In order to obtain some insight into the deformation behavior of the dispersed phase in the various flows and to evaluate the effects of various variables such as concentration of the dispersed phase and viscosity ratio, affine deformation equations were derived for some stratified shear and elongational flows. It was shown by the derived deformation equations that the volume fraction of the dispersed phase is a factor affecting the deformation of the dispersed phase, and the effect depends on viscosity ratio. The results from the stratified simple shear flow model predict that, for viscosity ratio >1, the deformation rate increases with the volume fraction, and the shear stress also increases, leading to the increase of the breakup time. Therefore, the total deformation of the dispersed phase, before breakup, increases with the increase of the volume fraction, resulting in the decrease of the size of the dispersed phase particles. The prediction was verified experimentally, in both the Haake batch mixer and the Couette flow mixer, using polyethylene/polyamide-6 blends compatibilized by adding maleic anhydride grafted polyethylene, when coalescence was suppressed. In the analysis of particle size data for the verification of the volume fraction effect, an effort was made to identify the contribution of coalescence. The experimental results of particle sizes in 1 wt% blends of the Haake mixer are in reasonable agreement with the transient deformation and breakup theory for simple shear flow. This suggests that the dominant flow in the mixer was shear flow. In some reactively compatibilized blends, at high shear rate, the particle sizes showed a maximum when either the weight fraction or the shear rate was increased. This behavior may be explained by coalescence effects related to the redistribution of the produced copolymers at the interface. It was shown experimentally that, for very high viscosity ratio (>3.5∼4), the deformation of large drops between gaps i

The knowledge of the viscoelastic properties of molten polymers and the ability to predict their behavior under deformation is of prime interest to polymer scientists and industry. The discrete linear relaxation spectrum $ lbrack G sb{i}, lambda sb{i} rbrack$ is one of the important viscoelastic properties and it is widely used to characterize molten polymers. This spectrum is obtained from experimental values of the dynamic moduli $ lbrack G sp prime( omega), G sp{ prime prime}( omega) rbrack$. A linear regression method with and without regularization and a nonlinear regression method were compared for inferring a discrete spectrum from experimental data. Since experimental values are used, errors in the data will affect the reliability of the spectrum. Because of the limitations of the experimental apparatus, the moduli can only be determined over a certain frequency range. The values of the relaxation times ($ lambda sb{i}$) and the corresponding elastic moduli ($G sb{i}$) depend on the range of frequencies over which the storage and loss moduli ($G sp prime( omega$) and $G sp{ prime prime}( omega$)) are measured and the method used to calculate them. Also, experimental sources of errors such as uncertainty in the gap measurement, variation in the shape of the edge, residual stress due to the preparation of the sample, and temperature uncertainty will induce experimental errors in $G sp prime( omega)$ and $G sp{ prime prime}( omega)$. This work investigates the effect of time-scale truncation and experimental errors on the discrete relaxation spectrum.

A series of crystalline, substituted polyoxetanes were studied using X-ray fibre diffraction as the primary investigative tool. Three systems were probed, each presenting a unique facet of structure analyses. / The structure of poly(3,3-bis(hydroxymethyl)oxetane) using X-ray fibre diffraction was proposed. Modelling studies and FT-IR have been used to arrive at a probable conformation in which the backbone was found to be planar zigzag and the hydroxyls in the sidechain were extended. Few reflections were observed and it was not possible to grow lamellar single crystals for electron diffraction. / The preliminary structure of poly(3,3-bis(hydroxymethyl)oxetane) diacetate using X-ray fibre diffraction on films and fibres and electron diffraction on lamellar single crystals provided a tentative packing scheme based on the most intense equatorial reflections. CP/MAS $ sp{13}$C NMR indicates slight deviations in the environments for the acetate groups on the same residue. / X-ray fibre diffraction of atactic P(MHMO) resulted in a unit cell of comparable dimensions as in P(BHMO). The intensity and quality of the fibre patterns suggest identical structures. P(BHMO-co-MHMO) is a random copolymer in which the MHMO units are incorporated into the crystalline lattice of P(BHMO). One melting endotherm is observed for all compositions and decreases linearly with increasing content of MHMO. These data support a phenomenon known as isomorphism.

