Dissertations / Theses: '030304 Physical Chemistry of Materials'

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O'Brien, Stephen. "The chemistry of mesoporous materials." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390532.

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Ngabe, Barnabe. "Physical chemistry of sulphide self-heating." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123024.

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ABSTRACTA prerequisite step towards building a self-heating (SH) model for sulphide materials is the determination of physico-chemical parameters such as the specific heat capacity (Cp), and the energy of activation (Ea). The specific heat capacity of one copper and three nickel concentrates was determined over the temperature range 50 to 80oC in the presence of 6% moisture using the self-heating (SH) apparatus and confirmed by Drop Calorimetry. The Cp values from both techniques were comparable. The Cp values were similar for all concentrates increasing from 0.4 to 1.4 Jg-1K-1 as temperature increased from 50 to 80oC. From the Cp values, the enthalpy change (ΔH), the entropy change (ΔS) and the Gibbs free energy change (ΔG) for self-heating, were determined. The ΔG was negative, demonstrating that self-heating of the concentrates was spontaneous.Using the self-heating apparatus the, activation energy (Ea) was determined for the Ni-and Cu-concentrates and for pairs of sulphide minerals. The Ea ranged from 22 to 30 kJ.mol-1, implying a common reaction. Further support for a common reaction is the strong positive correlation between Ea and ln(QA/Cp) where Q (J.kg-1) is the heat of reaction causing self-heating and A the Arrhenius pre-exponential factor (s-1). Comparing to literature, the Ea values correspond to partial oxidation of hydrogen sulphide, supporting the contention that H2S may be an intermediate product in the self-heating of sulphide minerals. A positive relationship between Ea and the rest potential difference (ΔV) for the sulphide pairs and a negative relationship between Cp and ΔV were demonstrated which support a connection between self-heating and the galvanic effect.
RESUMÉLa réalisation d'un modèle mathématique de l'auto-échauffement des concentrés sulfurés de nickel et de cuivre et des mélanges des minerais sulfurés, enjoint à la détermination des paramètres physico-chimiques tels que les capacités de chaleur spécifiques (Cp), et les énergies d'activation (Ea). Les capacités de chaleur spécifiques d'un concentré de cuivre et de trois concentrés de nickel contenant 6% d'humidité, ont été déterminées par utilisation d'un instrument de mesure de vitesse d'auto – échauffement et validées par la calorimétrie de chute dans l'intervalle de températures allant de 50 à 80oC. Les Cp (0.4 à 1.4 Jg-1K-1) obtenues sont similaires pour tous les échantillons. A partir des valeurs des Cp, les variations de l'enthalpie (ΔH), l'entropie (ΔS) et de l'énergie libre de Gibbs (ΔG) de l'auto échauffement ont été déterminées. La valeur négative de ΔG confirme le caractère spontané de l'auto échauffement des minerais sulfurés.Les énergies d'activation (Ea) pour l'auto-échauffement des concentrés de nickel et cuivre et des paires de minerais sulfurés étaient déterminées en faisant usage de l'appareil d'auto-échauffement. Les Ea ainsi obtenues oscillent entre 22 et 30 kJ.mol-1 : Ce qui est suggestif d'une rèaction chimique commune gouvernant l'auto-échauffement de ces matériaux. Ce fait est corroboré par la forte corrélation obtenue entre Ea et ln(QA/Cp) (Q (J.kg-1) est la chaleur de la rèaction chimique responsable de l'auto-échauffement et A (s-1) la constante d'Arrhenius).Ensuite celles-ci sont similaires à celle de l'oxydation partielle du H2S. Il se pourrait, ce faisant, que H2S soit un composé intermediaire lors de l'auto–échauffement des sulfures.Enfin, la corrélation positive entre Ea et la difference de potential (ΔV) dans les paires de minerais sulfurés et celle negative entre Cp et ΔV sont une preuve qu'il existe bel et bien une connection entre l'auto-échauffement et l'effet galvanique.

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3

Frank, Robert A. "Physical chemistry of carbothermic reduction of alumina." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15150.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Vita.
Bibliography: leaves 177-180.
by Robert A. Frank.
M.S.

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4

Tavener, P. "Electron spectroscopy of electrode materials." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370304.

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5

Yager, Kevin G. "Investigation of photomechanical surface patterning in azobenzene materials." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103017.

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Detailed modeling and experiments were conducted in order to elucidate the nature of photo-induced surface patterning in azobenzene materials. Using a cellular automaton simulation, it was established that both the absolute temperature rise, and the thermal gradient, in a film during patterning are negligibly small. These results, confirmed experimentally by patterning samples on substrates of differing thermal conductivity, eliminate purely thermal mechanisms as candidate explanations for mass transport. The length-scale of patterning was probed by monitoring the formation and thermal erasure of gratings as a function of film thickness. In both cases, film dynamics deviate from bulk behavior when film thickness decreases below ~150 nm. Moreover, mass transport is completely hindered below 40 nm. This deviation of polymer dynamics implies that photo-induced mass transport involves the coordinated motion of many polymer chains in the depth of the material, and not merely surface diffusion of individual chains.
Neutron reflectometry was applied to measure in detail the photomechanical response of azobenzene materials. A significant photo-expansion effect, up to 17%, was observed at 25°C, attributed to the molecular free volume requirement of azo isomerization. Above a well-defined crossover temperature, which occurs at ~50°C for poly(disperse red 1 acrylate), the material response is inverted. At these elevated temperatures, photo-contraction effects, of more than -15%, were instead measured. In this case the combination of photo-induced motion and thermally-enabled mobility enables aggregation, aromatic stacking, and crystallization of the azobenzene dipoles. Using localized surface patterning experiments, it was confirmed that the mass transport phenomenon exhibits the same trend and phase relationship as the photomechanical effect. It is argued that the fundamental origin of surface mass transport in azo materials is in fact this newly identified photomechanical effect. This suggestion enables explanation of a variety of previously contradictory results in the literature.

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Pope, Chris. "Hyroxylic polymers as materials for permanent holograms." Thesis, Cranfield University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357054.

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Rocheleau, Marie-Josée. "Investigation of membrane materials for solid-state, ion-selective electrodes." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74675.

