Synthesis and magneto-structural characterization of hydrogen bonded organic nitronylnitroxide and verdazyl radicals were done. 35diMeO–4OHPhNN displayed 1D antiferromagnetic interactions attributed to the chain contacts between radical NO groups. Benzimidazole-based verdazyl radicals 2BImverd, and 5BImverd did not give diffraction quality crystals and were only characterized by EPR. The analogues 2BImisoverd and 5BImisoverd both gave x-ray diffraction quality single crystals that displayed formation of hydrogen bonded chains through the imidazole moieties. The magnetic susceptibility results indicated the presence of weak 1D AFM interactions for both radicals. The weakness of interactions was attributed to bulky isopropyl groups pushing the molecules apart and decreasing spin orbital overlap. A series of organic radical solid solutions (alloys) were made using BImNN and its fluorinated analogue F4BImNN. (F4BImNN)x(BImNN) (1−x) with x < 0.8 gave orthorhombic unit cells, while x > 0.88 gave monoclinic unit cells. (F4BImNN) (x)(BImNN)(1−x) (x = 0.1, 0.17, 0.25, 0.5, 0.75, 0.83, 0.9) displayed ferromagnetic interactions with J/k = (+)14–22 K, mainly controlled by hydrogen-bonded assembly of the radicals. Magnetic analysis over 0.4–300 K showed ordering behavior for all of these materials. The ordering temperatures of the orthorhombic samples increased linearly as (1−x) increased from 0.25 to 1.00. The variation was attributed to increased inter-chain distance as more F4BImNN was added into the orthorhombic lattice. The monoclinic samples were not part of the same trend, which was attributed to a change in the inter-chain arrangement. This was the very first study giving such complete magnetostructural detail linking ordering behavior to specific crystallographic features and intermolecular contacts. The magnetic behavior of F4BImNN was investigated at increased external pressures. The crystallographic c-axis (along which hydrogen bonds form) was compressed by 3% at 10 kbar and by 4% at 17.8 kbar. The overall lattice volume contracted by 12% from ambient pressure to 17.8 kbar. The magnetic susceptibility measured over 1.8–300 K showed an increase in ferromagnetic exchange interactions as pressure increased. The increase in exchange strength was attributed to pressure-increased overlap of spin orbitals in the hydrogen-bonded chains, which favored 1D ferromagnetic interaction. Electron paramagnetic resonance experiments on a single crystal of F4BImNN were also performed. The variation in g-value as a function of the crystal's position with respect to the applied magnetic field was investigated. The angular dependence of g was more pronounced at temperatures below 30 K. Pyrrole-based nitronylnitroxide radicals mNNPP, N–PN and 35NNPP were studied. mNNPP displayed formation of 1D chains with weak intra-chain FM interactions, N–PN gave 1D AFM interactions, and 35NNPP showed intramolecular FM and intermolecular AFM interactions.

A series of para-linked aromatic polyamides synthesized with the aim of making optically uniaxial, transparent films and fibers for optical applications, are found to have anomalous properties. Stretched films of these polyamides are highly birefringent and non-crystalline at the same time. These rod-like polyamides do not form lyotropic solutions and are soluble in common solvents like THF, unlike other rod-like polymers. With the goal of understanding this behavior from a molecular standpoint we have quantitatively characterized the geometric, optical and hydrodynamic properties of one of these polyamides. With angle light scattering measurements on polyamide in THF were used in conjunction with electric birefringence measurements to determine the weight average molecular weight, M$\sb{\rm w}$, the root mean square z-averaged radius of gyration, R$\sb{\rm gz}$, the apparent second virial coefficient, A$\sb{\rm 2app}$ and the monomer molecular anisotropy ratio $\varepsilon$. The polydispersity correction was applied theoretically by assuming the most probable distribution. Hydrodynamic and optical properties were determined with viscometry and differential refractometry respectively. The aromatic polyamide studied can be satisfactorily modeled as a Kratky-Porod wormlike chain with a persistence length of 220 $\pm$ 50 A and a monomer optical anisotropy ratio of 2.3 $\pm$ 0.3. The excluded volume effect is found to be negligible in THF at 25$\sp\circ$C. The small axial ratio of 30 may be partly responsible for the non-lyotropic behavior. The refractive index of 1.67 is in good agreement with that of similar polyamides. The repeat unit has a high optical anisotropy leading to highly birefringent films. It is also conclusively established that there is no aggregation due to H-bonding in the absence of moisture. The light scattering theory of Nagai and the hydrodynamic theory adopted for semiflexible chains is found to hold very well for the polyamide studied. Based on the agreement between experiment and theory we infer that the molecular weight distribution is of the most probable type. Our depolarized light scattering data indicate that the straight line behavior observed in Zimm plots even for $\rm R\sb{g}\sp2q\sp2>1$, upto $\rm R\sb{g}\sp2q\sp2$ of 3.5 is due to the combined effect of polydispersity, large size and optical anisotropy of the molecule.

