(163ap) Dispersions of Core-Shell Dielectric Nanoparticles and the Optimization of Uv Scattering and Absorbance to Minimize the Transmittance of Novel Sunscreen Materials

The scattering, absorbance and transmittance of colloidal dispersions of dielectric core-shell nanoparticles fabricated by Atomic Layer Deposition (ALD) is evaluated in this work. The optical dispersion of dielectric nanoparticles, specifically zinc oxide (ZnO) and titania (TiO2), increases in importance as the wavelength approaches the ultraviolet (UV) spectrum, an inherent issue in resolving the effectiveness of inorganic sunscreen particles under incident solar irradiation. Ellipsometry is used here to understand the optical dispersion of nanothick ALD films of ZnO, alumina (Al2O3) and silica (SiO2) on 2-D surfaces; Particle-ALD is then utilized to deposit these dielectric films on both spherical and nonspherical particles to create 3-D nanocomposite structures for dispersion in liquids. The standard absorption/scattering theory for individual core-shell particles is expanded here in attempts to encapsulate optical effects due to colloidal aggregation in liquids, nonspherical core particles and multilayer shells with varying absorbing and scattering properties. Theory is compared to experiment using a UV-VIS Spectrophotometer and a diffuse transmittance integrating sphere analyzer.