This thesis is an experimental investigation of phase behavior, crystallization, gelation and phase separation kinetics of polymer solutions in dense fluids at high pressures. The miscibility and dynamics of phase separation were investigated in solutions of atactic polystyrene with low polydispersity (Mw = 129,200; PDI = 1.02) in acetone. Controlled pressure quench experiments were conducted at different polymer concentrations to determine both the binodal and the spinodal envelops using time- and angle resolved light scattering techniques. At each concentration, a series of rapid pressure quenches with different penetration depths in a range from 0.1 MPa to 3 MPa were imposed and the time evolution of the angular distribution of the scattered light intensities was monitored. The solution with 11.4 wt % polymer concentration underwent phase separation by spinodal decomposition mechanism for both shallow and deep quenches. Below this critical polymer concentration, phase separation was found to proceed by nucleation and growth mechanism for shallow quenches, but by spinodal decomposition for deeper quenches. Gelation and crystallization processes and the influence of pressure and the fluid [Cho et al. 1993]composition were investigated in solutions of poly(4-methyl-1-pentene) [P4MP1] in n-pentane + CO₂ and in solutions of syndiotactic polystyrene [sPS] in toluene + CO₂, and also in acetophenone + CO₂ fluid mixtures over a pressure range up to 55 MPa and carbon dioxide levels up to 50 wt %. In pure pentane, P4MP1 undergoes crystallization and leads to Form III polymorph at low pressures, but to Form II at high pressures. In n-pentane + CO₂ mixture fluids, the polymorphic state changes from a mixture of Forms III and II to Form II and eventually to Form I with increasing CO₂ content. High level of carbon dioxide (≥40 wt %) in the solution was found to lead to gelation instead of crystallization. No liquid-liquid phase boundaries could be observed in any of the P4MP1 solutions. In contrast to P4MP1 in n-pentane, syndiotactic polystyrene was found to undergo gelation in toluene or acetophenone forming a polymer-solvent compound with the δ crystal form. Also in contrast to P4MP1 systems, addition of carbon dioxide to sPS solutions alters the process from that of gelation to crystallization leading to the β crystal form. In solutions with high CO₂ level, in addition to the gelation or crystallization boundaries, a liquid-liquid phase separation boundary was also observed. The phase separation path followed was found to influence the eventual morphology and the crystal state of the polymer. In sPS solutions in toluene + CO₂, if the sol-gel boundary were crossed first by cooling the solution at a fixed pressure, the resulting morphology was found to be fibrillar and the polymer displayed the δ crystal form. If instead, the liquid—liquid phase boundary were crossed first by reducing pressure at a fixed temperature, the polymer-rich phase leads to a stacked-lamellar morphology with the β crystal form while the polymer-lean phase leads to a mixed morphology with lamellar layers connected by fibrils with the polymer displaying δ + β crystal forms. In solutions in acetophenone + carbon dioxide, when the gelation boundary is crossed first, the resulting structure is the δ form as in the toluene + CO₂ case. At comparable CO₂ levels, when the L-L phase boundary is crossed first, in the acetophenone system, polymer-rich phase was found to generate a mixture of δ + β forms while only the δ form was found in the polymer-lean phase, in contrast to the observations in the toluene + CO₂ systems. Based on crystallographic, spectral and microscopic data, a thermodynamic framework was developed which provides a mechanistic account for the formation of the different polymorphs. / Ph. D.

