Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 120-126. / by John Edward Blendell. / Sc.D.

Graduation date: 1997

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Ume, I. Charles; Committee Member: Dr. Book, Wayne; Committee Member: Dr. Kim, Yeong; Committee Member: Dr. Pan, Jiahui; Committee Member: Dr. Sitaraman, Suresh; Committee Member: Dr. Wu, C. F. Jeff.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The primary objective of the work was to investigate the negative thermal expansion of organic materials and to determine the mechanisms governing this phenomenon by using the principles of crystal engineering. To this end, the following three compounds were studied in detail: • 4,4'-Diiodobiphenyl • 4-Iodobenzoic acid • Methyl Paraben The rationale behind this work was to determine the mechanisms responsible for the observed negative thermal expansion and to uncover the structural factors that induce negative thermal expansion. Single-crystal X-ray diffraction was employed as the primary analytical tool, owing to the unique information it can provide regarding intermolecular interactions in the solid state. A total of twenty organic compounds were analysed, of which three exhibited negative thermal expansion. Each compound employs a specific mechanism for negative thermal expansion, two of which are closely related and the third distinct. / AFRIKAANSE OPSOMMING: Die hoof doel van hierdie studie was om ondersoek in te stel in die verskynsel van ‘negative thermal expansion’ in organiese materiale en gevolglik die meganisme vas te stel deur die beginsels van kristalmanipulsie (‘crystal engineering’) te gebruik. Gevolglik was drie organise stowwe ondersoek: • 4,4'-Diiodobiphenyl /4,4'-Diiodobifeniel • 4-Iodobenzoic acid /4-Iodobensoësuur • Methyl Paraben Die redenasie hieragter is om die meganisme verantwoordelik vir die ‘negative thermal expansion’ vas te stel en die verskillende faktore wat bydra tot dit te bevestig. Enkel-kristal diffraksie word benut as die primêre analitiese tegniek as gevolg van die unieke inligting wat verkry kan word met betrekking tot die intermolekulêre interaksies. 'n Totaal van twintig stowwe is geanaliseer waarvan drie die spesifieke termisie eienskap besit. Elk van die drie stowwe het ‘n ander meganisme te vore laat kom waarvan twee baie ooreenstem en die derde verskil.

This work focuses on the chemical substitution of cations and anions in the frameworks of materials that have been known to exhibit negative thermal expansion (NTE). Zr2(PO4)2(SO4) is a member of the A(2)M(3)O(12) family which has been known to exhibit NTE. We have shown that Zr2(PO4)2(SO4) exhibits anisotropic positive thermal expansion. We have also shown that this material has been characterized in the wrong space group. Hf2(PO4)2(SO4) behaves similarly to Zr2(PO4)2(SO4) and follows this trend. Under pressure, Hf2(PO4)2(SO4) appears to undergo a phase transition. We have still yet to determine what space group the materials transitions to. While many members of the AX(2)O(7) family of frameworks have been fully characterized, the thermal expansion of PbP2O7 has yet to be reported. We were unable to obtain a reproducible procedure for synthesis of PbP2O7 from its precursor. Finally, variable temperature and variable pressure studies were performed on ZrMo2O8 in an attempt to learn more about the local structure. We found that space groups P213 and Pa-3 gave poor fits of the local structure at low r. Behavior of the nearest neighbor Zr-Mo distance was very similar to the bulk CTE. On compression, pressure induced amorphization is observed in ZrMo2O8. All interatomic correlations above 4 angstroms are washed out. Zr-O-Mo linkages remain well defined and do not massively deform as the pressure is increased. Finally, we we observed that Zr-O-Mo linkages change geometry reversibly as the pressure is increased.

