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Santos, Flavio Bezerra dos. "Molecular structure and liquid crystallinity." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243176.
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Perry, Christopher Cecil. "Orientation and crystallinity of bifunctional adsorbates." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366426.
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Murphy, Lindsay Adams. "Morphological investigation of AFR-PEPA-N imide oligomers and their cured polyimides and the remodification of AFR-PEPA-N to achieve liquid-crystalline behavior." Texas A&M University, 2003. http://hdl.handle.net/1969.1/1174.
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The morphological investigation of AFR-PEPA-N and the development of a new polyimide have been established herein. AFR-PEPA-N is an imide oligomer that was created out of the need to attain a high temperature polyimide that is also resistant to hygrothermal and thermooxidative degradation. Previously, AFR700B was implemented in aerospace applications, but it was found to be hygrothermally unstable. It experienced a severe drop in its glass transition temperature and composite blistering. AFR700B was improved upon, by altering the chemical structure of the polyimide. The nadic end-cap was removed and replaced by a more hydrolytically stable end-cap. However this phenylethynyl-terminated end-group could possibly create semi-crystallinity or liquid-crystalline characteristics within the polymer.
Previous research suggests further study of the relationships between AFR-PEPA-N's oligomer crystallinity and the properties of phenylethynyl-terminated polyimides. This understanding is valuable in processing AFR-PEPA-N by resin transfer molding (RTM) to obtain its optimum properties. The investigation included the identification of a processing window, temperature overlap between the melting of residual crystals and crosslinking reactions, and liquid crystallinity behavior. These reactions were investigated primarily through birefringence.
The residual crystals were found to be innate in the oligomer powder and not created by preliminary thermal processing. Therefore a reasonable processing window was found based upon the reduction of crystal size by appropriate dissolution techniques. Possible nematic liquid-crystalline characteristics were found to be present at 360oC.
A new imide oligomer, which was based upon AFR-PEPA-N's original structure, was synthesized. The non-linear, flourinated backbone of AFR-PEPA-N was replaced with a co-linear backbone, pyromellitic dianhydride (PMDA). These modifications were made in hopes to improve upon the network structure by it becoming more regular and resistance to nano-sized defects in the final crosslinked structure. The initial characterization found that the new polyimide, AFR-P3, displayed a cure temperature at 350oC. The degree of cure reaches about 80 to 90 percent complete based upon the consumption of the carbon-triple bond. AFR-P3 did not show signs of liquid-crystalline behavior. However, there will be future work in creating a more rigid-rod, self-assembling oligomer that can attain optimum thermal and mechanical properties.
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Lehnert, Ralph Juergen. "Studies on the crystallinity of poly(tetrafluoroethylene)." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241181.
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Breeson, Andrew. "Control of crystallinity in photocatalytic titanium dioxide." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/10037914/.
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Powders and thin films of titanium dioxide (TiO2) were synthesised via wet chemical methods in two ways: a sol-gel synthesis, and a liquid phase deposition. Crystalline mixed phase powders, highly oriented films, and non-crystalline films of titanium dioxide have all been investigated. Specifically this investigation revealed dramatic differences in the XPS valance band spectra of the crystalline polymorphs of anatase and rutile, and subsequently a novel procedure for extracting quantitative phase information from X-ray photoelectron spectroscopy valence band spectra was developed. A linear relationship between the mixed phase TiO2 surface structure determined by this novel technique, and the ensuing photocatalytic activities were discovered. Additionally, highly oriented thin films of TiO2 were synthesised on single crystal substrates. Nitrogen doping of the films was achieved in two ways, and the distribution of the dopant within the films was revealed to be dramatically different for each method. Furthermore, N doping induced a phase transformation from highly aligned rutile to polycrystalline anatase. This result of a rutile to anatase transition at high temperature and not been observed previously. As before, these results were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy valance band analysis. Lastly, non-crystalline, unaligned films of TiO2 on glass substrates were synthesised. The film structure was revealed to be porous, and successively exhibited superhydrophilic abilities without ultraviolet light irradiation. Further investigation via X-ray absorption spectroscopy techniques revealed the films to have anatase-like short range order with a significant tetrahedral titania component. The films were also shown to be highly photocatalytically active. Powders and thin films of titanium dioxide (TiO2) were synthesised via wet chemical methods in two ways: a sol-gel synthesis, and a liquid phase deposition. Crystalline mixed phase powders, highly oriented films, and non-crystalline films of titanium dioxide have all been investigated. Specifically this investigation revealed dramatic differences in the XPS valance band spectra of the crystalline polymorphs of anatase and rutile, and subsequently a novel procedure for extracting quantitative phase information from X-ray photoelectron spectroscopy valence band spectra was developed. A linear relationship between the mixed phase TiO2 surface structure determined by this novel technique, and the ensuing photocatalytic activities were discovered. Additionally, highly oriented thin films of TiO2 were synthesised on single crystal substrates. Nitrogen doping of the films was achieved in two ways, and the distribution of the dopant within the films was revealed to be dramatically different for each method. Furthermore, N doping induced a phase transformation from highly aligned rutile to polycrystalline anatase. This result of a rutile to anatase transition at high temperature and not been observed previously. As before, these results were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy valance band analysis. Lastly, non-crystalline, unaligned films of TiO2 on glass substrates were synthesised. The film structure was revealed to be porous, and successively exhibited superhydrophilic abilities without ultraviolet light irradiation. Further investigation via X-ray absorption spectroscopy techniques revealed the films to have anatase-like short range order with a significant tetrahedral titania component. The films were also shown to be highly photocatalytically active.
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Fletcher, Ian David. "Liquid crystallinity and the role of molecular flexibility." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239472.
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Ismail, Yob Saed Bin. "Structure/property relationships associated with woven glass fibres reinforced polypropylene composites." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/11902.
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The objective of this work was to examine the effect of thermal history during cooling from the melt on the degree of crystallinity, morphology and as well as the relationship between morphology/thermal history and mechanical properties of a 60:40 weight % mixture of woven glass fibres/PP composites. Mechanical properties studied include low velocity falling weight impact strength, flexural properties (modulus and strength) and interlaminar shear strength (ILSS). However the main focus was low velocity impact strength. The composite laminates were manufactured within a flat mould using a compression moulding press. Three thermal treatments were employed: isothermal crystallization from the melt in the range 106 to 156°C for 10, 30, 60 and 240 minutes in an oven; non-isothermal crystallization from the melt at rates varying from 0.67°C/Min. to 62.4°C/Min; and quenching from 190°C to rzooc and then annealing at 155, 160 and 165°C for one hour. The degree of crystallinity developed in the matrix polymer was determine using differential scanning calorimetry (DSC) and the matrix morphology was examined by reflected light microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). TEM was used for quenched and annealed specimens.
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Zakrevskyy, Yuriy. "Liquid crystallinity and alignment of ionic self-assembly complexes." Phd thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982215908.
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Suryanarayanan, Rajagopalan. "Studies on the crystallinity and phase transitions of calcium gluceptate." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25978.
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Calcium gluceptate (calcium ɑ-glucoheptonate, CaC₁₄,H₂₆O₁₆) occurs as a crystalline hydrate (I) containing 3 1/2 molecules of water of crystallization per atom of calcium or as an amorphous anhydrate(III). Calcium gluceptate was synthesised commercially as III until 1980 but since then only I has been commercially available. The maximum aqueous solubility of III at room temperature was found to be > 2 molal while the equilibrium solubility of I at 25.5°C was 0.06 molal (≃3.3% w/v). A crystalline anhydrate (II) wtiich had an apparent water solubility of 1.3 molal was prepared from I by dehydration. The United States Pharmacopeia (USP) injection is an aqueous solution containing 20.8 to 23.3% w/v CaC₁₄H₂₆O₁₆ which is greater than the equilibrium solubility. Solutions prepared using II or III were supersaturated with respect to I and crystallized on storage. Pharmaceutically stable solutions could be prepared from II by autoclaving the solutions at 121°C for 20 minutes immediately after preparation which presumably destroyed seed crystals of I. When stored at relative humidities (RH) greater than 66% at 25°C, II was converted into I and the reverse process occurred at 0% RH. Above 0% and below 66% RH neither I nor II underwent a phase transition during one year of storage. The co-existence of I and II over a range of RH would be contrary to the phase rule. It is suggested that at RH less than 66%, the adsorption of a small amount of. atmospheric water vapor inhibits the II to I transition probably due to the formation of a surface layer of I which limits further diffusion of water. In addition to the phase transformations in aqueous solution and the dehydration and rehydration reactions, the effects of freeze drying and grinding on the interconvertibility of I, II and III were studied. On grinding II for increasing times, there were marked increases in apparent water solubility, decreases in the intensity of x-ray diffraction peaks, and heats of solution changed from endothermic to exothermic. The results were attributed to decreases in crystallinity, since surface area measurements showed that they could not be due to particle size reduction. Density is independent of particle size, and values obtained for II using a liquid suspension method changed progressively with grinding. The x-ray diffraction, calorimetric and density measurements were used both to quantify the degree of crystallinity of II and to test various models of crystallinity. According to the USP, solids are crystalline, non-crystalline (amorphous) or a mixture of the two. The degree of crystallinity depends on the fraction of crystalline material in the mixture (two-state model). An alternative concept is that the degree of crystallinity has a value between 100% (perfect crystal) and 0% (amorphous) depending on the state of order/disorder in the lattice (one-state model). It was concluded that grinding decreases the crystallinity of II by increasing lattice disorder according to the one-state model.Pharmaceutical Sciences, Faculty of
Graduate
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Kang, Chin-Shuo. "CONTROL OF TITANIUM DIOXIDE NANOFIBER CRYSTALLINITY, PARTICLE SIZE AND MORPHOLOGY." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron161960479044817.
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Crawford, Evan Cameron. "Klondike placer gold : new tools for examining morphology, composition and crystallinity." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31649.