The crystallization behavior of poly(p-phenylene sulfide) PPS has been studied. Two PPS samples with < M_w > = 43K and < M_w > = 83K were fractionated to remove low molecular weight oligomers yielding fractionated PPS samples with < M_w > = 57K and < Mw > = 113K. The fractionated samples were then treated with an ion exchange process to allow control over the nature of endgroup counterion. Isothermal rates of hulk crystallization were analyzed as a function of n1olecular weight of PPS, fractionation, and chen1ical nature of the endgroup counter-ion. Additionally the spherulitic growth rates and nucleation densities were studied as a function of the chemical nature of the endgroup counter-ion for fractionated PPS with < M_w > = 57K. As a function of endgroup counter-ion, crystal growth rates and overall rates of crystallization decreased in the following order: H > Zn > Na. No significant trends in nucleation density as a function of endgroup counter-ion were observed. Bulk crystallization rates, nucleation density, general morphological features, equilibrium melting point, and abso1ute crystalline percentage of linear and starbranched nylon-6 have been studied as a function of branch-point functionality and crystallization temperature. Overall bulk crystallization rates were described in terms of the Avrami equation. The crystallization half-times of star-branched nylon-6 as a function of <i>supercooling</i> were reduced relative to those of linear nylon-6 of comparable molecular weight. Irregularities in lame1lar structure were implied by SAXS experiments on samples with branch-point functionality as low as three. The effects of changing the block length of poly(dimethylsiloxane), PSX, blocks in poly(etheretherketone)-poly(dimethylsiloxane), PEEK-PSX, multi block copolymers and their ketimine precursors, PEEKt-PSX, were investigated. A dran1atic dependence on thermal history prior to crystallization was observed in both block copolymer systems. Block copolyn1crs crystallized from the glassy state obtained a much higher degree of crystallinity at a n1uch faster rate of crystallization than copolymers crystallized from the melt at identical crystallization temperatures. Thermal and mechanical behavior of bisphenol-A polycarbonate was studied as a function of thermal history and absorbed mass fraction of C0₂. Mechanical testing and gas absorption experiments were performed on physically aged and unaged polycarbonate. Gas absorption studies indicated that although initial diffusion was somewhat retarded in the aged samples, both aged and unaged polycarbonate samples showed identical equilibrium absorbed gas values at 6500KPa and identical gas desorption behavior. Absorbed C0₂ was shown to plasticize polycarbonate. Polymeric liquid crystalline foams were produced from star-branched polyoxybenzoate-po1yoxyphenoxybenzoate copolymers (POB-co-POPB) via gas supersaturation followed by thermal blowing. Solid state C0₂ gas absorption well as melt processability of star-branched POB-co-POPB was increased relative to the linear polymer of comparable molecular weight. While C0₂ blown foams of linear POB-co-POPB produced by the gas supersaturation technique had a relatively high density and showed highly anisotropic bubble growth, well defined, nearly isotropic foams of star-branched POB-co-POPB with mean cell size from 200 to 400μ were made using the gas supersaturation technique. / Ph. D.

Results are presented for two unrelated studies. The primary topic involved the crystallization behavior and morphological features of two polyimides, namely LARCCPI (Langley Research .Center Crystalline folyimide) and LARC-TPI (Thermoplastic folyimide). The LARC-CPI study first considered feature~ affecting crystallization behavior including inherent viscosity, crystallization temperature, and melt temperature and time. Data were analyzed using the A vrami analysis. Morphological features were investigated using techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and small angle x-ray scattering (SAXS). Permanganic etching combined with SEM successfully revealed morphological detail, further supported by TEM data. These data support the Avrami analysis results. SAXS data reflected the influence of several crystalliz.ation variables on the long spacing. SAXS results also revealed the presence of a broad second scattering peak for semicrystalline samples appearing in the same position regardless of crystalliz.ation temperature or inherent viscosity. Molecular modelling predicted a low-energy helical conformation with a near-periodic repeat distance corresponding to the second SAXS peak. This conformation is offered as a tentative explanation for that peak. Finally, the effe.ct of nucleating agent on the recrystalliz.ability of a higher inherent viscosity LARC-CPI was considered. One of several nucleators appeared effective in enhancing recrystallization. The LARC-TPI study involved the development of a thermal cycle based upon crystalliz.ation kinetics results, allowing the successful recrystallization of LARC-TPI following exposure to elevated temperatures. This cycle was then used to modify an existing composite fabrication process to produce semicrystalline composites. Two carbon fiber types were utilized to make composites via both fabrication cycles. These composites were evaluated using several techniques. The second unrelated project examined very localized orientation behavior in two types of semi crystalline superstructure using FTIR microspectroscopy. Results were obtained utilizing linear dichroism for orientation within spherulitic and transcrystalline superstructure in poly(glycolide co-lactide) and isotactic polypropylene. An increase in orientation on an absolute basis as a function of position was successfully measured. Orientation function values were higher on an absolute basis for the transcrystalline superstructure. However, the sign of the isotactic polypropylene spherulite orientation function values was the opposite of what was anticipated. These results were considered in light of spherulite W AXS data also obtained. / Ph. D.