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The preparation and characterization of new materials to make ion-selective membranes are described. The usefulness of zinc orthophosphate and zinc mercuric thiocyanate to make a carbon-support electrode responsive to zinc was investigated. Better results were obtained with zinc orthophosphate. However, the electrode response was lowered by the formation of acidic oxides on the surface of the electrode, and interferences from copper(II), lead(II), and cadmium(II) were observed. An indirect potentiometric method based on the selective monitoring of chlorozincate(II) or cyanozincate(II) anions with a coated-wire ion-selective electrode was proposed as an alternative for monitoring zinc ion. The application of quaternary ammonium, phosphonium, and alkyl phosphate ionic polymer membranes to potentiometric and voltammetric analysis was also studied. Ionic polymer membranes offer a number of advantages, namely improved membrane lifetime and enhanced adherence to solid-substrate electrodes, when compared to conventional ion-selective membranes. The last stage of this research focused on the application of ionic polymer membrane electrodes in flow injection analysis.

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Shaw, Christopher P. "Polymeric materials for piezoelectricity and second harmonic generation." Thesis, Cranfield University, 1991. http://dspace.lib.cranfield.ac.uk/handle/1826/3674.

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Studies have been undertaken to utilise the possible potential of the rodlike, helical structures associated with polyglutamates and polyisocyanates for piezoelectric (PE) and nonlinear optical (second harmonic generation (SHG)) applications. Various techniques have been employed to form samples/films of these polymers containing oriented helices whose bulk structures are non-centrosymmetric, (an important criterium for the aforementioned applications). Owing to the poor yields obtained for certain intermediates in the synthetic stages of these polymers, only poly('S-benzyl-L-glutamate) (PBzLG) and poly(n- hexylisocyanate) (PHIC) were available for subsequent studies. Piezoelectric work was limited to hydrostatic measurements (d3h) made on electrically poled, composite (guest host), polymer samples. Phase separation was common in all the samples, but no piezoelectric response was observed. However, low concentration (not greater than 10% w/w) of active polymer (PBzLG or PHIC) and high conductivity during the poling stage, may have accounted for the lack of response. Electrically poled, homopolymer samples of PBzLG and PHIC were achieved using a solvent evaporation technique. Nonlinear optical studies of these poled samples revealed threshold fields above which detectable levels of SHG could be observed, (i.e. PBzLG > 40 V/mm, PHIC > 150 V/mm). The variation of SHG signal versus the angle of polarisation of the incident laser light (1064 nm) relative to the poling direction of the film, implied biaxial symmetry was present in the case of PBzLG, whereas the more conventional uniaxial symmetry was observed for PHIC. The variation in SHG signal observed for a fixed thickness was attributed to varying degrees of alignment, resulting from uneven poling. Although PHIC and PBzLG showed low SHG activity (less than value for urea), little ageing of this activity occurred over the 6 month testing period. Langmuir Blodgett studies carried out on chemically modified, low molecular weight PBzLG molecules showed poor transference of the monolayer to a quartz substrate once ten layers had been deposited. In addition, areas per molecule (or per residue) calculated from the pressure-area isotherms, proved inconclusive when deducing possible orientations for the PBzLG helices. No SHG signal was observed for the L.B. films.

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9

Dennis, J. S. "The desulphurisation of flue gases using calcareous materials." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372626.

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Simpson, W. Mark. "Solid state NMR studies of molecular crystalline materials." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362006.

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11

Flora, Ware Howard. "Characterization and optimization of novel materials and interfaces in organic electronic devices." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280511.

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The research embodied in this text involves the characterization and optimization of novel materials and interfaces critical to the performance of organic electronic devices: Thrust 1. A scheme for elucidating the relative significance of energy vs. charge transfer (ET vs. CT) routes to guest dye emission in organic light-emitting diodes (OLEDs) was developed using near-IR emissive phthalocyanine (Pc) or naphthalocyanine (NPc) dopants. CT processes were observed to occur by an oxidized guest mechanism, which may be predicted from the solution electrochemistry of these materials. Additionally, a new series of quinacridone(QA)-based guest dyes were developed/characterized, modified at the N,N' positions to form four generations of Frechet dendrimers and their t-butyl-terminated analogues. As generation number increases, they exhibited decreased aggregation and increased luminescence efficiencies in the condensed phase. In solution, sharply declining rates of heterogeneous electron transfer were observed. Despite this trend, when these new molecules were doped into OLEDs, ET and CT routes to QA emission were not significantly inhibited. Thrust 2. A series of hybrid metal cluster-organic materials containing between one and seven [Re6(mu3-Se)8] 2+ clusters per molecule were electrochemically characterized. Dimer, trimer, and tetramer assemblies yielded uncoupled cluster oxidations. For cluster 7-mer dendrimers, uncoupled oxidations were observed for unconjugated linking groups, while coupled oxidations were observed with a conjugated linker, suggesting through-bond electrical polarization of the interior cluster. Thrust 3. The first UV-Vis attenuated total reflectance (ATR) method for the simultaneous determination of molecular tilt and azimuthal rotation for ultra-thin films of molecules with circularly-polarized electronic transition dipoles was developed, where a priori assumptions of the mean molecular orientation of either angle are not necessary in order to recover both mean angles. A model Pc-based system was evaluated, where this material is known to form in-plane molecular columns. Assuming a delta distribution in the orientation of each angle, it was determined that the mean tilt of the molecular plane away from the substrate surface is 80 ± 3°, and the mean azimuthal rotation of the molecular plane away from the column direction is 56.9 ± 0.8°. The dependence of molecular orientation on environmental exposure conditions and surface premodifiers was also evaluated.

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Longwell, David James. "The application of new materials to ion-selective electrodes." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334504.

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Mollison, Neil Bruce. "Structural characterisation of amorphous materials by solid state NMR." Thesis, University of Kent, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269106.

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Glarvey, Paul Anthony. "Synthesis and characterisation of novel conjugated liquid crystalline materials." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251250.

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15

Mann, Sandra Elizabeth. "Studies of charge transfer in electrophotographic and related materials." Thesis, University of Exeter, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303920.

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Szablewski, M. "Multi-functional D-#pi#-A materials for molecular electronics." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305322.

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17

Tschaufeser, Petra. "Computer simulation studies of zeolites and related microporous materials." Thesis, University of Bath, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306781.

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18

Bengtsson, Katarina. "Additive manufacturing methods and materials for electrokinetic systems." Licentiate thesis, Linköpings universitet, Ytors Fysik och Kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-121252.