This thesis explores the thermal expansion and high pressure behavior of some materials with the ReO₃ structure type. This structure is simple and has, in principle, all of the features necessary for negative thermal expansion (NTE) arising from the transverse thermal motion of the bridging anions and the coupled rotation of rigid units; however, ReO₃ itself only exhibits mild NTE across a narrow temperature range at low temperatures. ReO₃ is metallic because of a delocalized d-electron, and this may contribute to the lack of NTE in this material. The materials examined in this thesis are all based on d⁰ metal ions so that the observed thermal expansion behavior should arise from vibrational, rather than electronic, effects. In Chapter 2, the thermal expansion of scandium fluoride, ScF₃, is examined using a combination of in situ synchrotron X-ray and neutron variable temperature diffraction. ScF₃ retains the cubic ReO₃ structure across the entire temperature range examined (10-1600 K) and exhibits pronounced negative thermal expansion at low temperatures. The magnitude of NTE in this material is comparable to that of cubic ZrW₂O₈, which is perhaps the most widely studied NTE material, at room temperature and below. This is the first report of NTE in an ReO₃ type structure across a wide temperature range. Chapter 3 presents a comparison between titanium oxyfluoride, TiOF₂, and a vacancy containing titanium hydroxyoxyfluoride, Tiₓ(O/OH/F)₃. TiOF₂ was originally reported to adopt the cubic ReO₃ structure type under ambient conditions, therefore the initial goal for this study was to examine the thermal expansion of this material and determine if it displayed interesting behavior such as NTE. During the course of the study, it was discovered that the original synthetic method resulted in Tiₓ(O/OH/F)₃, which does adopt the cubic ReO₃ structure type. The chemical composition of the hydroxyoxyfluoride is highly dependent upon synthesis conditions and subsequent heat treatments. This material readily pyrohydrolyizes at low temperatures (~350 K). It was also observed that TiOF₂ does not adopt the cubic ReO₃ structure; at room temperature it adopts a rhombohedrally distorted variant of the ReO₃ structure. Positive thermal expansion was observed for TiOF₂ from 120 K through decomposition into TiO₂. At ~400 K, TiOF₂ undergoes a structural phase transition from rhombohedral to cubic symmetry. High pressure diffraction studies revealed a cubic to rhombohedral phase transition for Tiₓ(O/OH/F)₃ between 0.5-1 GPa. No phase transitions were observed for TiOF₂ on compression. In Chapter 4, an in situ variable pressure{temperature diffraction experiment examining the effects of pressure on the coefficients of thermal expansion (CTE) for ScF₃ and TaO₂F is presented. In the manufacture and use of composites, which is a possible application for low and NTE materials, stresses may be experienced. Pressure was observed to have a negligible effect on cubic ScF₃'s CTE; however, for TaO₂F the application of modest pressures, such as those that might be experienced in the manufacture or use of composites, has a major effect on its CTE. This effect is associated with a pressure-induced phase transition from cubic to rhombohedral symmetry upon compression. TaO₂F was prepared from the direct reaction of Ta₂O₅ with TaF₅ and from the digestion of Ta₂O₅ in hot hydro uoric acid. The effects of pressure on the two samples of TaO₂F were qualitatively similar. The slightly different properties for the samples are likely due to differences in their thermal history leading to differing arrangements of oxide and uoride in these disordered materials. In Chapter 5, the local structures of TiOF₂ and TaO₂F are examined using pair distribution functions (PDFs) obtained from X-ray total scattering experiments. In these materials, the anions (O/F) are disordered over the available anion positions. While traditional X-ray diffraction provides detailed information about the average structures of these materials, it is not suffcient to fully understand their thermal expansion. Fits of simple structural models to the low r portions of PDFs for these materials indicate the presence of geometrically distinct M{X{M (M = Ti, Ta; X = O, F) linkages, and a simple analysis of the TaO₂F variable temperature PDFs indicates that these distinct links respond differently to temperature.

The research presented in this thesis focuses on the structural studies and the high pressure behavior of oxide negative thermal expansion (NTE) materials that can be classified as framework materials. First two chapters were devoted to TaO2F which adopts the ReO3-type cubic structure. Our studies under pressure revealed a rather complicated high pressure behavior for this deceivingly simple compound. The diffraction measurements at variable temperature and high pressure indicated that pressure had a significant effect on the linear coefficient of thermal expansion of TaO2F. In the remainder of the thesis, compounds that belong to the Sc2W3O12 family were examined. High-pressure in-situ powder diffraction studies were conducted on Zr2WO4(PO4)2, Zr2MoO4(PO4)2, Hf2WO4(PO4)2, and Sc2W3O12 in order to investigate the effects of pressure on the coefficients of thermal expansion, existence of phase transitions, phase transition pressures and structural changes occurring upon phase transitions.

