Browsing by Subject "surface modification"
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Item Layer-by-layer assembly on polyethylene films via "click" chemistry(2009-05-15) Chance, Brandon ScottLayer-by-layer assembly has received much attention over the last fifteen years. This assembly process can be carried out using different methods including hydrogen-bonding, electrostatic, and to a lesser extent, covalent interactions. However, these assemblies are rarely seen on polyolefin substrates due to the lack of functionality on the surface. ?Click? chemistry has become very popular in recent years as a means to join modular compounds together. This thesis is the first published report to use ?click? chemistry as a means for layer-by-layer assembly on a polymeric substrate. By designing polymers that contain alkyne or azide groups, it is possible to assemble them layer-by-layer on a polyethylene substrate. Polymers based on tert-butyl acrylate were initially designed for use in organic solvents such as tetrahydrofuran. The copper catalyst that facilitated the 1,3-dipolar cycloaddition was air sensitive and expensive. To capture the true essence of ?click? chemistry, a new system was designed based on N-isopropyl acrylamide (NIPAM)-based polymers. These polymers were water soluble and allowed for ?click? chemistry to be performed in water and open to air in benign conditions. With the development of a water soluble polymer system that could be modified to contain either azide groups or alkyne groups, layer-by-layer assembly was carried out in water. A polyethylene film was modified in a series of reactions to have an alkyne-functionalized surface. The poly(N-isopropyl acrylamide)-based polymers were layered in an alternating fashion to form multilayer assemblies. A series of control reactions were also performed, showing that these layers were interconnected via triazole linkages. These assemblies were monitored by attenuated total reflectance spectroscopy. Once the layers were assembled, the polyvalent nature of the polymers allowed for further functionalization. Various surface functionalizations were established using fluorescence microscopy and contact angle analysis. By using spectroscopic and chemical means, layer-by-layer assembly on polyethylene films was proven. Control reactions showed the necessity of components for triazole formation. Therefore, layer-by-layer assembly using ?click? chemistry was achieved.Item Surface Modification of Layered Zirconium Phosphates: A Novel Pathway to Multifunctional Nanomaterials(2014-04-08) Mosby, Brian MatthewThe surface functionalization of inorganic nano particles for improved and novel applications is the topic of this dissertation; specifically the surface modification of inorganic layered materials. In this case the goal is to exclusively modify the surface or exterior layers of the material, while leaving the internal layers and structure unchanged. This allows for organic derivatives of layered materials in which the interlayer chemistry is not lost to achieve organic functionalization. The addition of organic character along with the retention of the original interlayer character produces a material with dual functionality and opens the window for many unique compounds and applications. The surface reactivity of ?- zirconium phosphate nano platelets was investigated with a variety of coupling agents. Initially, covalent attachment of molecules to the exterior surface of the nano particles was attempted with silanes and epoxides. Subsequently, the ion exchange character of the surface phosphate groups was used to deposit metal ions on the surface. The metal ion layer was then coordinated with phosphonic acid ligands to produce surface functionalized ZrP. In all cases the exclusive functionalization of the surface and covalent attachment of the reactive groups to the inorganic layer was confirmed using a combination of techniques including X-ray powder diffraction, XPS, electron microprobe, Solid State NMR, FTIR, and TGA. The viability of producing nano particles with both a controlled interior and exterior by combining the intercalation chemistry of ZrP with the newly developed surface chemistry was then investigated. Characterization of the resulting materials indicated that functionalization of intercalated ZrP was successful and an efficient procedure for the design of multifunctional nanoparticles. The control of the interlayer and surface allows for nanoparticles to be designed for particular applications. Polymer nanocomposites and a photo-induced electron transfer system were prepared using the multifunctional nanoparticles as test cases.Item Surface Modification of LiNi0.5Mn0.3Co0.2O2 Cathode for Improved Battery Performance(2012-10-19) Lynch, ThomasThis thesis details electrical and physical measurements of pulsed laser deposition-applied thin film coatings of Alumina, Ceria, and Yttria-stabilized Zirconia (YSZ) on a LiNi0.5Mn0.3Co0.2O2 (NMC) cathode in a Lithium ion battery. Typical NMC cathodes exhibit problems such as decreased rate performance and an opportunity for increased capacity exists by raising operation voltage beyond the electrolyte stability window. Very thin (~10 nm) coatings of stable oxides provide a pathway to solve both problems. As well, the electrochemical impedance spectra of the uncoated and coated cells were measured after different numbers of cycles to reveal the property variation in the cathode. Further understanding of the mechanism of rate performance enhancement and chemical protection by thin oxide coatings will continue to improve battery capability and open up new applications. Ceria-coated Li-NMC cells show the best capacity and rate performance in battery testing. Through electrochemical impedance spectroscopy (EIS), the surface film resistance was found to remain stable or even drop slightly after repeated cycling at high voltage. CeO2 is proposed as a coating for Lithium ion battery cathodes owing to its high chemical stability and the demonstrated but not yet well understood electrical conductivity. Alumina-coated cathode shows comparable performance as that of the uncoated cell in the early stage of the test, but through the course of testing the rate capability and recoverable capacity is improved. This is possibly due to Al2O3?s well-known abilities as HF scavenger and chemically inert nature. YSZ-coated cathode performs worse than the uncoated ones in terms of capacity, rate capability, and EIS-related figures of merit. The reason for the poor performance is not yet known, and repeatability tests are under way to verify performance. High voltage cycling reveals no obvious difference in irreversible loss between the coated or uncoated cells. The reason for the lack of distinction could be the relatively small percentage of surface coating compared to the thick doctor-blade processed cathode layer.