A new analytical technique to measure the chemical composition distribution (CCD) of polyolefins, crystallization elution fractionation (CEF), was introduced in 2006 during the First International Conference on Polyolefin Characterization. CEF is a faster and higher resolution alternative to the previous polyolefin CCD analytical techniques such as temperature rising elution fractionation (TREF) and crystallization elution fractionation (CRYSTAF) (Monrabal et al., 2007). Crystallization elution fractionation is a liquid chromatography technique used to determine the CCD of polyolefins by combining a new separation procedure, dynamic crystallization, and TREF. In a typical CEF experiment, a polymer solution is loaded in the CEF column at high temperature, the polymer is allowed to crystallize by lowering the solution temperature, and then the precipitated polymer is eluted by a solvent flowing through the column as the temperature is raised. CEF needs to be calibrated to provide quantitative CCD results. A CEF calibration curve consists of a mathematical relationship between elution temperature determined by CEF and comonomer fraction in the copolymer that could be estimated by Fourier transform infrared spectroscopy (FTIR) and carbon-13 nuclear magnetic resonance (13C NMR). Different comonomer types in ethylene/α-olefin copolymers will have distinct calibration curves. The main objective of this thesis is to obtain CEF calibration curves for several different ethylene/α-olefin copolymers and to investigate which factors influence these calibration curves. A series of homogeneous ethylene/α-olefin copolymers (1-hexene, 1-octene and 1-dodecene) with different comonomer fractions were synthesized under controlled conditions to create CEF calibration standards. Their average chemical compositions were determined by 13C NMR and FTIR and then used to establish CEF calibration curves relating elution temperature and comonomer molar fraction in the copolymer.

The work conducted in this thesis is two-fold. First, binary vapor liquid equilibria of several solvent/CO2 systems are measured at 40 ?? The systems analyzed are all gas-expanded liquids (GXLs) characterized with a Jerguson Cell apparatus. A Jerguson cell is a windowed pressure vessel that allows one to measure the height of the condensed liquid. Using this height and the known overall contents in the cell, one can calculate the liquid composition without using any external sampling. Secondly, this same setup is attached to a sampling system, and solid solubility (fractional crystallization) is measured for various GXL systems. The CO2 acts as an antisolvent in what is commonly known as a gaseous antisolvent (GAS) system. Essentially, this work shows that expansion of the tested solvents with CO2 will cause the precipitation of the solid solute. This work also analyzes the affect two solutes have on each other in a quaternary GAS system. Gas-expanded liquids combine desirable gaseous properties and liquid properties to yield a very useful solvent for many applications. An advantage of GXLs is that a relatively small change in pressure or temperature can greatly affect the solvation properties. The tunability of GXLs increases as the amount of the gas (usually CO2) increases in the liquid phase. With the benign chemical nature and environmental impact of CO2 processing, GXLs and supercritical fluids (SCFs) have garnered a lot of attention for industry and academia. Supercritical fluids in this work refer to pure CO2 above its critical temperature and pressure.

In the work presented in this dissertation, extensive molecular dynamics (MD) simulations have been performed to investigate various physical problems related to the solid-liquid transitions over a wide range of supercooling and superheating temperatures in model Lennard-Jones systems. The major focus of this work is to investigate the thermodynamics, kinetics, and underlying mechanisms of these problems. There are five topics in this work: (1) The classical nucleation theory (CNT) was tested for both liquid supercooling and solid superheating via different solid-liquid coexistence models. It is found that the CNT is valid for liquid supercooling but invalid for solid superheating. The arising elastic energy plays a significant role in affecting the liquid nucleation in a superheated solid. A new nucleation theory was proposed for describing the internal liquid nucleation of solid superheating. (2) Based on CNT, a new and accurate method was developed for calculating the crystal-melt interfacial free energy and its anisotropy. Our result is very close to Turnbulls experimental results. (3) The face, temperature, and size dependences of the crystallization rate were investigated in this work. The results show that the crystallization rate decreases substantially with the increasing system size. Different from the conventional models, a new model is developed to describe these dependences. (4) Melting from internal nanovoids was investigated in this work. It is found that the mechanism of void melting is quite different from bulk melting and nanoparticle melting. There are four different stages and three local melting temperatures in void melting. The mechanism of the complex melting sequence is systematically explained. (5) The homogenous melting at the upper limit of superheating was investigated in this work. For the first time, the ring diffusion is found to take place in superheated crystals and causes the spontaneous melting. The prevailing instability theories are unsuitable to describe this type of melting. The mechanism of the diffusion-loop mediated melting is carefully discussed in this work.

