Synthesis of Layered-Silica/Polymer Nanocomposites
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This dissertation includes four chapters. Chapter I is the introduction of nanocomposite materials, the traditional synthesis methods are discussed and the properties of the nanocomposites are reviewed. Chapter II provides a general introduction of mesoporous silicas, and introduces the synthesis of two lamellar phase silicas template by different surfactant mixtures based on published literature procesures. The preparation was successful, as confirmed by small-angle X-ray scattering (SAXS). Chapter III describes the synthesis of nanocomposites by surface-initiated atom transfer radical polymerization (ATRP) and Chapter IV introduces the synthesis of nanocomposites by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The mechanism and components of the reaction mixtures in the living ATRP are discussed. It is shown that 3-(chlorodimethylsilyl)propyl 2-bromo-2-methylpropanoate is a suitable initiator grafted on the surface of the layered silicas. It is described that polymerization of methyl methacrylate (MMA), styrene (St) and acrylonitrile (AN) was carried out by using ATRP or ARGET ATRP. The polymer loadings were accessed by thermogravimetric analysis (TGA), morphologies of the nanocomposites were examined by SAXS and transmission electron microscopy (TEM), and their thermal properties were accessed by using differential scanning calorimetry (DSC). Generally, normal ATRP was found to allow for better retention of lamellar (intercalated) morphology. However, ARGET ATRP also worked well and allowed us to lower the copper catalyst content to several ppm, that is, by about two orders of magnatitude.
Molecular Orbital Studies of Collagen and Tri-Alanine Peptides
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Joseph J. Dannenberg
The purpose of this thesis is to study the stability of the triple helix (collagen) like peptide structure using computational methods. I am focusing on the collagen stability by using molecular orbital (MO) methods to compare the energies of interaction of Collagen and Tri-Alanine peptides using density functional theory at the B3LYP/D95(d,p) level on the gas phase, aqueous solvation and solvated energies. I present the overall interaction energies as broken down into pure H-bonding between the strands at the geometries they assume in the triple helix.
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Nanolithography involves making patterns of materials with at least one dimension less than 100 nanometers. Surprisingly, writable CDs can provide polymer nanostructures for pennies a piece. Building on work previously done in the Drain lab, with an inherited home-built oven press, this research will explore the relationships between polymer chemical reactivity, polymer printing, and material surface energies. In addition, a relatively inexpensive entry point into high school and undergraduate education in nanolithography is presented. The ability to pattern cheaply at the nanoscale and microscale is necessary and attractive for many technologies towards biosensors, organic light emitting diodes, identification tags, layered devices, and transistors.
Supramolecularly Self-Organized Nanomaterials: from Inorganic Particles to Light-Harvesting Organic Materials
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In 2009 the U.S. National Science Foundation announced the realignment of the Chemistry Divisions introducing the new interdisciplinary program of "Macromolecular, Supramolecular and Nanochemistry." This statement officially recognizes a field of studies that has already seen the publication of many thousands of works in the past 20 years. Nanotechnology and supramolecular chemistry can be found in the most diverse disciplines, from biology to engineering, to physics. Furthermore, many technologies rely on nanoscale dimensions for more than one component. Nanomaterials and technologies are on the market with a range of applications from composite materials, to electronics, to medicine, to sensing and more. This thesis will introduce a variety of studies and applications of supramolecular chemistry to form nanoscale photonic materials from soft matter. We will first illustrate a method to synthesize metallic nanoparticles using plasmids DNA as a mold. The circular DNA functions as a sacrificial template to shape the particles into narrowly monodispersed nanodiscs. Secondly, we will describe the synthesis of a highly fluorinated porphyrin derivative and how the fluorines improve the formation of ultra thin films when the porphyrin is blended with fullerene C60. Finally, we will show how to increase the short-circuit current in a solar cell built with an internal parallel tandem light harvesting design. A blend of phthalocyanines, each with a decreasing optical band gap, is supramolecularly self-organized with pyridyl-C60 within thin films. The different band gaps of the single phthalocyanines capture a wider segment of the solar spectrum increasing the overall efficiency of the device. In conclusion, we have presented a number of studies for the preparation of inorganic and organic nanomaterials and their application in supramolecularly organized photonic devices.