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This work focuses on developing and expanding the utility of several new and previously used methods for examining the morphology, composition and crystallinity of placer gold. Several studies using samples from the Klondike District and surrounding areas in west-central Yukon investigating each of these properties are presented, along with potential future applications for the methods, and implications of the results already obtained. The new method for examination of the morphology of placer gold is centered around semi-automated digital image analysis. Automating morphological analysis allows more accurate and reproducible measurement of much larger number of grains as compared to manual methods, allowing for improved statistical analyses of placer gold morphology. Combining results from these new methods of morphological analysis with conventional electron microprobe analysis of composition has produced a detailed model relating placer gold grain morphology to the distance it has been alluvially transported. This model was developed with regard to geology and gold composition and is significantly superior to previous models. A new method using laser ablation - inductively coupled plasma - mass spectroscopy (LA-ICP-MS) has been developed to examine minor and trace element composition of placer gold. This new method allows for compositional fingerprints to be defined, and spatial variations in trace and minor elements to be measured within individual grains. Placer gold crystallinity has been observed, however remains poorly examined. We have utilized X-ray diffraction to study the internal crystallographic texture of placer gold, and confirm that several other methods previously used for this purpose do probe internal crystallinity. These new methods have significantly broadened the range of techniques available to investigate placer gold. Examination of the results from these methods has yielded new insights into the potential genesis of gold deposits in the Klondike, the nature of gold crystallinity, and the changes in morphology that occur during alluvial transport. These early studies also indicate that there is still significant work to be done, and that these new methods have significant potential in the study of placer gold.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Strachan, Clare, and n/a. "Spectroscopic investigation and quantitation of polymorphism and crystallinity of pharmaceutical compounds." University of Otago. School of Pharmacy, 2005. http://adt.otago.ac.nz./public/adt-NZDU20070427.141108.
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Spectroscopy is increasingly used to investigate and monitor the solid state forms of pharmaceutical materials and products. Spectroscopy�s speed, nondestructive sampling, compatibility with fibre optics and safety also make it attractive for in-line monitoring.
In this thesis, the spectroscopic techniques Fourier transform Raman spectroscopy, terahertz pulsed spectroscopy and second harmonic generation were used to characterise and quantify polymorphism and crystallinity of pharmaceutical compounds. Where possible, the multivariate analysis technique partial least squares was used for quantitative analysis. Fourier transform Raman spectroscopy detects polarisability changes mainly associated with molecular vibrations. Terahertz pulsed spectroscopy is a new spectroscopic technique that operates between the infrared and microwave regions of the electromagnetic spectrum and detects dipole moment changes mainly associated with crystalline phonon vibrations in the solid state. Second harmonic generation is a nonlinear optical phenomenon that depends on the dipole moment in crystals and crystal symmetry.
Several materials capable of existing in different solid state forms were used. FT-Raman spectroscopy was able to differentiate carbamazepine forms I and III, enalapril maleate forms I and II and γ-crystalline and amorphous indomethacin. Combined with partial least squares the technique could quantify binary mixtures of CBZ forms I and III with a limit of detection as low as 1%, and mixtures of enalapril maleate with a limit of detection of as low as 2%.
Terahertz pulsed spectroscopy obtained very different spectra for carbamazepine forms I and III, enalapril maleate forms I and II, γ-crystalline and amorphous indomethacin, crystalline and supercooled thermotropic liquid crystalline fenoprofen calcium, three forms of lactose, and five forms of sulphathiazole. At present the modes in the spectra cannot be attributed to specific phonon modes. Quantitation of binary mixtures of different forms of a compound using partial least squares analysis usually resulted in a limit of detection of about 1%.
Second harmonic generation was used to quantify binary mixtures of different forms of enalapril maleate and lactose, as well as binary mixtures of enalapril maleate form II and polyvinylpyrrolidone. A quantitative relationship was present for each of the mixtures, however the limits of detection were usually above 10%. The high value is probably due to the machine being a prototype and univariate analysis associated with a single output variable. Future improvements to the apparatus and measurement parameters are likely to reduce the limits of detection. Ranitidine hydrochloride polymorphs could also be differentiated using second harmonic generation, however γ-crystalline and amorphous indomethacin and forms I and III of carbamazepine could not.
The methods used in this thesis were successfully used for qualitative and quantitative analysis of polymorphism and crystallinity of pharmaceutical compounds. TPS and SHG are useful additions to the range of experimental techniques that can be used to investigate and monitor properties of pharmaceutical solids.
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Royaud, Isabelle Anne-Marie. "Conformation and crystallinity in polymers - a study using novel Raman techniques." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236347.
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Greyling, Corinne Jean. "Electrospinning of polyacrylonitrile nanofibres with additives : study of orientation and crystallinity." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/3996.
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Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Polyacrylonitrile, (PAN), polymers are of interest due to their many unique characteristics in comparison to most other fibre forming polymers. The focus of this study was the effect of electrospinning variables and additives on their unusual thermal properties and internal molecular morphology with the objective of improving the performance of this fibre in industrial application, or at least contributing to the understanding of how the fibre processing variables affect the thermal performance. The process of electrospinning was used to process samples of PAN fibres with additives in order to determine their effect on the molecular orientation and crystallinity of the resultant nano- and micronsized fibres. The effect of additives in the forms of low molecular weight oligomers, blends of conductive polymers and nanoparticles and conductive salts (mainly copper and lithium based) on the molecular structure and thermal properties is reported. In addition the effect of certain electrospinning processing variables such as the PAN polymer grade, the type of solvent, the temperature, the spinning voltage and the spinning distance were evaluated in terms of their effect on the resultant fibre molecular structure. The crystallinity and molecular orientation are quantified using various analytical techniques including: Fourier-Transform Infra-Red Spectroscopy (FTIR); Differential Scanning Colorimetry; (DSC) Thermal Gravimetric Analysis, TGA, Scanning and Transmission Electron Microscopy; Wide-Angle X-ray Diffractometry, XRD, Small-angle Neutron Scattering; SANS, Solid-state 13C Nuclear Magnetic Resonance Spectroscopy; NMR, and Electron-spin Resonance Spectroscopy, ESR. The researcher has ascertained in this study that the orientation of electrospun PAN is comparable to that in commercial wet-spun fibres when the electrospinning field strength is greater than 0,75 kV per cm. The process of electrospinning leads to chemical degradation of the PAN polymer only previously noted by other fibre scientists after heating PAN fibres to more than 280 C. This is due to the high mechanical stress on the high surface area electospun fibres spun into an oxygen rich air atmosphere. The addition of certain salts, particularly lithium chloride and copper nitrate, to the PAN electrospinning dope by the researchers produced fibres with improved thermal stability in comparison to the control PAN samples with no additives. In addition these salts lower the endotherm for the production of carbonized fibres from PAN fibres and will therefore make more structured, stronger, high tenacity carbon fibres. The XRD revealed that through the addition of certain salts to disrupt the dipole interations in PAN, that fibres with a 2D hexagonal crystal structure can be electrospun and have a structure similar to wet spun PAN. It is shown that fibres in a non-aligned electrospun mat have a 3D crystal structure and lower molecular orientation that wet spun fibres. Some industrial applications of electrospinning using PAN fibres are developed and reported.
AFRIKAANSE OPSOMMING: Polyakrilonitrielpolimere (PAN) is van belang weens die baie unieke eienskappe wat hulle het in vergelyking met die meeste ander vesel-vormende polimere. Die fokus van hierdie studie op die effek van verskeie veranderlikes en byvoegmiddels op hul buitengewone termiese eienskappe en interne molekulêre morfologie, met die doel om die werksverrigting van hierdie vesel in industriële toepassings te verbeter, of ten minste by te dra tot die begrip van hoe die vesel-prosesveranderlikes die termiese werksverrigting beïnvloed. Die elektrospinproses is gebruik om monsters van PAN met bymiddels te prosesseer om vas te stel wat die effek sou wees op die molekulêre oriëntering en kristalliniteit van die gelewerde nano- en mikrongrootte vesels. Verslag word gelewer oor die effek van bymiddels in die vorm van oligomere met „n lae molekulêre gewig, mengsels van geleidende polimere en verskillende nano-partikels en geleidende soute (meestal koper- en litium-gebaseerd). Die effek van sekere veranderlikes in die elektrospinproses, soos die PAN polimeer-graad, die temperatuur, die tipe oplosmiddel, die spin-spanning en spin-afstand, is geëvalueer in terme van hulle effek op die vesels wat gelewer word. Die kristalliniteit en molekulêre oriëntering word gekwantifiseer deur verskeie analitiese tegnieke te gebruik, onder meer: Fourier-Transform Infrarooispektroskopie; Differensiële Skandeerkolorimetrie; Termiese Gravimetriese Ontleding; Skandeeringelektronmikroskopie; Transmissie Elektron Mikroskopie; Wye-hoek X-straal Diffraktometrie; Klein-hoek Neutronstrooiing; Vaste-toestand 13C Kern Magnetiese Resonansiespektroskopie; en Elektronspin Resonansiespektroskopie. Dit is in hierdie studie vasgestel dat die oriëntering van elektro-gespinde PAN vergelykbaar is met kommersiële nat-gespinde vesels as die elektro-spin veldsterkte groter is as 0,75 kV per cm. Die elektro-spin proses lei tot chemiese degradasie van die PAN polimeer, wat voorheen slegs deur ander vesel-wetenskaplikes waargeneem is nadat PAN tot meer as 280 C verhit is. Dit word veroorsaak deur die hoë meganiese spanning op die hoë-oppervlakarea vesels wat in „n suurstofryke lug-atmosfeer gespin word. Die byvoeging van sekere soute, veral litiumchloried en kopernitraat, by die PAN elektro-spin spinlak (dope) deur die navorser het vesels gelewer met verbeterde termiese stabiliteit in vergelyking met die kontrole PAN-monsters sonder bymiddels. Verder verlaag hierdie soute die endoterm vir die produksie van gekarboniseerde vesels uit PAN-vesels, en dit sal daarom meer gestruktureerde, sterker koolstofvesels met hoë taaiheid lewer. X-straaldiffraksieanalise het gewys dat gewone elekrospin vesels ‟n driedimensionele struktuur het maar as gevolg van die byvoeging van sekere soute, wat die dipoolinteraksies in PAN opbreek, dat vesels wat 'n soortgelyke tweedimensionele struktuur het as dié van groot skaalse kommersiële nat-spin vesels, maklik d.m.v. die elektrospinproses berei kan word. Enkele nywerheidstoepassings van elektrospin is ontwikkel, en beskryf.
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Czerewko, Mourice Andrew. "Diagenesis of mudrocks, illite 'crystallinity' and the effects on engineering properties." Thesis, University of Sheffield, 1997. http://etheses.whiterose.ac.uk/14669/.