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Fabrication of miniaturized devices is usually time-consuming, costly, and the materials commonly used limit the structures that are possible to create. The techniques most often used to make microsystems involve multiple steps, where each step takes considerable time, and if only a few systems are to be made, the price per device becomes excessive. This thesis describes how a simple syringebased 3D-printer, in combination with an appropriate choice of materials, can reduce the delay between design and prototype and simplify fabrication of microsystems. This thesis suggest two types of materials that we propose be used in combination with 3D-printing to further develop microsystems for biology and biochemistry. Analytical applications in biology and biochemistry often contain electrodes, such as in gel electrophoresis. Faradaic (electrochemical) reactions have to occur at the metal electrodes to allow electron-to-ion transduction through an electrolyte-based system to drive a current when a potential is applied to the electrodes in an electrolyte-based system. These electrochemical reactions at the electrodes, such as water electrolysis, are usually problematic when miniaturizing devices and analytical systems. An alternative to metal electrodes can be electrochemicallyactive conducting polymers, e.g. poly(3,4-ethylenedioxythiophene) (PEDOT), which can be used to reduce electrolysis when driving a current through water-based systems. Paper 1 describes gel electrophoresis where the platinum electrodes were replaced with the conductive polymer PEDOT, without affecting the separation. Manufacturing and prototyping of microsystems can be simplified by using 3Dprinting in combination with a sacrificial material. A sacrificial template material can further simplify bottom-up manufacturing of more complicated forms such as protruding and overhanging structures. We showed in paper 2 that polyethylene glycol (PEG), in combination with a carbonate-based plasticizer, functions well as a 3D-printable sacrificial template material. PEG2000 with between 20 wt% and 30 wt% ethylene carbonate or propylene carbonate has properties advantageous for 3D-printing, such as shear-thinning rheology, mechanical and chemical stability, and easy dissolution in water.

In the printed version the thesis number 1720 on the cover is incorrect. The correct thesis number is 1724 which is corrected in the electronic version.

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Booth, Ryan Steven. "Experimental and theoretical studies on the decomposition mechanisms of geminal dinitro energetic materials." Thesis, The University of Chicago, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3615632.

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These studies combine crossed laser-molecular beam scattering, velocity map imaging and computation to study the thermal decomposition mechanisms of geminal dinitro energetic materials. In our experimental studies, we photolytically generate two key intermediates in the decomposition of such energetic materials, 2-nitro-2-propyl radical and 2-nitropropene by photodissociating 2-bromo-2-nitropropane at 193 nm. These intermediates were produced at high internal energies and access a number of competing unimolecular dissociation channels. The scattering and imaging experiments provided evidence for four photodissociation pathways of 2-bromo-2-nitropropane along with a total of twelve subsequent dissociations of the resulting intermediate. In addition to the experimental studies, extensive calculations were conducted at the G4//B3LYP/6-311++g(3df,2p) level to compute the energetics of these dissociation events. Interestingly, a novel transition state (TS) for NO loss was discovered for the 2-nitro-2-propyl radical, which has a reaction barrier substantially lower than a traditional nitro-nitrite isomerization mechanism would suggest. This pathway is only available to nitroalkyl radicals and is extremely exothermic. To confirm the presence of this novel TS in a real-world system, the potential energy surface (PES) of a new energetic material, 1,1-diamino-2,2-dinitroethene (FOX-7), was calculated. This PES confirms the presence of the novel NO loss TS in FOX-7; this new TS allows for a low energy pathway to the production of NO in the unimolecular decomposition of FOX-7. In addition, these calculations demonstrate that initial loss of NO is competitive with simple C-N bond fission in unsaturated energetic materials. This low barrier and high exothermicity may be responsible for the extensive NO production and energy release observed in energetic materials with geminal dinitro groups.

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Le, Baut Nicolas. "Physical and adhesive properties of some materials made by "click" chemistry." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060712.161329/index.html.

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21

Yau, Hon P. "Permeability of gases in copolymers, physical blends and composite particle materials." Thesis, Lancaster University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282409.

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22

Ashton, Melanie. "The study of surface interactions of polymeric materials and related molecules." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316462.

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23

Jackson, Toby. "Synthesis, characterisation and analysis of triarylamines as potential charge transport materials." Thesis, University of Aberdeen, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300957.

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The application of triarylamines as charge transport materials is an important consideration in the modern electrophotographics industry. The ability of these materials to form stable amorphous glasses and the electrochemical properties they exhibit has led to the use of compounds such as 4,4'-bis-[N-(3-methylphenyl-N-phenylamino)]biphenyl (TPD) as charge materials in electrophotography and electroluminescence. In order to develop this science an understanding of the structural properties that facilitate the use of triarylamines in such devices is required so that new charge transport materials can be developed with improved performance and stability. With this intention Ullmann condensation reactions were employed to prepare a series of substituted triphenylamines and triarylamine starburst compounds containing differing structural units for which the synthesis and characterisation are detailed. Alkene linked triarylamines were prepared employing Wadsworth-Emmons reactions, Wittig reactions, McMurry coupling reactions and Grignard reactions. Further, palladium catalysed cross coupling reactions were undertaken to prepare acetylene linked triarylamines. Thermal analysis was undertaken using the differential scanning calorimetry (DSC) technique which identified those compounds which display an amorphous nature, indicated by a glass transition temperature. The importance of this property is linked to the requirement of charge transport materials to either formulate in an inert polymeric binder as part of a charge transport layer or form an amorphous thin film monolayer. Electrochemical analysis was undertaken by cyclic voltammetry (CV) and time of flight techniques (TOF). This analysis of triarylamines explores the viability of the concepts of polyfunctionality and intramolecular charge mobility as well investigating the effects of structure on the stability, electrochemical reversibility and oxidation potentials of the radical cations of triarylamines prepared.

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Hassen, J. H. "Spectroscopic analysis of adsorbed macrocyclic complexes on ceramic and related materials." Thesis, University of Essex, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.481601.

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Chong, M. W. S. "Incorporation of spiropyran functionality into framework materials." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33949/.