O impacto ambiental causado pelo descarte indevido de embalagens a base de polímeros sintéticos, desperta interesse na necessidade de desenvolvimento de embalagens a partir de materiais biodegradáveis. O objetivo deste trabalho foi desenvolver e caracterizar bandejas a base de espuma de amido de mandioca para embalagem de alimentos, obtidas pelo processo de expansão térmica. Foram testadas diferentes proporções de amido e água, como agente expansor, na formulação das espumas de amido. Como plastificantes, foram utilizados o glicerol, sorbitol e poli (álcool vinílico) (PVA), nas concentrações de 2,5; 5,0 e 7,5% m/m sob a massa de amido. A fim de melhorar as características de hidrofilia das espumas, foi aplicado revestimento a base de poli (ácido lático) (PLA) na superfície das bandejas. Testou-se a aplicação das bandejas como embalagem no armazenamento de morangos. A caracterização das embalagens foi realizada através de análises de espessura e densidade, MEV, capacidade de absorção de água (CAA), solubilidade, isotermas de sorção, resistência à tração, ângulo de contato e degradação enzimática. A proporção amido:água que produziu espumas com a melhor combinação entre as características de densidade, capacidade de absorção de água e aspecto visual foi 47,5:52,5. O aditivo que resultou em espumas de amido com a maior possibilidade de aplicação como embalagem para alimentos, por apresentar a menor CAA, ser menos solúvel e com os valores mais baixos de umidade de equilíbrio, foi o PVA em concentração de 5%. A aplicação de revestimento a base de PLA na superfície das bandejas de espuma de amido resultou em diminuição de 86% na CAA das bandejas e ângulo de contato de 84,4° (maior hidrofobia). Os modelos que melhor se ajustam a isoterma de sorção das bandejas sem revestimento são os de GAB e Oswin. Enquanto que para bandejas com revestimento de PLA, o modelo de Oswin apresenta o melhor ajuste. O ensaio de degradação enzimática por amilases microbianas revelou ocorrência da hidrólise do amido nas primeiras 8 horas do teste, indicando característica de biodegradabilidade das bandejas. Os resultados do presente estudo, obtidos através do teste de aplicabilidade das bandejas, comprovam a possibilidade da utilização da embalagem à base de amido de mandioca revestidas com PLA em alimentos com alta atividade de água. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-06-25T13:40:08Z No. of bitstreams: 1 Dissertacao Fernanda Stoffel.pdf: 3201484 bytes, checksum: 203dc77998956c27e8e954d02d1b8c0e (MD5) / Made available in DSpace on 2015-06-25T13:40:08Z (GMT). No. of bitstreams: 1 Dissertacao Fernanda Stoffel.pdf: 3201484 bytes, checksum: 203dc77998956c27e8e954d02d1b8c0e (MD5) / Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul. / The environmental impact caused by improper disposal of packaging materials based on synthetic polymers, arouses interest in development packaging from biodegradable materials. The objective of this study was to develop and characterize trays base of cassava starch foam for food packaging, obtained by the thermal expansion process. Different proportions of starch and water, as blowing agent, in the formulation of the starch foams was tested. As plasticizers were used glycerol, sorbitol, and poly (vinyl alcohol) (PVA) at concentrations of 2.5; 5.0 and 7.5% w/w on starch weight. In order to improve the hydrophilic characteristics of the foams, coating was applied of poly (lactic acid) (PLA) in the surface of the trays. The application of the trays as packaging strawberries in storage was tested. Packaging characterization was performed by thickness and density analysis, SEM, water absorption capacity (WAC), solubility, sorption isotherms, tensile strength, angle of contact and enzymatic degradation. The ratio starch:water who produced foams with the best combination of density, water absorption capacity and visual aspect characteristics was 47.5:52.5. The starch additive resulted in foams with the highest possibility of application as packaging for food for presenting the lowest WAC be less soluble and lowest values equilibrium moisture, was PVA concentration of 5%. The use of PLA-based coating on the surface of the starch foam trays resulted in a decrease of 86% in WAC trays and contact angle of 84.4 ° (higher hydrophobicity). The models that best fit the sorption isotherm of uncoated trays are the GAB and Oswin models. While for trays with PLA coating, Oswin model presents the best fit. The assay of enzymatic degradation by microbial amylases revealed the occurrence of the hydrolysis of starch in the first 8 hours of the test, indicating the biodegradability characteristics of the trays. The results of this study, obtained through the applicability of the test trays prove the possibility of the use of tapioca starch-based packing covered with PLA foods with high water activity.