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This study deals with the changes in mineralogy and fabric of a suite of mudrocks due to increased induration caused by diagenetic history, and the subsequent controls on geotechnical properties. Burial diagenesis of mudrocks has important implications on their engineering behaviour, in particular the liberation of Si and Ca during illitisation of smectite and mixed layer clay minerals leading to cementation. The objective of the research has been to provide a means of predicting engineering performance of mudrocks from mineralogical composition. A suite of 41 mudrock samples ranging from Cambrian slates to Carboniferous Coal Measures in age and variable diagenetic rank has been sampled and tested. A detailed mineralogical evaluation of the samples was conducted and it was found that the proportion of mixed layer clays and kaolinite decreased with an increase in diagenetic rank of the material, but not necessarily with increasing ages of the samples. The diagenetic histories of the samples was assessed using illite 'crystalinity' and vitrinite reflectance measurement, which indicated that the samples ranged low diagenetic to epizonal in rank. The textures of the samples was studied using back-scattered scanning electron microscope imagery. The novel application of this technique to textural analysis in the field of engineering geology resulted in the diagenetic rank parameter classification scheme being devised. The classification parameter consists of a systematic approach to the evaluation of pore and microfracture distribution, clay mineral orientation and degree of recrystallization, degree of contact of clastic mineral constituent and the degree of cementation. The physical properties of the mudrocks were assessed in terms of bulk index properties, swelling, slaking and strength. In evaluating the test data, it was found that that the principal controls on the durability of indurated mudrocks was the distribution of micro fractures and the mixed layer clay content. With increasing diagenetic rank measured by illite 'crystallinity' determination, the durability of the samples increased due to the development of a more mature rock fabric as seen by the use of back-scatter scanning electron microscope imagery. With increasing diagenetic rank there is a decrease in microfracture distribution due to recrystallization of clay mineral species and subsequent recementation of the sample also due to release of Ca and Si from the conversion of clay mineral species. This process reduces void space, eliminates micro fractures and creates a non expansive clay mineral suite resulting in a durable mudrock less susceptable to swelling and slaking effects. An additional controlling factor on mudrock durability was found to be the presence of calcareous and organic carbon cements. These controls were found to be short term, as seen in natural weathering experiments, where samples of high calcareous and carbonate contents were found to start slaking after a period of 6 to 8 months of exposure, and samples of low carbonate and calcareous content began to degenerate almost instantaneously. The controls of cementation on the durability of mudrocks are eventually broken down due to the effects of air breakage in voids and swelling stress resulting from the expansive clay mineral species present. A range of simple index tests were used to physically characterise the mudrock samples and their potential in determining mudrock durability was evaluated. A mudrock rank durability classification approach is presented which is based on the modified jar slake test, methylene blue adsorption and moisture absorption determination. These index tests were found to correlate strongly with void and microfracture distributions and proportions of mixed layer clays within the samples. This classification approach was tested on the samples in the study and found to be effective in distinguishing between non-durable, moderately durable, and durable mud rocks.
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Wen, Ming. "The effect of carbon black crystallinity on dispersion in SBR matrix." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1619022632906256.
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Polam, Anudeep. "Thermal and Draw Induced Crystallinity in Poly-L-Lactic Acid Fibers." Cleveland State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1439843418.
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Zarringhalam, Hadi. "Investigation into crystallinity and degree of particle melt in selective laser sintering." Thesis, Loughborough University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479221.
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Heifferon, Katherine Valentine. "Designing Functionality into Step-Growth Polymers from Liquid Crystallinity to Additive Manufacturing." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/99829.
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Step-growth polymerization facilitates the synthesis of a wide range of industrially applicable polymers, such as polyesters and polysulfones. The choice of backbone and end group structure within these polymers drastically impacts the final material properties and processability emphasizing the necessity for thorough understanding of structure-property relationships. Seemingly simple changes, such as exchanging a monomer for its regioisomer, affects the polymers fundamental packing structure triggering a domino effect ultimately influencing the morphological, thermal, mechanical and barrier properties. In conjunction, end groups provide a means by which tunable mechanical properties and application into unique processing methods can be achieved.
Synthesizing polyesters with bibenzoate based monomers generates a large range of morphologies. Linear, 4,4' bibenzoate (4,4'BB), is widely considered a mesogenic monomer due to its ability to impart a liquid crystalline (LC) morphology on semi-aromatic polyesters with linear aliphatic spacers. In this body of work, semi-aromatic polyesters using one of 4,4'BB's regioisomers, either 3,4'BB or 3,3'BB, largely resulted in amorphous or semi-crystalline polymers depending on the selection of aliphatic diol. Incorporation of the meta isomer (3,4'BB) into traditionally LC polymers, such as poly(diethylene glycol 4,4'-bibenzoate) and poly(butylene 4,4'-bibenzoate), through copolymerization afforded two polymer series with tunable LC properties. The 3,4'BB exhibited selective disruption of crystalline domains over the LC phase generating a number of polymers with LC glass morphologies.
The application of 3,4'BB to a fully-aromatic polyester enabled the synthesis of a novel melt-processable homopolyester with high thermal stability, poly(p-phenylene 3,4' bibenzoate). This structure afforded a nematic LC morphology which revealed beneficial shear-thinning properties similar to industrial standards. The unique LC morphology of this homopolyester inspired further characterization of the range of achievable properties using the basic structure, poly(phenylene bibenzoate), with all the possible regioisomers. This study afforded six polymers systematically varied in chain linearity from a completely meta to a completely para backbone configuration. A range of morphologies were achieved from high Tg amorphous polymers for the meta configurations to semi-crystalline or LC in the polymers with greater linearity.
End group functionalization generates influence on polymer properties while limiting the impact on beneficial properties achieved through the backbone structure and packing. Post-polymerization reactions or the addition of a monofunctional endcapper to the polymerization both achieve end group control. In this dissertation, the addition of a monofunctional diester with a sulfonate moiety to a semi-aromatic LC polyester synthesis resulted in a telechelic ionomer. The non-covalent interaction of the ionic groups will hopefully improve the compression and transverse mechanical properties of the LCP. In contrast, post-polymerization functionalization incorporated acrylate groups onto the ends of a basic polysulfones. These reactive groups provided a handle for photo-curing which enabled the 3D printing of the polysulfones using vat photopolymerization.Doctor of Philosophy
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Modutwane, Angel Tumelo. "The optimization of the ZSM-5 catalyst activity with respect to crystallinity." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/6697.
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In the synthesis of zeolites optimization of factors such as crystallinity, which encapsulates morphology, and acidity can result in optimal activity. Optimal activity is vital in chemical industries due to the fact that it results in higher yields, better selectivities and lower operational costs. In this project the effect of crystallinity on activity is investigated to get a better understanding of performance in terms of activity of amorphous, partially crystalline and highly crystalline materials using isomerisation of para-xylene as the probe reaction.
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Jeong, Yong Soo. "Poly(ethylenedioxythiophene) Derivatives Embodying Chirality and Liquid Crystallinity-Synthesis and Electrochemical Properties." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/131886.
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Bentley, Phillip Arthur. "The application of vibrational spectroscopy to topical problems in qualitative and morphological analysis." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307284.
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Han, Peilin. "New Advances to Control Morphology and Crystallinity in Solution Processed Polymer Solar Cells." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/349209.
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En aquest treball es demostren nous mètodes prometedors en la fabricació de cèlules solars orgàniques obtingudes per processos en dissolució. Més concretament, s'ha demostrat que l'envelliment de la sol·lució i la utilització de solvents ternaris són utls per a la modificació de la nanomorfologia i la fase cristalina de la capa activa en cel·les basades en PTBx:PCBM. L'estudi es centre en comprendre com l'envelliment de la sol·lució i la barreja de solvents influencien les morfologies de la barreja de polímers a la cel·la, la seva cristalinitat i la eficiència del dispositiu. En base a mesures de AFM i GIXS es demostra que l’envelliment de la solució millora significativament la separació de microfases, la morfologia i la interpenetració bi-continua de la barreja PTB1:PCBM. S’ha demostrat un millora significativa del 19% en eficiència de cel·les obtingudes per envelliment de solució enfront de cel·les sense aquest procés. A més, s’han fabricat estructures c-PSC i i-PSC basades en PTB7:PCBM utilitzant una barreja de solvents ternària de CB/CHN/DIO. S’ha trobat que l’addició de CHN a la solució de CB/DIO permet controlar no només la cristalinitat dels polímers a la capa activa sinó també la seva composició superficial. Després d’utilitzar CB/CHN/DIO, les mesures de GIXS revelen la formació de dominis estructurals i una millora de la distància entre cadenes del polímer PTB7. Això te per conseqüència un augment del corrent foto-generat i de l’eficiència. Mesures d’angle de contacte demostren la presència de PTB7 enriquit a la superfície superior de la capa activa. Això indueix una major selectivitat a l’ànode, en particular per estructures i-PSC en comparació amb dispositius c-PSC. D’aquesta manera, s’aconsegueix una eficiència del 8.05 % per a dispositius i-PSC obtinguts amb solució de CB. Aquesta és significativament més gran que la dels dispositius c-PSC (6.86%).En este trabajo se demuestran nuevos métodos prometedores en la fabricación de células solares orgánicas obtenidas mediante procesos en disolución. Más concretamente, se ha demostrado que el envejecimiento de la solución y el uso de solventes ternarios son útiles para la modificación de la nanomorfología y la fase cristalina de la capa activa en células basadas en PTBx:PCBM. El estudio se centra en comprender como el envejecimiento de la solución y la mezcla de solventes influencian las morfologías de la mezcla de polímeros en la celda, su cristalinidad y la eficiencia del dispositivo. En base a medidas de AFM y GIXS se demuestra que el envejecimiento de la solución mejora significativamente con la separación de microfases, la morfología y la interpenetración bi-contínua de la mezcla PTB1:PCBM. Se ha demostrado una mejora significativa del 19% en la eficiéncia de células obtenidas mediante envejecimiento de la solución, frente a células sin este proceso. Además se han fabricado estructuras c-PSC y i-PSC basadas en PTB7:PCBM usando una mezcla de solventes ternaria CB/CHN/DIO. Se ha encontrado que la adición de CHN a la solución de CB/DIO permite controlar no solamente la cristalinidad de los polímeros en la capa activa, sino también en su composición superficial. Después de usar CB/CHN/DIO, las medidas de GIXS revelan la formación de dominios estructurales y una mejora de la distancia entre cadenas del poímero PTB7. Esto, por consecuencia lleva a un aumento de la corriente foto-generada y de la eficiencia. Medidas de ángulo de contacto demuestran la presencia de PTB7 enriquecido en la superficie superior de la capa activa. Esto induce una mayor selectivitat en el ánodo, en particular para estructuras i-PSC en comparaci´n con dispositivos c-PSC. De esta manera, se consigue una eficiencia del 8.05% para dispositivos i-PSC obtenidos con una solución de CB. Esta es significativamente mayor que la de los dispositivos c-PSC (6.86%).
