Role of rheological behavior of sunscreens containing nanoparticles on thin film preparation

Abstract In this study, blade-coating deposition was investigated for the ability to prepare thin films of unmodified sunscreens on substrates. The effect of rheological behavior on film thickness prepared by blade coating deposition was examined by employing four sunscreen formulations (SF1–SF4) with different amount of gelling agent as a model system. The highest thixotropy (18336.31 dyne/cm2·s) and viscosity (9.6 Pa·s) of SF4 applied with the slowest deposition speed (17 µm/s) showed the thinnest film thickness below 10 µm. Two commercial sunscreens (SC1 and SC2) were employed to evaluate the validation of SFs model regarding the relationship between viscosity and film thickness. With similar viscosity values, film thicknesses of SC1 and SC2 prepared with same deposition speeds were close to those of SF1 and SF2, respectively. This work demonstrated a strong influence of rheological behavior in terms of viscosity and blade coating deposition speed on film thickness of sunscreen.