Dissertations / Theses on the topic 'Co-crystalline'

2010 - 2011
Crystalline phases are extremely relevant for properties and applications of many polymeric materials. In fact, their amount, structure and morphology constitute the main factors controlling physical properties of fibers, films and thermoplastics and can be also relevant for properties of rubbers and gels. It is also well known that processing and physical properties of polymer-based materials are strongly affected by the occurrence of polymorphism (i.e. the possibility for a given polymer to crystallize in different crystalline forms) and mesomorphism (i.e. the occurrence of “disordered” crystalline phases, characterized by a degree of structural organization that is intermediate between those identifying crystalline and amorphous phases). Different has been the destiny of polymeric co-crystalline forms, i.e. structures were a polymeric host and a low-molecular-mass guest are co-crystallized. Systems composed of solid polymers and of low molecular mass molecules find several practical applications, including advanced applications. In several cases, additives (often improperly referred as guest molecules) are simply dispersed at molecular level in polymeric amorphous phases, although frequently, to reduce their diffusivity, the active molecules are covalently attached to the polymer backbone, either by polymerization of suitable monomeric units or by grafting the active species onto preformed polymers. A more simple alternative method to reduce diffusivity of active molecules in solid polymers and to prevent their self-aggregation consists in the formation of co-crystals with suitable polymer hosts. Polymeric co-crystalline forms are quite common for several regular and stereoregular polymers, like e.g. isotactic and syndiotactic polystyrene (s-PS), syndiotactic poly-p-methyl-styrene, syndiotactic poly-m-methyl-styrene, syndiotactic poly-p-chloro-styrene, syndiotactic poly-p-fluorostyrene, polyethyleneoxide, poly(muconic acid), polyoxacyclobutane, poly(vinylidene fluoride), syndiotactic polymethylmethacrylate. The removal of the low-molecular-mass guest molecules from co-crystals can generate nanoporous-crystalline phases. In this respect, it is worth noting that nanoporous crystalline structures can be achieved for a large variety of chemical compounds: inorganic (e.g., zeolites), metal-organic as well as organic. These materials, often referred as inorganic, metal-organic and organic “frameworks” are relevant for molecular storage, recognition and separation techniques. The removal of the low-molecular-mass guest molecules from polymer co-crystalline forms generates host chain rearrangements, generally leading to crystalline forms that, as usual for polymers, exhibit a density higher than that one of the corresponding amorphous phase. However, in few cases (to our knowledge, up to now only for s-PS), by using suitable guest removal conditions, nanoporous crystalline forms, exhibiting a density definitely lower than that of the corresponding amorphous phases are obtained. Poly-4-methyl-1-pentene isotactic (i-P4MP1) is a polymer characterized by a complex polymorphism and 4 different crystalline forms, some of which are obtainable only by crystallization with solvent, have been described in the literature. Monolithic and highly crystalline aerogels of isotactic poly(4-methyl-pentene-1) (i-P4MP1) have been prepared by sudden solvent extraction with supercritical carbon dioxide from thermoreversible gels. The cross-link junctions of i-P4MP1 gels, depending on the solvent, can be constituted by pure polymer crystalline phases (I or III or IV) or by polymer-solvent co-crystalline phases (for cyclohexane and carbon tetrachloride gels). Gels with co-crystalline phases lead to aerogels exhibiting the denser crystalline form II while all the other considered gels lead to aerogels exhibiting the thermodynamically stable form I. The effect of solvent on the aerogels pore structure and morphology has been also investigated by scanning electron microscopy and N2 sorption measurements. In all cases the areogels present highly porous interconnected structures with macropores and a large heterogeneity of mesopore size but without micro-sized pores. Poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) is a linear regular polymer, which as s-PS has the advantage to be a commercial thermoplastic polymer. PPO exhibits a high free volume or ultrapermeable amorphous phase and has been recognized as a membrane material with high permeation parameters. Although few papers have recognized that PPO crystalline phases can play a role in gas sorption and transport processes, no correlation between the amount or nature of the crystalline phase and guest sorption properties has been reported. This is mainly due to the scarce information available in the literature relative to the crystalline phases of PPO. Crystalline modifications, exhibiting largely different X-ray diffraction patterns, have been obtained for poly(2,6-dimethyl-1,4-phenylene)oxide (PPO), by gel desiccation procedures as well as by solvent-induced crystallization of amorphous films. The choice of the solvent allows controlling the nature of the crystalline phase. Both amorphous and semicrystalline samples of this commercial thermoplastic polymer exhibit a high uptake of large guest molecules (like, e.g., benzene or carbon tetrachloride), both from vapor phases and from diluted aqueous solutions. Surprisingly, the semicrystalline PPO samples present guest solubility much higher than fully amorphous PPO samples. These sorption experiments, as well as density measurements and classical BET experiments, clearly indicate that the obtained PPO crystalline phases are nanoporous. For these thermally stable PPO-based materials exhibiting nanoporous crystalline and amorphous phases, many applications are predictable. Finally, the preparation procedures and the thermal stability of the co-crystalline phase and FTIR and VCD analysis are presented. In particular co-crystalline phases with racemic and non-racemic guest molecules have been prepared and characterized. The experimental data indicates that the PPO/a-pinene co-crystalline form is chiral, i.e. the unit cell includes all right or left handed polymer helices and (1S-(–) or (1R)-(+) a-pinene guest molucules, respectively. [edited by author]
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2013 - 2014
Polymers can crystallize in different crystalline forms; polymorphism is the term to indicate this ability. It is known that processing and physical properties of polymer-based materials are strongly affected by the occurrence of ‘‘polymorphism’’ and ‘‘metamorphism’’ (i.e., the occurrence of ‘‘disordered’’ crystalline phases, characterized by a degree of structural organization that is intermediate between those identifying crystalline and amorphous phases). My PhD thesis is focused on the study and on the characterization of polymer films with co-crystalline and nanoporous crystalline phases. Many polymers are able to form co-crystals i.e. molecules of low molecular weight (guest) trapped in the crystalline polymer lattice (host). Over the past two decades it has been observed that some polymers, with co-crystalline phases, such as syndiotactic polystyrene (sPS) and poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) after guest removal can form nanoporous crystalline phases, able to absorb suitable guest molecules also at low activity. During this work, I have studied the possible molecular orientations that may be induced by solvents during cocrystallization process in polymeric films, (chapter 2); the development of chiro optical response, after co-crystallization with temporary chiral guest (chapter 3) and the possibility to realize photonic crystals by using polymers able to form nanoporous crystalline forms (chapter 4). In detail, in chapter 1 the procedure to obtain disordered nanoporous crystalline phases in sPS films and their possible application is reported. This disordered nanoporous crystalline phase rapidly absorb low molecular mass molecules, also from very dilute aqueous solutions. It is known in literature that nanoporous δ form of sPS is also able to absorb ethylene2b and carbon dioxide 2c-d, that have negatively effects for vegetable. Active packaging by nanoporous-crystalline films, based on the removal of molecules generated by the vegetables being detrimental for their preservation 2e, could be complemented by the slow release of antimicrobial molecules, which could be included as guest of the film crystalline cavities. Therefore the preparation of s-PS co-crystalline films that include guests with antimicrobial activity, in particular the carvacrol guest has been studied and reported in chapter 1. The kinetics of release, in variable concentrations of carvacrol in films with different thickness, has been analyzed. It was observed that the location of antimicrobial molecules mainly in the crystalline phase assure a decrease of desorption diffusivity and hence a long-term antimicrobial release. In chapter 2, the study of the possible molecular orientations that can be developed in polymer films able to form cocrystalline phases, are reported. This phenomenon has been observed only for sPS films until now. In particular, in my thesis has been shown that also other polymers, such as poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) and poly (L-lactide) (PLLA), able to form co-crystalline phases, can develop orientations during the co-crystallization process with solvents. These orientations can be useful to the structural studies on PPO and PLLA co-crystalline forms. We have also investigated on the shrinkage behaviour developed in syndiotactic polystyrene (sPS) films after cocrystallization procedures leading to co-crystalline phases. High shrinkage values have been measured on sPS d cocrystalline phase showing a crystalline phase orientation. In order to minimize this effect, novel procedures have been developed. Another aspect of my work is focused on the study of chiro optical response of a racemic polymer crystallized with a temporary chiral guest, as reported in chapter 3. In particular, I evaluated the degree of circular polarization of different thickness sPS films, and of the achiral guests, such as azulene and 4-nitroaniline, included in the polymer crystalline phase after guest exchange procedure. These studies have been useful to investigate on the nature of this phenomenon. Finally, in chapter 4, a method to realize a photonic crystal (PhC) with polymeric materials is reported. A PhC is an object composed by two or more materials with different refractive index and an alternated periodicity. The main advantage to use polymers rather than inorganic materials is the ease and the speed to obtain thin films by spin coating and the low cost of materials. In order to realize a photonic crystal, by using thin layers of PPO presenting nanoporous crystalline phase, it has been necessary to characterize amorphous as well as crystalline phases for this purpose. Techniques such as IRRAS and ellipsometry have been used (as reported in section 4.3 of chapter 4). [edited by Author]
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In this study, crystalline poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-co-AAc) nanoparticle network in organic solvents was obtained by self assembling precursor particles in acetone/epichlorohydrin mixture at room temperature followed by inter-sphere crosslinking at ~98 °C. The crystals thus formed can endure solvent exchanges or large distortions under a temporary compressing force with the reoccurrence of crystalline structures. In acetone, the crystals were stable, independent of temperature, while in water crystals could change their colors upon heating or changing pH values. By passing a focused white light beam through the crystals, different colors were displayed at different observation angles, indicating typical Bragg diffraction. Shear moduli of the gel nanoparticle crystals were measured in the linear stress-yield ranges for the same gel crystals in both acetone and water. Syntheses of particles of different sizes and the relationship between particle size and the color of the gel nanoparticle networks at a constant solid content were also presented. Temperature- and pH- sensitive crystalline PNIPAm-co-AAc hydrogel was prepared using osmosis crosslinking method. Not only the typical Bragg diffraction phenomenon was observed for the hydrogel but also apparent temperature- and pH- sensitive properties were performed. The phase behavior of PNIPAm nanoparticles dispersed in water was also investigated using a thermodynamic perturbation theory combined with lightscattering and spectrometer measurements. It was shown how the volume transition of PNIPAM particles affected the interaction potential and determined a novel phase diagram that had not been observed in conventional colloids. Because both particle size and attractive potential depended on temperature, PNIPAM aqueous dispersion exhibited phase transitions at a fixed particle number density by either increasing or decreasing temperature. The phase transition of PNIPAm-co-AAc colloids was also studied. The results from the comparison between pure PNIPAm and charged PNIPAm colloids showed that the introducing of carboxyl (-COOH) group not only contributed to the synthesis of three-dimensional nanoparticle network but also effectively increased the crystallization temperature and concentration range. The phase transitions at both low and high temperatures were observed from the turbidity change by using UV-Vis spectrometer. Centrifugal vibration method was used to make crystalline PNIPAm-co-AAc dispersion at high concentration (8%). The turbidity test proved the formation of iridescent pattern.