In the work, we have demonstrated that solution aging and ternary solvent mixture were promising methods to modify nanomorphology and crystal phase of the active layer in PTBx:PCBM polymer solar cells. We focus on understanding how the solution aging and solvent mixture influence the blend morphologies and crystallinity of polymers, further affecting the device performance. Supported by AFM and GIXS measurements, the results showed solution aging significantly improves microphase separation morphology and bi-continuous interpenetrating network of the PTB1:PCBM blend. A significant improvement exceeding 19% in PCE in device with solution aging processed are found compared to without solution aging. In addition, we fabricated the c-PSC and i-PSC structures based on PTB7:PCBM with a CB/CHN/DIO ternary solvent mixture treatment. We found that addition of CHN into CB/DIO solution can control not only crystallinity of polymers the of the active layer but also surface compositions . After using CB/CHN/DIO, GIXS measurements reveal the formation of oriented crystalline structure domains and improvement increase of interchain stacking distance between PTB7 polymer, which consequently leads to a more efficient increase in photo-generated current. Enriched PTB7 on the top surface of active layer, detected via contact angle measurements, induces higher hole selectivity at the anode contact and is favorable to i-PSC compared with c-PSC device. Thus, PCE of 8.05% for i-PSC device from CB solution is obtained, which is significantly higher than the one obtained from c-PSC device (6.86%).
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Lai, Lo Ming. "Synthesis, optical activity, and liquid crystallinity of polyacetylenes containing naturally occurring building blocks /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202006%20LAI.
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Farrand, Fiona Jane. "The influence of the linking group on the liquid crystallinity of dimeric molecules." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285627.
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Fernandez, Lorences Jose O. "Crystallinity changes in PET and Nylon 11 with strain, strain rate and temperature." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/32894.
Full textAbstract:
The mechanical properties of PET (widely used in bottles and synthetic fibres) and Nylon 11 (also used in the fabrication of synthetic fibres) were studied over several decades of strain rate at different temperatures in an effort to provide a more complete description of these materials behaviour. Processing techniques can be improved if such information is available. Tests were carried out using a conventional Hounsfield machine and two in-house-developed dropweight and a cross bow systems from 10°C to 200°C. The three systems enable true stress vs. true strain curves to be calculated.
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Keridou, Ina. "Study on crystallinity, properties and degradability of poly-4-hidroxybutyrate and related polyesters." Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/672122.
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In the last decades, polymeric biomaterials, due to their advanced physical and mechanical properties, have been used in a vast variety of surgical and
pharmaceutical applications. In this thesis, a study on crystallinity, properties, and degradability of poly-4-hydroxybutyrate (P4HB), commercially marketed as MonoMax® by B. Braun Surgical S.A.U. as an absorbable monofilament suture, and related polyesters is presented.
Part of this work has been executed under the collaborative research project established between PSEP (Polímeros Sintéticos. Estructura y Propiedades) research group of Universitat Politècnica de Catalunya and B.Braun Surgical S.A.U. (Center of Excellence for Closure Technologies) with the principal purpose of evolving and investigating polymeric systems with specific biomedical applications.
This study covers different topics related to P4HB such as (a) the physical, chemical, thermal and mechanical characterization; (b) the study of the crystallization kinetics; (c) the study of the degradation behavior of P4HB; and
(d) the production of nanofibers by the electrospinning technique. Moreover,
the work includes a study on blends of two different polyesters: PGA/PCL
blends also produced employing the electrospinning technique and biphasic
PLA/PA blends.
Crystallization was studied under both isothermal and non-isothermal
conditions using optical microscopy and differential scanning calorimetry.
Furthermore, supplementary experiments performed in a synchrotron radiation facility provided us with further information about the lamellae morphology, crystal structure, and molecular orientation.
Hydrolytic and enzymatic degradation of different matrices of P4HB was
carried out in different buffered media. The hydrolytic degradation has been
studied considering media of different pH values and temperatures. Enzymatic degradation has also been evaluated at physiological conditions using two different lipases. The hydrolytic degradation mechanism differs from the enzymatic, where bulk degradation and a random chain scission are
characteristic of samples exposed to hydrolytic media, whereas surface erosion
and successive removal of monomer units are characteristic of samples exposed to enzymatic media. For annealed fibers, small-angle X-ray diffraction studies revealed a supramolecular structure with two different types of lamellar stacks.
The spherulitic morphology of the enzymatically degraded films was highlighted by the elimination of the amorphous regions.
Nanofibers of PGA/PCL and P4HB were prepared using the electrospinning technique. The PGA/PCL nanofibers were also loaded with pharmacological drugs and used as a reinforcing agent of biodegradable polymer matrices. On the other hand, the biological performance of P4HB nanofibers was achieved with the incorporation of fibroblast growth factors.
For this purpose, wound healing assay for two different cell lines (e.g., epithelial and fibroblast) were studied.
Finally, a study on the blends of PLA and Polyamide 6,10 was carried out to investigate the confinement effect of neighboring polymer domains on the phase separation and the structure and the influence of the disperse phase of polyamide in promoting PLA crystallization.En los últimos años se ha extendido el uso de los biomateriales poliméricos en una amplia variedad de aplicaciones quirúrgicas y farmacéuticas debido a sus óptimas propiedades físicas y mecánicas. En esta tesis doctoral se presenta un estudio sobre la cristalinidad, propiedades y degradabilidad del poli-4-hidroxibutirato (P4HB) y poliésteres relacionados. El P4HB se comercializa por la empresa B. Braun Surgical S.A.U. bajo la marca comercial MonoMax® como sutura monofilamento absorbible. Parte de este trabajo se ha realizado bajo un convenio de colaboración entre la Universidad Politécnica de Cataluña, concretamente entre el grupo de investigación PSEP (Polímeros Sintéticos. Estructura y Propiedades) y la empresa B. Braun Surgical S.A.U. (Centro de Excelencia para Cierre de Heridas) con el principal objetivo de investigar acerca de sistemas poliméricos con determinadas aplicaciones biomédicas. El estudio abarca diferentes temas relacionados con el P4HB como son: (a) la caracterización física, química, térmica y mecánica, (b} el estudio de la cinética de cristalización, (c) el estudio del comportamiento de degradación y d) la producción de nanofibras mediante la técnica de electrohilado. Además, el trabajo incluye un estudio de mezclas de dos sistemas poliméricos diferentes, por una parte, mezclas de dos poliésteres: poliglicolato (PGA) y poliéaprolactona (PCL) y por otra mezcla de ácido pollláctico (PLA) y poliamida. Los procesos de cristalización se estudiaron en condiciones isotérmicas y no-isotérmicas utilizando microscopía óptica y calorimetría diferencial de barrido. También, se llevaron a cabo experimentos con fuentes de luz sincrotrón que proporcionaron información adicional sobre las morfologías de las lamelas, la estructura cristalina y la orientación molecular. La degradación hidrolítica y enzimática de las diferentes matrices de P4HB se realizó en medios tamponados. La degradación hidrolítica se estudió en medios con diferente pH y temperatura y la degradación enzimática en condiciones fisiológicas con dos lipasas diferentes. El mecanismo de degradación hidrolítica resultó ser diferente al de degradación enzimática, caracterizándose el primero por una degradación en masa con rotura de cadenas al azar y el segundo por una erosión de la superficie y posterior eliminación de unidades de monómero. Los estudios de difracción de rayos X a bajo ángulo de fibras templadas revelaron una estructura supramolecular con dos diferentes tipos de apilamiento de lamelas. La morfología de las esferulitas se puedo observar en películas de material degradado enzimáticamente al eliminar la parte amorfa. · Mediante electrohilado se prepararon nanofibras de PGA/PC.L y P4HB. Las primeras se cargaron con agentes farmacológicos para su uso como reforzantes de matrices poliméricas biodegradables. Por otra parte, la funcionalidad biológica de las na11ofibras de P4HB se logró con la incorporación de factores de crecimiento y se estudió la cicatrización de heridas con dos líneas celulares diferentes, epiteliales y fibroblastos. Por último, se ha estudiado la mezcla inmiscible formada por poliamida 6,1O y PLA para investigar sobre el efecto del confinamiento de pequeños dominios de polímero en la separación de fases y sobre la influencia de la fase dispersa de poliamida en la cristalización de PLA.
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Macià, Escatllar Antoni. "Computational Modelling of TiO2 and Mg-silicate nanoclusters and nanoparticles - Crystallinity and Astrophysical Implications." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/669508.
Full textAbstract:
The research presented in this thesis contributes to the understanding of both titania and silicate nanosystems by providing new information on energetic stability and properties of nanometer sized particles using computational modelling. Particular emphasis is placed on the importance of two nanosized regimes: i) tens of atoms, and ii) several hundred up to thousands of atoms. We differentiate these two size regimes by naming nanoclusters the structures containing between tens up to a hundred of atoms, and using the term nanoparticles (NPs) for the structures containing hundreds to thousands of atoms.
Titania (TiO2) is the most studied photocatalyst, and thus research is mostly focused on understanding the electronic properties of different morphologies of TiO2 NPs. In detail, for TiO2 the present thesis benchmarks the ability of several interatomic potentials (IPs) to reduce the computational cost of Density Functional Theory (DFT) calculations, as well as a detailed analysis of the energetic stability of three different morphologies of NPs together with an analysis of their band-gap. We show that the Anatase crystal structure becomes the most stable for particle sizes of ~2-3 nm in diameter, while for smaller sizes amorphous particles are the most stable. Within the Anatase structure, we see that Wulff construction is the most stable for large sizes (above 2 nm), but amorphous shell-crystalline core nanoparticles are within the same energy range below a radius of 2 nm. We also find that spherical particles have a band-gap consistent with the so-called black TiO2.
