Effects of Environmental Factors on Functional Properties of Particulate Matter

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Date
2022
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University of Alabama Libraries
Abstract

The properties of the material are determined by its structure and the functional motif, understanding the structure of a material can explain its behavior under certain conditions. The effects of environmental factors on the functional properties of thin films of particulate matter due to fabrication method or exposure to the environment are investigated. Understanding the mechanism behind material defects/degradation provides insight to optimize the functional properties of the film, suitability for the application, or robustness for a potential application. This dissertation explores the effect on the functional properties of the material due to aerosol deposition method, interaction with chemical warfare agents, and environmental exposure. Barium Hexaferrite (BaM) films deposited on a-plane sapphire substrate by aerosol deposition are investigated in a subtractive wedge series to determine the extent of energetic substrate damage and indentation. The Al2O3 particulates ejected from the substrate surface during growth and the estimate of indentation depth is ~600 nm. The magnetic moment of the deposited film is lower than the bulk and thickness dependence is consistent with the fractional increase of Al2O3 content in the film.Fe2O3 nanoparticles exhibit chemical changes due to contact with the four chemical warfare agents simulants. Due to the exposure, a redox reaction occurs and Fe2O3 nanoparticles show lowered magnetic moment. The differentiable, frequency-dependent responses to the simulants are observed due to changes in the sensor material that opens the possibilities for the use of Fe2O3 nanoparticles for frequency-dependent impedance fingerprinting. The effects of UV and visible light exposure in dry air and humid environments have been investigated using the Zr-based metal-organic framework, UiO-66-NH2. The metal-organic framework undergoes irreversible photochemical change due to prolonged UV light and blue light exposure. These changes happen more rapidly and grow larger in total cumulative magnitude as the atmospheric humidity increases. However, humidity introduced in dark or with lower energy photons than blue light results in no material change to the MOF. Impedance data modeling suggests that humidity increases the ionic conductivity of the material and that the degradation occurs at grain boundaries, to a depth that increases with humidity. Importantly, the result of the degradation is the loss of chemical sensitivity, defining the conditions for applications in both aqueous and airborne filtration and sensing applications.

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