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This thesis describes developments towards incorporating spiropyran functionality into metal-organic frameworks (MOFs). Chapter 1 outlines the reported literature concerning the study of photochemistry with respect to MOFs; such materials have demonstrated potential as both alternative environments for the study of photoactivated processes and platforms to integrate photosensitive moieties. Incorporation of photoactive groups into MOFs has enabled these supramolecular materials to be altered chemically and physically via photo-initiated processes. Existing studies into reversible photoswitching groups are largely focussed on azobenzene. The chronological development of azobenzene incorporation into MOFs reflects the evolving strategies of exploiting this functionality to achieve photocontrol over the properties of MOF materials. These advances in accommodating photoswitching azobenzene into MOFs have been applied in reported studies with other photochromic groups and taken into consideration with the work described herein concerning spiropyrans. Chapter 2 focusses on the preparation of a carboxylic acid functionalised salicylaldehyde 3-formyl-4-hydroxybenzoic acid (H2L1), a key precursor in the synthesis of carboxylic acid functionalised spiropyrans. The serendipitous outcome in solvothermal reaction of H2L1 and copper nitrate in dimethylformamide affords {Cu2L12·(DMF)2(H2O)}n (1-Cu-DMF) which has been crystallographically characterised and is further described in this chapter. Channels run through the direction of the crystallographic a-axis of 1-Cu; its connectivity and porosity is retained upon solvent exchange of the single crystals with ethanol and tetrahydrofuran. Gas sorption experiments show 1-Cu exhibits type I adsorption behaviour with a Brunauer-Emmett-Teller (BET) surface area of 948 ± 1 m2 g−1. Notably, 1-Cu adsorbs negligible quantities of methane compared to carbon dioxide and other C2Hn hydrocarbons; the selectivities are confirmed by analysis via the ideal adsorbed solution theory (IAST) and Henry’s law. Of particular importance, 1-Cu demonstrates exceptional selectivity for acetylene, which has applicability in separation technologies for the isolation of acetylene. Chapter 3 details the design and synthesis of a series of carboxylic acid functionalised spiropyrans and bisbenzospiropyrans. These compounds serve as ligand precursors for MOFs but also have interesting photophysical properties as organic compounds, which are studied in this chapter. Condensation of prefunctionalised fragments, H2L1 and carboxylic acid functionalised Fischer’s base 5, afforded a novel dicarboxylic acid functionalised spiropyran H2L2. A second synthetic route to extended ligand precursors, via Suzuki-Miyaura cross coupling of ethyl ester functionalised boronic acids to dibrominated photoactive cores and subsequent hydrolysis, is described. Crystallographic characterisation of the ethyl esters indicates flexibility of the core moieties around the spiro carbon. Comparison of the UV-visible absorption spectra shows the properties of related spiropyrans and bisbenzospiropyrans to be influenced by electronic effects arising from both the type and positioning of the functional groups. The fluorescence quantum yields of novel spiropyrans 13, 15 and H2L5 have been determined as 0.025, 0.032 and 0.068 respectively. Cyclic voltammetric experiments show the electrochemical behaviour of spiropyrans to be influenced primarily by electronic effects related to the type of functional group attached, whereas the electrochemical properties of bisbenzospiropyrans is dominated by electronic effects arising from the positioning of the functional groups. Density functional theory (DFT) calculations of the spectroscopic properties are described and are consistent with experimental observations. Chapter 4 describes investigations to incorporate the carboxylic acid compounds prepared in Chapter 3 into framework materials. To mitigate potential instability problems from using solely photoresponsive and highly flexible components, co-crystallisation with pillaring agents was considered. Reaction of H2L2 with zinc nitrate and a dipyridyl terephthalamide pillaring agent L7 affords coordination network 2 Zn. Two isomers, {Zn(L2)(syn-L7)·(DMF)3(H2O)}n (2-syn-Zn) and {Zn(L2)(anti-L7)·(DMF)3.5(H2O)1.5}n (2-anti-Zn), have been crystallographically characterised; their differences rest upon the conformations adopted by ligand L7. The structure of the 2 anti Zn isomer has higher potential porosity, appearing as rhomboid channels running down the direction of the crystallographic b-axis. The two dimensional sheets of both 2-syn-Zn and 2-anti-Zn are linked in a third dimension through hydrogen bonding interactions between the carboxylate of (L2)2− and amide moiety of L7 in adjacent layers. UV irradiation (325 nm) of single crystals of both forms of 2 Zn initiates a growth in fluorescence of the material observed in situ on a Raman microscope. In situ monitoring of the fluorescence using a 785 nm laser shows a decay over 23 hours to recover the original Raman spectrum of the material. The fluorescence decay can be fitted to a biexponential process; the faster process (13 270 s−1 and 1290 s−1, 2-syn-Zn and 2-anti-Zn respectively) is approximately an order of magnitude greater than the slower process (3980 s−1 and 350 s−1 respectively). DFT calculations suggest the theoretical spectroscopic and electrochemical properties of (L2)2− are not significantly changed by coordination to zinc in 2-Zn. The structures 2-syn-Zn and 2-anti-Zn are the first known examples of spiropyran functionality being incorporated into frameworks.

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Dartnell, Nicholas John. "Dry etching of silicon based semiconductor materials : plasma diagnostics and reaction mechanics." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239655.

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27

McCleese, Christopher. "Femtosecond Time-Resolved Spectroscopy Studies of Interfacial Charge Separation Processes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case149182204612303.

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28

Redeker, Neil. "MORPHOLOGY AND CONFORMATION OF POLYTHIOPHENE DERIVATIVES IN ANISOTROPIC CORE-SHELL NANOCOMPOSITES AND SOLUTION." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1144.

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Conjugated semiconducting polymers have garnered substantial interest in recent years due to the potential for use in various applications, particularly in the field of electronic devices such as photovoltaic cells and light emitting diodes. Conjugated polymers offer numerous advantages in these applications, including low cost and high flexibility, but electronic devices based on these materials are currently limited by poor performance. Because of these limitations, increased focus has been placed on improving conjugated polymers for use in commercially viable products. Here, a novel core shell hybrid nanocomposite based on anisotropic zinc oxide nanowires and a side-chain functionalized polythiophene is reported. This nanocomposite exhibits confirmed covalent side-on linkage between the polymer and the nanowires, and the crystalline, thermal and photophysical properties of the nanocomposite are investigated, revealing elongated conjugation length in the polymer backbone, increased crystallinity and thermal stability and rapid charge transfer. Additionally, the conformational transitions of side-chain functionalized polythiophenes are investigated in dilute solution through the use of ultraviolet-visible absorption spectrophotometry. A coil-to-rod conformational transition is identified, and is found to be induceable through temperature and solvent changes. Study into the kinetics of the transition reveals a first-order rate law, and the effects of polymer structure on the conformational transition are substantiated.

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Terrones-Maldonado, Mauricio. "Production and characterisation of novel fullerene-related materials : nanotubes, nanofibres and giant fullerenes." Thesis, University of Sussex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361404.

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30

Stimson, Lorna M. "Phase behaviour of macromolecular liquid crystalline materials : computational studies at the molecular level." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/3144/.