The formation of the solid crystalline phase of sugars plays an important role in many food products. The conventional crystallisation of sucrose gives solid, dense cubic crystals that have a limited surface area. On the other hand, co-crystallisation of sucrose is a process where a second ingredient is added to a supersaturated sucrose solution before crystallisation. The crystals obtained reveal a sponge-like appearance with considerable void space and interstices with the additive ingredient located in these interstices. The crystalline sugar products are said to be dry, granular, free-flowing and readily dispersible in water. It was shown that the co-crystallisation process improves the properties of a product such as its solubility, wettability and emulsification. Even though a number of patents have been reported on the subject, little research works have been published. In particular, little information was available on the thermal properties of the materials formed and the crystalline characteristics of the agglomerate matrix. In a preliminary work, the co-crystallisation of sucrose with honey was investigated. The Differential Scanning Calorimetry (DSC) and X-ray analyses showed that neither glucose nor fructose crystallised during the process. Nevertheless, glucose crystallised in the monohydrate form upon storage when a granulated honey was used. In addition, different types of glucose were co-crystallised with sucrose in the proportions glucose-sucrose 10/90, 15/85 and 20/80. The DSC analysis showed varying crystallisation behaviour depending on the type of glucose used. The co-crystallisation of glucose with sucrose was extended to the proportions 85/15, 90/10 and 95/5. The process was adapted to glucose as main ingredient. During the characterisation of the co-crystalline materials by DSC, an extra peak around 150°C was observed that could not be assigned to the second ingredient added or to a new crystalline phase formed by the constituents of the materials. The study of different sources of sucrose showed different behaviours by DSC analysis concerning this first melting peak. It was found that the purest sugar in terms of mineral salt content gave the highest intensity for this peak at 150°C. Further work under specific conditions of temperature and relative humidity permitted to isolate this phase believed to be due to a hydrated form of sucrose. Finally, the process of co-crystallisation of glucose with sucrose was scaled up to 5kg. The DSC traces showed that the ingredient present in minority did not crystallise during the process and remained in the amorphous form even after several months of storage. The materials thus prepared were used in confectionery applications. A co-crystalline material containing 10% of glucose was tested in chocolate but proved to thicken it up. This result was believed to be due to the porosity of the co-crystalline product. As a consequence, its potential for fat retention was studied. The co-crystalline material was found to reduce the migration of hazelnut oil in a dark chocolate coating. Furthermore, pressed sweets were prepared with co-crystalline materials containing 10 and 90% of glucose respectively. They showed good tabletting properties even without the use of binding agent. The tablets prepared had a crushing strength similar to superior to those prepared with a granulated powder. They also showed good flavour retention.

