Monte Carlo calculations of UV protective properties of emulsions containing TiO₂, Si and SiO₂ nanoparticles

In this paper, we investigate the effect of nanoparticles made of different materials, such as titanium dioxide (TiO₂), silicon (Si), and silica (SiO₂) on UV protective properties of transparent emulsion used for sunscreens within the range of diameters d=10-200 nm by means of Monte Carlo simulations. As a result, silicon nanoparticles of appropriate sizes are the most protective-efficient within the whole UV spectral range among all kinds of investigated particles. Within one kind of particles, specific sizes are the following. For shorter wavelengths of the considered range (λ = 290 nm) 20-100-nm TiO₂ and 30-100-nm Si particles are the most effective protectors. For longer wavelengths (350 and 400 nm) the most pronounced attenuation is obtained with: a) for Si: d = 40 - 120 nm (λ = 350 nm) and d = 60 - 140 nm-sized (λ = 400 nm) particles, b) for TiO₂: d = 80 - 160 nm (λ = 350 nm) and d = 120-180 nm-sized (λ = 400 nm) particles. Silica particles are much less protective than those mentioned above due to small refractive index mismatch between them and the surrounding emulsion.