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Molecular simulations provide an increasingly useful insight into the static and dynamic characteristics of materials. In this thesis molecular simulations of macro-molecular liquid crystalline materials are reported. The first liquid crystalline material that has been investigated is a side chain liquid crystal polymer (SCLCP). In this study semi-atomistic molecular dynamics simulations have been conducted at a range of temperatures and an aligning potential has been applied to mimic the effect of a magnetic field. In cooling the SCLCP from an isotropic melt, microphase separation was observed yielding a domain structure. The application of a magnetic field to this structure aligns the domains producing a stable smectic mesophase. This is the first study in which mesophases have been observed using an off-lattice model of a SCLCP. The second material that has been investigated is a dendrimer with terminal mesogenic functionalization. Here, a multi-scale approach has been taken with Monte Carlo studies of a single dendrimer molecule in the gas phase at the atomistic level, semi-atomistic molecular dynamics of a single molecule in liquid crystalline solvents and a coarse-grained molecular dynamics study of the dendrimer in the bulk. The coarse-grained model has been developed and parameterized using the results of the atomistic and semi-atomistic work. The single molecule studies showed that the liquid crystalline dendrimer was able to change its structure by conformational changes in the flexible chains that link the mesogenic groups to the core. Structural change was seen under the application of a mean field ordering potential in the gas phase, and in the presence of liquid crystalline solvents. No liquid crystalline phases were observed for the bulk phase studies of the coarse-grained model. However, when the length of the mesogenic units was increased there was some evidence for microphase separation in these systems.

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31

Rice, Craig R. "The synthesis of novel organic materials and the study of attractive intramolecular interactions." Thesis, University of Kent, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385089.

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32

Ahmed, A. S. "Dispersions of chemical and natural materials to produce composites with commercially useful properties." Thesis, City University London, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375827.

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33

Perkins, Steven Patrick. "The effect of molecular structure on the mesogenic properties of liquid crystalline materials." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302348.

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Peters, Kyle C. "Sustainable Materials and Processes for Optoelectronic Applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554397264722736.

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35

Headspith, David Andrew. "The preparation and characterisation of mixed-anion and non-oxide materials." Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:2680.

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Traditionally, research in solid-state chemistry has focused largely on the chemistry of oxides and on chemical tailoring of the structure and physical properties via cationic substitutions. Consequentially, the chemistry of non-oxide ompounds and other means of chemical tailoring, such as anionic substitutions, have been comparatively overlooked by the scientific community. Non-oxides offer a wide diversity of chemistry, most noticeable in unusual oxidation states and coordination geometries found for metals in these compounds. Furthermore, the development of anionic substitutions could open up an alternative avenue for the modification of the structure and properties in solids and the preparation of novel compounds. The work reported here covers: (1) the preparation of non-oxide compounds (Ba2CoS3, Ba2MnS3, Ce2MnN3, Ce2-xLaxMnN3) and mixed-anion compounds (Ce2MnN3F2-δ, apatite oxide-nitrides) via direct synthesis and/or cationic and anionic substitutions; (2) the characterisation of their structure and (3) the characterisation of selected physical properties. The three-dimensional magnetic cell of Ba2CoS3, which undergoes a transition to long-range order at 46 K, was found to be double the size of the crystallographic unit cell, along the c-axis. A conclusive representation of the magnetic cell of Ba2MnS3, with similar structure to Ba2CoS3, could not be achieved and two possible models are proposed. A one-step synthetic route for Ce2MnN3, more convenient than the route reported in the literature, was developed in this work. Cationic substitutions led to the preparation of the solid solution Ce2-xLaxMnN3 and anionic manipulation of the lattice, via fluorination, led to the preparation of the first example of a quaternary nitride-fluoride Ce2MnN3F2-δ. The structure of Ce2MnN3F2-δshowed layers of distorted MnN5F octahedra and staged fluorine occupancy of the interstitial sites. A range of novel oxide-nitrides were prepared via reaction of the apatite-type oxides La9.33Si6O26, La8+xSr2−xM6O26+x/2 (M = Si, Ge; 0 less than or equal to x less than or equal to 2), La9.67Si5CoO26 and La10M5CoO26.5 (M = Si, Ge) with gaseous ammonia at temperatures above 700°C, most retaining the apatite structure with nitrogen located in interstitial sites.

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36

Shepherd, Paul David. "The synthesis and possible non-linear optical second harmonic generation of some organosilicon materials." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385998.

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Cross, Gregory John. "The synthesis and evaluation of highly polarisable organic materials for third-order nonlinear optical applications." Thesis, University of Hull, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363335.

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Lee, Darren Frank. "The catalysed reactions of allyl alcohol using the microporous materials zeolite Y and TS-1." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386828.

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Buley, Jill Marie. "The study of the dissolution and solubility kinetics of thin polymer films for resist materials." Thesis, University of Bath, 1993. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358772.

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40

Psarras, Peter Campbell. "Toward an Understanding of Methane Selectivity in the Fischer-Tröpsch Process." Cleveland State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=csu1407953187.

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Sacco, Amanda C. "An Extensive Study of Soft Materials Containing Carboxylic Acid Moieties to Determine Hydrogen Bond Energies Using Analytical and Theoretical Methods." Youngstown State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1442486805.

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42

Debnath, Sudeep. "Surface/Geochemistry of Iron and Manganese Oxide Nano-Materials in the Environment." Diss., Temple University Libraries, 2009. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/30879.

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Chemistry
Ph.D.
Nanomaterials possess physical and chemical properties that may benefit medicine, catalysis, and environmental remediation. Apart from understanding the structure of nanomaterials, significant amount of research has focused on understanding the structural properties of nanoparticles that lead to their unique reactivity. Ferric hydroxides are important mineral components and the subject of much scientific research in environmental and soil sciences because of their ubiquity in soil, ground water and aquatic sediments Iron oxide nanoparticles found in the environment exhibit size-dependent behavior. Iron oxides also play an important role in environmental chemistry. Ferrihydrite is an important iron oxide mineral as they exist in most of the sediment environment, necessary precursors for more stable iron oxides like hematite. Iron oxides are also important in many living organisms and stored as protein-encapsulated iron(III) oxyhydroxide nanoparticles. Because of the ubiquitous nature of ferrihydrite in soil and sediments, understanding correlation between the surface reactivity and the structure, phase of ferrihydrite ie. homogeneous or heterogeneous phase dependent reaction is important from environmental point of view. Iron oxides also play an important role in atmospheric chemistry and size dependent surface catalytic properties towards atmospheric gases. Green house gases are frequently generated during the burning of fossil fuels in factories and power plants, or derived from natural processes such as volcanic eruptions. Both natural and engineered metal oxides have been utilized as catalysts or sorbents for removal or minimization of green house emissions. In an attempt to understand the structure and reactivity relationship, we have presented ferrihydrite dissolution under reducing conditions and in situ kinetic studies were performed on isolated individual single particles of ferrihydrite using AFM. Bulk batch studies are also presented, where particles exist as agglomerates. Interface dissolution reaction has been characterized with FTIR and results were confirmed with theoretical calculations. Normalized dissolution rate of individual ferrihydrite particle sheds light on the phase behavior of this material. This study indicates that the ferrihydrite is uniform in composition and supports the Michel et al model. The size-dependent reactivity of ferrihydrite toward the environmentally important gas sulfur dioxide SO2 was also studied as atmospheric emission of SO2(g) affects the environment because it promotes the production of acid rain. In this investigation, nano-ferrihydrite particles were synthesized with a narrow size distribution. The surface chemistry and reactivity (SO2(g) sorption) was studied with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy in combination with molecular orbital/density functional theory (MO/DFT) frequency calculations. Results showed that SO2(g) sorption may be a sensitive function of the structural properties and size of the nanoparticles. Like Iron oxides, Manganese oxides also play a distinctive role in superficial soil or near surface environments. Birnessite is one of the most commonly occurring manganese oxides in the soils and sediments. Birnessite are known to provide a suitable surface for heterogeneous oxidation of As(III) to As(V), and thus contribute to the environmental fate of arsenic species in soil and sediments. In the present study we have made an effort to understand this fundamental geochemistry occurring at birnessite surface at the molecular scale using advanced surface sensitive tools like AFM and spectroscopic techniques like FTIR and XPS. Nano size manganese oxide was also prepared via biological routes. Nano-size manganese oxide was prepared using ferritin protein as the biological precursor. Solution phase arsenic oxidation studies were performed with Ferritin Manganese oxide. Ion chromatography is performed to investigate oxidation of As(III) and reduction of manganese, along with XPS analysis to monitor the oxidation states of arsenic and manganese species. Results were also verified with FTIR spectroscopy for interface speciation.
Temple University--Theses