This doctorate was funded by the Regione Emilia Romagna, within a Spinner PhD project coordinated by the University of Parma, and involving the universities of Bologna, Ferrara and Modena. The aim of the project was: - Production of polymorphs, solvates, hydrates and co-crystals of active pharmaceutical ingredients (APIs) and agrochemicals with green chemistry methods; - Optimization of molecular and crystalline forms of APIs and pesticides in relation to activity, bioavailability and patentability. In the last decades, a growing interest in the solid-state properties of drugs in addition to their solution chemistry has blossomed. The achievement of the desired and/or the more stable polymorph during the production process can be a challenge for the industry. The study of crystalline forms could be a valuable step to produce new polymorphs and/or co-crystals with better physical-chemical properties such as solubility, permeability, thermal stability, habit, bulk density, compressibility, friability, hygroscopicity and dissolution rate in order to have potential industrial applications. Selected APIs (active pharmaceutical ingredients) were studied and their relationship between crystal structure and properties investigated, both in the solid state and in solution. Polymorph screening and synthesis of solvates and molecular/ionic co-crystals were performed according to green chemistry principles. Part of this project was developed in collaboration with chemical/pharmaceutical companies such as BASF (Germany) and UCB (Belgium). We focused on on the optimization of conditions and parameters of crystallization processes (additives, concentration, temperature), and on the synthesis and characterization of ionic co-crystals. Moreover, during a four-months research period in the laboratories of Professor Nair Rodriguez-Hormedo (University of Michigan), the stability in aqueous solution at the equilibrium of ionic co-crystals (ICCs) of the API piracetam was investigated, to understand the relationship between their solid-state and solution properties, in view of future design of new crystalline drugs with predefined solid and solution properties.

This doctorate was funded by the Regione Emilia Romagna, within a Spinner PhD project coordinated by the University of Parma, and involving the universities of Bologna, Ferrara and Modena. The aim of the project was: - Production of polymorphs, solvates, hydrates and co-crystals of active pharmaceutical ingredients (APIs) and agrochemicals with green chemistry methods; - Optimization of molecular and crystalline forms of APIs and pesticides in relation to activity, bioavailability and patentability. In the last decades, a growing interest in the solid-state properties of drugs in addition to their solution chemistry has blossomed. The achievement of the desired and/or the more stable polymorph during the production process can be a challenge for the industry. The study of crystalline forms could be a valuable step to produce new polymorphs and/or co-crystals with better physical-chemical properties such as solubility, permeability, thermal stability, habit, bulk density, compressibility, friability, hygroscopicity and dissolution rate in order to have potential industrial applications. Selected APIs (active pharmaceutical ingredients) were studied and their relationship between crystal structure and properties investigated, both in the solid state and in solution. Polymorph screening and synthesis of solvates and molecular/ionic co-crystals were performed according to green chemistry principles. Part of this project was developed in collaboration with chemical/pharmaceutical companies such as BASF (Germany) and UCB (Belgium). We focused on on the optimization of conditions and parameters of crystallization processes (additives, concentration, temperature), and on the synthesis and characterization of ionic co-crystals. Moreover, during a four-months research period in the laboratories of Professor Nair Rodriguez-Hormedo (University of Michigan), the stability in aqueous solution at the equilibrium of ionic co-crystals (ICCs) of the API piracetam was investigated, to understand the relationship between their solid-state and solution properties, in view of future design of new crystalline drugs with predefined solid and solution properties.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2006.
"May, 2006." Title from electronic dissertation title page (viewed 10/11/2006) Advisor, James L. White; Committee members, Avraam I. Isayev, Thein Kyu, Darrell H. Reneker, Shing-Chung "Josh" Wong; Department Chair, Sadhan C. Jana; Dean of the College, Frank N. Kelley; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

ABSTRACT HYDROGEN STORAGE IN MAGNESIUM BASED THIN FILMS Akyildiz, Hasan Ph.D., Department of Metallurgical and Materials Engineering Supervisor : Prof. Dr. Tayfur Ö
ztü
rk Co-Supervisor : Prof. Dr. Macit Ö
zenbas October 2010, 146 pages A study was carried out for the production of Mg-based thin films which can absorb and desorb hydrogen near ambient conditions, with fast kinetics. For this purpose, two deposition units were constructed
one high vacuum (HV) and the other ultra high vacuum (UHV) deposition system. The HV system was based on a pyrex bell jar and had two independent evaporation sources. The unit was used to deposit films of Mg, Mg capped with Pd and Au-Pd as well as Mg-Cu both in co-deposited and multilayered form within a thickness range of 0.4 to 1.5 &mu
m. The films were crystalline with columnar grains having some degree of preferred orientation. In terms of hydrogen storage properties, Mg/Pd system yielded the most favorable results. These films could desorb hydrogen at temperatures not greater than 473 K. The study on crystalline thin films has further shown that there is a narrow temperature window for useful hydrogenation of thin films, the upper limit of which is determined by the intermetallic formation. The UHV deposition system had four independent evaporation sources and incorporated substrate cooling by circulating cooled nitrogen gas through the substrate holder. Thin films of Mg-Cu were produced in this unit via co-evaporation technique to provide concentrations of 5, 10 and 15 at. % Cu. The films were 250-300 nm thick, capped with a thin layer of Pd, i.e. 5-25 nm. The deposition was yielded nanocrystalline or amorphous Mg-Cu thin films depending on the substrate temperature. At 298 K, the films were crystalline, the structure being refined with the increase in Cu content. At 223 K, the films were amorphous, except for Mg:Cu=95:5. The hydrogen sorption of the films was followed by resistance measurements, with the samples heated isochronally, initially under hydrogen and then under vacuum. The resistance data have shown that hydrogen sorption behaviour of thin films was improved by size refinement, and further by amorphization. Among the films deposited, amorphous Mg:Cu=85:15 alloy could absorb hydrogen at room temperature and could desorb it at 223 K (50 º
C), with fast kinetics.

AbstractThe aim of the present project was to investigate the possibilities of using a Zr55Cu30Ni5Al10 Bulk Metallic Glass (BMG) alloy as articulating surface in an artificial hip joint.In order for a material to be used in human body as an implant, the foremost requirement is the acceptability by the human body. The implantations should not cause diseases or other complications for the patients. Moreover, the biomaterials should possess sufficient mechanical strength, high corrosion and wear resistance in harsh body environment with varying loading conditions.There have been extensive research on the properties of stainless steel, Co-Cr-Mo alloys and Ti alloys regarding their bio-compatibility and they are currently being used as orthopedic implants, however less information is available for bulk metallic glasses. So, understanding the corrosion properties of BMGs is one of the key issues to evaluate their potential as biomaterials.In the first phase of the project there was an attempt to develop a Zr-based BMG from pure elements in a vertical resistance furnace and quenching in liquid nitrogen. Afterwards, samples were examined by X-Ray diffraction and microscopically to investigate the presence of crystalline phases. The second phase was electrochemical measurements to study the passivation behavior and the susceptibility to pitting corrosion for the crystalline Zr55Cu30Ni5Al10, amorphous Zr55Cu30Ni5Al10 BMG (received from Japan) and comparing the result with stainless steel and Co-Cr-Mo (F75). Investigations on corrosion properties were made in phosphate-buffered saline (PBS) with and without the addition of albumin fraction V, at a room temperature of 20 °C and body temperature (37°C) and in different pH values of 7.4 and 5.2. Running the experiment in lower pH shows the behavior of the implant against any probable inflation in the patient body.The last phase was to investigate the interaction between the protein and surface of materials. For this purpose, FTIR spectroscopy and Electrochemical Impedance Spectroscopy (EIS) were carried out.Keys words: Biomaterials, Bulk Metallic Glass, Crystalline Zr55Cu30Ni5Al10, Co-Cr-Mo alloy, Stainless steel, Polarization curve, FTIR, Impedance.

