Chemical and Physical Properties of Nanomaterials for Model Catalytic Systems and Smart Polymer Membranes
Skiles, Stephanie Lyn
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The increased development of surface science in the last half century has opened up new fields for exploration. Surfaces from the pristine to the complex can now be studied with relative ease. These developments along with the industrial society?s desire for improvement have led to the study of smart materials and model systems. Smart materials are designed to have a significant property change in response to a stimulus. Smart polymers can be synthesized that respond to a variety of stimuli including temperature, pH or light. The polymer responds to the stimulus by undergoing a transition that can affect its color, conductivity, shape, etc. Even slight changes in environment can induce large changes in the polymer. This work focuses on covalent layer-by-layer assembly grafts of the thermoresponsive polymer poly(N-isopropylacrylamide) and silica nanoparticles. When grafted to a surface, the system response to external stimuli inducing changes in topography and wettability. Utilizing nanoindentation the polymer graft?s switching elastic modulus was probed as it was exposed to varying external stimuli. It was found that the modulus of the polymer graft changed an order of magnitude based on the polymer?s history and current environment. Covalent layer-by-layer assembly additionally was used to functionalize porous substrates. The polymer?s conformational change was leveraged in the development of an oil and water separation membrane capable of demulsification. The polymer?s transition to a non-soluble configuration blocked pore passageways, preventing the oil from permeating the substrate leading to a pure water filtrate. Advances in surface science have pushed ahead the development of cheaper and better performing catalyst systems. These systems can be developed and tested using model catalyst systems. Herein, two model systems were investigated: a supported cobalt nanoparticle catalyst and a bimetallic palladium-copper system. In the cobalt system, the smallest particles are oxidized and deactivated during the Fischer-Tropsch reaction. In the bimetallic system, the electronic effect of metal alloying was investigated using X-ray photoelectron spectroscopy. The stable alloy was surface enriched with copper. The promotion effect of copper on palladium for the acetylene hydrogenation reaction was investigated. These model systems allow for the study of fundamental phenomena on a controlled surface.