Electrochemistry with Nanoelectrodes
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Electrochemistry with nanoelectrodes By Jeyavel Velmurugan Adviser: Prof Michael V. Mirkin Nanometer-sized electrodes have drawn considerable interest in recent years. One of the reasons is that with nanoelectrodes one can obtain a high rate of mass transport and study kinetics of fast heterogeneous electron transfer (ET) reactions. They can also be used for high-resolution chemical imaging of surfaces and interfaces and as microscopic chemical sensors. We developed methodologies for preparation and characterization of electrochemical nanoprobes and their use as tips in the scanning electrochemical microscope (SECM). The applications range from studies of hydrogen adsorption and spillover to high-resolution imaging of surface topography and reactivity to nanofabrication. Finally, some unusual physicochemical phenomena can be observed at nanointerfaces but are not accessible by macroscopic electrochemical probes will be discussed. Visualization of the nanoelectrode surface is challenging, and the interpretation of the electrochemical response often relies on assumptions about its shape and size. Recently, we obtained the first AFM images of nanoelectrodes, which provide detailed and unambiguous information about the electrode geometry. In-situ AFM is also useful for monitoring surface reactions at nanoelectrodes. This approach was used to control electrodeposition of Pt black into an etched nanocavity and prepare well-shaped platinized nanoelectrodes for intracellular measurements of reactive oxygen and nitrogen species. Another example is the study of nucleation and growth of individual metal clusters on nanoelectrodes monitored by the AFM.
Nanoelectrochemical sensors for kinetic measurements and electroanalytical chemistry
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My PhD research is in the field of nanoelectrochemistry. It includes both fundamental kinetics studies of charge transfer processes and chemical reactions at nanoscopic liquid/liquid and solid/liquid interfaces and applications of the nanometer-sized probes and scanning electrochemical microscopy (SECM) as analytical tools. Nanopipettes can be used to study kinetics of heterogeneous ion transfer (IT) reactions. Common ion voltammetry was developed for determining the kinetic parameters of the rapid tetraethylammonium transfer at the dichloroethane/water interface. This new type of voltammetry provides two limiting currents corresponding to the ingress of the common ion into the pipette and its egress to the external solution, from which one can evaluate the related geometric and transport parameters. Then, the kinetics of IT processes of tetrabutylammonium and similarly sized but asymmetric 1-methyl-3-octylimidazolium at the water/ionic liquid nanointerface was determined for the first time by employing this new approach. Nanopipettes were also used as SECM tips to carry out feedback-mode imaging of various substrates with the nanoscale resolution. Quantitative SECM measurements performed with the polished pipettes as small as 8 nm radius at extremely short tip/substrate distances (~1 nm). A new mode of the SECM operation--electron transfer/ion transfer mode--was developed for simultaneous mapping of surface reactivity and topography. We developed the methodology for resistive-pulse sensing with nanopipettes and used it to detect Au nanoparticles, nanoparticles coated with an allergen epitope peptide layer, and gold particles with bound antipeanut antibodies on the peptide layer. The current pulses produced by antibody-conjugated particles and either bare gold or Au-peptide nanoparticles occurred at different translocation voltages and exhibited opposite signs of the current change, which is essential for selective resistive-pulse sensing of antibodies with nanopipettes. I modified Pt nanoelectrodes with platinum black and then used them to detect reactive oxygen and nitrogen species (ROS and RNS) inside macrophages. Our results supported the hypothesis of the ROS/RNS leakage from phagolysosomes. The data also showed that a macrophage can avoid oxidative damage by rapidly reducing ROS/RNS concentration levels in its cytoplasm.
