Abstract

Because emulsions are metastable, predicting their stability and phase behavior is a crucial topic of research. Indeed, emulsions are widely used in the chemical industry and formulators must be able to assess their stability e.g. life-cycle or shelves-life. Although several devices, available on the market, are claiming to be able to assess emulsions´ stability, they often use laser or ultrasound diffraction techniques which offer limited capabilities for studying opaque emulsions. This study is describing how the usage of a simple light microscope, already present as a standard equipment in lots of laboratories, can lead to the precise assessment of the particle-size distribution of various cosmetic o/w emulsions. The light microscope was equipped with an objective (40x) having a negative phase-contrast ring. The particle-size characterization by means of phase-contrast microscopy enabled to draw conclusion about the stability over time of two o/w emulsions and to observe the influence of additives on their phase behavior. This novel image analysis method delivered relevant information about the particle-size distribution i.e. stability, of the emulsions at an earlier stage than classical stability tests methods.