On the other hand, research on silicates is mainly focused on calculating the properties of nanoclusters and NPs, with the objective of obtaining a better understanding of the relevance of such species in interstellar space. In detail, we propose global minima (GM) candidates for numerous nanoclusters based on extensive global optimization (GO) searches and compare their spectroscopic and chemical properties with literature values, where the later values are mostly derived from extrapolation using macroscale laboratory samples. The GO searches were done with a reparameterization of the FFSiOH where we included the Mg element. We also evaluate whether silicate nanoclusters can be the origin of the anomalous microwave emission (AME), a foreground emission in the microwave (MW) region of the spectra from an unknown source and find that indeed nano silicates have the appropriate dipole moments in order to be a strong source of the AME. We indicate that the amount of nano silicates in the interstellar medium is constrained by the AME emission. Finally, the IR spectra of large NPs of around 4 nm in diameter is compared on the basis of their crystallinity. We find that for such sizes, the IR spectra of the crystalline particle corresponds to a broad band similar to the amorphous material, which we ascribe to the large fraction of surface atoms. We conclude that the IR spectra is not sufficient to characterize the crystallinity of astronomical silicates with sizes of several nanometers in diameter. We also show that amorphous silicate nano particles with sizes of ~1 nm in diameter are more stable than their crystalline counterparts. We extrapolate the tendency and propose that the crystalline nanoparticles become more stable than amorphous particles at particle sizes of ~12 nm in diameter.En la presente tesis se estudian la estructura y propiedades de nano partículas de TiO2 y de silicatos de magnesio. Mediante cálculos de teoría del funcional de la densidad y cálculos de potenciales interatómicos se muestra, para TiO2, cómo la estructura de la nano partícula tiene un factor clave para entender la diferencia de energía entre la banda de conducción y la banda de valencia. Además, Comparamos la estabilidad energética de nano partículas de Anatasa con diferente geometría respecto a nano partículas y nano clúster amorfos, mostrando como la geometría de Wulff es energéticamente la más estable a partir de 2nm, pero para tamaños inferiores los clúster amorfos son más estables. Para silicatos de magnesio, se describe la estructura, espectro infra-rojo y microondas de clúster de MgSiO3 y Mg2SiO4, así como la similitud del espectro infra-rojo en materiales cristalinos y amorfos de tamaños ~4 nm. Los resultados se comparan con los modelos usados para entender las propiedades del medio interestelar. Se muestra que para nano partículas de hasta algunos nanómetros de radio no es posible diferenciar el material cristalino del amorfo en base a espectroscopia infrarroja. Finalmente, se calcula la intensidad de emisión en microondas (10-60 GHz) de nano clústers de silicatos de ~100 átomos y se demuestra a nivel teórico la capacidad de los silicatos como fuente viable de la emisión anómala de microondas.
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Quinlan, Erin. "Thermal and crystallinity profiles in laminates manufactured with the automated thermoplastic tow placement process." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103584.
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Automated Tow Placement (ATP) is an increasingly desirable manufacturing technique for composite materials for aerospace applications. Historically, thermoset composites have been the desired material for ATP. However, high performance thermoplastics have proven they can perform as well as the thermoset matrix. The three main goals to further the research on thermoplastics used in ATP are the following. First, to model the crystallinity level of a thermoplastic composite material with Differential Scanning Calorimetry (DSC) experiments on thermoplastic films. Second, to provide a thermal analysis through the thickness of the material profile and determine cooling rates that occur in carbon fiber-thermoplastic matrix laminates during processing. Last, to measure by DSC method the post processing crystallinity levels through the thickness of a laminate manufactured in ATP. A set of DSC experiments using isothermal and dynamic cooling measured the crystallinity levels in thermoplastic films. Each experiment was compared with models from literature. After comparing three different models, none fit well to the experimental data. In order to fit properly, the constants in the literature models had to be refit to the data collected by method of least squares; however, the models fit well for the slower cooling rates only. Experiments on ATP to measure the temperatures and calculate the cooling rates through the part thickness showed that the cooling rate is affected by the material that the composite tow is laid onto. The same manufactured parts that had thermocouples implanted were also used to test the crystallinity levels through three sections of the part thickness. There was not much difference in crystallinity level through the thickness since the material used is a high crystalline material. Generally, the material properties are related to the crystallinity level found in the thermoplastic matrix. Since it does not require the secondary post cure step as thermoset composites require, the ATP manufacturing process for thermoplastic composites is an in-situ method. This thesis seeks to provide more clarity in modeling crystallinity levels and the ATP manufacturing process for thermoplastic composites.L'attrait envers la fabrication de pièces en matériaux composites par des méthodes de placement de fibre automatisés (ATP) est actuellement en pleine croissance dans les milieux aéronautiques. Traditionnellement, ce sont les matrices thermodurcissables qui ont dominées les applications d'ATP. Par contre, les matrices thermoplastiques de haute performance ont prouvés qu'elles pouvaient être comparables aux thermodurcissables. Les trois objectifs principaux de la présente recherche se décrivent comme suit : Tout d'abord, modéliser le taux de cristallinité d'une pièce en matériaux composites à l'aide d'expérimentations de calorimétrie à balayage différentiel (DSC) sur des films thermoplastiques. Ensuite, déterminer les taux de refroidissement lors de la fabrication d'un laminé de fibre de carbone-thermoplastique afin d'analyser le profile thermique d'une pièce à travers son épaisseur. Finalement, mesurer, à l'aide de la méthode DSC, les taux réels de cristallinité à travers l'épaisseur d'un laminé fabriqué par procédé ATP. Le taux de cristallinité de films thermoplastiques ayant subies des phases de refroidissement dynamique et isotherme a été mesuré à l'aide d'une série de tests en DSC. Les résultats de chaque échantillon ont été comparés à des modèles provenant de la littérature. La comparaison a révélée qu'aucun des différents modèles ne correspondait bien aux données recueillies de façon expérimentale. Afin d'obtenir une correspondance adéquate, des méthodes de moindres carrés ont dû être utilisées sur les données expérimentales afin de recalculer les constantes proposées par les modèles. Par contre, seuls les résultats pour les taux de refroidissement les plus lents ont démontrés une bonne corrélation avec les modèles. Des expérimentations servant à mesurer les températures et à calculer les taux de refroidissement à traves l'épaisseur de pièces fabriquées par procédés ATP ont démontré que le taux de refroidissement est dépendent de la nature du matériau sur lequel les fibres sont déposées. Les mêmes pièces, dans lesquelles des thermocouples avaient été introduits lors de la fabrication, ont également été utilisées afin de mesurer les taux de cristallinité de trois sections localisées à travers l'épaisseur de ces dernières. Les différents taux de cristallinité obtenus se sont avérés être très similaires, ce qui pourrait s'explique par le fait que, à la base, le matériau utilisé est un matériau très cristallin. De façon générale, les propriétés des matériaux composites à matrice thermoplastiques sont reliées au taux de cristallinité de ces dernières. Les procédés de fabrication par ATP de composites à base de thermoplastiques sont considérés comme des méthodes in-situ puisque, à l'encontre de leurs équivalents thermodurcissables, ils ne requièrent aucun traitement particulier, tel que la cuisson, après avoir terminé la déposition des différentes couches du laminé. Le présent mémoire a pour but d'apporter plus de précisions quant à la modélisation des taux de cristallinité ainsi qu'aux procédés de fabrication par ATP de composites à matrices thermoplastiques.
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Wang, Shiping. "THICKNESS AND CRYSTALLINITY DEPENDENT SWELLING OF POLY (ETHYLENE OXIDE) /POLY (METHYL METHACRYLATE) BLEND FILMS." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1556831245474707.
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Seeley, Zachary Mark. "Titanium dioxide-based carbon monoxide gas sensors : effects of crystallinity and chemistry on sensitivity." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Dissertations/Fall2009/z_seeley_120209.pdf.
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Dupee, James David. "On-line crystallinity and temperature measurements of nylon 6,6 using a remote laser Raman probe." Thesis, Queen Mary, University of London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287935.
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Eburneo, Juliana Aparecida Marques [UNESP]. "Características físico-químicas de amidos extraídos de batatas cultivadas sob diferentes doses de adubação nitrogenada." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/150005.
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A batata é a hortaliça com maior área cultivada no Brasil, sendo que sua produção se concentra nos estados da região sul e sudeste. Na cultura da batata o manejo inadequado da adubação nitrogenada pode causar crescimento exagerado da parte aérea, reduzir a qualidade de tubérculos e aumentar o custo de produção. Além disso, as condições de cultivo também podem influenciar as características do amido, principal carboidrato de reserva da batata, o que pode levar a interferências na aplicabilidade deste pelas indústrias alimentícias. Frente ao exposto, este trabalho teve por objetivo caracterizar amidos extraídos de batata cv Ágata cultivada sob diferentes doses de adubação nitrogenada e avaliar a possível interferência desta prática sobre a morfologia e distribuição de tamanho dos grânulos de amido, teor de amilose, teores de fósforo, cálcio, potássio e magnésio, composição físico-química, propriedades de pasta e térmicas; parâmetros estes determinantes para o estabelecimento das potencialidades de aplicabilidades do amido pelas indústrias. Para o alcance deste objetivo foram utilizados tubérculos de batata resultantes da colheita de ensaio experimental com adubação nitrogenada instalado em propriedade rural na região da cidade de Avaré, estado de São Paulo. Após o cultivo de 117 dias, as batatas foram colhidas, lavadas e processadas para a extração e análise do amido. Os resultados obtidos mostram que o amido de batata extraído de plantas cultivadas sem a aplicação de adubo nitrogenado apresentou grânulos redondos e ovalados, com predomínio de diâmetro maior na faixa de 26 a 50μm, padrão de difração de raio X do tipo B, 22,16% de cristalinidade relativa, elevada pureza, presença de 1090 ppm de fósforo, 893 ppm de potássio, 200 ppm de cálcio e 88 ppm de magnésio. Temperatura de pasta de 67,94°C, pico de viscosidade de 796,88 RVU, quebra de viscosidade de 622,03 RVU, viscosidade final de 236,28 RVU e tendência a retrogradação de 65,76 RVU. A gelatinização iniciou em 65,85°C, com pico em 68,03°C e final em 70,79°C, com variação de entalpia de 9,92 J g-1. A análise dos dados mostrou interferência da adubação nitrogenada sobre as características do amido de batata cv Ágata, sendo que o incremento nas doses de nitrogênio levou a obtenção de amidos com menor cristalinidade relativa, menores teores de fósforo, cálcio e magnésio, menor resistência à temperatura e agitação e menores temperaturas de gelatinização. Estes resultados indicam que o manejo cultural pode afetar importantes propriedades determinantes de aplicabilidade do amido de batata.
