Gabriela Oliva Fonseca

Concentrated oil-in-water (O/W) emulsions, such as medium and high internal phase emulsions (MIPEs and HIPEs), offer a promising approach for sustainable and dilutable waterless cosmetic formulations. However, incorporating adequate oncentrations of water-soluble ingredients is challenging due to limited water availability, requiring an optimized preparation method. This thesis designed, optimized, and characterized concentrated O/W emulsions composed of cationic surfactants (distearoylethyl dimonium chloride – DEEDMAC, stearamidopropyl dimethylamine – SAPDMA, or cetrimonium chloride – CTAC), fatty alcohol, and biopolymers, ensuring sufficient water-soluble ingredient concentrations for cosmetics. Emulsion properties and stability were evaluated via Small Angle X-Ray Scattering (SAXS), laser diffraction, centrifugation, optical microscopy, and rheology, providing insights into their colloidal physico chemistry and resulting in two scientific manuscripts. We proposed an optimal fatty alcohol:surfactant molar ratio of 2:1 in HIPEs – lower than that used in conventional, less concentrated emulsions – leveraging droplet close-packing to improve stability and rheology, and reaching small droplets (≤ 2.0 µm). A rapid and low-energy reparation method (1500 rpm) enabled incorporation of water-soluble polymers at effective concentrations, offering advantages over traditional methodologies. Formation of a viscous network by the high molecular mass biopolymer in the aqueous medium reduced water availability for surfactant molecules, thereby hindering HIPE formation with the more hydrophobic surfactant, DEEDMAC. Conversely, the low molecular mass biopolymer disrupted DEEDMAC lamellar phase order and enabled O/W HIPEs formation. The resulting emulsions served as a robust chassis for new waterless cosmetics, aligning with the industry’s shift toward more sustainable formulations.

Doutorado em Química | 2025