This thesis concentrates on three main areas of research in the field of poly(vinyl chloride), PVC: (1) microstructure determination and local chain motions of PVC in a plasticized system, (2) permeability of PVC and plasticized PVC to gases, and (3) computer modeling of the thermal degradation of PVC. / A quantitative carbon-13 NMR spectrum of PVC in 1,1,2,2-tetrachloroethane-d$ sb2$ (TCE-d$ sb2$) was recorded. Theoretical predictions using Bernoullian statistics permitted the reassignment of several resonances. Carbon-13 spin-lattice relaxation times and NOE values were measured as a function of temperature at two magnetic fields for PVC in two solvents, di-butyl phthalate (DBP) and TCE-d$ sb2$. The difference found in the simulation parameters, from the Dejean-Laupretre-Monnerie model, for PVC in the two solvents were rationalized by assuming a specific interaction between DBP and the CHCl group of PVC and to the relative solvent quality. / The permeability coefficients, P, of PVC films to oxygen were measured as a function of temperature and plasticizer type and concentration. The plasticizers used were di-(2-ethylhexyl) phthalate (DOP), tri-butyl phosphate (TBP), and a binary mixture of the two with a concentration of $ rm Phi sb{DOP}$ = 0.6). The effect of plasticizer type on the permeation coefficients of oxygen followed the trend: P(TBP) $>$ P($ rm Phi sb{DOP}$ = 0.6) $>$ P(DOP). Arrhenius plots of the permeability coefficients showed that the unplasticized and plasticized PVC films of low concentration of plasticizer ($ rm Phi sb{plas} < 0.2$) displayed a discrete change in the slope, in the vicinity of the glass transition temperature, that reflected changes in the activation energy for permeation. In addition, the permeation and diffusion coefficients of oxygen and hydrogen chloride gases in an unplasticized PVC film were measured as a function of temperature. The results suggest that the increase in segmental mobility of the polymer chains above the T$ rm sb{g}$ increases the diffusivity as well as the zone of activation for diffusion leading to the increase in segmental mobility of the polymer chains above the T$ rm sb{g}$ increases the diffusivity as well as the zone of activation for diffusion leading to the increase in both energy and entropy of activation. / A computer program has been written which simulates, according to Bernoullian statistics, the relative handedness of successive monomer units during polymerization and calculates the probabilities of configurational sequences before and after a specified degradation mechanism. At levels of degradation that are accessible to experimental verification by solution NMR ($<$2%), the changes in isotacticity that are predicted by these simulations are at (or under) the limits of experimental error. Furthermore, the simulations indicate that for the degradation to result in double bond lengths that correspond to experimentally determined values requires that the dehydrochlorination also include some atactic and syndiotactic sequences which, in turn, reduces the changes in P$ rm sb{mm}$. (Abstract shortened by UMI.)

Thermolysis of mixtures of linear low density polyethylene, LLDPE, and polystyrene, PS, was investigated. Mixtures having various polyethylene/polystyrene ratios were reacted in a stirred, batch reactor under a nitrogen atmosphere at moderate temperatures, ranging between 350 and 420$ sp circ$C. The major products collected included a volatile product, which was liquid at room temperature, and a wax-like residue. The liquid products were consistently found to contain over 90 percent styrene and toluene with the yield of styrene decreasing as the percentage of polyethylene in the mixture increased. Two fractions were identified in the residue: a high molecular weight polyethylene fraction and a lower molecular weight polystyrene fraction. A significant increase in the solubility of the residue in organic solvents at room temperature was observed as the polystyrene content was raised. The residue became completely soluble in chloroform at a 60/40 ratio of polyethylene/polystyrene. The effect of temperature on the degradation of a selected mixture was also investigated. At temperatures below 390$ sp circ$C, the volatile/residue ratio was independent of the reaction temperature. Above 390$ sp circ$C, the styrene and total liquid product yields increased with increasing temperature, while the yield of residue decreased.

No description available.

