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Generalized Ellipsometry Based Methods to Measure and Visualize the Deposition of Titanium Dioxide Nanoparticles Onto Model Rough Surfaces
In recent years, characterization and detection of engineered nanoparticles like titanium dioxide nanoparticles (nTiO2) have increased importance in the fields of environmental engineering. They can enter the subsurface and interact with natural soils and sands. Due to highly heterogeneous rough surfaces of natural substrates (e.g., soils and sediments), measuring the interaction of nTiO2 and natural substrates has been very challenging. ^ In this dissertation, three-dimensional nanostructured slanted columnar thin films (SCTFs) with well-defined height were used to mimic surface roughness on proposed substrates (i.e., QCM-D sensors, glass). Interactions between nTiO2 and SCTF surfaces were measured in-situ using QCM-D and generalized ellipsometry (GE) techniques simultaneously. The effects of various parameters, such as roughness height and ionic strength of the solution, on the deposition of nTiO2 on SCTF surfaces were evaluated. It was discovered that typical QCM-D models based on viscoelastic effect only could overestimate the attached areal mass density of nTiO2 due to the water entrapment in between nanoparticles and the pore structure of SCTF. A new model was developed to couple viscoelastic and surface roughness effect. For the first time, this work was able to evaluate the porosity of attached nTiO2 on SCTF surface using appropriate QCM-D and GE model. ^ Another significant contribution of this work is to detect pico-grams of nTiO2 attached on anisotropy surface of SCTFs using a newly developed anisotropy contrast optical microscopy (ACOM) that operates based on generalized ellipsometry technique. Using this technique, we were able to image and quantify the deposition of nTiO2 on SCTF surfaces in a label-free manner. In order to investigate the role of flow on the deposition of nTiO2, we developed a glass microfluidic channel with built-in SCTF surface. The method of preparing the microfluidic channel was meticulously designed not to invade SCTF structure. Using ACOM technique and the microfluidic channel, we present the first effort to sense the transport of nTiO2 over time and quantify the distribution of deposited titanium dioxide nanoparticles on the model surfaces.^
Kananizadeh, Negin, "Generalized Ellipsometry Based Methods to Measure and Visualize the Deposition of Titanium Dioxide Nanoparticles Onto Model Rough Surfaces" (2017). ETD collection for University of Nebraska - Lincoln. AAI10271782.