When an aqueous solution has a certain amount of surfactant molecules, micelles are formed. The hydrophilic heads of the surfactant molecules orient themselves toward the water molecules while the hydrophobic tails orient towards each other, avoiding contact with water. These spherical aggregates are widely used in drug delivery, cosmetics, water treatment, detergents, and more. Characterization of these molecules can help qualify their performance. One common way of characterizing solutions like these is using non-invasive laser light scattering. This technique can be used to measure particle size, charge, and rheological properties.<br/>A popular facial cleanser on the cosmetic market right now is micellar water. Many companies carry this product and tout its ability to remove dirt, oil, and makeup while not irritating skin. The main ingredients of the commercial cleanser are water, surfactant, and moisturizer; with fragrance often added. Currently, it is not clear whether a qualification or characterization method for these formulations has been established. The presence of micelles and the solution’s dilute nature makes it a candidate for characterization by laser light scattering.<br/>In order to determine if light scattering could be used to characterize commercial micellar waters, four different commercial brands and formulations were obtained. A fifth micellar water was made in the laboratory using the three main ingredients to serve as a control. All five solutions were measured by Dynamic Light Scattering (DLS) to obtain size information, Phase Analysis Light Scattering (PALS) to obtain zeta potential information, and microrheology to obtain complex viscosity information using a Brookhaven Instruments NanoBrook Omni. All formulations contained a major size population around 10 nm, while also containing larger populations up to the single micron range. Two formulations revealed a negative zeta potential while the remaining three were neutral. Microrheology results were nearly the same across all formulations. All of these results may provide insight into how additives behave and influence micellar behavior as well as the formulation's efficacy and stability.<br/>Overall, this study was successful in demonstrating the effectiveness of light scattering as a way to characterize micellar water. Light scattering analysis could provide a simple and effective QC processing method and help improve formulations in the future.<br/>

Micellar water characterization: A laser light scattering application

256th National Meeting (2018)

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