Dispersing co-crystals in a polymeric carrier may improve their physicochemical properties such as dissolution rate and solubility. Additionally co-crystal stability may be enhanced. However, such dispersions have been little investigated to date. This study focuses on the feasibility of dispersing co-crystals in a polymeric carrier and theoretical calculations to predict their stability. Acetone/chloroform, ethanol/water, and acetonitrile were used to load and grow co-crystals in a HPMCAS film. Caffeine-malonic acid and ibuprofennicotinamide co-crystals were prepared using solvent evaporation method. The interactions between each of the co-crystals components and their mixtures with the polymer were studied. A solvent evaporation approach was used to incorporate each compound, a mixture, and co-crystals into HPMCAS films. Differential scanning calorimetry data revealed a higher affinity of the polymer to acidic compounds than their basic counterparts as noticed by the depression of the glass transition temperature (Tg). Moreover, the same drug loading produced films with different Tgs when different solvents were used. Solubility parameter values (SP) of the solvents were employed to predict that effect on the depression of polymer Tg with relative success. SP values were more successful in predicting the preferential affinity of two acidic compounds to interact with the polymer. This was confirmed using binary mixtures of naproxen, flurbiprofen, malonic acid, and ibuprofen. On the other hand, dispersing basic compounds such as caffeine or nicotinamide with malonic acid in HPMCAS film revealed the growth of co-crystals. A dissolution study showed that the average release of caffeine from films containing caffeine-malonic acid was not significantly different to that of films containing similar caffeine concentration. The stability of the caffeine-malonic acid co-crystals in HPMC-AS was prolonged to 8 weeks at 95% relative humidity and 45°C. The theory developed in this project, that an acidic drug with a SP value closer to the polymer will dominate the interaction process and prevent the majority of the other material from interacting with the polymer, may have utility in designing co-crystal systems in polymeric vehicles

This thesis focuses on the effects of dopant compensation on the electrical properties of crystalline silicon relevant to the operation of solar cells. We show that the control of the net dopant density, which is essential to the fabrication of high-efficiency solar cells, is very challenging in ingots crystallized with silicon feedstock containing both boron and phosphorus such as upgraded metallurgical-grade silicon. This is because of the strong segregation of phosphorus which induces large net dopant density variations along directionally solidified silicon crystals. To overcome this issue, we propose to use gallium co-doping during crystallization, and demonstrate its potential to control the net dopant density along p-type and n-type silicon ingots grown with silicon containing boron and phosphorus. The characteristics of the resulting highly-compensated material are identified to be: a strong impact of incomplete ionization of dopants on the majority carrier density, an important reduction of the mobility compared to theoretical models and a recombination lifetime which is determined by the net dopant density and dominated after long-term illumination by the boron-oxygen recombination centre. To allow accurate modelling of upgraded-metallurgical silicon solar cells, we propose a parameterization of these fundamental properties of compensated silicon. We study the light-induced lifetime degradation in p-type and n-type Si with a wide range of dopant concentrations and compensation levels and show that the boron-oxygen defect is a grown-in complex involving substitutional boron and is rendered electrically active upon injection of carriers through a charge-driven reconfiguration of the defect. Finally, we apply gallium co-doping to the crystallization of upgraded-metallurgical silicon and demonstrate that it allows to significantly increase the tolerance to phosphorus without compromising neither the ingot yield nor the solar cells performance before light-induced degradation.

Monodispersed nanoparticles of poly-N-isopropylacrylamide-co-allylamine (PNIPAM-co-allylamine) and PNIPAM-co-acrylic acid (AA) have been synthesized and used as building blocks for creating three-dimensional networks. The close-packed PNIPAM-co-allylamine and PNIPAM-co-AA nanoparticles were stabilized by covalently bonding neighboring particles at room temperature and at neutral pH; factors which make these networks amicable for drug loading and release. Controlled release studies have been performed on the networks using dextran markers of various molecular weights as model macromolecular drugs. Drug release was quantified under various physical conditions including a range of temperature and molecular weight. These nanoparticle networks have several advantages over the conventional bulk gels for controlling the release of biomolecules with large molecular weights. Monodispersed nanoparticles of poly-N-isopropylacrylamide-co-allylamine (PNIPAM-co-allylamine) can self-assemble into crystals with a lattice spacing on the order of the wavelength of visible light. By initiating the crystallization process near the colloidal crystal melting temperature, while subsequently bonding the PNIPAM-co-allylamine particles below the glass transition temperature, a nanostructured hydrogel has been created. The crystalline hydrogels exhibit iridescent patterns that are tunable by the change of temperature, pH value or even protein concentration. This kind of soft and wet hydrogel with periodic structures may lead to new sensors, devices, and displays operating in aqueous solutions, where most biological and biomedical systems reside. The volume-transition equilibrium and the interaction potential between neutral PINPAM particles dispersed in pure water were investigated by using static and dynamic light-scattering experiments. From the temperature-dependent size and energy parameters, the Sutherland-like potential provides a reasonable representation of the inter-particle potential for PNIPAM particles in swollen and in collapsed phases. An aqueous dispersion of PNIPAM particles can freeze at both high and low temperatures. At low temperatures, the freezing occurs at a large particle volume fraction, similar to that in a hard-sphere system; while at high temperature, the freezing occurs at low particle concentrations, driven by the strong van der Waals attraction due to the collapsed microgel particles. The calculated phase diagram has been confirmed semi-quantitatively by experiments.

Pas de résumé en français
Plasmonic circuitry is considered as a promising solution-effectivetechnology for miniaturizing and integrating the next generation ofoptical nano-devices. The realization of a practical plasmonic circuitry strongly depends on the complete understanding of the propagation properties of two key elements: surface plasmons and electrons. The critical part constituting the plasmonic circuitry is a waveguide which can sustain the two information-carriers simultaneously. Therefore, we present in this thesis the investigations on the propagation of surface plasmons and the co-propagation of surface plasmons and electrons in single crystalline metal nanowires. This thesis is therefore divided into two parts. In the first part, we investigate surface plasmons propagating in individual thick penta-twinned crystalline silver nanowires using dual-plane leakage radiation microscopy. The effective index and the losses of the mode are determined by measuring the wave vector content of the light emitted in the substrate. Surface plasmon mode is determined by numerical simulations and an analogy is drawn with molecular orbitals compound with similar symmetry. Leaky and bound modes selected by polarization inhomogeneity are demonstrated. We further investigate the effect of wire geometry (length, diameter) on the effective index and propagation losses. On the basis of the results obtained during the first part, we further investigate the effect of an electron flow on surface plasmon properties. We investigate to what extend surface plasmons and current-carrying electrons interfere in such a shared circuitry. By synchronously recording surface plasmons and electrical output characteristics of single crystalline silver and gold nanowires, we determine the limiting factors hindering the co-propagation of electrical current and surface plasmons in these nanoscale circuits. Analysis of wave vector distributions in Fourier images indicates that the effect of current flow on surface plasmons propagation is reflected by the morphological change during the electromigration process. We further investigate the possible crosstalk between co-propagating electrons and surface plasmons by applying alternating current bias