Organic pi-stacking Semiconducting Material: Design, Synthesis and the Analysis of Structure and Properties
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Organic semiconducting materials have been under intensive investigation in the recent decades for potential applications in various electronic or optoelectronic devices such as light emitting diodes, photovoltaic cells and field effect transistors. Compared to inorganic counterparts, organic charge transport materials are attractive for their abilities of forming thin-films, large area manufacturing, compatibility with flexible substrate, light weight and potential low fabrication cost. The charge transport property of the organic active layer is one of the key factors to the electronic or optoelectronic performance of devices. Research projects presented in this thesis focused on improving charge carrier mobility of organic charge transport materials as it is a property determined by the hierarchical structure of the material. Strong effort has been made to the design of advanced molecular structures and controlling self-assembly behaviors. Chapter 1 introduces the general background of charge transport materials, including: the nature of charge transport in organic semiconducting materials, three widely used methods for charge carrier mobility measurements and the current development of organic charge transport materials. Advantages and drawbacks in applications were analyzed with ordered and disordered organic systems. A more thorough review was given to the engineering and the application of the discotic columnar liquid crystalline (DCLC) phase. Chapter 2 describes a DCLC phase with a novel hierarchical structure in which each supra-molecular column features a bundled-stack structure. The molecular design rationale was explained and the thermal behavior and phase structure were characterized. Charge carrier mobility of compound 1 was measured to be 0.05 cm2V-1s-1 with pulse radiolysis time-resolved microwave conductivity. The incorporation of the bundled stack structure may potentially be a fundamental solution towards enhancing the organic semiconductor's electronic performance. Chapter 3 introduces three chain functionalized perylene tetracarboxylic monoimide diester derivatives (PEIs) with monotropic DCLC phases. The intra-column rotation angle was determined to be 60 o between neighboring PEI molecules, which is a substantial improvement of the transfer integral compared to the perylene tetracarboxylic diimides with a 90 o rotation angle. The rotation angle was further tuned by incorporating branched aliphatic substitution to the PEI core as described in chapter 4. By reducing the length of the alkyl swallow tail, the rotation angle changes from 60 o to 72 o which is even more favorable to the electronic coupling between neighboring PEI units. Through those studies, we have shown that the engineering of DCLC phase may lead to substantial improvements on charge transport properties of organic semiconducting materials.
SYNTHESIS AND INVESTIGATION OF BIPHENYLENE PLANARIZED AROMATIC AND ANTI-AROMATIC SYSTEMS
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The aim of the dissertation was to develop synthetic routes to biphenylene planarized aromatic and anti-aromatic systems such as bis(diacetylene)biphenylene 109, and 4,5,6,7-dibenzocyclobutathionin(biphenylenothionin) 110. Bis(diacetylene)anthracene 209 was prepared by Nakagawa by dimerization of 1,8-diethynylanthracene 208. In the first part of this dissertation, biphenylene systems were synthesized by different methods: by aryne generation, coupling a biphenyl and by extrusion of gas. Key intermediate 1, 8-diacetylene biphenylene 114 was synthesized successfully by coupling dihalo substituted biphenylene and alkyne. Nucleophilic addition of sulfide ion to 1, 8-diacetylene biphenylene 114, instead of an expected nine-membered ring compound 4,5,6,7-dibenzocyclobutathionin 110, gave an unexpected eight-membered ring compound (Z)-1-methylene-1H-biphenyleno[1,8-cde]thiocine 189, with structure confirmed by DEPT 13C NMR, IR , X-ray and GC-MS. Two comparisons of 4,5,6,7-dibenzocyclobutathionin 110, (Z)-5, 6-dihydrodibenzo[d,f]thionine 111 and dibenzo[d,f]thionine 112, were synthesized and NMR data were analyzed and compared.
SYNTHESIS, CHARACTERIZATION AND OPTICAL APPLICATIONS OF NANOMATERIALS
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Nanomaterials have been studied extensively due to their potential application in electronics, photonics and nanodevices. There are a wide variety of methods developed to create the nano-scale materials. Chemical colloidal synthesis is the way most used since it is reproducible and high efficiency. Nanoparticles lie at the heart of nanoscience for their novel electronic, magnetic and optical properties. In this dissertation, there are two parts where researches have been performed based on the synthesis of metal and semiconductor nanoparticles. In part I, Semiconductor type-II core-shell quantum dots (QDs) ZnO-CdS have been synthesized by chemical colloidal method which was carried out in a two-step process. We initially synthesized ZnO core nanoparticles and overcoat them with CdS shell. UV-Visible spectra, photoluminescence spectra (PL), high resolution TEM images and X-ray microanalysis for composition studies of the core-shell nanoparticles were characterized. PL lifetime measurements showed this type-II ZnO-CdS core-shell QDs presented extended exciton lifetime due to the spatial separation of electrons and holes between the core and the shell, which opens various useful applications in biosensors and photovoltaic devices. In part II, normal Raman (NR) and surface enhanced Raman scattering (SERS) spectra of 3-hydroxyflavone (3-HF) have been measured. The SERS spectra were obtained both on a Ag electrode surface and on Ag colloidal nanoparticles. The experimental results support the DFT geometry calculations, which show that an adatom site at the vertex of Ag20 cluster binding with the 3-HF molecular plane tilted at an angle of about 53ºto the surface is a low-energy structure. This is consistent with the enhancement of in-plane vibrational modes. Furthermore, the effect of fluence level on the discoloration of marble surfaces after the removal of the encrustation by 355 nm laser pulses was comparatively studied. Considering the thermochemical reaction possibly occurring in the encrustation during laser irradiation, the mechanism responsible for the discoloration of the cleaned marble surface was analyzed. The reduction of iron oxides by graphite plays a key role in determining the final color of the cleaned marble surface. The marble surfaces before and after laser irradiation were characterized in terms of the chemical components through surface enhanced Raman spectroscopy on Ag colloidal nanoparticles. To analyze the working mechanism of the liquid layer covering the marble encrustation, distilled water, ethanol and acetone were used in marble cleaning to compare the cleaning efficiency at different fluence levels. Surface-enhanced Raman spectroscopy (SERS) on silver colloidal nanoparticles was also used to identify the chemical constituents of the cleaned marble with these three different liquids.
