INIDS2-1610
Decoding Inorganic Sunscreen efficacy through Rheology-Holography analysis
Topic
IDS2. Frontiers in Cosmetic Science and Technology (Sponsored by COSMAX)
When and Where
Sep 30, 2026
15:00 - 15:25
Room 102
Session Chairs
Hyerim HWANG
Presenter(s)
Gi-Ra Yi (POSTECH)
Co-Author(s)
Abstract
The efficacy of mineral sunscreens is largely determined by how well titania (TiO₂) particles are dispersed. When these particles aggregate, they cause an undesirable white cast and reduce the film's protective coverage. To understand this submicron-scale instability, we investigated the 12-week kinetic stability of titania suspensions with three different surface modifications: unmodified (T-OH), stearic acid-modified (T-S), and stearic/palmitic acid co-modified (T-SP). We utilized a combined analytical approach using oscillatory rheology for macroscopic network structure and in-line holographic microscopy for the size, refractive index, and porosity of individual aggregates. Surprisingly, the T-SP sample, which exhibited the most robust colloidal stability, yielded the lowest Sun Protection Factor (SPF). We reveal that this is due to a limitation in standard testing protocols, where large aggregates artificially inflate SPF via multiple-scattering artifacts. Our findings emphasize that high-performance sunscreen design must prioritize true dispersion uniformity over artifactual SPF gains, and we provide a comprehensive multiscale framework to evaluate this formulation stability.