Twist grain boundaries, which are widely observed in block copolymer samples of lamellar phases, have been investigated through both direct numerical solution and multiple scale analysis of a coarse-grained mesoscopic model equation. We show that the twist boundary profile can be well described by a pair of Ginzburg-Landau equations (amplitude equations) characterizing the slow evolution of the lamellae. The stability of the grain boundary configuration has been examined, and our results show that the boundary width, albeit varying with twist angle, is of order epsilon-1/4 , with epsilon the measure of the distance to the order-disorder threshold. We also study the motion of twist grain boundaries subjected to slow transverse modulations of lamellae, and obtain both analytically and numerically the traveling velocity of the boundary as well as its dependence on modulation wavenumber.

The first part of this study concerns the examination of tetrahydrofuran ring-opening polymerization mediated by the palladium insertion polymerization catalysts, (bipy)Pd(CH3)(L)+ OTf- (L = NCCH3, PhN=C(H)Tol, tBuN=C(H)Tol, CH3 N=C(H)Tol). Mechanistic studies reveal a series of metal-based reactions prior to ring-opening, which can be utilized to control polymer molecular weights and end-groups. / The feasibility of combining this ring-opening reaction to insertion polymerization to generate new block co-polymers is subsequently investigated, and it forms the primary objective of the study. / The dual-functional palladium(II) complex (bipy)Pd(CH3)(NCCH 3)+OTf- is found to mediate a novel, single-step coupling of insertion and ring-opened monomers (CO, norbornene, THF) into new polymers. This coupling process follows an unusual route, involving enol lactone as an intermediate, and facilitated by weak Lewis acid. Similar coupling chemistry has been applied to the synthesis of polyTHF end-capped with a small polynorbornene fragment.

<p> Colloidally prepared nanocrystals of transparent conducting oxide (TCO) semiconductors have emerged in the past decade as an exciting new class of plasmonic materials. In recent years, there has been tremendous progress in developing synthetic methods for the growth of these nanocrystals, basic characterization of their properties, and their successful integration into optoelectronic and electrochemical devices. However, many fundamental questions remain about the physics of localized surface plasmon resonance (LSPR) in these materials, and how their optoelectronic properties derive from their underlying structural properties. In particular, the influence of the concentration and distribution of dopant ions and compensating defects on the optoelectronic properties of TCO nanocrystals has seen little investigation. </p><p> Indium tin oxide (ITO) is the most widely studied and commercially deployed TCO. Herein we investigate the role of the distribution of tin dopants on the optoelectronic properties of colloidally prepared ITO nanocrystals. Owing to a high free electron density, ITO nanocrystals display strong LSPR absorption in the near infrared. Depending on the particular organic ligands used, they are soluble in various solvents and can readily be integrated into densely packed nanocrystal films with high conductivities. Using a combination of spectroscopic techniques, modeling and simulation of the optical properties of the nanocrystals using the Drude model, and transport measurements, it is demonstrated herein that the radial distribution of tin dopants has a strong effect on the optoelectronic properties of ITO nanocrystals. </p><p> ITO nanocrystals were synthesized in both surface-segregated and uniformly distributed dopant profiles. Temperature dependent measurements of optical absorbance were first combined with Drude modeling to extract the internal electrical properties of the ITO nanocrystals, demonstrating that they are well-behaved degenerately doped semiconductors displaying finite conductivity at low temperature and room temperature conductivity reduced by one order of magnitude from that of high-quality thin film ITO. </p><p> Synchrotron based x-ray photoelectron spectroscopy (XPS) was then employed to perform detailed depth profiling of the elemental composition of ITO nanocrystals, confirming the degree of dopant surface-segregation. Based on free carrier concentrations extracted from Drude fitting of LSPR absorbance, an inverse correlation was found between surface segregation of tin and overall dopant activation. Furthermore, radial distribution of dopants was found to significantly affect the lineshape and quality factor of the LSPR absorbance. ITO nanocrystals with highly surface segregated dopants displayed symmetric LSPRs with high quality factors, while uniformly doped ITO nanocrystals displayed asymmetric LSPRs with reduced quality factors. These effects are attributed to damping of the plasmon by Coulombic scattering off ionized dopant impurities. </p><p> Finally, the distribution of dopants is also found to influence the conductivity of ITO nanocrystal films. Films made from nanocrystals with a high degree of surface segregation demonstrated one order of magnitude higher conductivity than those based on uniformly doped crystals. However, no evidence was found for differences in the surface electronic structure from one type of crystal to the other based on XPS and the exact mechanism for this difference is still not understood. </p><p> Several future studies to further illuminate the influence of dopant distribution on ITO nanocrystals are suggested. Using synchrotron radiation, detailed photoelectron spectroscopy on clean ITO nanocrystal surfaces, single-nanoparticle optical measurements, and hard x-ray structural studies will all be instructive in elucidating the interaction between oscillating free electrons and defect scattering centers when a plasmon is excited. In addition, measurements of temperature and surface treatment-dependent conductivity with carefully controlled atmosphere and surface chemistry will be needed in order to better understand the transport properties of ITO nanocrystal films. Each of these studies will enable better fundamental knowledge of the plasmonic properties of nanostructures and improve the development of nanocrystal based plasmonic devices.</p>