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Alkaabi, Khalifa. "The synthesis, chemical and physical characterisation of selected energetic binder systems." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1080.

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Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009.
Due to numerous accidents involving munitions, recent interest has focused on the development and use of insensitive munitions (IM). Polymeric materials are used in insensitive munitions as binders or plasticizers. Most of the polymeric binders used are based on polycondensation reaction via using urethane linkages. The main aim of this study was the synthesis and characterization of selected energetic thermoplastic elastomers binder based on utilizing controlled free radical polymerization. This was achieved by using hydroxyl terminated poly (epichlorohydrin) (PECH-diol) and hydroxyl terminated glycidyl azide polymer (GAP-diol) as starting materials, and the subsequent synthesis of different macroinitiators. These macro-initiators were used to polymerize methyl methacrylate (MMA) to obtain thermoplastic elastomers. PECH-diol was prepared by cationic ring-opening polymerization (CROP) based on using borontrifluoride etherate (BF3-etherate) as catalyst and a low molecular weight diol as initiator. GAP-diol was synthesized by the reaction of PECH-diol with sodium azide in organic solvent.. Poly(epichlorohydrin-methyl methacrylate) (PECH-PMMA) and poly(glycidyl azidemethyl methacrylate) (GAP-PMMA) block copolymers were prepared by free radical polymerization of MMA monomer in presence of PECH and GAP macro-azoinitiator (MAI). The MAIs were prepared by the polycondensation reaction of hydroxyl terminated groups of elastomer with 4,4' azobis (4-cyanopentanoyl chloride) (ACPC). The phase behavior of blends of amorphous PMMA/PECH-diol and PMMA/GAP-diol was also investigated. Poly(epichlorohydrin-methyl methacrylate) (PECH-PMMA) and poly(glycidyl azidemethyl methacrylate) (GAP-PMMA) graft copolymers were synthesized by photopolymerization of MMA in presence of PECH and GAP with pendant N,Ndiethyldithiocarbamate groups as macro-photoiniferters. . Photopolymerization of MMA proceeded in a controlled fashion. A macro RAFT agent, based on the reaction of PECH with pendent dithiobenzoate was prepared. The macro-RAFT agent was used in the controlled thermal bulk polymerization of methyl methacrylate. Finally, living/controlled radical polymerization of MMA with four different photoiniferters, namely benzyl diethyl dithiocarbamate (BDC), 2-(N,N-diethyldithiocarbamyl) propionic acid (PDC), 2-(N,Ndiethyldithiocarbamyl) isobutyric acid (DTCA), and diethyl dithiocarbamateepichlorohydrin was achieved.

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44

Lin, Andrew. "Metal-Organic Frameworks and Graphene-Based Support Materials for Heterogeneous Catalysis." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5574.

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Nanoparticles are involved in a broad range of applications, including heterogeneous catalysis. Nanoparticles tend to quickly lose their well-defined shapes and facets due to aggregation under duress such as heat. A series of highly studied materials are explored as support materials for nanoparticle supports. These supports include metal-organic frameworks (MOF), graphene oxide (GO), and a MOF-PRGO (partially reduced graphene oxide) hybrid. The inclusion of a support with the palladium increased lifespan of the catalyst by separation of nanoparticles. The choice of support material not only allowed for supporting of palladium nanoparticles, but allowed for rational catalyst synthesis in order to design catalysts with improved catalytic activity. CO oxidation, vanillin hydrogenation, and Suzuki cross coupling were studied. For the CO oxidation reaction, a cerium-based MOF, Ce-MOF, is shown to increase activity of palladium nanoparticles by capturing reactant gases and acting as an oxygen reservoir that cycles between (III) and (IV) states while transferring oxygen to palladium nanoparticles at the Pd/Ce-MOF interface. A hybrid Ce-MOF-PRGO was synthesized to increase the surface area and acidity of Ce-MOF materials and was shown to be active for vanillin hydrogenation. Smaller rod-like Ce-MOF crystals were observed, indicating intercalation of crystals on GO. Zirconium-based MOF UiO-66-NH2 was acidified via incorporation of tungstophosphoric acid (HPW), which increased the selectivity of products by adjusting the mechanistic pathway. GO was partially functionalized with aromatic amines to improve the coupling of bromobenzene and phenylboronic acid. Small amounts of aromatic amines increased the Pd(0) content and decreased nanoparticle size.

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45

Kanigan, Tanya. "Integrated optics spectroscopy of polymer thin films." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40157.