Pi-Stack Engineering of Semiconducting Perylene Tetracarboxylic Derivatives
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Abstract Pi-Stack Engineering of Semiconducting Perylene Tetracarboxylic Derivatives By Chenming Xue Advisor: Professor Shi Jin In the past decades, there has been intensive research in generating novel perylene tetracarboxylic derivatives because of a vast number of applications based on their semiconducting characteristics. The properties of the new materials rely heavily on not only the single molecular structure, but also the way of molecular packing in condensed states. The formation of effective π-stacking structures is the key issue. In this thesis, I focused in synthesizing novel perylene tetracarboxylic derivatives by attaching various substituents at the imide nitrogens. Consequently different phases appeared and exhibited different way of molecular packing. In Chapter 1, it is the general background of perylene tetracarboxylic derivatives including (a) synthesis routes, (b) optical and electronic properties, (c) the molecular packing in condensed phases or assembling in solutions; and also the introduction of condensed state phases including amorphous, crystalline and liquid crystalline (LC) phases. In Chapter 2, a series of solution processible amorphous glassy perylene tetracarboxylic diimides (PDIs) has been designed, synthesized and characterized. The π-stacking order in the amorphous glass phase was successfully tailored by the steric means and qualitatively evaluated. In Chapter 3, the n-alkyl chain length dependence of a series of two-dimensional (2D) smectic LC PDIs has been explored. When the n-alkyl chain is no shorter than decyl group, the PDI could exhibit a novel 2D crystalline smectic LC phase. In this phase, the PDI cores microphase separate from flexible n-alkyl chains forming 2D crystalline layers. Thermoanalysis data quantitatively reveal that the n-alkyl chains in this phase have the essentially the same order as that in the isotropic liquid state. Such truly disordered n-alkyl chains effectively decouple the inter-layer molecular correlation and make the phase genuine LC. The PDI -stacking order in this LC phase is crystalline because it is a part of the 2D crystalline intra-layer order. Chapter 4, PDI -stacking order has been engineered in the crystalline phase. By introducing two structuring factors, a series of crystalline PDIs with finely tunable PDI -stacking order was obtained. The crystalline PDIs with exceptionally red-shifted max were obtained. Several PDIs possess max values greater than any literature-reported ones. These materials can be excellent candidates in solar cell devices. In Chapter 5, new chiral main-chain PDI containing polymers were synthesized. These polymers can form intramolecular helical π-stacks in diluted solutions. In Chapter 6, a novel synthetic route leading to unsymmetrical perylene tetracarboxylic derivatives has been developed. Based on this synthetic method, more perylene tetracarboxylic derivatives can be generated. In my research in this thesis, not only synthesis is an important part because it provides novel materials, but the characterization is critical as well. Infrared spectroscopy, Ultra-violet, fluorescence, differential scanning calorimetry, circular dichroism, polarized light microscopy, gel permeation chromatography, X-ray diffraction including both small angle and wide angle have been used. Additionally, molecular simulation is also very useful in design and obtaining details in molecular packing. Overall, the achievements in this research contribute a considerable advance in the field of generating semiconducting perylene tetracarboxylic derivatives which have versatile potential applications such as in solar cell devices, organic field effect transistors and light emitting diodes.