Potato is a vegetable with the largest cultivated area in Brazil and its production is concentrated in the states of the southeast region. In potato cultivation nitrogen fertilization management can cause overgrown growth, reduce the quality of tubers and increase the cost of production. In addition, the cultivation conditions may also influence the characteristics of the starch, main reserve carbohydrate of the potato, which can lead to interference in applicability of starch by industries. In view of the above, the objective of this work was to characterize starches extracted from Ágata cultivar cultivated under different rates of nitrogen fertilization, and to evaluate possible interference on morphology and size distribution of starch granules, amylose content, phosphorus, calcium, potassium and magnesium, physical-chemical composition, pasting and thermal properties, important characteristics for establishing the potential of starch application by industries. In order to reach this objective was analyzed tubers obtained from experimental area in the region of the Avaré city, state of São Paulo. After cultivation of 117 days potatoes were harvested, washed and processed for extraction and analysis of the starches. The results obtained show that potato starch extracted from plants cultivated without a nitrogen fertilizer application showed round and oval granules, with a larger diameter in the range of 26 to 50μm, pattern type B of X-ray diffraction, 22,16% of relative crystalline, high purity, presence of 1090 ppm of phosphorus, 893 ppm of potassium, 200 ppm of calcium and 88 ppm of magnesium. The pasting temperature was 67.94°C, viscosity peak was 796.88 RVU, viscosity breakdown was 622.03 RVU, final viscosity was 236.28 RVU and seatback was 65.76 RVU. The gelatinization of starch granules started at 65.85°C, with peak at 68.03°C, and final at 70.79°C, with enthalpy variation of 9.92 J g-1. The analysis of the data showed the interference of nitrogen fertilization on the characteristics of Ágata potato starch. The increase in nitrogen rates led to the obtaining of starches with lower relative crystalline, lower phosphorus, calcium and magnesium contents, lower resistance to temperature and agitation and lower gelatinization temperatures. These results indicate that cultural management can affect important determining properties of potato starch application, which is of great interest to the food industry.
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Romine, William Whittington Alan G. "Flow and heat transfer properties of Mono Craters rhyolites effects of temperature, water content, and crystallinity /." Diss., Columbia, Mo. : University of Missouri--Columbia, 2008. http://hdl.handle.net/10355/5685.
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The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 5, 2009). Thesis advisor: Dr. Alan G. Whittington. Includes bibliographical references.
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Gilley, Andrew. "Amorphous solid dispersion effects on in vitro solution concentrations of quercetin." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/72864.
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Quercetin is a flavonol with potential health benefits including activities against cardiovascular disease, obesity, and oxidative stress. However, the benefits of quercetin are likely limited by poor bioavailability, primarily attributed to its poor aqueous solubility (due to its hydrophobicity and crystallinity) and extensive phase-II metabolism. Improving the apparent solubility of quercetin has the potential to improve its in vivo bioavailability. Strategies to increase solution concentrations in the small intestinal lumen have the potential to substantially increase quercetin bioavailability, and efficacy. We aimed to achieve this by incorporating quercetin into amorphous solid dispersions (ASDs) with cellulose derivatives, eliminating crystallinity, and selectively releasing amorphous quercetin under simulated intestinal conditions (pH 6.8, 37C). Amorphous quercetin was dispersed in cellulose esters including 6-carboxycellulose acetate butyrate (CCAB), hydroxypropylmethylcellulose acetate succinate (HPMCAS) and cellulose acetate suberate (CASub) to achieve stability and provide pH-triggered release. In addition, polyvinylpyrrolidone (PVP) containing CASub and CCAB blends were prepared to further promote enhanced dissolution. The ASD employing 10% quercetin in 20% PVP:70% CASub was most successful at enhancing the solution concentration of quercetin, providing an 18-fold increase in the area under the concentration/time curve (AUC) compared to quercetin alone. These results warrant in vivo assessment of quercetin-loaded ASDs formulated with CASub and its blend with PVP towards improving the bioavailability of quercetin.Master of Science in Life Sciences
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Yan, Bing. "Effects of Thermal Treatments on Perfluorosulfonate Ionomer Membranes." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/44195.
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Perfluorosulfonate ionomer (PFSI) membranes were annealed at elevated temperature for various periods of time in order to investigate the morphological effects of thermal treatments. For Nafion® 117, the DSC thermograms of Na+-, Cs+- and tetramethylammonium(TMA+)-form membranes show an endothermic peak develops upon annealing at 200ºC, indicating the development of crystallinity in the membrane. For these three samples annealed under same conditions, the heat of fusion (ΠH) values of the endothermic event increases with increasing counterion size. Larger tetraalkylammonium ions, tetraethylammonium(TEA+) and tetrapropylammonium(TPA+), result in no significant peak upon annealing at 200ºC. DSC thermograms of annealed Na+-form 3M Ionomer show no peak upon annealing and DSC thermograms of annealed TMA+-form 3M Ionomer show a very small peak that develops with annealing time at high equivalent weights. Annealed TMA+-form Dow Ionomer, which has a side chain shorter than both Nafion® and 3M Ionomer and a smaller mole% of side chains at the same equivalent weight, shows a relatively high ΠH value, which might also be related to its blocky nature. These results show that the isothermal crystallization kinetics of PFSI is affected by the counterion attached to the sulfonate group, the length of side chain, the mole% of side chains and the nature of the membrane. Water uptake analysis has been performed on annealed membranes, and the result shows that water uptake decreases with increasing degree of crystallinity.Master of Science
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Öman, Tommy. "Multivariate Analysis of 2D-NMR Spectroscopy : Applications in wood science and metabolomics." Doctoral thesis, Umeå universitet, Kemiska institutionen, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-80201.
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Wood is our most important renewable resource. We need better quality and quantity both according to the wood itself and the processes that are using wood as a raw material. Hence, the understanding of the chemical composition of the wood is of high importance. Improved and new methods for analyzing wood are important to achieve better knowledge about both refining processes and raw material. The combination of NMR and multivariate analyses (MVA) is a powerful method for these analyses but so far it has been limited mainly to 1D NMR. In this project, we have developed methods for combining 2D NMR and MVA in both wood analysis and metabolomics. This combination was used to compare samples from normal wood and tension wood, and also trees with a down regulation of a pectin responsible gene. Dissolving pulp was also examined using the same combination of 2D-NMR and MVA, together with FT-IR and solid state 13C CP-MAS NMR. Here we focused on the difference between wood type (softwood and hardwood), process type (sulfite and sulfate) and viscosity. These methods confirmed and added knowledge about the dissolving pulp. Also reactivity was compared in relation to morphology of the cellulose and pulp composition. Based on the method and software used in the wood analysis projects, a new method called HSQC-STOCSY was developed. This method is especially suited for assignment of substances in complex mixtures. Peaks in 2D NMR spectra that correlate between different samples are plotted in correlation plots resembling regular NMR spectra. These correlation plots have great potential in identifying individual components in complex mixtures as shown here in a metabolic data set. This method could potentially also be used in other areas such as drug/target analyses, protein dynamics and assignment of wood spectra.
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Hu, Jiahuan. "Strain-Induced Crystallization of Natural Rubber and Isoprene Rubber Studied by Solid-State NMR Spectroscopy." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1397087771.
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Davis, Kedzie. "The effect of cooling rate on toughness and crystallinity in poly(ether ketone ketone) (PEKK)/G30-500 composites." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-09182008-063310/.
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Murata, Kazuya, Masafumi Ito, Masaru Hori, and Toshio Goto. "Control of seed layer for a low temperature formation of polycrystalline silicon with high crystallinity and a smooth surface." American Institute of Physics, 1999. http://hdl.handle.net/2237/7079.
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Ostermann, Rainer [Verfasser]. "Design and physico-chemical characterization of nanowires and multicomponent metal oxide films with tailored mesostructure and crystallinity / Rainer Ostermann." Gießen : Universitätsbibliothek, 2011. http://d-nb.info/1062972732/34.
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Madathingal, Rajesh Raman. "Nanoscale confinement and interfacial effects on the dynamics and glass transition/crystallinity of thin adsorbed films on silica nanoparticles." Diss., Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/116348.
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ChemistryPh.D.
