation, studies on coacervates formed by non-sulfate shampoos are relatively scarce. In this study, we focused on examining the coacervates that form during the dilution process of a commercially available non-sulfate shampoo. We employed a variety of analytical techniques, including turbidity measurements, dynamic light scattering, ζ-potential analysis, rheology, small-angle X-ray scattering (SAXS), and microscopy, to investigate the structural changes of these coacervates throughout the dilution process. Our findings revealed that as the shampoo is diluted, the coacervates exhibit increased elasticity, and at specific relative concentrations, they form a lamellar structure. Additionally, we observed significant structural transitions as dilution progressed further. These results contribute to a deeper understanding of coacervation in non-sulfate shampoos and provide insight into the structural characteristics that differentiate them from traditional sulfate-based shampoos. Further investigation of a model formulation with a well-defined composition is needed to explore the broader implications of these findings on shampoo formulation and performance.