This thesis presents the results of a study on the blends of an aliphatic crystallizable polyamide (nylon 6/6) and trace quantities of a polar non-crystallizable diluent (poly(vinylpyrrolidone)). This study is based on the preliminary findings of Keith et al. who reported striking morphological changes in nylon 6/6 upon addition of small amounts of poly(vinylpyrrolidone) (PVP). The melting behavior of pure nylon 6/6 was also studied during the course of this investigation. The melting behavior of nylon 6/6 was studied using a differential scanning calorimeter (DSC). Samples were isothermally crystallized at various temperatures from the melt. Subsequent DSC analysis showed the presence of three distinct melting endotherms. The behavior of these three endotherms was studied as a function of the crystallization temperature (T_C), annealing time, and DSC heating rate. X-ray studies (small and wide angle) and hot stage optical microscopy studies were also carried out to determine the cause of the multiple endotherms. The influence of addition of PVP on the crystal morphology of nylon 6/6 was studied using DSC, x-ray and hot stage photomicroscopy. The addition of PVP has a dramatic effect on the spherulitic morphology of nylon. The addition of PVP to nylon caused a striking reduction in the nucleation density of spherulites, modification of lamellar organization in spherulites (as evidenced by the occurrence of banding), and modification of interlamellar spacings. / Master of Science

A study was made cf the cost per pound of magnesium sulfate monohydrate produced by a "Krystal" crystallizer at recirculation rates from 20 to 40 gallons per minute and operating temperatures from 150 to 180 °F. From these tests, the optimum operating conditions within the range of these variables were derived. The problem was studied by operating the equipment at all sixteen combinations of these variables in unit steps of ten. The crystallizer was operated at each set of conditions, the product collected, and the cost per pound determined. The operating conditions were found to affect power and steam costs greatly, varying from 1.689 mills/lb at 50 gallons per minute and 170 °F to 0.737 mills/lb at 20 gallons per minute and 180 °F, representing a decrease. cf 0.952 mills per pound upon correct choice of operating temperature and recirculation rate. / Master of Science

Clinoamphibole from a mylonitic amphibolite, located on Senja, Norway, exhibits microstructures characteristic of dynamic recrystallization, including larger host grains in a finer grained matrix of needle shaped amphibole. The matrix amphibole defines an LS fabric and host grains have core and mantle structures with a core containing undulose to patchy extinction and (100) deformation twinning surrounded by a mantle of recrystallized grains. In addition intragranular grains also occur within the cores. TEM analysis of the host grains revealed high densities of dislocations, dislocation arrays/subgrain boundaries parallel to (hk0), stacking faults, and (100) deformation micro-twins. Dark field, weak beam images show that the dislocations are commonly dissociated. Diffraction contrast experiments compared with computer simulation of dislocation images indicate the primary unit Burgers vector is [001]. This information in conjunction with trace analysis of glide loops and dislocation line direction shows that the following glide systems were operative: [001]{110}, [001](100), and possibly [001](010), in order of relative occurrence. These data along with dislocation energies are considered in order to propose a possible model for the [001] unit Burgers vector in the clinoamphibole structure. TEM also showed that matrix grains and intragranular grains have relatively low defect densities, and that the intergranular new grains occur at localities in the host grains characterized by high densities of dislocations. These observations along with the chemical and orientation relationships between the recrystallized grains and their host indicate that the new grains may have formed by heterogeneous nucleation and that further growth probably occurred by both strain assisted and chemically induced grain boundary migration or liquid film migration. This recrystallization event is interpreted to be synkinematic based on the fact that no recrystallization textures are present in the matrix grains and that the matrix grains define an LS fabric. However, the low defect densities in the matrix grains and the lack of intracrystalline strain in other phases indicate that post-kinematic recovery processes were active. / Ph. D.