The research investigated in this dissertation has focused on understanding the structure-property-function relationships of polymer nanocomposites. The properties of composite systems are dictated by the properties of their components, typically fillers in a polymer matrix. In nanocomposites, the polymer near an interface has significantly different properties compared with the bulk polymer, and the contribution of the adsorbed polymer to composite properties becomes increasingly important as the filler size decreases. Despite many reports of highly favorable properties, the behavior of polymer nanocomposites is not generally predictable, and thus requires a better understanding of the interfacial region. The ability to tailor the filler/matrix interaction and an understanding of the impact of the interface on macroscopic properties are keys in the design of nanocomposite properties. In this original work the surface of silica nanoparticles was tailored by: a) Changing the number of sites for polymer attachment by varying the surface silanols and, b) By varying the size/curvature of nanoparticles. The effect of surface tailoring on the dynamic properties after the adsorption of two model polymers, amorphous polymethyl methacrylate (PMMA) and semicrystalline polyethylene oxide (PEO) was observed. The interphase layer of polymers adsorbed to silica surfaces is affected by the surface silanol density as well as the relative size of the polymer compared with the size of the adsorbing substrate. The non-equilibrium adsorption of PMMA onto individual colloidal Stöber silica (SiO2) particles, where Rparticle (100nm) > RPMMA (~6.5nm) was compared with the adsorption onto fumed silica, where Rparticle (7nm) ~ RPMMA (6.5nm) < Aggregate (~1000nm), both as a function of silanol density [SiOH] and hydrophobility. In the former case, TEM images showed that the PMMA adsorbed onto individual nanoparticles, so that the number of PMMA chains/bead could be calculated, whereas in the latter case bridging of PMMA between aggregates occurred. The anchoring point densities were comparable to the silanol densities, suggesting that PMMA adsorbed as trains rather than loops. For hydrophilic SiO2, Tg increased with [SiOH], as more carbonyl groups hydrogen bonded to the silanols, and was independent of particle morphology. For methylated silica, (CH3)3-SiO2, the adsorption isotherms were identical for colloidal and fumed silica, but Tg was depressed for the former, and comparable to the bulk value for the latter. The increased Tg of PMMA adsorbed onto fumed (CH3)3-SiO2 was attributed to the larger loops formed by the bridging PMMA chains between the silica aggregates. For nanocomposites the interphase region becomes more important as the surface/volume ratio of the nanoparticles increases. Polymers have chain dimensions (characterized by the radius of gyration, Rg) similar to the nanoparticles (Rnanoparticle) themselves, so that chain conformation, mobility and crystallinity can be affected by Rg/Rnanoparticle. Here, both the glass transition temperature (Tg) and degree of crystallinity (Xc) of polyethylene oxide (PEO) on individual SiO2 nanoparticles of nominal 15, 50 and 100 nm diameter (2 RSiO2) , in which Rg (PEO) was greater, equal to or less than RSiO2 was investigated. Plateau adsorption of PEO on SiO2 nanoparticles (PEO-SiO2) increased in the order PEO-SiO2 (100 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (15 nm). At plateau adsorption after melting and solidification, the samples were completely amorphous. The Tg of the adsorbed PEO increased in the order PEO-SiO2 (100 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (15 nm); since the Tgs were above 25oC in all cases, the PEO behaved more like a brittle solid than an elastomer. For comparable amounts of PEO that were adsorbed from solution but not melted, the melt endotherm increased in the order PEO-SiO2 (15 nm) > PEO-SiO2 (50 nm) > PEO-SiO2 (100 nm). These trends were interpreted as due to an increase in loop/tail lengths and thus flexibility, with a concomitant ability to crystallize, as Rg (PEO)/RSiO2 decreased and which was the result of less hydrogen bond formation between the oxygens of PEO and the silanols (SiOH) of the SiO2 as the nanoparticle size decreased. This in turn was attributed to the energetically unfavorable conformations necessary for the PEO chains to adopt in order to hydrogen bond with silanols on the smaller nanoparticles. The degradation behavior of amorphous PMMA and semicrystalline PEO on silica (SiO2) nanoparticles as a function of silanol density and nanoparticle size was investigated by derivative thermogravimetric analysis (DTGA) for adsorption amounts below plateau adsorption. For PMMA Td decreased as the number of SiOH/C=O contacts decreased, either from heat treatment of the SiO2, which reduced the silanol density, or as the nanoparticle size decreased, reducing the numbers of places that the PMMA chain contacted the nanoparticles.
Temple University--Theses
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Demirel, Bilal, and bilal demirel@student rmit edu au. "Optimisation of Petaloid Base Dimensions and Process Operating Conditions to Minimize Environmental Stress Cracking in Injection Stretch Blow Moulded PET Bottles." RMIT University. SAMME, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090305.154433.
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ABSTRACT Injection stretch blow moulded PET bottles are the most widely used container type for carbonated soft drinks. PET offers excellent clarity, good mechanical and barrier properties, and ease of processing. Typically, these bottles have a petaloid-shaped base, which gives good stability to the bottle and it is the most appropriate one for beverage storage. However, the base is prone to environmentally induced stress cracking and this a major concern to bottle manufacturers. The object of this study is to explain the occurrence of stress cracking, and to prevent it by optimising both the geometry of the petaloid base and the processing parameters during bottle moulding. A finite element model of the petaloid shape is developed in CATIA V5 R14, and used to predict the von Mises stress in the bottle base for different combinations of three key dimensions of the base: foot length, valley width, and clearance. The combination of dimensions giving the minimum stress is found by a statistical analysis approach using an optimisation and design of experiments software package ECHIP-7. A bottle mould was manufactured according to the optimum base geometry and PET bottles are produced by injection stretch blow moulding (ISBM). In order to minimise the stresses at the bottom of the bottle, the ISBM process parameters were reviewed and the effects of both the stretch rod movement and the temperature profile of the preform were studied by means of the process simulation software package (Blow View version 8.2). Simulated values of the wall thickness, stress, crystallinity, molecular orientation and biaxial ratio in the bottle base were obtained. The process parameters, which result in low stress and uniform material in the bottle base, are regarded as optimum operating conditions. In the evaluation process of the optimum bottle base, bottles with standard (current) and optimized (new) base were produced under the same process conditions via a two-stage ISBM machine. In order to compare both the bottles, environmental stress crack resistance, top load strength, burst pressure strength, thermal stability test as well as crystallinity studies ¬¬¬via modulated differential scanning calorimetry (MDSC) and morphology studies via environmental scanning electron microscopy (ESEM) and optical microscopy were conducted. In this study carried out, the new PET bottle with the optimised base significantly decreased the environmental stress cracking occurrence in the bottom of the bottle. It is found that the bottle with optimised base is stronger than the bottle with standard base against environmental stress cracking. The resistance time against environmental stress cracking are increased by about % 90 under the same operating process conditions used for standard (current) bottles; and by % 170 under the optimised process conditions where the preform re-heating temperature is set to 105 oC.
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Li, Ding. "LOCALIZED MECHANICAL DEFORMATION AND DISSOLUTION OF 45S5 BIOGLASS." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/91.
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Bioactive glasses react with the human physiological solution in control of their biofunctionality. The stress state in bioactive glasses determines the chemomechanical reaction and their biofunctionality. Using the microindentation technique, the effect of the indentation deformation on the surface damage and material dissolution of 45S5 bioglass was investigated.
The indentation-induced residual stresses were calculated. Complete anelastic recoveries of the indentation depths and the impression marks were observed for the first time, which was likely driven by the stored strain energy over the anelastic deformation zone. The indentation-induced local surface damages were revealed before and after the immersion tests in phosphate buffer solution (PBS). The growth of the cracks in the PBS solution displayed the stress-corrosion behavior with the crack-growth speed being a linear function of the indentation load.
45S5-bioglass was crystallized at temperature of 650 ºC. Microindentation technique also was used to study the localized mechanical behavior of the crystallized 45S5-bioglass. The crystallization had little effect on the indentation hardness, and the indentation hardness of the crystallized 45S5-bioglass is the same as that of the corresponding material in vitreous state. The fracture toughness is about 3 times less than that of annealed 45S5-bioglass in vitreous state, suggesting the preference of using bioactive glasses of vitreous state in the implant applications. Also, the effect of crystallization on the material dissolution was examined in phosphate buffer solution.
We also studied the growth and mechanical behaviors of the Ca-P precipitate layers formed on 45S5 bioglass in simulated body fluid. The thickness of the Ca-P precipitate layers was proportional to the square root of the immersion time, and the ratio of Ca/P in the Ca-P precipitate layers increased with the immersion time and approached 1.67, corresponding to the stoichiometric hydroxyapaptite (HA).Using the indentation technique, the indentation behavior of the Ca-P precipitate layers was investigated. The indentation hardness of the HA layers formed in SBF was found to be 0.40 GPa, and the contact modulus was 12.0 GPa. The contact modulus of 12.0 GPa is close to that of cortical bone. In this thesis, the primary mechanical properties of the non-crystalline and crystalline bioglass 45S5 were revealed. The relationship between the dissolution rate and localized residual stresses are discussed. With such knowledge, the evaluation of implants with respect to manufacturing processes, control, and service conditions now has another variable to consider and evaluate against performance.
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Horta, Daniela Gomes. "Efeito da cristalinidade e da cinética de dissolução no desempenho da flotação de apatitas e calcitas." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3134/tde-06072014-215639/.
