Microscopic Analysis of the Water/Glycerol/EO30PS System in Bulk and on a Solid Substrate

Area of Science:

• Colloid and Surface Science
• Materials Science
• Cosmetic Science

Background:

• Surfactant systems are key in cosmetic formulations, concentrating as they dry on skin.
• Understanding how surfactants self-assemble during drying is vital for product performance.

Purpose of the Study:

• To investigate the self-assembled structures of water/glycerol/polyoxyethylene (30) phytosteryl ether (EO30PS) in bulk versus on a solid substrate during drying.
• To elucidate the impact of substrate interactions on surfactant self-assembly compared to bulk behavior.

Main Methods:

• Small-angle neutron scattering (SANS) to analyze bulk structures.
• Neutron reflectometry to study surfactant adsorption on a silicon (Si) surface.

Main Results:

• In bulk, increasing water loss led to higher ordering of densely packed ellipsoidal polyoxyethylene (30) phytosteryl ether (EO30PS) micelles with minimal structural changes.
• On a Si surface, EO30PS formed bilayers, with high concentrations (20 wt %) showing an average of two bilayers (double bilayer).
• The adsorbed EO30PS layer was thin, with tilted molecules, limited solvent, and low order.

Conclusions:

• Drying significantly alters surfactant self-assembly, with distinct behaviors observed in bulk and on surfaces.
• The formation of thin, tilted bilayers on surfaces provides insights into the structural properties of cosmetic formulations.
• This research enhances the understanding of surfactant behavior in applied cosmetic products like lotions.