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This thesis describes the design and construction of an integrated optics (IO) spectrometer for the purpose of characterizing optically transparent polymer thin films (1-10 $ mu$m). IO spectroscopy exploits the properties of electromagnetic fields that exist in a polymer film when it is used as a planar dielectric waveguide. The spectrometer measures waveguide propagation constants and Raman spectra excited by guided modes. These data are used to characterize the structures of solution cast cellulose acetate (CA) films and glassy cellulose films regenerated from them, and laser induced anisotropy in organically modified silicate (ORMOSIL) sol-gel films.
Waveguide Raman spectra indicate partial alignment of CA chains within the plane of the film. Deacetylation of CA films in aqueous ammonia to form glassy regenerated cellulose (RC) waveguides preserves orientational anisotropy of the parent CA film. Refractive index profiles are reconstructed from measured optical propagation constants of CA, RC and partially regenerated CA waveguides using inverse Wentzel-Kramers-Brillouin approximation methods. Partially regenerated CA films possess an asymmetric reflective index gradient attributed to depth inhomogeneity present in CA films prior to regeneration.
The effects of deviations from right angle scattering geometry on polarized waveguide Raman spectra are discussed. Polarization mode conversion is attributed to the presence of off-diagonal elements in the film dielectric tensor. In CA films, these off-diagonal elements result from excessive pressure on the coupling prism and partial orientation of polymer chains. Coupled mode theory is used to predict the effects of polarization mode conversion on the polarized Raman spectra as a function of film parameters and coupling angle.
Photoinduced birefringence and photoalignment are observed in ORMOSIL sol-gel films after exposure to guided light from an argon ion laser (514.5 nm and 488.0 nm lines). By simultaneously exciting TE and TM modes, non-transient, reversible off-diagonal dielectric tensor elements are introduced in the film. These off-diagonal elements cause coupling between the orthogonal TE and TM modes, which is, in turn, observed in polarized waveguide Raman spectra collected from the film. Photorefractive effects are attributed to photoinduced anisotropy (PIA) and glass photosensitivity phenomenon previously observed (by others) in doped silicate glasses.

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46

Donakowski, Martin Daniel. "Syntheses, Local Environments, and Structure-Property Relationships of Solid- State Vanadium Oxide-Fluorides." Thesis, Northwestern University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3615500.

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Vanadium oxide-fluorides can exhibit properties of piezoelectricity, second harmonic generation (SHG) activity, electrochemical activity, and other phenomena. The first two properties derive from the second-order and Jahn-Teller distortions, respectively, of d⁰ and d¹ vanadium; the electrochemistry derives from the reduction of V^V to V^IV,III,II.

An examination of the immediate environment of a vanadium cation facilitates an understanding of how a cation influences the structure of a compound and its resulting properties. In the inorganic hydrate CuVOF₄(H₂O)₇, the CuVOF₄(H₂O)₆ basic-building unit (BBU) has a Λ-shape that compels polar packing in a structure that has SHG properties. The compound is a very rare example of a carbonless, SHG-active molecular crystal. Influences for its packing are reasoned with principles previously used within organic molecular crystallography.

The early transition metals (ETMs) of vanadium, niobium, and molybdenum within compounds of formulae K₁₀(M₂O_nF_11-n)X (M = V^V, Nb^V, n = 2, M = Mo^VI, n = 4; X = halide) show a related packing motif of Λ-shaped BBUs in different structures. Owing to the absence or presence of Λ-shaped BBUs, these heterotypical structures crystallize decidedly into SHG-inactive or SHG-active forms when M = V^V or M = Nb^V, Mo^VI, respectively. The future use and development of Λ-shaped BBUs within solid-state systems can result in SHG-active materials.

The material CuVOF₄(H₂O)₇ presents an interesting coordination: the late transition metal (LTM, Cu^II) coordinates solely to the oxide anion of the vanadyl cation owing to hard-soft acid-base (HSAB) properties. The materials Na₂[M(H₂O)₂][V₂O₄F₆] (M^II = Co, Ni, Cu) show the LTM coordinates solely to the oxide anions of the V^V cation while the alkali cation (Na^I) coordinates solely to the fluoride anions. These HSAB properties were used to generate layers of hard or soft cation/anion rich regions in the electrochemically-active double wolframite AgNa(VO₂F₂)₂.

These structure-property examinations of solid state vanadium oxide-fluorides are presented as principles for (i) fundamental understanding of ETM and BBU crystallographic environments, (ii) materials discovery for fundamental investigations, (iii) materials design, and (iv) materials for use in SHG, piezoelectric, and electrochemical processes.

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47

Zaker, Yeakub. "Facile Size Focusing Synthesis of Silver Nanoparticles Capped with Aliphatic Thiol Ligands." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1480456850511426.

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48

Madathingal, Rajesh Raman. "Nanoscale confinement and interfacial effects on the dynamics and glass transition/crystallinity of thin adsorbed films on silica nanoparticles." Diss., Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/116348.

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Chemistry
Ph.D.
The research investigated in this dissertation has focused on understanding the structure-property-function relationships of polymer nanocomposites. The properties of composite systems are dictated by the properties of their components, typically fillers in a polymer matrix. In nanocomposites, the polymer near an interface has significantly different properties compared with the bulk polymer, and the contribution of the adsorbed polymer to composite properties becomes increasingly important as the filler size decreases. Despite many reports of highly favorable properties, the behavior of polymer nanocomposites is not generally predictable, and thus requires a better understanding of the interfacial region. The ability to tailor the filler/matrix interaction and an understanding of the impact of the interface on macroscopic properties are keys in the design of nanocomposite properties. In this original work the surface of silica nanoparticles was tailored by: a) Changing the number of sites for polymer attachment by varying the surface silanols and, b) By varying the size/curvature of nanoparticles. The effect of surface tailoring on the dynamic properties after the adsorption of two model polymers, amorphous polymethyl methacrylate (PMMA) and semicrystalline polyethylene oxide (PEO) was observed. The interphase layer of polymers adsorbed to silica surfaces is affected by the surface silanol density as well as the relative size of the polymer compared with the size of the adsorbing substrate. The non-equilibrium adsorption of PMMA onto individual colloidal Stöber silica (SiO2) particles, where Rparticle (100nm) > RPMMA (~6.5nm) was compared with the adsorption onto fumed silica, where Rparticle (7nm) ~ RPMMA (6.5nm) < Aggregate (~1000nm), both as a function of silanol density [SiOH] and hydrophobility. In the former case, TEM images showed that the PMMA adsorbed onto individual nanoparticles, so that the number of PMMA chains/bead could be calculated, whereas in the latter case bridging of PMMA between aggregates occurred. The anchoring point densities were comparable to the silanol densities, suggesting that PMMA adsorbed as trains rather than loops. For hydrophilic SiO2, Tg increased with [SiOH], as more carbonyl groups hydrogen bonded to the silanols, and was independent of particle morphology. For methylated silica, (CH3)3-SiO2, the adsorption isotherms were identical for colloidal and fumed silica, but Tg was depressed for the former, and comparable to the bulk value for the latter. The increased Tg of PMMA adsorbed onto fumed (CH3)3-SiO2 was attributed to the larger loops formed by the bridging PMMA chains between the silica aggregates. For nanocomposites the interphase region becomes more important as the surface/volume ratio of the nanoparticles increases. Polymers have chain dimensions (characterized by the radius of gyration, Rg) similar to the nanoparticles (Rnanoparticle) themselves, so that chain conformation, mobility and crystallinity can be affected by Rg/Rnanoparticle. Here, both the glass transition temperature (Tg) and degree of crystallinity (Xc) of polyethylene oxide (PEO) on individual SiO2 nanoparticles of nominal 15, 50 and 100 nm diameter (2 RSiO2) , in which Rg (PEO) was greater, equal to or less than RSiO2 was investigated. Plateau adsorption of PEO on SiO2 nanoparticles (PEO-SiO2) increased in the order PEO-SiO2 (100 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (15 nm). At plateau adsorption after melting and solidification, the samples were completely amorphous. The Tg of the adsorbed PEO increased in the order PEO-SiO2 (100 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (15 nm); since the Tgs were above 25oC in all cases, the PEO behaved more like a brittle solid than an elastomer. For comparable amounts of PEO that were adsorbed from solution but not melted, the melt endotherm increased in the order PEO-SiO2 (15 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (100 nm). These trends were interpreted as due to an increase in loop/tail lengths and thus flexibility, with a concomitant ability to crystallize, as Rg (PEO)/RSiO2 decreased and which was the result of less hydrogen bond formation between the oxygens of PEO and the silanols (SiOH) of the SiO2 as the nanoparticle size decreased. This in turn was attributed to the energetically unfavorable conformations necessary for the PEO chains to adopt in order to hydrogen bond with silanols on the smaller nanoparticles. The degradation behavior of amorphous PMMA and semicrystalline PEO on silica (SiO2) nanoparticles as a function of silanol density and nanoparticle size was investigated by derivative thermogravimetric analysis (DTGA) for adsorption amounts below plateau adsorption. For PMMA Td decreased as the number of SiOH/C=O contacts decreased, either from heat treatment of the SiO2, which reduced the silanol density, or as the nanoparticle size decreased, reducing the numbers of places that the PMMA chain contacted the nanoparticles.
Temple University--Theses

