Analyzing the Deposition of Titanium Dioxide Nanoparticles at Model Rough Mineral Surfaces Using a Quartz Crystal Microbalance with Dissipation Monitoring

Abstract:

Titanium dioxide nanoparticles (nTiO2) is the most extensively manufactured engineered materials. nTiO₂ from sunscreens was found to enter sediments after released into a lake. nTiO₂ may also enter the subsurface via irrigation using effluents from wastewater treatment plants. Interaction of nTiO₂ with soils and sediments will largely influence their fate, transport, and ecotoxicity. Measuring the interaction between nTiO₂ and natural substrates (e.g. such as sands) is particularly challenging due to highly heterogeneous and rough natural sand surfaces. In this study, an engineered controllable rough surface known as three dimensional nanostructured sculptured columnar thin films (SCTFs) has been used to mimic surface roughness. SCTFs were fabricated by glancing angle deposition (GLAD), a physical vapor deposition technique facilitated by electron beam evaporation. Interaction between nTiO2 and SCTF coated surfaces was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). In parallel, a Generalized Ellipsometry (GE) was coupled with the QCM-D to measure the deposition of nTiO2. We found that the typical QCM-D modeling approach, e.g. viscoelastic model, would largely overestimate the mass of deposited nTiO2, because the frequency drops due to particle deposition or water entrapment in rough areas were not differentiated. Here, we demonstrate a new approach to model QCM-D data for nTiO2 deposition on rough surfaces, which couples the viscoelastic model with a model of flow on the non-uniform surface.