Various important aspects of discontinuous fiber composites have been studied in detail both experimentally and theoretically through a model composite containing polydiacetylene (PDA) single crystal as the reinforcement fiber and epoxy resin as the matrix. The aspects encompass varying degrees of fiber behavior as well as fiber/matrix interaction, such as compressive behavior of the reinforcement fiber, geometry effects of the fiber on the stress distribution along the fiber, fiber orientation, residual thermal stress, and the role of fiber/matrix interfacial properties on the performance of composites. The compressive failure mode of the PDA fiber used in this study is the formation of readily observable kink bands. The critical compressive strain of the fiber was found to be 0.3%. By monitoring the behavior of the C$\equiv$C bond frequency in PDA in response to applied compressive loads, the stress along the fiber can be determined leading to the establishment of a calibration curve describing the relationship between the frequency change of the bond and the compressive strain due to residual thermal stress caused by differences in thermal expansion between fiber and matrix. This thermal stress will cause fiber compressive failure if the critical compressive strain is achieved. A quantitative analysis of the data reveals that no slippage occurs at the fiber/matrix interface during the build-up of thermal stress. The geometry of the fiber was found to play a significant role. Both experimental and finite element analysis demonstrate the advantage of tapered end fiber over the ordinary blunt end fiber, i.e. fiber with a uniform diameter. The experimental apparatus constructed in this study allows the measurement of tensile strain distribution of the fibers orientated at any angle with respect to the draw direction to be determined accurately. For a thin layer coating of the fiber, it was found that the tensile strain distribution along the fiber was unaffected, and so by extension neither would the modulus of a composite in fiber axial direction be affected. This observation indicates that for most composite systems perfect bonding is easily formed at the fiber/matrix interface as far as tensile stress transfer is concerned. (Abstract shortened with permission of author.)

This dissertation presents a new technique for determining the residual stresses and material properties of polyimide coatings. The primary materials studied are polyimides, pyromellitic dianhydride-oxydianiline (PMDA-ODA) and poly (N,N$\sp\prime$(phenylene)-3,3$\sp\prime4,4\sp\prime$-biphenyl tetracarboxylic diimide) (BPDA-PDA). The determination of the internal stresses which develop during processing in these coatings is critical for reliability prediction and material selection for the microelectronics industry. For any given coating on a rigid substrate, the shear and normal tractions between the two materials goes to zero away from the edges. A portion of the substrate can therefore be removed leaving a simply supported membrane (coating) with its original state of stress intact. Classical vibration theory states that the square of the resonant frequency of a membrane is proportional to its biaxial stress. Real-time holographic interferometry is used to identify the resonant modes of vibration. It is also shown that using this technique the orthotropic axes of polymer films can be identified, thus simplifying the determination of all nine orthotropic elasticity coefficients.