The crystallization behaviour of poly (p-phenylene sulfide) (PPS) has been studied. lsothermal rates of bulk crystallization, spherulitic radial growth rates, and nucleation densities were analyzed as functions of molecular weight of PPS, branching agent concentration, and chemical nature of the endgroup counter-atom. The overall rate of bulk crystallization was described by an Avrami equation with exponent ~3. As molecular weight increased in the 24,000-63,000 range, the rates of spherulitic growth and bulk crystallization decreased by a factor of 4. The nucleation density of PPS with <M_w>=24,000 was 32-fold lower than those of the higher molecular weight polymers. Introduction of 0.2% by weight of branching agent trichlorobenzene in the synthesis vessel reduced the spherulitic growth rate to 1/2, and the rate of bulk crystallization and the nucleation density to 1/4 of those of the linear polymer of the same molecular weight. The decreasing order of crystal growth rates for the endgroup counter-atoms is Ca>H>Zn>Na with calcium providing growth rates two·foId higher than the sodium counter-atom. The rates of overall bulk crystallization (K) followed the decreasing trend H>Zn>Ca>Na. For hydrogen, K was 17-fold higher than that of sodium counter-atom. The nucleation densities presented a different trend, H> Na>Zn>Ca. The spherulitic growth rates were analyzed in terms of equations proposed to explain the molecular weight dependence. The logarithm of the crystal growth rate followed a linear function of the logarithm of the number average molecular weight proposed by Cheng and Wunderlich. Since most processing operations occur under non-isothermal conditions, the non-isothermal crystallization of PPS was also studied. Differential scanning calorimetry data folIowed a model proposed by Ozawa for non-isothermal kinetics of crystallization. This model allowed the determination of the Avrami exponent under non-isothermal conditions. The values of the Avrami exponent obtained were in good agreement with values determined isothermally. The morphological textures of semicrystalline poly (p-phenylene sulfide) (PPS) were investigated utilizing two etching techniques to enhance the finer details. One technique was based on the partial attack of chromic acid solutions at high temperature (100°C), whereas the other used suspensions of anhydrous aluminum chloride at lower temperature (35°C). The aluminum chloride approach was shown to be more appropriate and successful in enhancing the fine details in textures of PPS. This reagent selectively attacked amorphous PPS enhancing the crystalline textures to a greater extent than the chromic acid approach. This technique allowed the observation of the spherulitic growth habit and the “interconnectivity” between impinged spherulites. The morphology of PPS in composite materials containing few carbon fibers was analyzed. Low crystallization temperatures, slow cooling rates, low molecular weight polymer and local orientation favored the nucleation of transcrystallinity at the carbon fiber surface. T300U carbon fibers were the most effective in nucleating transcrystallinity. Fiber anodization in H₂SO₄ and NaOH electrolytes decreased the nucleating ability of the fibers possibly due to an increase of polarity at the fiber surface. Utilization of the aluminum chloride etching technique in conjunction with scanning electron microscopy conürmed that PPS was nucleating at the fiber surface and showed the radial growth habit and cylindrical symmetry of the transcrystalline regions. / Ph. D.