This study indicate that the chemical inter-diffusion between the Cr-doped glass/glass ceramic and quartz (SiO2) influence the fluorescence properties of glass, mainly because of Cr4+ replacing by tetrahedral of Si4+. Cr4+ fluorescence intensity was reduced and its emission band was shifted to longer wavelength (red shift). We selected the SiO2-based glass composition: Mg2SiO4 glass-ceramic and reduced a ratio of SiO2 sintered into the ceramic powder. This paper used diffusion characteristics of quartz (SiO2) to compensate for reduced SiO2 in the ceramic powder. After diffusing with quartz (SiO2), ceramics powder changed into glasses. The intensity of fluorescence and the crystal field had been improved. The center of Cr4+ fluorescence is about 1100nm belonging to Cr4+:Mg2SiO4 crystal. The ratio of Cr4+ in Mg2SiO4 crystal/Cr4+ in MgO-SiO2 glass increases from 0.33 to 1.74. The goal is to develop a novel glass which is resistant to SiO2 inter-diffusion degradation during fiber fabrication, and provide the new fiber technology to avoid the influence of inter-diffusion This study provides new types of treatment: Laser induced crystallization. Laser heat-treatment can more quickly induce crystals in glass during seconds, than traditional heat-treatment which require several hours. This study also indicate that one step laser heat-treatment induce micro-crystals, but one step laser heat-treatment induce nano-crystals. We successfully produced nano-crystallization during seconds.

Reported is a study of the crystallization behavior of syndiotactic polystyrene (sPS) and its copolymers (with 4-bromostyrene as the comonomer or with atactic polystyrene arms grafted on the comonomer sites) via three sets of experiments. The first involves the study of structural identification of negatively birefringent spherulites by means of polarized light microscopy (PLM) and scanning electron microscopy (SEM). Results indicated that the optically positive and optically negative spherulites have same morphological features. Differences in the optical texture are due entirely to differences in orientation of the (anisotropic) sheaf-like precursors: the rigid nature of crystalline lamellae renders incomplete development of spherical symmetry even at the axialitic size of tens of microns. In the second part, we propose a modified approach for more precise determination of the Tm* value by taking advantage of the dual-mode distribution of crystalline lamellae in analyzing small-angle X-ray scattering (SAXS) profiles. This method should be generally applicable to other semi-crystalline polymers with dual-mode distribution in lamellar thickness. Results from wide-angle X-ray diffraction (XRD) suggest the presence of ?'-to-?" phase transformation at ca. 264 oC; no indications for the previously proposed ?-to-? transformation are identified. We therefore conclude that the ?' form is truly metastable; the ?"-form is the entropically favored high temperature phase (with Tm* = 300 oC) whereas the more ordered ?' phase (with Tm* = 288 oC) is enthalpically favored at lower temperatures. In the third set of experiments, identification of effects of copolymerization has been studied via a combination of PLM, differential scanning calorimetry (DSC), XRD, SAXS, and transmission electron microscopy (TEM). Results show that the equilibrium melting temperatures (determined via either Hoffman¡VWeeks or Gibbs¡VThomson plots) of the copolymers are significantly lower than that of the corresponding sPS homopolymer. The PLM observations indicate that the axialitic growth rates in copolymers are drastically lower than that of the corresponding homopolymer at comparable backbone length and supercooling. Both XRD and TEM results indicate preferred formation of the ?" phase upon melt crystallization in the bulk state; however, the ?" phase (instead of ?' phase that is the more commonly observed for sPS homopolymers in the bulk state) is dominant in thin films.