Polymer surface modification can be accomplished by several techniques including chemical reaction and adsorption. In Chapter I, a simple and versatile technique to introduce carboxylic acid functionality to the surfaces of three fluoropolymer film samples is described. In Chapter II, the adsorption of neutral poly(scL-lysine) (PLL) from solution to the water-fluoropolymer interface is described. Chapter III combines the methods of surface modification described in Chapters I and II and discusses the adsorption of charged PLL to a carboxylic acid-functionalized fluoropolymer film surface. The hydrophobic interaction as a driving force for adsorption is further studied in Chapter IV where the synthesis and adsorption of poly(ethylene oxide) (PEO) and its derivatives are discussed. The syntheses of carboxylic acid-functionalized fluoropolymer films rely upon a two step mechanism where unsaturation, introduced in the first step, is oxidatively removed in the second step; one acidic group per twelve to sixteen repeat units was introduced to the surface. Contact angles ($\theta\sb{\rm A}$/$\theta\sb{\rm R}$) of the acid-functionalized fluoropolymer films decrease with increasing pH: PVF$\sb2$-CO$\sb2$H (77$\sp\circ$/39$\sp\circ$ decreases to 68$\sp\circ$/25$\sp\circ$); PCTFE-CO$\sb2$H (93$\sp\circ$/55$\sp\circ$ decreases to 93$\sp\circ$/43$\sp\circ$); and FEP-CO$\sb2$H (101$\sp\circ$/78$\sp\circ$ decreases to 97$\sp\circ$/61$\sp\circ$). The adsorption of poly(scL-lysine) (PLL) to the water-FEP interface was controlled by pH of the aqueous solution and PLL solution conformation. Only neutral, $\alpha$-helical PLL adsorbed to FEP (FEP-PLL). The adsorption of PLL to carboxylic acid-functionalized FEP, FEP-CO$\sb2$H, was controlled by an electrostatic interaction; both a hydrogen bonding interaction between FEP-carboxylic acid and PLL backbone and an ionic interaction between FEP-carboxylate and PLL-ammonium enhanced adsorption. Both FEP-PLL (80$\sp\circ$/16$\sp\circ$) and FEP-CO$\sb2$H-PLL (78$\sp\circ$/29$\sp\circ$) are more hydrophilic than FEP. FEP-PLL-$\varepsilon$-amine reacts with 3,5-dinitrobenzoyl chloride in 65% yield whereas FEP-CO$\sb2$H-PLL-$\varepsilon$-amine reacts in 100% yield. Adsorption of PLL to FEP and FEP-CO$\sb2$H improves the peel strength of adhesive joints prepared with these substrates and the adhesion and growth of biological cells on these film samples. PEO (5,000 to 50,000 g/mole and polydispersity indices of 1.07 to 1.17) was synthesized by anionic ring opening polymerization of ethylene oxide in THF with triethylene glycol monomethyl ether potassium initiation. PEO was end-capped (PEO-R) by reaction with a (perfluoro)alkyl acid chloride in THF with pyridine catalysis. A polar interaction between substrate and segment controlled adsorption at the fluoropolymer-water interface; PEO adsorbed preferentially to PVF$\sb2$ over PCTFE and FEP. Both PEO and PEO-R adsorbed to the polystyrene latex-water interface; the latter formed a thicker adsorbed layer. PEO-R showed increased surface activity over PEO at the air-water interface; PEO-perfluorodecanoate decreased the surface tension of water to 35 dyn/cm.

The compressive failure of high-modulus polymer fibers, such as poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisthiazole) (PBZT), occurs at stresses an order of magnitude smaller than their tensile failure. A literature review is presented which covers the numerous theories and models for the compressive strength and failure of these fibers as well as of uniaxial composites, which are structurally similar and fail in an analogous fashion. It is pointed out that the smallest shear modulus of any material is a fundamental upper bound to its compressive strength. Physical combination of high-modulus polymers with rigid inorganic materials by impregnation or by deposition of coatings are presently the most promising routes to improved compressive strength and are the research topics presented in this dissertation. PPTA fibers, obtained by spinning from nematic solution, have been impregnated with up to 20 wt-% of a waterborne, highly crosslinkable melamine-formaldehyde resin and with approximately 5 wt-% of sodium silicate from a colloidal aqueous solution. PBZT fibers have also been impregnated with approximately 5 wt-% of sodium silicate. PPTA fibers, obtained by spinning from isotropic solution, have been impregnated with up to 40 wt-% of sodium silicate. None of the impregnations has led to improved compressive strength or other mechanical properties. Kevlar$\sp\circler$ 49 PPTA fibers and heat-treated PBZT fibers have been surface modified with siloxane and silicate functionalities in order to make fibers wettable by aqueous solutions of sodium silicate and to provide good adhesion to silicate coatings. The surfaces of as-received and modified fibers have been characterized by X-ray photoelectron spectroscopy. PBZT and PPTA fibers showed little or no decrease of their tensile properties as a consequence of the surface modification. Glass coatings have been applied to single filaments by dip-coating in aqueous sodium silicate solution followed by drying. Coated PPTA and PBZT fibers with shear moduli as high as 5 GPa have been prepared. The compressive strain at failure of PPTA filaments coated with a 0.5 $\mu$m thick silicate coating was raised to 0.6%, compared to 0.4% for uncoated filaments. These compressive failure strains correspond to compressive strengths of approximately 500 and 400 MPa, respectively.

