No description available.

This thesis seeks to characterize the size of the interaction volume in a sample subject to electric force microscope (EFM) probing. It discusses the historical relevance of the EFM and the experimental method used. It then discusses the modeling of the fields surrounding the grating sample with the equivalent charge model (ECM) where a tip or other rotationally symmetric conducting element is replaced by a series of point charges on the vertical axis that mimic the original fields. The results of the model were then compared to the experimental data as well as a model simulated using COMSOL, a finite element analysis package. The electrostatic model was found to have good agreement with the simulated and experimental results and was then used to estimate the volume of interaction and the lateral resolution of this technique. The volume of interaction was estimated at 6000 μm3 and the lateral resolution was estimated at 10 μm.

The thesis's principal aim is to investigate the distributional impact of the introduction of the Council Tax as the Community Charge's replacement in England in April 1993. The thesis's empirical analyses consider the distribution of the local tax burden at the household level in terms of income groups, household types and geographical location. The research models the introduction of the Council Tax using a large set of data provided by the Nationwide Anglia Building Society. These data comprise details of over 75,000 mortgages granted by the Building Society between 1988 and 1990 and are sufficiently detailed to allow calculation of individual and household liability for both Community Charge and Council Tax. The Council Tax is chiefly a property tax based on the capital value of domestic property. Because the capital value of domestic property is unevenly distributed both geographically and across income groups, necessarily the Council Tax's burden is also distributed geographically and across income groups. Previous distributional analyses of the impact of the Council Tax have been unable to consider this spatial distribution. However, the Nationwide Anglia data allow analysis of this spatial distribution. The thesis considers a number of influences on the tax's distribution - the use of capital value as a tax base; the operation of the Revenue Support Grant; the Council Tax Transitional Relief Scheme; the Council Tax's hybrid personal / property tax design; as well as the distributional implications of the transition to a form of property tax from the Community Charge's flat- rate poll tax. The final chapter uses the implications of the preceding distributional analyses to consider the Council Tax in the longer term as part of a broader solution to the historic difficulties of the overall local government finance system.

This thesis seeks to characterize the size of the interaction volume in a sample subject to electric force microscope (EFM) probing. It discusses the historical relevance of the EFM and the experimental method used. It then discusses the modeling of the fields surrounding the grating sample with the equivalent charge model (ECM) where a tip or other rotationally symmetric conducting element is replaced by a series of point charges on the vertical axis that mimic the original fields. The results of the model were then compared to the experimental data as well as a model simulated using COMSOL, a finite element analysis package. The electrostatic model was found to have good agreement with the simulated and experimental results and was then used to estimate the volume of interaction and the lateral resolution of this technique. The volume of interaction was estimated at 6000 μm3 and the lateral resolution was estimated at 10 μm.

Particle stabilized emulsions, also known as Pickering emulsions, have been widely used in many industry applications. While the breadth of potential applications for Pickering emulsions keeps growing, our fundamental understanding of Pickering emulsions is still poor. My thesis work addresses both fundamentals and applications of particle stabilized emulsions. In the fundamental part of this thesis work, we investigated the effects of particle charge on particle adsorption and the particle contact angle, and to investigate their ensuing consequences for the stability of Pickering emulsions. We provided the first experimental hint that the widely overlooked image charge repulsion can hinder the adsorption of particle to the oil-water interface and prevent the formation of Pickering emulsions. Consistently with the experimental suggestion, our theoretical model also confirmed that the image charge repulsion has the right order of magnitude, relative to the other forces acting on the particle, to impede particle adsorption and Pickering emulsification. For the conditions in which particle adsorption to the liquid interface does occur, the particle contact angle will play an important role in influencing the stability and type of Pickering emulsions. Our experimental work showed that the equilibrium contact angle of particles at interfaces and the type of emulsions preferentially stabilized by these particles can be strongly affected by the particles' charging state, which we attribute to a free energy contribution from the electric field set up by the charged particle and its asymmetric counterion cloud. A very simplistic calculation considering only the dipole field as the leading contribution and treating the water phase as a perfect conductor, found that the energy stored in the field is indeed strong enough and shows sufficient variation with the particle position to shift the equilibrium position significantly from where it would be based on interfacial tension alone. In a separate, more application oriented part of this thesis work, we have fabricated microcapsules from double Pickering emulsions and demonstrated that the combined use of hard silica particles and pH-responsive dissoluble polymer particles at the emulsion interface imparts a combination of pH-responsiveness (stimulated pore opening) and structural integrity to resulting capsules. We have further demonstrated the first double Pickering emulsion templated capsules in which interfacial polymerization was carried out at both emulsion interfaces, yielding a capsule with two composite shells, composed of polyurethane and silica particles, and characterized the transport of a model cargo through the capsules walls as well as the capsules' mechanical properties.