Vitrocerâmicas contendo cristais de diopsídio (CaMgSi2O6 = CMS2) têm sido consideradas promissoras para diferentes aplicações. Entretanto, quando tratado termicamente, o vidro de diopsídio exibe somente cristalização superficial. Uma maneira de se obter cristalização no volume neste vidro é através da adição de agentes nucleantes em sua composição. O objetivo inicial desta tese de doutorado foi verificar a eficiência da adição dos compostos TiO2, ZrO2 e Fe2O3, como agentes nucleantes no processo de cristalização volumétrica no vidro de diopsídio. Os vidros foram obtidos pelo método de fusão-resfriamento e, em seguida, foram submetidos a um tratamento térmico de nucleação e crescimento de cristais. Os resultados mostraram que somente a adição de Fe2O3 acima de 7% molar ao vidro CMS2 favorece a cristalização no interior da amostra. O vidro contendo 9 mol% de Fe2O3 apresenta como característica principal uma distribuição homogênea de cristais no volume da amostra vítrea. As fases cristalinas originadas foram caracterizadas por Difratometria de Raios X e o mecanismo de nucleação de cristais foi estudado através do método de Análise Térmica Diferencial (ATD) e análise microestrutural quantitativa de amostras submetidas aos seguintes ciclos de tratamento isotérmico: i) dois estágios (o primeiro de nucleação e o segundo de crescimento de cristais) e ii) um único estágio de nucleação e crescimento de cristais. As amostras contendo 9 mol% de Fe2O3 apresentaram somente a fase cristalina diopsídio com os íons de ferro aparentemente incorporados em sua rede cristalina. Através da análise dos dados de ATD em regime isotérmico da amostra contendo 9 mol% de óxido de ferro foi possível determinar o valor médio do coeficiente de Avrami (n) como sendo próximo a 3,0 para temperaturas de 760, 770, 780 e 790 °C. De acordo com a literatura, estes valores de n indicam que o vidro CMS2 contendo 9 mol% de Fe2O3 exibe um mecanismo de cristalização volumétrica caracterizado pelo aumento e saturação do número de núcleos de cristais tridimensionais de diopsídio férrico e por um mecanismo de crescimento de cristais controlado por interface. Além disso, os resultados do método de microscopia para os dados experimentais correspondentes ao tratamento térmico de simples estágio mostraram que o mecanismo de cristalização volumétrica do vidro CMS2 9F é descrito pelo caso mais geral da equação de KJMAY, onde as taxas de nucleação e de crescimento são dependentes do tempo e podem variar ao longo do processo de cristalização isotérmica. / Glass-ceramics containing diopside crystals (CaMgSi2O6 = CMS2) have been considered promising for different applications. However, when thermally treated, diopside glass exhibits only surface crystallization. One way of obtaining volume crystallization in this glass is by the addition of nucleating agents in its composition. The initial objective of this PhD thesis was to verify the efficiency of the addition of the TiO2, ZrO2 and Fe2O3 compounds as nucleating agents in the process of volume crystallization in diopside glass. Glasses were obtained by the melt-cooling method and were then subjected to a nucleation and crystal growth heat treatment. The results showed that only the addition of Fe2O3 above 7 mol% to the CMS2 glass favors crystallization in the sample volume. Glass containing 9 mol% Fe2O3 has as main characteristics a homogeneous distribution of crystals in the sample volume. The crystalline phases originated were characterized by X-ray diffraction and the crystal nucleation mechanism was studied through the Differential Thermal Analysis (DTA) method and quantitative microstructural analysis of samples submitted to double - and single - stage thermal treatments. The samples containing 9 mol% of Fe2O3 presented only the ferric diopside crystalline phase with the iron atom apparently incorporated in its crystalline network. By analyzing the DTA data in the isothermal regime of the sample containing 9 mol% of iron oxide, it was possible to determine the average value of the Avrami coefficient (n) as being near to 3.0 for temperatures of 760, 770, 780 and 790 oC. According to the literature, these values of n indicate that CMS2 glass containing 9 mol% Fe2O3 exhibits a volume crystallization mechanism characterized by increase and saturation of the number of nuclei and an interface-controlled growth of ferric diopside three-dimensional crystals. In addition, the results of the microscopy method for the experimental data corresponding to the single-stage heat treatment showed that the CMS2 9F glass volume nucleation mechanism is described by the more general case of the KJMAY equation, where the rates of nucleation and growth are time dependent and can vary throughout the isothermal crystallization process.