Trace impurity determinations in volatile, pyrophoric organometallic materials is complicated owing to its chemical nature. Furthermore, trends toward high semiconductor circuit density demand that impurity determinations are performed at increasingly low levels. Volatility of the impurities is also desired as it plays a significant role in impurity incorporation in semiconductor products. Determination of both volatile and nonvolatile impurities in semiconductor-grade organometallic reagent materials has been accomplished using electrothermal vaporization - inductively coupled plasma spectrometry. Solid or liquid materials can be dispensed directly onto a graphite microboat, and application of an appropriate time-temperature ramp allows separation of impurities based on volatility. Temporal separation allows quantitative capabilities on both volatile and nonvolatile signals in a single ETV run. Calibration efforts for volatile impurities have been compared with results from exponential dilution and direct vapor sampling techniques. Nonvolatile impurity determinations can be reasonably performed with aqueous external standard calibration. Inductively coupled plasma-mass spectrometry provides an alternate and more sensitive, multielement detection method. Several spectroscopic and non-spectroscopic difficulties with volatile impurity detection remain. Nonetheless, qualitative and semi-quantitative ($<$50% RSD) determination of most impurities may be performed in a single ETV run.

<p> The primary aim of this study was to develop mesoporous nanocatalysts for (i) hydrogen production via steam reforming of methanol (SRM) in a tubular reactor, and (ii) syngas conversion to hydrocarbons via Fisher-Tropsch synthesis using silicon microchannel microreactors. The mesoporous catalysts for SRM were prepared by an optimized one-pot hydrothermal synthesis procedure. The catalysts were investigated for SRM activity in a packed bed tubular reactor using metals, namely, Cu, Co, Ni, Pd, Zn, and Sn. The metals were incorporated in different supports -MCM-41, SBA-15, CeO₂, TiO₂, and ZrO₂ to investigate the influence of support on catalyst properties. A sharp contrast in catalyst performance was noticed depending on the type of support employed. For example, in SRM at 250 &deg;C, Cu supported on amorphous silica SBA-15 and MCM-41 produced significantly less CO (&lt; 7%) compared to other crystalline supports Cu-TiO₂ and Cu/ZrO₂ that showed high CO selectivity of &sim;56% and &sim;37%, respectively. Amongst all the metals studied for SRM activity using 1:3 methanol:water mole ratio at 250 &deg;C, 10%Cu-MCM-41 showed the best performance with 68% methanol conversion, 100% H₂ , &sim;6 % CO, 94% CO₂ selectivities, and no methane formation. Furthermore, 10%Cu-CeO₂ yielded the lowest CO selectivity of 1.84% and the highest CO2 selectivity of &sim;98% at 250 &deg;C. Stability studies of the catalysts conducted for time-on-stream of 40 h at 300 &deg;C revealed that Cu-MCM41 was the most stable and displayed consistent steady state conversion of &sim;74%. Our results indicate that, although coking played an influential role in deactivation of most catalysts, thermal sintering and changes in MCM-41 structure can be responsible for the catalyst deactivation. For monomtetallic systems, the MCM-41 supported catalysts especially Pd and Sn showed appreciable hydrothermal stability under the synthesis and reaction conditions. While bimetallic Pd-Co-MCM-41 and Cu-Ni-MCM-41 catalysts produced more CO, Cu-Zn-MCM-41 and Cu-Sn-MCM-41exhibited better SRM activity, and produced much less CO and CH4. In spite of the improved the stability and dispersion of the monometallic active sites in the support, no noticeable synergistic activity was observed in terms of H₂ and CO selectivities in the multimetallic catalysts. For the Fisher-Tropsch (F-T) studies, Co-TiO₂, Fe-TiO₂ and Ru-TiO₂ catalysts were prepared by the sol-gel method and coated on 116 microchannels (50&mu;m wide x 100&mu;m deep) of a Si-microreactor. The F-T process parameters such as temperature, pressure and flow rates were controlled by an in-house setup programmed by LabVIEW^&reg;. The effect of temperature on F-T activity in the range of 150 to 300&deg;C was investigated at 1 atm, a flow rate of 6 ml/min and a constant H₂:CO molar ratio of 2:1. In our initial studies at 220 &deg;C, 12%Ru-TiO₂ showed higher CO conversion of 74% and produced the highest C₂-C₄ hydrocarbon selectivity-of &sim;11% ethane, 22% propane and &sim;17% butane. The overall catalyst stability and performance was in the order of 12%Ru-TiO₂>> 12%Fe-TiO₂ > 12%Co-TiO₂.</p>

