Stability Study of O/W Cosmetic Emulsions Using Rosmarinus officinalis and Calendula officinalis Extracts

Abstract

Cosmetic emulsions, as all macro emulsions, are inherently unstable systems, from a thermodynamic viewpoint. More specific eco-friendly oil/water (O/W) cosmetic emulsions are usually less stable than conventional ones as milder chemicals or less intense (energy consuming) production processes are involved. In this context, two traditional techniques an optical technique and a volumetric one have been used for the assessment of the stability of cosmetic emulsions and compared to each other. Eco-friendly cosmetic emulsions were produced with different olive oil/water extracts (Rosmarinus officinalis and Calendula officinalis extracts) and emulsifier (Glycerol monostearate, GMS) concentrations. Emulsions’ stability was registered simultaneously by 1) Microscopy photos of samples withdrawn at regular intervals from the test vessel; 2) global volumetric measurements of the different phases (water/oil/emulsion) inside the test vessel made at regular intervals for determining the evolution of the location of the phases separation interface. Analysis of the results of each technique and comparisons among them are presented and discussed in detail.