Behavior and Applications of Solid-State Particles on Surfaces Based on Nanotechnology

Abstract

In surface treatment research, solid-state particles on surfaces are a significant threat to surface properties. When undesired contaminants are deposited on surfaces, they can reduce heat exchange efficiency or narrow the diameter of pipes, causing them to clog. In some cases, the deposition of solids on surfaces is preventable, but in other cases it is unavoidable due to the operating environment. Current research on controlling the behavior of solids on surfaces is limited to the self-cleaning effectiveness of superhydrophobic surfaces using Arizona Test Dust. In this dissertation, research has focused on controlling the behavior of solid phases deposited on surfaces and its application. First, a method was developed to remove soot particles that adhere by the phenomenon of thermophoresis. Soot particles are generated from incomplete combustion processes and are therefore hydrophobic, consisting of hydrocarbon molecules. The gas-solid mixture containing soot particles has a relatively high temperature, so the soot particles adhere to the chimney or surrounding surfaces with lower temperatures through thermophoresis. The soot particles are in the form of spheres with a diameter of about 10 nm, which are irregularly attached to the surface and form a hierarchical structure, making the surface superhydrophobic. In recent years, power generation using waste heat from diesel engine exhaust has gained attention. Initially, it shows high power generation efficiency, but the problem is that soot particles adhere to the surface and act as an insulation layer, causing a sharp decrease in efficiency. Despite the increasing interest in how to effectively clean the soot particles attached to the surface, no self-cleaning method has been reported. Therefore, we developed a method to effectively remove the soot particles attached to the surface. We found that the self-cleaning effect occurs when the wettability between the cleaning solution and the surface and the wettability between the cleaning solution and the contaminant are reversed by cleaning the soot with water on the superhydrophilic surface and oil on the superoleophobic surface. Second, a method was developed to control the precipitation phenomenon caused by supersaturation due to solvent evaporation. In a saturated aqueous solution, we observed that in the case of supersaturation due to solvent evaporation, precipitation occurs along the surface depending on the surface microstructure. For untreated and nanostructured surfaces without microstructures, precipitation started at the three-phase interface of aqueous solution, surface, and gas, rising along the surface and producing a wide range of precipitates, while for microstructured and micro/nanostructured surfaces with microstructures, precipitation started at the three-phase interface was common, but the precipitates were thick and did not spread widely. Based on the fact that the microstructure of the surface affects the direction of precipitation, we developed a selective precipitation technology by preventing precipitation on the microstructured surface for the microstructure-patterned surface. Third, a method was developed to induce and suppress precipitate accumulation caused by supersaturation due to a decrease in solution temperature inside the pipe. Precipitate buildup in pipe flows occurs in most pipe systems and is an issue in the emerging lithium brine extraction process. During the process of transporting a highly concentrated slurry, the temperature drop causes supersaturation of the solution, and if the resulting precipitate clogs the pipe, it threatens the entire system. In a saturated aqueous solution, when the solution is supersaturated and precipitates due to a temperature drop, the degree of precipitate buildup was observed to depend on the surface characteristics: precipitate buildup was induced on superhydrophilic surfaces and inhibited on superhydrophobic surfaces. Based on this, we found that when a bare pipe and a superhydrophilic pipe are placed, precipitate accumulation is inhibited on the bare pipe and induced on the superhydrophilic pipe, and when a bare pipe and a superhydrophobic pipe are placed, precipitate accumulation is induced on the bare pipe and inhibited on the superhydrophobic pipe. Therefore, by crossing the wettability of the pipe, we found that it is possible to induce precipitate accumulation in a specific area and stabilize the entire system by periodically replacing it.