<p> Nanomaterials are the focus of intense research efforts in a variety of fields because of dramatic differences in properties when compared to the corresponding bulk materials. Catalysis is one material property that can become more pronounced at the nanoscale. By lowering energy requirements for chemical reactions, catalysts reduce production costs in diverse sectors of the economy, including medicine, transportation, environmental protection, oil and gas, food, and synthetic materials. Transition metals are an important class of catalysts capable of facilitating reduction and oxidation of molecular species. Since the discovery of transition metal catalysts nearly 200 years ago, certain metals were considered more active as catalysts (i.e., Pt, Pd, and Ru), while others (Au) appeared to have negligible catalytic activity as bulk materials. In recent years, gold nanoparticles (AuNPs) have become a fast-growing field of research owing to their unexpected catalytic properties not present in the bulk material. However, unsupported AuNPs are highly prone to flocculation and subsequent reduced catalytic activity. The choice of an appropriate aggregation-resistant stabilizing ligand for these nanoparticles is an important part of maintaining nanoscale catalytic properties. Additional stability is provided by anchoring AuNPs to support materials, allowing for dramatic improvements in catalyst lifetimes. This work discusses the development of novel diamond support materials for improving the stability of catalytically active AuNPs. Synthetic nanodiamond is a widely available, inexpensive, and robust material that has found applications in a wide range of commercial abrasives, lubricants, and composite materials. By exploiting the rich surface chemistry of nanodiamond, we have developed versatile catalyst support materials that offer unrivaled chemical and mechanical stability. Various nanodiamond surface modifications are readily prepared using a combination of chemical vapor deposition, photo-active polymer chemistry, and synthetic organic chemistry techniques. Control over the surface chemistry and properties of the resulting nanodiamond allow for increased stability of AuNPs via surface anchored thiol and amine moieties. The use of diamond as a support material should allow a wide variety of noble and nonprecious metal composite materials to be used as catalysts in harsh chemical environments not suitable for existing support materials.</p><p>

<p> Poly(ethylene terephthalate) (PET) is a semi-crystalline polymer that has mechanical and thermal properties suitable for many applications. The rate of crystallization in manufacturing environments influences the final physical, mechanical, and optical properties of PET. Many industrial PET processes occur under dynamic or non-isothermal conditions and in the melt phase. The final material properties are influenced by the size, dimension, and distribution of crystallites and morphology that develop upon cooling from the melt. PET films of varying thickness for optical applications require clarity and transparency. One way achieving clarity and transparency in PET films is to limit or inhibit the quiescent crystallization, while not completely eliminating useful strain-induced crystals. The crystallization behavior of PET is influenced by many things including molecular weight, catalyst remnants, nucleating additives, and the addition of linear and multifunctional comonomers (i.e. branching agents). Branching agents have been reported to inhibit the crystallization of PET. It is of interest to study the effects of branching agents on branched PET (BPET). </p><p> In this investigation the influence of branching agent concentration and geometry on the non-isothermal crystallization behavior and kinetics of BPET was studied. To study the influence of branching agent concentration and geometry, two structural isomers of benzenetricarboxylic acid (<i> n</i>=3) were used at concentrations of 0.10, 0.25, 0.50, and 1.00 mol% (with respect to purified terephthalic acid). The branching agents used were 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA) and 1,2,4-benzenetricarboxylic acid (trimellitic acid, TMLA). TMA and TMLA were used to study the influence of branching agent geometry because TMA is planar and TMLA is non-planar. Two different series of BPET were made to evaluate the influence of catalyst remnants and process on the non-isothermal crystallization behavior of BPET. The Jeziorny-modified Avrami model, the Ozawa model, and the Mo model were applied to study the effects of the branching agent concentration and geometry on the non-isothermal crystallization kinetics of BPET at various cooling rates (5, 10, 20, 50 &deg;C/min). </p><p> The results from the study showed that equivalent amounts of TMA and TMLA produced different non-isothermal crystallization results even though the molecular weight and catalyst concentration remained approximately constant. Increasing branching agent content did not produce a systematic decrease in the crystallization peak temperatures <i>T</i>c. The Mo model was successful in characterizing the non-isothermal crystallization behavior and kinetics of BPET. The crystallization rate was inhibited at concentration of 0.25 and 0.50 mol% TMA and 0.50 and 1.00 mol% TMLA. However, the crystallization rate was enhanced at 0.10 and 1.00 mol% TMA and 0.10 and 0.25 mol% TMLA. It is thought that at small concentrations of the branching agents, regardless of geometry, the branching agents act as nucleating agents. At other branching agent concentrations it is thought that the branching agent geometry influenced the non-isothermal crystallization behavior.</p>