<p> Atomic Layer Deposition (ALD) is a an excellent technique for depositing conformal thin films on complex geometries in layer by layer fashion. The mechanisms of depositing TiO₂, platinum, and ethoxysilane molecules were probed with <i>in situ</i> Fourier transform infrared (FTIR) in order to better understand and improve the process. Each of these studies involves TiO₂. </p><p> There are many uses for thin films of titanium dioxide, a semiconductor and high dielectric material. Current Atomic Layer Deposition (ALD) of TiO₂ generally involves water or ozone, which can oxidize and corrode some substrates of interest. Ritala et al. successfully deposited an assortment of metal oxides using no water, but instead, metal alkoxides and metal halides as precursors. Presented is a study of ALD of titanium dioxide using titanium tetrachloride (TiCl₄) and titanium tetraisopropoxide (TTIP). In situ Fourier transform infrared (FTIR) studies revealed that the mechanism for TiO₂ ALD using titanium tetrachloride and titanium tetraisopropoxide changed with temperature. At temperatures between 250 and 300&deg;, the isopropoxide species after TTIP exposures quickly underwent &beta;-hydride elimination to produce TiOH species on the surface. The observation of propene by quadrupole mass spectrometry supported the &beta;-hydride elimination reaction pathway. Deposition was investigated between 150 and 300&deg; on substrates including zirconia, alumina, and silica. Quartz crystal microbalance results and X-ray reflectivity showed that the system grew 0.5&ndash;0.6 &Aring;/cycle at 250&deg; X-Ray photoelectron studies also confirmed TiO₂ film growth. </p><p> In another aspect of ALD use, self-limiting chemistry assisted with terminating a surface with alkoxysilanes. Tire rubber contains additives such as carbon black or silica particles to provide strength. Although in theory Kevlar fibers would provide strength while lowering the density and increasing car fuel efficiency, in practice Kevlar fibers disperse only very poorly in the rubber, leading to inhomogeneity. In order the increase the mixing likelihood between rubber and Kevlar, the reactions of some sulfurous siloxanes were examined on both aluminum oxide and titanium oxide. The titanium oxide adhesion layer allowed the deposition of molecules on the surface that looked promising for improving mixing with rubber and decreasing the weight of tires. </p><p> Atomic layer deposition offers the possibility of more precision in platinum deposition. In a platinum deposition study, the nucleation and growth of non-conformal platinum on TiO₂ and WO_x powder using Pt(hfac)₂ and formalin was examined with in-situ FTIR and transmission electron microscopy (TEM). Interest in substitution of Pt/C as the oxidation reduction reaction catalyst in polymer electrolyte membrane fuel cells (PEMFCs) led to the ALD synthesis of Pt/WO_x and Pt/TiO₂. A nucleation period on the order of 100 cycles was observed, after which, platinum loading and particle size measurably increased with increasing cycle number. The adsorption of the hfac ligand on the metal oxide substrate effectively inhibits nanoparticle coalescence during the growth phase, which led to further investigation of its use as a site-blocking agent. The results showed that Pt particle distance could be increased with the use of hfacH.</p>