Silicone rubber is a promising candidate for the next generation of electrical insulators on account of the prolonged hydrophobicity of the polymers. However, microalgae biofouling is always a concern for high voltage insulators installed in coastal regions. To understand how microalgae species interact with polymer surfaces that are used in electrical insulator applications, a study has been conducted to determine the interactions of a benthic and a pelagic algal species with polydimethylsiloxane surfaces. The adhesion strength of algal species were quantified with two different types of flow cells employed for our studies. These two types of flow cells are microfluidic chips and a laser-cut flow cell chamber, which provide a high and low wall shear stress, respectively. A video analysis software was designed to automate all aspects of the flow rate profile, data acquisition, and image analysis. Pristine poly(dimethyl siloxane) (PDMS), deionized water-exposed PDMS, and salt solution-exposed PDMS samples were used as substrates in adhesion experiments. The results indicate that surface hydrophobicity played a critical role in adhesion strength. At low shear stress, both B. braunii and T. rotula cells demonstrate a strongest adhesion strength onto the pristine PDMS surface, while show the weakest adhesion strength onto the salt solution exposed PDMS surface. At high shear stress, all PDMS surfaces provide an equal adhesion environment to the both species. / Graduate / 2021-12-11

Removing pyrite from coal and pyrrhotite from pentlandite play a critical role in coal and nickel production, respectively, to meet the stringent restriction on SO2 emission. The present project investigates first the mechanism of xanthate adsorption on gold using Atomic Force Microscope (AFM), then the depression of pyrite and pyrrhotite using the synthetic polymers developed by Cytec Industries. The results show that for xanthate/gold system, dixanthogen is the only species that renders the surface hydrophobic. Chemisorbed xanthate is observed on the gold surface but is hydrophilic. The synthetic polymers may adsorb on pyrite and pyrrhotite possibly through the hydrophobic interaction between the hydrophobic moiety of the polymer and the mineral surface that has been hydrophobized by collector adsorption. The hydrophilic moieties of the polymer are exposed to the aqueous phase and render the surface hydrophilic. / Master of Science

We propose a new dynamically feasible trajectory generation algorithm that incorporates sternward motion for unmanned surface vehicles. This work is motivated by riverine applications where the operating environment is large and poorly known. We extend a navigation approach for forward path planning into a more versatile framework that includes safe and dynamically feasible backward trajectories. We pose the backward trajectory generation problem as a finite-horizon optimal control problem and transform it into a nonlinear programming problem by utilizing the direct shooting method. The nonlinear programming problem is solved using the Hooke-Jeeves numerical algorithm. We provide successful simulation and field-trial results that demonstrate the performance of backward path planning algorithm. / Master of Science

The study of the structure-activity relationship of electrode surfaces is fundamentally important in electrocatalysis research. Yet, the methods and techniques used for the examination of structure-activity relationship so far are limited by their capabilities, and the exploration of electrochemistry at complex surfaces is very challenging. In this study, the correlation between the electrode surface structure and its corresponding activity in two electrochemical reactions were investigated: an electrochemical etching reaction and an electrocatalysis reaction. A polycrystalline Pt electrode was galvanically etched to expose the underlying well-defined crystallites serving as pseudo-single-crystal electrodes. Atomic force microscopy (AFM) complemented with electron backscatter diffraction (EBSD) was employed for the elucidation of the effects of electrode surface structure on its etching rate. Electrochemical measurements of the electrocatalytic activity of the hydrogen oxidation reaction on individual grain surfaces were performed with high spatial resolution scanning electrochemical microscopy (SECM) coupled with electron backscatter diffraction (EBSD). The etching experiment and surface characterization results show the more deeply etched regions on polycrystalline Pt surface correspond to Pt(100). The etching rate of the Pt catalyst is Pt(111), Pt(100), and Pt(110) in increasing order. The structure-reactivity relationship showed that the catalytic activity for hydrogen oxidation reaction (HOR) increases in the order Pt(100) < Pt(110) < Pt(111), where the Miller index plane represents the terrace orientation of the high-index facets. A clear correlation is observed between the increase in HOR activity and step sites density on a given base orientation. Quantitative kinetic measurements at crystal domains were made from current-potential plots and SECM approach curves.

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