Plasmonic circuitry is considered as a promising solution-effectivetechnology for miniaturizing and integrating the next generation ofoptical nano-devices. The realization of a practical plasmonic circuitry strongly depends on the complete understanding of the propagation properties of two key elements: surface plasmons and electrons. The critical part constituting the plasmonic circuitry is a waveguide which can sustain the two information-carriers simultaneously. Therefore, we present in this thesis the investigations on the propagation of surface plasmons and the co-propagation of surface plasmons and electrons in single crystalline metal nanowires. This thesis is therefore divided into two parts. In the first part, we investigate surface plasmons propagating in individual thick penta-twinned crystalline silver nanowires using dual-plane leakage radiation microscopy. The effective index and the losses of the mode are determined by measuring the wave vector content of the light emitted in the substrate. Surface plasmon mode is determined by numerical simulations and an analogy is drawn with molecular orbitals compound with similar symmetry. Leaky and bound modes selected by polarization inhomogeneity are demonstrated. We further investigate the effect of wire geometry (length, diameter) on the effective index and propagation losses. On the basis of the results obtained during the first part, we further investigate the effect of an electron flow on surface plasmon properties. We investigate to what extend surface plasmons and current-carrying electrons interfere in such a shared circuitry. By synchronously recording surface plasmons and electrical output characteristics of single crystalline silver and gold nanowires, we determine the limiting factors hindering the co-propagation of electrical current and surface plasmons in these nanoscale circuits. Analysis of wave vector distributions in Fourier images indicates that the effect of current flow on surface plasmons propagation is reflected by the morphological change during the electromigration process. We further investigate the possible crosstalk between co-propagating electrons and surface plasmons by applying alternating current bias

Дисертаційна робота присвячена вивченню закономірностей формування структури, фазового складу, електрофізичних і магніторезистивних властивостей плівкових сплавів CoNi (в інтервалі концентрацій 0 < сСо < 100 мас.%) і FeNi (cFe=50 мас.%) в інтервалі товщин 5-200 нм та температур 300-700 К, та магніторезистивних властивостей тришарових плівок на основі цих сплавів.Невідпалені плівки мають дрібнозернисту структуру (розмір кристалітів менше 5-10 нм). В результаті відпалу розмір кристалітів збільшується до 40-60 нм. Плівкові сплави CoNi при вмісті Со менше 70 мас.% мають однофазний склад (ГЦК-твердий розчин). Параметр решітки при збільшенні вмісту Со змінюється у відповідності з правилом Вегарда. При сСо>70 мас.% у відпалених до 700 К плівках спостерігається двофазний склад (ГЦК+ГЩП). Плівкам сплаву Fe50Ni50 притаманна ГЦК-решітка з параметром а=0,359-0,361 нм. Плівкам з ефективною товщиною до 10 нм властива експоненціальна залежність опору з від’ємними значеннями температурного коефіцієнта опору(ТКО), що вказує на термічно активовану провідність і обумовлене структурною і електричною несуцільністю плівок. Одержана розмірна залежність енергії активації провідності. Для плівок сплавів CoNi і FeNi з товщинами більше 20 нм характерні додатні значення ТКО і квадратична залежність питомого опору від температури. Визначено параметри електроперенесення на основі теоретичних моделей розмірних ефектів електропровідності. Досліджено концентраційні і розмірні залежності магнітоопору плівкових сплавів FeNi і CoNi. Максимальна величина магнітоопору (3,5 % для поздовжнього і 2,5 % для поперечного ефекту) спостерігається для плівок CoNi при вмісті Со 40 мас.%. Встановлено, що для невідпалених тришарових плівок CoNi/Cu(Ag)/ FeNi, CoNi/Cu(Ag)/Co, FeNi/Cu(Ag)/Со з товщиною немагнітного шару 3-15 нм спостерігається гігантський магнітоопір. Термічна обробка до температури 500-700 К приводить до переходу від ГМО до анізотропного магнітоопору. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/20820
Диссертационная работа посвящена изучению закономерностей формирования структуры, фазового состава, электрофизических (удельное сопротивление и температурный коэффициент сопротивления (ТКС)) и магниторезистивных свойств пленочных сплавов CoNi (в интервале концентраций 0<сСо<100 мас.%) и FeNi (cFe=50 мас.%) в интервале толщин 5-200 нм и температур 300-700 К, и магниторезистивных свойств трехслойных пленок на основе этих сплавов. Установлено, что в процессе осаждения пленочных сплавов CoNi испарением готового сплава состав полученной пленки практически совпадает с составом исходного материала, что определяется близостью физических свойств компонент. Для сплава Fe50Ni50 при таком способе осаждения наблюдается обогащение пленок железом. Неотожженные пленки имеют мелкозернистую структуру (размер кристаллитов менее 5-10 нм), в результате отжига размер кристаллитов увеличивается (40-60 нм в случае пленок сплава CoNi, до 30-50 нм для сплава Fe50Ni50). Пленочные сплавы CoNi при содержании Со менее 70 мас.% имеют однофазный состав (ГЦК-твердый раствор), параметр решетки при увеличении содержания Со изменяется в пределах а=(0,352-0,355 нм) в соответствии с правилом Вегарда. При сСо>70 % неотожженным пленкам свойственна ГПУ-решетка, в результате отжига в пленках наблюдается двуфазный состав (ГЦК+ГПУ). Стабильность ГЦК-фазы может быть объяснена снижением температуры фазового перехода для части кристаллитов малого размера за счет фазового размерного эффекта. Для пленок сплава Fe50Ni50 свойственна ГЦК-решетка с параметром а=0,359-0,361 нм. Исследование температурных зависимостей сопротивления пленок показало, что для первого цикла отжига характерно необратимое уменьшение сопротивления, связанное с процессами роста кристаллитов и отжигом дефектов кристаллической структуры. В дальнейших циклах термообработки наблюдается повторение хода температурных зависимостей. Для пленок с эффективной толщиной менее 10 нм характерна экспоненциальная зависимость сопротивления с отрицательными значениями ТКС, что указывает на термически активированную проводимость и связано с образованием структурно и электрически несплошных (островковых) пленок. Показано, что энергия активации проводимости определяется размером островков и промежутков между ними и не зависит от состава сплава. Получена размерная зависимость энергии активации проводимости.Для пленок сплавов CoNi и FeNi с толщинами более 20 нм характерны положительные значения ТКС и квадратичная зависимость удельного сопротивления от температуры, свойственная ферромагнитным металлам и связанная с электрон-магнонным взаимодействием. Изучены размерные зависимости удельного сопротивления и ТКС пленок, на основании которых определены параметры электропереноса в рамках ряда теоретических моделей размерных эффектов электропроводности. В работе проведены исследования зависимости сопротивления однослойных пленочных сплавов от величины напряженности внешнего магнитного поля. Установлено, что для всех исследованных образцов наблюдается анизотропное магнитосопротивление. Для полевых зависимостей магнитосопротивления характерно наличие гистерезиса и экстремумов, что связано с изменением доменной структуры образцов в процессе перемагничивания. Для пленочных сплавов FeNi и CoNi исследованы концентрационные и размерные зависимости. Максимальная величина магнитосопротивления (3,5 % для продольного и 2,5 % для поперечного эффекта) наблюдается для сплавов CoNi при содержании Со 40 мас.%. В работе также показана возможность создания на базе рассмотренных пленочных сплавов трехслойных спин-вентильных систем с гигантским магнитосопротивлением (ГМС). Установлено, что для неотожженых трехслойных пленок CoNi/Cu(Ag)/FeNi, CoNi/Cu(Ag)/Co, FeNi/Cu(Ag)/Со с толщиной немагнитного слоя 3-15 нм наблюдается изотропное магнитосопротивление, что является характерным признаком ГМС. Максимальная амплитуда ГМС (1,1 % при Т=300К и 2 % при Т=150К) получена для системы CoNi/Ag/FeNi с толщиной слоя Ag 4-7 нм. Термическая обработка до температуры 500-700 К приводит к переходу от изотропного к анизотропному магнитосопротивлению, что может быть объяснено нарушением сплошного немагнитного слоя в результате диффузионных процессов. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/20820
The thesis is devoted to the study of mechanisms of the formation of structure, phase composition, electrophysical and magnetoresistive properties of CoNi film alloys (within the concentration interval 0 < сСо< 100 wt.%) and FeNi (cFe=50 wt.%) within the thickness interval of 5-200 nm and temperature interval of 300-700 К, as well as magnetoresistive properties of three-layer films on the basis of these alloys. Unannealed films have fine-grain structure (crystals size is lower than 5-10 nm). Crystals size increase to 40-60 nm as the result of annealing. CoNi film alloys with the Со content lower than 70 wt.% have one-phase composition (FCCsolid solution). Provided Со content is increased, the lattice parameter will be changed according to the Vergard’s rule. Two-phase content (FCC + HCP lattice) will be observed, provided сСо is more than 70 wt.% within the films that are annealed to 700 К. The FCC lattice with the parameter of а=0,359-0,361 nm is the characteristic of Fe50Ni50 alloy films. The films with the effective thickness up to 10 nm are characterized by the exponential dependence of resistance with the negative values of temperature coefficient of resistance. The dependence indicates thermally activated conductivityand is conditioned by the structural and electrical discontinuous films. The size dependence of the conductivity activation energy is obtain. The films of the CoNi and FeNi alloys with the thicknesses more than 20 nm are characterized by the positive values of temperature coefficient of resistance and the quadratic dependence of resistivity on the temperature. The parameters of electric transfer are being determined on the basis of the theoretical models of the size effects of electric conduction. Concentration and size dependences of FeNi and CoNi film alloy magnetoresistance are studied. The maximum value of magnetoresistance (3,5 % for longitudinal and 2,5 % for transverse effect) is observed for the CoNi films with the Со content of 40 wt.%. It has been determined, that GMR is observed within CoNi/Cu(Ag)/FeNi, CoNi/Cu(Ag)/Co, FeNi/Cu(Ag)/Со unannealed three-layer films with the nonmagnetic layer thickness that equals 3-15 nm. The thermal treatment up to the temperature of 500-700 К leads to the change from GMR to anisotropic magnetoresistance. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20820