This dissertation is focused on modeling charge-transport in π-conjugated organic materials, which serve as the active materials in light-weight, flexible, organic photovoltaic cells, offering the potential for cheap, ubiquitous renewable energy. In particular, we used computational chemistry to gain insight into the fundamental processes of charge transport within organic semiconductors to derive an understanding of chemical and physical phenomena that can not be explained through experiment alone in order to further the performance of organic-based electronic devices. In order to accurately model the organic materials, a combined quantum-mechanical and classical approach is needed, with the ground and excited state electronic properties of isolated organic materials determined using DFT/TD-DFT as a first step and coupled with molecular dynamics and mechanics. This allows for an understanding of the molecular order and packing within nanoscale structures as well as the impact of the intermolecular interactions. However, standard DFT methods suffer from intrinsic errors resulting from approximations to the exchange-correlation potential that can be corrected using a simple non-empirically tuning procedure. We briefly review the electronic structure methods that we use and the non-empirically procedure for DFT that allows for a substantial improvement over standard DFT methods. We then discuss the main results of this research. In Chapter 3, we detail the understanding of the limitations in DFT (currently one of our main tools) and improvements that can be achieved through non-empirically tuning a specific DFT method for the system of study. We detail the dependence of the range-separation parameter used in long-range corrected hybrid functionals on both the size and degree of conjugation for a given system. We also demonstrate the effect that self-interaction corrections employed through range-separated hybrid functionals can have in describing thermodynamic and electronic properties for large, organic π-conjugated systems. In this study, we chose a property that critically depends on the degree of delocalization (i.e., torsion potentials) to correlate the degree of delocalization with the choice of a given method in order to understand how the self-interaction errors affects this property. These results are published in C Sutton et al. “Accurate Description of Torsion Potentials in Conjugated Polymers using Density Functionals with Reduced Self-interaction Error” Journal of Chemical Physics, 140, 054310, 2014. In Chapter 4, we discuss how non-empirically tuning DFT can be used to rigorously model electron transfer in single-molecule systems (i.e., organic mixed-valence systems), where we modeled the symmetry breaking and charge (de)localization in charge-transfer complexes compared with high-level methods. The results presented in Chapter 4 are published in C Sutton et al. “Towards a Robust Quantum-Chemical Description of Organic Mixed-Valence Systems” Journal of Physical Chemistry C, 118, 3925, 2014. In Chapter 5, we applied this method to interpret photoelectron spectroscopy spectra in order to elucidate the localized nature of a charge carrier in prototypical organic semiconductors; this understanding was then extended to quantify the relaxation energy in finite molecular clusters in the presence of an excess charge from a combined multi-layer quantum-mechanical/molecular-mechanical method. In Chapter 6, we determined the effect of choosing various DFT methods on the intermolecular electronic couplings and band structure calculations in organic molecules, which are published by C Sutton et al. in "Understanding the Density Functional Dependence of DFT-Calculated Electronic Couplings in Organic Semiconductors” Journal of Physical Chemistry Letters, 4, 919, 2013. Finally, conclusions and further considerations are discussed in Chapter 7.

No description available.

The derivatives of boradiazaindacene (BODIPY) are highly fluorescent dyes which have quantum yields near 1.0. These dyes that have exceptional spectral and photophysical stability as compared to other fluorescent groups are used for several different applications. The fluorescent sensor molecules for the detection of cations with PET (photoinduced-electron transfer) mechanism in general have been obtained by the differentiation of the BODIPY core. The extension of conjugation over the pyrrole ring shifts the absorption and emission at longer wavelength. Moreover, it is seen that red emission occurs from an ICT (intramolecular-charge transfer) state. iii In this study, we designed and synthesized an unsymetrically substituted BODIPY dye series, carrying a cation-sensitive phenylazacrown ether group conjugated to the core, and investigated the ion sensing properties of these compounds. Both aza-crown derivatives displayed selectivity towards Ca(II).

This dissertation work is a study of positronium formation for positron-hydrogen and positron-helium collisions in the Ore gap (the energy region between the threshold for ground-state positronium formation and the first excitation level of the target atom) using variational K-matrices. We have fitted the K-matrices using multichannel effective range theories and using polynomials. Using the variational K-matrices and their fits, we have located zeros in the positronium-formation scattering amplitude and corresponding deep minima in the positronium-formation differential cross section. The zeros are related to the vortices in the extended velocity field associated with the positronium-formation scattering amplitude. For positron-hydrogen collisions, we have found two zeros in the positronium-formation scattering amplitude, and corresponding deep minima in the positronium-formation differential cross section, while we have obtained a zero in the positronium-formation scattering amplitude for positron-helium collisions. We have connected the zeros in the positronium-formation scattering amplitude to vortices in the extended velocity fields. Our work shows that vortices can occur for charge exchange in atomic collisions.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Mar. 4, 2008). Vita. Includes bibliographical references.