Assessment of kinetic stability of cosmetic emulsions formulated with different emulsifiers using rheological and sensory analyses

Emulsions are considered thermodynamically unstable systems and the establishment of technical criteria to select suitable components and concentrations to achieve the kinetic stability is a complex task. Theoretical studies have been aimed at obtaining better results and more stable emulsion systems, but relatively little information is available in the literature to support the development of complex emulsion systems. Thus, to address this knowledge gap, the kinetic stability of a cosmetic emulsion containing three different emulsifiers (anionic, cationic and non-ionic) was studied using rheological analysis. The emulsifiers were tested at different concentrations (1.0, 3.0, 5.0 wt%) and the emulsions were aged at different temperatures (5–60 °C) and for various time periods (2 weeks to 6 months). Rheological results based on flow curves, frequency sweep and amplitude sweep show the influence of the concentrations and chemical aspects of the emulsifiers on the emulsion stability. The best behaviors were observed for the samples with 3.0 wt% of cationic and anionic emulsifiers. This result presented good agreement with sensorial tests performed with consumers, who had a preference for the emulsion with 3% of cationic emulsifier. The correlation between the rheological and sensorial results verified the effectiveness of predictive studies based on rheological analysis, which can eliminate or reduce the long time periods required for kinetic studies (aging) and sensory testing in humans.