Microscopy and physical stability of cosmetic emulsions
Due to their complexity, emulsions are thermodynamically unstable systems and, over time, can incur phenomena of physical instability, such as the coalescence of the internal phase, sedimentation, or phase separation.
As any formulator knows, a cosmetic, in addition to being safe and effective, must also be stable.
In the case of emulsions, a methodology that can help the researcher to investigate the stability of his product is undoubtedly microscopy.
Optical microscopy, through the direct observation of the sample, allows the quality of the product to be assessed already in the research and development phase.
Through this qualitative analysis, it is possible to detect the homogeneity of the formulations, the morphology, the size and the interaction of the drops of the internal phase of the emulsions, the correct dispersion of powders, such as filters and pigments and, finally, the organization and the structure of the crystal lattices formed by the various rheological modifiers included in the formula.
Through the preliminary study of the internal organization, to be integrated with the accelerated stability assessments commonly carried out during product development, it is possible to predict the chemical-physical stability of the cosmetic and optimize the formula, intervening in advance on all those factors that may influence its quality.
Below, as an example, we report the images of an emulsion that is undergoing coalescence.
Let’s see how the insertion of a new raw material in low concentration in an emulsion can lead to instability that is easily visible under the microscope:
Furthermore, in the scale-up phases, in the passage from prototype to industrial batch, the different forces and temperatures involved can lead to differences in the morphological structure of the product compared to the laboratory sample.
Microscopy allows monitoring the different batches and highlights significant differences, to optimize the process and obtain the desired product.
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