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Diferentes estratégias de flotação (reagentes, pH e rota) têm sido utilizadas na separação entre apatita e carbonatos em todo o mundo. Há evidências na literatura de que a cristalinidade afeta a flotação de apatitas e calcitas com oleato de sódio. Além disso, a dissolução dos sais semi-solúveis pode influenciar a interação entre a superfície dos minerais e os reagentes de flotação, uma vez que o mecanismo de adsorção mais importante é a precipitação de oleato de cálcio na interface sólido/líquido. Portanto, o objetivo deste trabalho é investigar a relação entre cristalinidade, cinética de dissolução e resposta à flotação de apatitas e calcitas de diferentes gêneses (ígnea, metamórfica e sedimentar) e origens. Quatro tipos de minerais foram utilizados: purificados a partir de minérios, previamente purificados, naturalmente puros e amostras de coleção. As amostras foram caracterizadas por fluorescência de raios-X e microanálise (WDS/EDS). Características físicas como densidade (d), área superficial (S) e porosidade (P) também foram determinadas. O método de Rietveld aplicado à difração de raios-X foi usado tanto para comprovar a pureza das amostras como para estudar a cristalinidade dos minerais por meio da determinação dos parâmetros de rede (distâncias a e c, e volume da cela unitária- VCU), além do grau de cristalinidade (GC), tamanho de cristalito (TC) e microdeformação (MD). Ensaios de dissolução, conduzidos na ausência de CO2, forneceram a quantidade (mol) de íons Ca2+ (nCa2+) dissolvidos em função do tempo (t) e normalizada em relação à área superficial. Os resultados se ajustam a um modelo de primeira ordem: nCa2+ = Ca2+MAX(1- e-kt). Este procedimento permitiu calcular os valores da quantidade máxima de íons Ca2+ dissolvidos (Ca2+MAX), bem como da constante cinética (k). Além disso, a velocidade de dissolução foi determinada para a etapa rápida (VR), que caracteriza o início da reação, e para a etapa lenta (VL), que ocorre nas proximidades do estado estacionário. A resposta à flotação com oleato de sódio foi determinada por meio de experimentos de microflotação. Várias relações de causa e efeito são encontradas: flotabilidade (F) versus VR, e VR versus características intrínsecas (parâmetros de rede, de cristalinidade e físicos). VR foi selecionado para participar de tais modelos, pois, caracteriza o intervalo de tempo em que o condicionamento (1 minuto) e a microflotação (1 minuto) ocorrem. Observa-se que a flotabilidade dos minerais aumenta com o aumento de VR, sugerindo que apatitas e calcitas que disponibilizam mais íons Ca2+ em solução para interagir com o oleato, exibem mais elevada flotabilidade. Equações lineares de F em função de VR em pH 8 (R = 0,97 para apatitas e R = 0,66 para calcitas) e pH 10 (R = 0,95 para apatitas e R = 0,63 para calcitas) foram encontradas. Correlações lineares múltiplas foram utilizadas para relacionar VR (em pH 8 e 10) com as características intrínsecas que exercem maior influência sobre este parâmetro. Para as apatitas, VR foi equacionado em função de GC, TC e c, enquanto para as calcitas, os parâmetros GC, TC, d e P foram selecionados para compor o modelo. Os valores de VR calculados se ajustam aos observados dentro de um intervalo de confiança de 95%. As equações lineares propostas para as apatitas foram usadas para se estimar F das amostras de Anitápolis-SC e Tapira-MG, que não foram submetidas aos ensaios de dissolução. Os valores de F calculados estão em concordância com aqueles experimentalmente determinados.Different flotation strategies (reagents, pH and route) have been adopted to separate apatite from carbonates around the world. Literature provides evidences that crystallinity affects flotation response of apatite and calcite with sodium oleate. Furthermore, dissolution of salt-type minerals influences the interaction between mineral surface and flotation reagents, because the most important adsorption mechanism is the surface precipitation of calcium oleate onto mineral/water interface. Therefore, the objective of this research is to investigate the relationship between crystallinity, dissolution kinetics and flotation response of apatites and calcites from different genesis (igneous, metamorphic and sedimentary) and origins. Four sorts of minerals were utilized: minerals purified from ores, minerals previously purified, naturally pure minerals and collection samples. They were characterized by X-ray fluorescence and X-ray microanalysis (WDS/EDS). Physical characteristics, as specific gravity (d), surface area (S) and porosity (P), were also determined. The Rietveld method applied to X-ray diffraction data was used either to probe the purity of samples or to study the crystallinity of the minerals by means of determining their lattice parameters (a and c dimensions plus lattice volume-VCU), in addition to crystallinity degree (GC), crystallite size (TC) and microstrain (MD). Dissolution experiments, conducted in the absence of CO2, yielded curves which relate the amount (mol) of dissolved Ca2+ ions (nCa2+) versus time (t), normalized by the surface area. They fit a first order model: nCa2+ = Ca2+MAX(1- e-kt). Curve fitting via exponential adjustment was accomplished to calculate values of the maximum amount of dissolved Ca2+ ions (Ca2+MAX) and the kinetic constant (k). In addition, the dissolution rate was determined for the fast step (VR), which characterizes the beginning of the reaction, and for the slow step (VL), as it tends to the steady state. Flotation response with sodium oleate was determined by microflotation experiments. Several cause-effect relationships are found: floatability (F) versus VR, and VR versus intrinsic characteristics of minerals (lattice, crystallinity and physical parameters). VR was selected to participate in the model because it characterizes the length of time along which reagent conditioning (1 minute) plus microflotation (1 minute) take place. It is observed that F increases as VR becomes greater, suggesting that samples of apatites and calcites which place more Ca2+ ions in solution to interact with oleate exhibit higher flotation performance. Linear equations of F versus VR at pH 8 (R = 0,97 for apatites and R = 0,66 for calcites) and pH 10 (R = 0,95 for apatites and R = 0,63 for calcites) were found. Likewise, multiple linear correlations were used to relate VR (at pH 8 and 10) with the intrinsic characteristics of apatites and calcites that affect VR to a greater extent. For apatites, VR was modeled as a function of GC, TC and c, while for calcites, the parameters GC, TC d and P were selected to compose the model. The calculated VR values fit the experimental ones within 95% of confidence. The linear equations developed for apatites were used to estimate floatability of the samples from Anitápolis-SC and Tapira-MG, which were not submitted to dissolution experiments. The values of calculated floatability are in agreement with the experimental ones.
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Melnyk, I. A., V. V. Klepko, and N. I. Lebovka. "Effect of Molecular Weight on the Properties of Polyethyleneglycols Doped with Multiwalled Carbon Nanotubes." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42546.
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The aim of this study is to analyze the changes in the structure, thermal properties and electrophysical behavior of polyethylene glycol doped with multiwalled carbon nanotubes. The differential scanning calorimetry and electrical conductivity methods were used to study influence of doping multiwalled carbon NTs on the properties of polyethylene glycol of different molecular weights, Mw (PEG-400, PEG-1000, PEG-
10000). Dependencies of the polymers degree of crystallinity and temperature behavior of conductivity on the concentration of NTs were researched. The obtained data indicates a strong influence of the molecular weight of PEG on the spatial distribution of NTs and electrical conductivity of researched systems.
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Duncan, Laura Kristin. "Characterization of C60 Nanoparticles in Aqueous Systems." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/32439.
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The discovery that negatively charged aggregates of C60 fullerene are stable in aqueous environments has elicited concerns regarding the potential environmental and health effects of these aggregates. Although many previous studies have used aggregates synthesized using intermediate organic solvents, this work primarily employed an aggregate production method that more closely emulates the fate of C60 upon accidental release into the environment â extended mixing in water. The aggregates formed via this method (aqu/nC60) differ from those produced using the more common solvent exchange methods. The aqu/nC60 aggregates are heterogeneous in size (20 nm and larger) and shape (angular to round), negatively charged, and crystalline in structure â exhibiting a face centered cubic (fcc) system. Solution characteristics such as aqu/nC60 aggregate size and concentration were found to be dependant upon preparation variables such as stirring time, initial C60 concentration, and initial particle size.
Additional experiments indicate that aggregate charge, structure, and stability are highly dependant upon the identity of co-solutes (NaCl, CaCl2, sodium citrate) and their concentrations. Citrate concentrations greater than 0.5 mM resulted in the formation of very small (< 20 nm) spherical aqu/nC60 particles. At moderate citrate concentrations (~ 1 mM) a more negative surface charge was observed, which may be an indication of increased nC60 stability. In contrast, high concentrations of monovalent and divalent electrolytes result in aggregation and sedimentation of nC60 out of solution. Our research describes the effect that solution composition has on aggregate formation and stability, and suggests that C60 fate and transport will be a function of solution composition.Master of Science
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Jonzon, Julia. "Characterization andmodeling of amorphous andcrystalline ratios in poly-acrylates." Thesis, Mittuniversitetet, Avdelningen för kemiteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-40092.
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At Nouryon Stockvik the Expancel production site is located. Expandable microspheres areused in for many types of applications and is a technically challenging product. At ExpancelStockvik they are constantly striving to improve product properties in line with customerexpectations. To be able to do this, it is important to understand the properties of themicrospheres such as crystallinity and crystallite size.Films was prepared from microspheres dissolved in DMA and analyzed with High-resolutionSEM, Powder X-Ray Diffraction and Raman Spectroscopy. The aim was to develop a methodto investigate and determine crystalline ratios and crystallite size within the microsphere filmsand the microspheres before film preparation. The eventual correlation between morphologyand crystallinity was also studied. An attempt of finding an amorphous reference sample wasalso performed, this was done by grinding microspheres in liquid nitrogen, unfortunately, nosuccess was reached. Gauss-fitting was therefore performed to be able to find the amorphousregions of the XRD Diffractogram for the calculations of crystallinity and crystallite size. TheGauss-fitting was successfully performed with good R-square values.During the Raman analysis some fluorescence problems occurred, this problem will probablybe solved if a laser source with higher excitation frequency is used in future analysis. Evenwith fluorescence problems, Raman analysis could successfully be performed and giveinformation of the composition. The crystallite size was in general larger for the microspheresbefore they were prepared from dissolving them to make films. Generally, it seems as there isa correlation between the morphology, crystallinity, and crystallite size.
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Liu, Nan. "Tailoring Crystalline Phase and Surface of Lanthanide-Based Nanoparticles for MRI Applications." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39868.
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Lanthanide-based nanoparticles (Ln3+-based NPs) are promising candidates as magnetic resonance imaging (MRI) contrast agents. The present thesis aims to investigate the effect of the crystalline phase of Ln3+-based NPs on their MRI contrast performance. Understanding the phase-dependent MRI contrast behaviour of Ln3+-based NPs will provide insights into the development of brighter MRI contrast agents for future in vivo biomedical applications. A set of NaGdF4 NPs (6-8 nm) in cubic and hexagonal phases in the same size range was synthesized by employing a microwave-assisted approach, allowing the influence of host crystallinity on MRI T1 relaxivity to be investigated (chapter 4). The results showed that cubic NaGdF4 NPs exhibited superior performance as MRI T1 contrast agents than their hexagonal analogues, irrespective of the chosen surface modification, e.g. small citrate groups or longer chain poly(acrylic acid). NaDyF4 NPs (3 nm) were synthesized in both phases to assess whether phase-dependent MRI contrast behaviour consistently exists in other Ln3+-base NPs of the NaLnF4 family (chapter 5). Again, it was demonstrated that cubic NaDyF4 NPs had a better contrast performance as T2 contrast agents than the hexagonal NPs. Alternatively, cubic NaEuF4 NPs, exhibiting additional optical properties (e.g. red emission under UV excitation), were prepared as potential candidates for the preparation of chemical exchange saturation transfer (CEST) contrast agents (chapter 5). Chapter 6 introduces preliminary dispersion stability studies of cubic NaGdF4 NPs dispersed in different buffer solutions, the obtained hydrodynamic diameters indicated that NaGdF4 NPs possessed better dispersity in saline than that in PBS solution.
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Whittington, II Richard Allen. "Clay Mineralogy and Illite Crystallinity in the Late Devonian to Early Mississippian Woodford Shale in the Arbuckle Mountains, Oklahoma, USA." Digital Archive @ GSU, 2009. http://digitalarchive.gsu.edu/geosciences_theses/13.
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Commonly the thermal maturity of the Late Devonian to Early Mississippian Woodford shale found on the flanks of the Arbuckle Mountains of Oklahoma is determined by vitrinite reflectance, values ranging from 0.3-1.5%. Using phyllosilicate minerals, specifically diagenetic mixed layer illite/smectite and diagenetic illite, an understanding of the extent and processes leading to the thermal maturation may be developed. Analysis by XRD of the clay mineralogy of the Woodford shale found kaolinite and mixed layer illite/smectite with <5% smectite and R≥3 stacking order. Modeling of the Woodford shale also suggests the percentage of smectite present in mixed layer illite/smectite to be <5% and commonly <2.5%. Deconvolution of the illite (001) peak supports the low smectite content and high illite crystallinity. The long range ordered illite, R≥3, and high illite crystallinity values are indicative of diagenesis to anchizone conditions suggesting a higher thermal maturity relative to previously measured values of vitrinite reflectance.