This thesis focuses on the effects of dopant compensation on the electrical properties of crystalline silicon relevant to the operation of solar cells. We show that the control of the net dopant density, which is essential to the fabrication of high-efficiency solar cells, is very challenging in ingots crystallized with silicon feedstock containing both boron and phosphorus such as upgraded metallurgical-grade silicon. This is because of the strong segregation of phosphorus which induces large net dopant density variations along directionally solidified silicon crystals. To overcome this issue, we propose to use gallium co-doping during crystallization, and demonstrate its potential to control the net dopant density along p-type and n-type silicon ingots grown with silicon containing boron and phosphorus. The characteristics of the resulting highly-compensated material are identified to be: a strong impact of incomplete ionization of dopants on the majority carrier density, an important reduction of the mobility compared to theoretical models and a recombination lifetime which is determined by the net dopant density and dominated after long-term illumination by the boron-oxygen recombination centre. To allow accurate modelling of upgraded-metallurgical silicon solar cells, we propose a parameterization of these fundamental properties of compensated silicon. We study the light-induced lifetime degradation in p-type and n-type Si with a wide range of dopant concentrations and compensation levels and show that the boron-oxygen defect is a grown-in complex involving substitutional boron and is rendered electrically active upon injection of carriers through a charge-driven reconfiguration of the defect. Finally, we apply gallium co-doping to the crystallization of upgraded-metallurgical silicon and demonstrate that it allows to significantly increase the tolerance to phosphorus without compromising neither the ingot yield nor the solar cells performance before light-induced degradation.

Vingt-quatre nouveaux complexes d'halogénures de métaux 3 D : mx::(2) (m = co,ni,cu; x = cl,br) sont préparés et caractérisés. Leurs structures sont déterminées par diffraction des rayons X pour deux des composés et, à partir de celles-ci, pour l'ensemble des complexes grâce à la spectroscopie infrarouge et à la spectroscopie électronique. Le calcul des constantes de stabilité et des paramètres thermodynamiques correspondants par titrimétrie thermométrique est décrit.

碩士
國立臺灣師範大學
物理學系
100
This study is separated into two parts: (1) Using oblique deposition to change the surface morphology. (STM measurement) We investigated the corresponding magnetic behavior (MOKE measurement), and the crystalline structure (XRD, EXAFS measurement) in Pd/Fe/Al2O3(0001) system. (2) H2 effect in MOKE, we absorption H2 from 10-3 mbar to 1013 mbar and measured MOKE in Pd/Fe,Co,Ni/Al2O3(0001) systems. In many studies, surface morphology plays an important role in magnetic behavior. They are many methods to change it, like ion-sputtering, different stepped substrate…etc. One of the feasible methods is changing the surface morphology by different deposit angle. In Pd/Fe/Al2O3(0001) system. In normal deposition, Fe atoms were follow the sapphire (0001) growth, and the corresponding magnetic hysteresis loop was almost square, it was isotropy. In oblique deposition, Fe grains were connected to form a 1-dimenstorn ripple structure, and habited interesting magnetic behavior. The easy axis is parallel to the ripples, and the hard axis is perpendicular to the ripples. In easy axis, the magnetic hysteresis loop was also square but the coercivity was much bigger than normal deposition. In hard axis, we could see the obvious uniaxial magnetic anisotropy. Another ideal in this experiment was H2 absorption effect on MOKE. We capped Pd films on the top surface after Fe deposition. There are two reasons for the Pd capping layer, one is to protect Fe films oxidation, the other is Pd can adsorption H2 and the optical of MOKE is changed. key words: oblique deposition, magnetic optical Kerr effect

碩士
國立臺灣大學
物理學研究所
88
Magnetic alloy ultrathin films CoxNi1-x/Cu(100) were prepared to characterize its behavior of spin reorientation transition (SRT). With the double check of MEED oscillation and quantitative AES analysis, the composition of the alloy films was determined within an accuracy of ± 0.5 %, which allows us to prepare alloy films in very low Co concentration. So the sensitive effect of alloy composition in crystalline structure, morphology and magnetic properties can be characterized in situ by LEED, I/V-LEED and MOKE. The critical thickness of spin reorientation transition (SRT) in magnetic alloy ultrathin films CoxNi1-x /Cu(100) were 7~8, 9~10, 13~14, 17~18 ML for x = 0, 3, 5.5, 8 % respectively, and for x = 10 %, alloy films always reveal in-plane anisotropy up to 20.6 ML. Despite of the composition induced very different SRT behavior when x ￡ 10%, the vertical inter-layer distance and the morphology of all the films did not show any significant difference. Comparing with other experimental and theoretical results, it is concluded that the magnetic properties such as magnetic anisotropy were extremely sensitive to the average filling 3d electron in the alloy films.

