SCREENING ANALYTICAL METHODS FOR THE EVALUATION OF PHYSICAL STABILITY IN EMULSION-BASED COSMETIC PROTOTYPES

Stability is a crucial requirement in the development of emulsion-based cosmetic formulations. The initial phase of product development demands analytical methods that accelerate the screening of the most promising formulas. In this study we used analytical centrifugation, rheology and optical microscopy techniques to identify the most stable prototypes, which will advance to the next stage of developing a moisturizing cream composed of a biosurfactant in the emulsifying system. Analytical centrifugation analysis allowed us to rank the samples based on an emulsion instability index, comparing the samples by the degree of clarification due to creaming process. Optical microscopy results revealed that the most stable prototype formed a birefringent region around the emulsion globules, indicating the formation of liquid crystals. Compared to the use of a polymer-based rheological modifier, the combination of components that favored the formation of this type of microstructure showed greater efficacy in promoting emulsion stability. Rheological characterization of the samples demonstrated that all prototypes exhibited a thixotropic flow profile and viscoelastic solid characteristics. Differences in consistency index values, hysteresis area and parameters of the linear viscoelastic region, in addition to inferring the physical stability of the emulsions and correlating with the analytical centrifugation results, allowed preliminary inferences about consumer sensory perception during product use.