Adhesion and friction forces of colloidal particles in atmospheric systems
Kweon, Hyo Jin Jin
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Interactions of colloidal particles with surfaces occur in natural and engineered systems, and they influence the transport of contaminants through diffusion, aggregation, filtration, and sedimentation. To quantify the transport and fate of colloidal particles and their influence on environmental systems, it is important to understand their interactions with surfaces. These interactions are influenced by physical and chemical surface properties such as hydrophobicity, charge density, and roughness, as well as environmental conditions such as relative humidity (RH). In atmospheric systems, RH induces the capillary force and also influences the contributions of van der Waals and electrostatic forces. To investigate the role of surface properties and RH in the interaction of colloidal particles with surfaces, atomic force microscopy was employed to measure the adhesion and friction forces of colloidal particles including Bacillus thuringiensis spores, silica, and gold at various experimental conditions with several types of surfaces including mica, silica, and radioactive gold. Contributions to the adhesion force by van der Waals, capillary, and electrostatic forces were theoretically calculated and compared to measured forces. Through experimental results and theoretical studies, it was identified how surface properties of interacting surfaces and experimental conditions influence the interfacial interactions of colloidal particles in atmospheric systems. The role of RH in adhesion and friction depends on the hydrophobicity or contact angles of interacting surfaces and surface roughness. Relative humidity also influences the contribution of electrostatic force to the total adhesion force by screening the strength of surface potential or providing a passage for charge leakage. The results of this thesis provide a better understanding of particulate processes that are influenced by the interactions of colloidal particles with surfaces and can be useful in monitoring and control of contamination in atmospheric systems.