O impacto ambiental causado pelo descarte indevido de embalagens a base de polímeros sintéticos, desperta interesse na necessidade de desenvolvimento de embalagens a partir de materiais biodegradáveis. O objetivo deste trabalho foi desenvolver e caracterizar bandejas a base de espuma de amido de mandioca para embalagem de alimentos, obtidas pelo processo de expansão térmica. Foram testadas diferentes proporções de amido e água, como agente expansor, na formulação das espumas de amido. Como plastificantes, foram utilizados o glicerol, sorbitol e poli (álcool vinílico) (PVA), nas concentrações de 2,5; 5,0 e 7,5% m/m sob a massa de amido. A fim de melhorar as características de hidrofilia das espumas, foi aplicado revestimento a base de poli (ácido lático) (PLA) na superfície das bandejas. Testou-se a aplicação das bandejas como embalagem no armazenamento de morangos. A caracterização das embalagens foi realizada através de análises de espessura e densidade, MEV, capacidade de absorção de água (CAA), solubilidade, isotermas de sorção, resistência à tração, ângulo de contato e degradação enzimática. A proporção amido:água que produziu espumas com a melhor combinação entre as características de densidade, capacidade de absorção de água e aspecto visual foi 47,5:52,5. O aditivo que resultou em espumas de amido com a maior possibilidade de aplicação como embalagem para alimentos, por apresentar a menor CAA, ser menos solúvel e com os valores mais baixos de umidade de equilíbrio, foi o PVA em concentração de 5%. A aplicação de revestimento a base de PLA na superfície das bandejas de espuma de amido resultou em diminuição de 86% na CAA das bandejas e ângulo de contato de 84,4° (maior hidrofobia). Os modelos que melhor se ajustam a isoterma de sorção das bandejas sem revestimento são os de GAB e Oswin. Enquanto que para bandejas com revestimento de PLA, o modelo de Oswin apresenta o melhor ajuste. O ensaio de degradação enzimática por amilases microbianas revelou ocorrência da hidrólise do amido nas primeiras 8 horas do teste, indicando característica de biodegradabilidade das bandejas. Os resultados do presente estudo, obtidos através do teste de aplicabilidade das bandejas, comprovam a possibilidade da utilização da embalagem à base de amido de mandioca revestidas com PLA em alimentos com alta atividade de água. / Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul. / The environmental impact caused by improper disposal of packaging materials based on synthetic polymers, arouses interest in development packaging from biodegradable materials. The objective of this study was to develop and characterize trays base of cassava starch foam for food packaging, obtained by the thermal expansion process. Different proportions of starch and water, as blowing agent, in the formulation of the starch foams was tested. As plasticizers were used glycerol, sorbitol, and poly (vinyl alcohol) (PVA) at concentrations of 2.5; 5.0 and 7.5% w/w on starch weight. In order to improve the hydrophilic characteristics of the foams, coating was applied of poly (lactic acid) (PLA) in the surface of the trays. The application of the trays as packaging strawberries in storage was tested. Packaging characterization was performed by thickness and density analysis, SEM, water absorption capacity (WAC), solubility, sorption isotherms, tensile strength, angle of contact and enzymatic degradation. The ratio starch:water who produced foams with the best combination of density, water absorption capacity and visual aspect characteristics was 47.5:52.5. The starch additive resulted in foams with the highest possibility of application as packaging for food for presenting the lowest WAC be less soluble and lowest values equilibrium moisture, was PVA concentration of 5%. The use of PLA-based coating on the surface of the starch foam trays resulted in a decrease of 86% in WAC trays and contact angle of 84.4 ° (higher hydrophobicity). The models that best fit the sorption isotherm of uncoated trays are the GAB and Oswin models. While for trays with PLA coating, Oswin model presents the best fit. The assay of enzymatic degradation by microbial amylases revealed the occurrence of the hydrolysis of starch in the first 8 hours of the test, indicating the biodegradability characteristics of the trays. The results of this study, obtained through the applicability of the test trays prove the possibility of the use of tapioca starch-based packing covered with PLA foods with high water activity.