Antiquitin (ATQ) belongs to the superfamily of aldehyde dehydrogenase (ALDH). It is an evolutionarily conserved protein as shown from its high amino acid sequence identity between human and its plant counterparts. Therefore, ATQ is believed to play an important physiological role. Until now, however, studies on ATQ are limited and its cellular function is uncertain. Recently, we have first demonstrated the aldehyde oxidizing ability of ATQ purified from the liver of black seabream (Acanthopagrus schlegeli). To further investigate this protein, different attempts have been made. / Recombinant ATQ has been successfully expressed in E. coli. Kinetics studies showed that it possessed similar characteristics with its native enzyme. The recombinant protein was produced in large amount for protein crystallization. Crystal of ATQ was obtained and its X-ray structure was solved to 2.8 A in complex with NAD+. Tetrameric ATQ was a dimer of dimer. Three domains can be found in the subunit structure of ATQ, the NAD+-binding domain, catalytic domain and oligomerization domain. In each of the NAD+-binding domain, one molecule of NAD + could be found. The overall structure of ATQ was similar to other tetrameric ALDHs, but the coenzyme binding was in a single "hydride transfer" conformation and the density was well-defined which was contrast to most ALDH structures. Structural study of the substrate-binding pocket explained the failure of ATQ in oxidizing several aldehydes which is specific to certain members of ALDH. / The ATQ full-length cDNA of black seabream was obtained. It consisted of 2309 by with a 153 nucleotide long 5' UTR, and a 209 nucleotide long 3' UTR. An ORF of 1533 by which encoded a protein with 511 amino acids was found. This putative protein showed the highest of 87% sequence identity with zebrafish ATQ, and &sim;60% with plant ATQs. Tissue distribution was studied by RT-PCR. A high level of mRNA expression was observed in liver and kidney. Subcellular localization study using green fluorescent protein (GFP) fusion protein showed that ATQ was expressed in cytoplasm. However, another in-frame initiation methionine (M1) was found 31 residues before this generally accepted methionine (M2). Both iPSORT analysis and experimental studies using GFP fusion protein indicated that the 31 amino acid peptide contained a mitochondrial-targeting signal. / Tang Wai Kwan. / "July 2005." / Adviser: Fong Wing Ping. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3603. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 130-145). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

There are two main goals of this thesis: to investigate the flow-induced crystallization behaviour of Polybutene-1 (PB-1 samples, and to study the effects of molecular parameters on the crystallization behaviour While flow-induced crystallization is not a new area in polymer research, well-defined experimental methods that allow access to high flow rate range comparable to that encountered in real processing are still lacking. Two types of flow are considered: shear and uniaxial elongational. Regarding the second aim, several molecular parameters considered are: molecular weight, molecular weight distribution, isotacticity, presence of nucleating agents, and copolymer content. For this purpose an array of PB-1 samples were used. It is found that each of these parameters can have significant effect on the crystallization behaviour. Mainly rheological methods were utilized to conduct the flow-induced crystallization experiments. Crystallization onset time is define d from the change in viscosity or other related parameters. The experiments begin with low shear rate range, to ensure that the results are comparable with literature data. In this range we encounter the quasi-quiescent onset time at very small. shear rates, which draws an interesting comparison with another physical parameter, the gel time. Beyond a critical flow rate a decrease in the onset time is seen, and a plateau-and-slope trend is evident for a curve of onset time vs. shear rate. Using a combination of three experimental methods, shear rates ranging from Q0001 - 500 s-1 are successfully achieved, and a good agreement between these methods is observed. Furthermore, a normalization procedure is introduced, which yields temperature-invariant curves for the mentioned range of shear rate. For the uniaxial elongation flow, the Elongational Viscosity Fixture (EVF) is employed, with the strain rate ranging from 0.0001 - 10 s'. A greater reduction in onset time as compared to shear (at the same shear/strain r ate) is observed, and the difference in the onset times for shear and elongation already reaches more than one decade for a flow rate of 10 5. This quantitative comparison is particularly important; since not so many data on elongation-induced crystallization are available in the literature. Finally, the thesis compares several flow induced crystallization models that can be useful as prediction tools and selects one of these models to be compared with the experimental data. A qualitative agreement is found, however, for better quantitative prediction the model still needs to be.