In this study, the aim was identification and classification of the enzyme having phenol oxidase activity produced by a thermophilic fungus, Scytalidium thermophilum. For this purpose, enzyme production, purification, biochemical characterization and structural analysis by X-ray crystallography studies have been performed. At the beginning of the research, this enzyme was considered as a phenol oxidase and analyzed accordingly. However, during purification, amino acid sequencing and structural studies, the enzyme was shown to be a catalase, with an additional catechol oxidase activity. This novel bifunctional catalase-catechol oxidase (CCO) was purified 10 fold with 45 % yield by anion exchange and gel filtration chromatographies. CCO was determined as a tetrameric protein having total and subunit molecular weights of 320 and 80 kDa, respectively. Isoelectric point of CCO was verified as 5.0. CCO catalase and catechol oxidase activities were characterized in terms of their kinetic behavior at different pH and temperatures. Depending on the substrate specificity and inhibitor studies of CCO, the phenol oxidase activity was determined as catechol oxidase but not tyrosinase or laccase. The best crystallization condition for CCO was determined and X-ray diffraction data was collected at the Daresbury Synchrotron Radiation Source (United Kingdom) at 2.7 &Aring / resolution. The preliminary structure was solved by molecular replacement method using Penicilium vitale catalase structure. CCO was verified to have a tetrameric structure with two homodimers and a metal center in each polypeptide chain.

No description available.

No description available.

Non-isothermal crystallization of the PET/PTT copolyesters was studied at five different cooling rates over 1-20oC/min by means of differential scanning calorimetry (DSC). Both the Ozawa equation and the modified Avrami equation have been used to analyze the crystallization kinetics. The non-isothermal kinetics of most copolymers cannot be described by the Ozawa analysis, except the copolyester with a composition of 66.3% trimethylene- (TT) and 33.7 %ethylene- terephthalates (ET). It may be due to the inaccuracy of the Ozawa assumptions, such as the secondary crystallization is neglected. From the kinetic analysis using the modified Avrami equation, the Avrami exponents, n, were found to be in the range of 2.43-4.67 that are dependent on the composition of the copolyesters. The results indicated that the primary crystallization of the PET/PTT copolymers followed a heterogeneous nucleation and a spherulitic growth mechanism during the non-isothermal crystallization. In the cases of the copolyesters with either TT or ET less than 10%, we found the molten temperature is a key factor to decide whether the Ozawa equation can be succeeded in analyzing the dynamic crystallization. For the non-isothermal crystallization, a single exothermic peak was detected in each DSC curve regardless of the composition and the cooling rate. It indicated that a single-mode distribution of the crystallite sizes was formed during the cooling process. After the non-isothermal crystallization, the melting behavior of the specimens was monitored by temperature modulated DSC (TMDSC) in the conventional mode and the modulated mode. Multiple endothermic peaks were observed in both modes. The wide-angle X-ray diffraction (WAXD) patterns of these copolymers showed that the peak height became sharper and sharper as the crystallization temperature increased, but the position of the diffraction peaks did not change apparently. It indicated that the multiple melting behaviors did not originate from the melting of the crystals with different structures. The melting behavior of these PET/PTT copolyesters can be explained logically by using the melt-recrystallization model. From the reversing and non-reversing signals of TMDSC, the melting-recrystallization-remelting phenomena were further verified. In addition, a small endothermic peak was found at the highest melting temperature in the reversing thermogram for TT-enriched copolyesters. It is reasonably to believe that this endotherm is attributed to the melting of the crystals that are formed in regime I during the heating scan. The cocrystallization of the PET/PTT copolyesters was studied using DSC and WAXD. A clear endothermic peak in the DSC thermogram was detected over the entire range of copolymer composition. A minimum melting temperature was found for the copolyester with 50% ET. The WAXD patterns of these copolymers can be divided into two groups with sharp diffraction peaks, i.e., PET type and PTT type crystals. The transition of crystal structure between PET type and PTT type occurred around the eutectic composition (50 % ET and TT), determined from the variation of the melting temperature with the composition. In addition, the fiber diagram and the WAXD pattern of the copolyester with the eutectic composition showed a different crystalline structure. These results indicated that the cocrystallization behavior of the PET/PTT copolyesters was isodimorphic.

The major innovation of this work is an establishment of a novel chiral separation process using preferential crystallization coupled with a membrane barrier. This hybrid process was proved to be promising from a significant increase in product yield and purity compared to existing chiral separation processes. This work sets up a process design platform to extend the use of this hybrid process to a separation of other mixtures. This novel process especially is a promising alternative for chiral separation of pharmaceutical compounds which include more than fifty percent of approved drugs world-wide. A better performance chiral separation technique contributes to cut the operating cost and to reduce the price of chiral drugs.