Wettability of cosmetic powders and pigments

Interfacial chemistry measuring methods for powder wetting and dispersion stability

The majority of cosmetic products contain powder and pigments for coloring, skin protection or to assist cleansing. Dispersing agents in the form of surfactants ensure a fine distribution of the powder and a stable mixture. In return, powder surfaces are frequently modified to match them to liquid phases before manufacture. Surface chemical measurements on liquids and powders help in quality assurance and in the development of new products.

 

 

Measuring surface tension to determine liquid wetting

In aqueous cosmetics, surfactant additives reduce the surface tension to improve powder wetting and produce a stable, finely distributed mixture. Our tensiometers measure this surface-tension-reducing effect of surfactants with high precision.

 

In order to ensure good skin compatibility, it is often important to keep the surfactant content low. Our instruments measure the efficiency of surfactants fully automatically based on the critical micelle concentration (CMC). At this concentration, the surface is completely covered with surfactant molecules. At higher concentrations, clusters of surfactant molecules, so-called micelles, form within the solution. These are responsible among other things for the cleansing action. The surface tension does not reduce further above the CMC. The CMC is an important parameter for optimum surfactant dosing.

 

 

Measuring the contact angle to determine powder wettability

Our tensiometers determine the wettability of the powder based on the contact angle. Data relating to the surface energy and its polar fraction, which can also be measured, provide information on the degree of affinity with the liquid phase. Alternatively, the contact angle of a drop on a powder bed can be measured optically.

 

For products such as nail varnish or lipstick, inorganic powders with partly polar characteristics are often coated to prepare them for use in a hydrophobic environment. The effect of this pre-treatment is likewise quantified by means of the powder contact angle.

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