碩士
國立臺灣大學
材料科學與工程學研究所
105
Conducting polymers are important materials in the fabrication of optoelectronic devices. The orientation of the polymer crystalline is critical to achieve high charge carrier mobility and performance in the devices. In general, the edge-on orientation is preferred for utilities of organic field-effect transistors, and the face-on orientation is desired for applications in organic solar cells. However, the detail mechanisms behind the cause of favored crystal orientation of conducting polymers are not clearly understood currently. The systematic studies of molecular design and synthesis for the desired crystal orientation are relatively few present in the literatures. In this research, we design and synthesize eight different co-oligomers, poly(thienoisoindigo-alt-(xoctylthiophene)n, PTInT-xC8, where thienoisoindigo unit (TI) acting as an acceptor is conjugated with thiophene (T) as a donor; n is the number of thiophene in a donor segment, and xC8 denotes the number of n-octyl substituted on thiophenes in a repeat unit. We could tailor the crystal orientation by varying two parameters: (1) side-chain attachment density by changing the number of n-octyl substituents (x) on the thiophenes, and (2) the backbone curvature by changing the number of thiophene (n). The co-oligomers were synthesized successfully via either Stille coupling reaction or direct arylation polycondensation, and were characterized by nuclear magnetic resonance spectroscopy (NMR) for chemical structures, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF) for molecular weights, grazing-incidence wide angle X-ray scattering (GIWAXS) for crystalline structures, ultraviolet－visible－near infrared absorption spectroscopy (UV－Vis－NIR) for optical properties and cyclic voltammetry (CV) for band gap determination, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) for thermal properties. The differences among 8 co-oligomers are also studied in details by modeling the molecules by the density functional theory (DFT) calclations. The results indicate that: (1) increasing the number of substituted n-octyl chains (x) on the donor segment of thiophenes while the number of thiophenes (n) is fixed, the polymer backbone will be twisted dramatically as shown by molecular modeling. From the absorption spectra, the relative absorption peak intensity of electrons excited from donor’s HOMO to donor’s LUMO (λ1) is increased while the one symbolized intramolecular transfer (λ2) is decreased. The GIWAXS results also indicate that the π-π stacking distances (dπ-π) in the direction of (010) increase. For example, the dπ-π of PTI2T-0C8 and PTI2T-2C8 are 3.57 Å and 4.83 Å, respectively; the π-π interaction of PTI2T-4C8 is weakened enough that no diffraction peaks could be defined. (2) Increasing the number of thiophene (n) on donor segment while fixing the number of substituted n-octyl chains (x) on thiophenes will distort the backbone due to the increasing freedom of torsion, which shortens the π-conjugation length, and the band gap is increased accordingly. For example, Egsol of PTI2T-2C8, PTI3T-2C8 and PTI4T-2C8 is 1.00, 1.18 and 1.25 eV, respectively; Egfilm is 0.87, 1.14 and 1.20 eV, respectively. The GIWAXS study shows the lamellar distances (d(100)) of PTI3T series are larger than those series of PTI2T and PTI4T. The results are due to the comformation differences between the odd and even number of thiophene (n) in donor segment on the backbone. The even number n gives a centrosymmetric structure whereas the odd number exhibits an axisymmetric configuration. Meanwhile, the steric hindrance of side-chain also influences the packing of polymer backbones. Thus, the centrosymmetric polymers (n = 2 or 4) exhibit the edge-on crystal orientation of long-range order due to the strong π-π interaction. Their orientation will be gradually changed to face-on orientation when the number of side-chains (x) on thiophenes equal to 2 or larger. The change of orientation is far more dramatic for axisymmetric co-oligomerss when the number of side-chains is changed due to the the nonlinear characteristic of backbone which are not suitable for standing on substrate. The edge-on packing is observed for co-oligomers (PTI3T-0C8) without side-chain attached on thiophenes. However, the packing orientation becomes well-ordered face-on with two side-chains added onto the donor segment of thiophenes, and amorphous structure is obtained with adding two more side-chains. The CV results also reveal that most of the PTInT could be used as a p-type semi-conductor materials, and part of the co-oligomers are quiet stable at high temperature with the decomposition temperature as high as 390°C. The outcomes of this research provide pathways for designing and synthesizing conducting polymers with desired crystal orientation for specific optoelectronic device applications.

碩士
國立成功大學
資源工程學系碩博士班
95
Strontium barium niobate ( SBN ) ceramic is a good electro-optic material and has been widely used. Although SBN single crystals could be used in wide applications, high cost and difficult fabrication have limited its practical use. For optical applications, a ceramic with almost full density and uniform microstructure is greatly desired. Strontium barium niobate co-doped Ce2O3、Cr2O3 is investigated into the crystalline structure and the dielectric properties. Due to the increase of the quantity of the additive, the a axis is increased, but the c axis is decreased. In the dielectric properties, Tmax and εmax decreased with the increase of the content of Ce2O3、Cr2O3, which is essentially determined by the structural change of the NbO6 units in SBN. The remanent polarization is studied by the Hysteresis loop. Due to the increase of the quantity of the additive, decrease the remanent polarization.

博士
元智大學
化學工程與材料科學學系
97
Free volume properties in the amorphous region of a series of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) membranes, which were prepared by cold- and melt-crystallization processes, were investigated using positron annihilation lifetime (PAL) spectroscopy in this study. From the lifetime parameters, the temperature dependence of free volume size, amount, free volume size distribution, and fractional free volume, and the thermal expansion of free volume were discussed. Furthermore, the knee temperature was first observed in the melting process of the crystallized PHBV membranes. It indicated that there was structural transition of polymer chains during melting as the corresponding results observed with in situ FTIR measurement. A model which assumed that amorphous phase was subdivided into mobile and rigid amorphous fractions (MAF and RAF) in the semi-crystalline polymer was considered to interpret the temperature dependence of those free volume properties. The difference of free volume properties among various PHBV membranes was created according to the crystalline structure of the polymer from different thermal history. The polymer crystallized at higher temperatures resulted in higher crystallinities, less free volume amounts and lower fractional free volumes. Based on the crystallization conditions, the effect of the crystallization rate of PHBV polymer was first proposed to explain the thermal expansion coefficients of free volume size. The faster crystallization rate is, the higher thermal expansion coefficient and the larger free volume size at higher measuring temperatures are. Morphological observation of the semi-crystalline polymer by small-angle X-ray scattering (SAXS) indicated that the cold-crystallized membranes showed a much thinner thickness of the repeating lamellar/amorphous layers and most likely higher amount of RAF, which restrained the chain motion, than the melt-crystallized membranes. Larger dispersion of the free volume size of melt-crystallized membranes was observed as a result of the bimodal distribution of the lamellar periodicity and less amount of RAF than that of the cold-crystallized membranes. In conclusion, the relationship between the crystalline structure and the free volume properties within the amorphous phase of PHBV polymer was well established. Free volume size and thermal expansion of the free volume in PHBV membranes were affected by the kinetic of crystallization; comparatively, the total amount of free volume and fractional free volume were determined by the final crystallinity. The size distribution of free volume was associated with the crystalline lamellar structure which was dominated by the crystallization conditions.