Orientadores: Alexandre Fontes da Fonseca, Douglas Soares Galvão / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-30T22:34:48Z (GMT). No. of bitstreams: 1 Sandoval_SergioAndresHernandez_M.pdf: 2919242 bytes, checksum: d3485fcd4e2480883a74cd6b7fddf8a6 (MD5) Previous issue date: 2016 / Resumo: A descoberta experimental do grafeno, atraiu a atenção dos cientistas pela demonstração da possibilidade da existência de materiais 2D, quando se pensava que isso não era possível, e pelas suas propriedades muito interessantes como, por exemplo, alta mobilidade e condutividade elétrica. No entanto, o grafeno apresenta limitações como sua energia de gap zero, que impede de utilizá-lo diretamente no desenvolvimento de dispositivos nanoeletrônicos. Na busca pelo desenvolvimento de semicondutores em escala nano, além da funcionalização do grafeno, outras estruturas bidimensionais tem sido estudadas. Desta maneira, o interesse em estruturas conhecidas como grafinos e grafidinos ressurgiu nos últimos anos, estruturas essas que são objeto de interesse do presente estudo. Essas estruturas são feitas de carbono apenas e podem ser imaginadas como estruturas similares ao grafeno onde algumas ligações carbono-carbono são trocadas por estruturas de acetileno ou diacetileno. Este trabalho, portanto, apresenta o cálculo das propriedades térmicas e mecânicas dos grafinos e grafidinos através de simulações de dinâmica molecular clássica. Além de considerar um número maior de estruturas de grafinos e grafidinos, em comparação à literatura, este é o primeiro trabalho que calcula suas propriedades térmicas por dinâmica molecular clássica. Os resultados mostram que os grafinos e grafidinos apresentam um coeficiente de expansão térmica uma ordem de grandeza maior que o do grafeno, em concordância com outros trabalhos. Além disso, os coeficientes de expansão térmica mostram uma dependência linear com a densidade da estrutura. Também calculamos as propriedades mecânicas de grafinos e grafidinos, mostrando que eles apresentam um módulo de Young menor que o do grafeno. Mostramos, também, que alguns grafinos e grafidinos possuem razão de Poisson maior que 0.5, próximo de zero, ou mesmo negativa / Abstract: The experimental discovery of graphene, attracted the attention of scientists not only because it proved the existence of 2D materials, when they thought that it was not possible, but also because of its very interesting properties such as high mobility of its charge carriers. However, graphene has limitations such as zero band gap. Looking for similar nanomaterials but without the above limitation, scientists came out with the idea of functionalization of graphene, or the development of other 1D or 2D nanomaterials. In this sense, there have been renewed interest in old structures known as graphynes and graphdiynes. These structures can be imagined as being formed by the substitution of some bonds in graphene by acetylene and diacetylene chains. This work, then, presents the study of some thermal and mechanical properties of graphynes and graphdiynes through classical molecular dynamics simulations. As far as we know, this work is the first that considered more types of graphynes and graphdiynes structures and, in addition, it is the first one that calculated the thermal properties using classical molecular dynamics. The results show that graphynes and graphdiynes have a thermal expansion coefficient one order of magnitude larger than of graphene, in good agreement with other studies. The thermal expansion coefficients show a linear dependence on the density of the structure. Also we show that graphynes and graphdiynes have smaller Young's modulus than graphene. The Poisson's ratio of some graphyne and graphdiyne structures were shown to be larger than 0.5, close to zero, or negative / Mestrado / Física / Mestre em Física / 1370438/2014 / CAPES