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49

Gao, Ruixuan. "Designing Novel Semiconductor Nanowire Structures: Synthesis and Fabrication for Localized Photodetection and Sensing." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17463963.

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Semiconductor nanowires display a wide range of structural and functional diversity, and as such provide a platform for nanomaterials research. At present, a number of nanowire structural motifs have been discovered and configured into devices with unique electrical and optical functionalities. For example, a kinked nanowire with a localized axial dopant modulation can record intracellular action potentials when incorporated into a three dimensional device. A radially modulated p-i-n nanowire can function as a nanoscale photovoltaic device to power logic gates and sensors. This thesis focuses on novel electrical and optical device functionalities based on rational design, synthesis and characterization of semiconductor nanowire structures for applications in the physical, chemical and biological sciences. First, I will present the design, synthesis and fabrication of two nanodevices for intracellular sensing that are based on core/shell and branched nanowire structural motifs. In both types of devices, a nanotube bridge templated by nanowires conducts the intracellular electrical and chemical potentials to the gating regions and the change in potential is recorded as the change of the device conductance. Both nanowire-based devices can sense extra- and intracellular action potentials with high spatial resolution. Furthermore, they can be easily multiplexed and scaled up to record intracellular action potentials at multiple sites from either a single cell or cellular network. Second, I will discuss the synthesis of tapered nanowire structures and their electrical and optical characterization. By finely tuning growth temperature, precursor partial pressure, and catalyst size, detailed control of the nanowire tapering angle can be achieved. Moreover, tapered core/shell nanowires can be configured into devices with highly-localized electrical and optical functionalities. I show that control of the tapering angle plays an important role in determining the electrical and optical properties of nanowires. Finally, I will demonstrate a novel nanowire structural motif, termed tip-modulated nanowire, in which the modulation of material and dopant is localized at the nanowire tip so that a tip-localized device is encoded. I describe rational bottom-up synthesis of tip-localized p-n junctions, which are connected to the p-type nanowire core and isolated n-type nanowire shell. The electrical and optical properties of the tip-modulated nanowires are investigated by configuring them as devices with electrically independent core and shell contacts. Spatially-resolved electrical and optical characterizations show that a potentiometric sensor as well as a highly sensitive p-n diode photodetector can be localized at the nanowire tip. In addition, a top-down strategy for wafer-scale synthesis and fabrication of vertical tip-modulated nanowires and nanowire device arrays is presented. Finally, by combining the tip-modulated nanowire structure with other structural motifs, we can rationally design self-sustained multi-functional nanodevices. The new tip-modulated nanowire structural motif opens up novel applications in the physical, chemical and biological sciences.
Chemistry and Chemical Biology

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50

Day, Robert Watson. "Crystal Growth on One-Dimensional Substrates: Plateau-Rayleigh Crystal Growth and Other Opportunities for Core/Shell Nanowire Synthesis." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17464133.

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Nanowires hold significant promise for both fundamental studies and technological applications ranging from energy conversion to electronics to biological sensing. The detailed understanding of nanowire synthesis and the realization of new synthetic approaches have enabled precise control over their size, morphology, and composition, and, consequently, their material properties. While much of the work on synthesis in the literature relates to axial nanowire growth, where growth proceeds in the direction of its long axis, this thesis has focused on probing the unique opportunities of shell growth, where material deposits radially around a nanowire core. To this end, I will show, first, that faceted Si core/shell nanowires can be synthesized with embedded pn junctions and that these structures can function as efficient photovoltaic devices with enhanced light absorption properties distinct from bulk Si devices. Second, through choice of reactants and reaction conditions used for shell growth, we demonstrate fine control over the size and morphology of these nanowires, which, in turn, drastically enhances their light absorption at particular wavelengths. Finally, we report for the first time a growth phenomenon that is unique to one-dimensional materials and which combines the underlying physics of the Plateau-Rayleigh instability with crystal growth. By exploiting this phenomenon, which we term Plateau-Rayleigh crystal growth, we demonstrate the growth of periodic shells on one-dimensional substrates. Specifically, we show that for conditions near the Plateau-Rayleigh instability the deposition of Si onto uniform-diameter Si cores, Ge onto Ge cores, and Ge onto Si cores can generate diameter-modulated core/shell nanowires. Rational control of deposition conditions enabled tuning of distinct morphological features, including diameter-modulation periodicity, amplitude and cross-sectional anisotropy. More generally, Plateau-Rayleigh crystal growth highlights the opportunities in understanding the thermodynamics and kinetics unique to crystal growth on nanowires and other low dimensional systems.
Chemistry and Chemical Biology

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Dissertations / Theses on the topic '030304 Physical Chemistry of Materials'

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