碩士
國立中正大學
物理系
92
Experiments have been performed by using series of crystalline Co(500 )/Fe(50 )/MgO(X)/Fe(500 ) films (where X=8、16、25).The samples have prepared by molecular beam epitaxy on MgO(001,011,111) substrates. The hysteresis and magnetoresistance measurements have performed and have found the some meaningful result.They are (1)MR ratios are not found very high and the average values are smaller than 0.2%. (2)The thickness of insulating MgO layer makes a little factor of MR ratio and it shows higher for the sample which has thickness of insulating layer is 25, grown on MgO (111). (3) Intensive anisotropic (4) Inverse tunnel magnetoresistance under some direction of magnetic field indicates some important significant in the present experiment. Inverse tunnel magnetoresistance maybe have relation with polarization of Co. Different MR ratio due to changing of direction of magnetic field means that each place of the surface of sample has different density of state. So Fermi sphere is unsymmetrical and shows the different polarization due to applying magnetic field at different angle. The anisotropic has relation with MgO lattice planes and it has 180∘or 90∘symmetry. The experimental values of MR ratio due to circumrotation of magnetic field, match with cos2θperiod, where as the MR ratio fit with cos4θ period for the sample Co(500 )/Fe(50 )/MgO(8)/Fe(500 )/MgO(001) .

碩士
逢甲大學
纖維與複合材料學系
100
Crystalline-crystalline Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(ethylene glycol) block copolymers (PHEGs) were synthesized form PHBV2000 and PEG with different number-average molecular weights. This study focused on the microstructure of the concentric spherulite of double crystalline block copolymers. The crystallization and melting behaviors were studied by a differential scanning calorimeter (DSC). The concentric spherulite morphology was observed with a hot stage polarizing microscope (HSPM). The conformation were investigated by an In-situ Fourier transform infrared spectrometer (In-situ FTIR). The microstructure was probed by small angle x-ray scattering (SAXS). Based on DSC and HSPM studies, two crystallization peaks were observed in the PHEGs during the cooling process, where the high temperature crystallization peak related to the PHBV block and low temperature crystallization peak corresponded to the PEG block, respectively. There was a crystallization exothermic peak in PHEG copolymer under isothermal crystallization conditions. It indicated that PHBV block and PEG block crystallized in the same isothermal crystallization condition. In addition, the concentric spherulite morphology of the PHEG2000, PHEG4000, and PHEG6000 were observed using HSPM. The spherulite growth in the PHEG4000 of PHBV block formed first at 35 ℃, then the PEG block crystallized within confined space between the formerly formed PHBV crystal lamellae. The most stretched PEG chain at the center of the PHBV spherulite may nucleate easily under the enough crystallization time, resulting in the formation of the concentric spherulite. The spherulite growth rate of individual spherulites from the PEG block and PHBV block in PHEGs depends on the crystallization environment. However, the growth rate of the unrestricted PHBV block was faster than that of the confined PHBV block and the growth rate of the confined PEG block was faster than that of the unrestricted PEG block. FTIR and SAXS results showed that the PHBV chains were observed in preferred conformations in the crystalline states during the cooling process at 70 ℃, and then continuously adjusted conformational transition in PEG chain were rearranged to form the crystalline during the isothermal crystallization at 35 ℃. SAXS result, the first growth PHBV spherulite acted as the template for the spherulite growth of the PEG block. In addition, we heated to 70 ℃ for melting the PEG block. The long period (L) and amorphous thickness (la) increased. It was possible that the melting of the PEG block existing in the PHBV crystal lamellae.

In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.

The past few decades have witnessed an almost exponential increase in interest in the field of metal organic frameworks (MOFs), which can be evidenced from the large number of scientific articles being published routinely in this area. The MOFs are crystalline hybrid materials built via the judicial use of inorganic metal ions and organic linkers, thereby bridging the gap between purely inorganic and organic materials. The structural versatility and the potential tunability of the MOFs imparts unique physicochemical and thermomechanical properties, which have rendered them immensely useful in the branches of chemistry, material science, physics, biology, nanotechnology, medicine as well as environmental engineering. The MOFs have been shown to be promising as materials for gas storage and separation, sensors, ferroelectric and non-linear optical materials, magnetism, catalysis, drug delivery etc and researchers have been devising strategies to utilize the MOFs to tackle a number of global challenges of the twenty-first century. A survey of the literature reveals that the linear organic linkers, 1,4- benzenedicarboxylic acid (BDC) and 4,4’-biphenyldicarboxylic acid (BPDC), have been the organic linkers of choice for the construction of stable, porous and multifunctional MOFs. The aim of this thesis has been to monitor the effect that the presence of a functional group in between the benzene rings of the BPDC would have on the overall structures and the properties of the MOFs. Thus, as part of the investigations, the preparation of the MOF compounds using 4,4’-sulfonyldibenzoic acid (SDBA) and 4,4’- azodibenzoic acid (ABA) have been accomplished. Along with the conventional hydrothermal and solvothermal synthetic techniques, the liquid-liquid biphasic reaction method was also utilized for the synthesis of some of the compounds. The structures of the compounds were ascertained from single crystal X-ray diffraction technique. Proton conductivity studies were performed on Mn based porous MOFs using AC impedance spectroscopy. The ferroelectric behavior in a Co based porous MOF was established using dielectric and polarization vs electric field measurements. The labile nature of the lattice solvent molecules was established utilizing single crystal X-ray diffraction studies and water sorption experiments. In addition, the site selective substitution in a homometallic MOF and the subsequent conversion to a mixed-metal spinel oxide upon thermal decomposition, have also been studied. Chapter 1 of the thesis is a brief overview of the metal organic framework compounds and summarizes the various important structures that have been reported in literature and the interesting properties that they exhibit. In chapter 2, the proton conductivity behavior, solvent mediated single crystal to single crystal (SCSC) and related structural transformations in a family of Mn and Co based porous MOFs with SDBA have been presented. Also presented are the results of the site selective substitution of Mn by Co in a homometallic Mn based MOF and it’s subsequent decomposition to CoMn2O4 spinel oxide nanoparticles. In chapter 3, the syntheses, structures and the magnetic properties of the pentanuclear Mn5 based MOF compounds with SDBA have been presented. The role of the time and the temperature in the formation of the compounds has also been presented. In chapter 4, the dehydration/rehydration mediated switchable room temperature ferroelectric behavior, the single crystal to single crystal solvent exchange studies and selective gas sorption behavior in an anionic Co based MOF with SDBA has been discussed. In chapter 5, the use of the liquid-liquid biphasic synthetic route in the formation of Zn and Cd based MOFs with ABA has been discussed. Structural transformations between the one dimensional Zn based compounds and the heterogeneous catalytic studies using the Cd based compounds have also been presented.