Thesis (doctoral)--University of Göteborg, 1994.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 123-132).

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxi, 225 p.; also includes graphics (some col.). Includes bibliographical references (p. 218-225). Available online via OhioLINK's ETD Center

In this thesis we employ computer simulations and statistical physics to understand the origin of liquid-liquid phase transitions and their relationship with anomalies typical of liquid water. Compared with other liquids, water has many anomalies. For example the density anomaly: when water is cooled below 4 C the density decreases rather than increases. This and other anomalies have also been found to occur in a few other one-component liquids, sometimes in conjunction with the existence of a liquid-liquid phase transition (LLPT) between a low-density liquid (LDL) and a high-density liquid (HDL). Using simple models we explain how these anomalies arise from the presence of two competing length scales. As a specific example we investigate the cut ramp potential, where we show the importance of "competition" in this context, and how one length scale can sometimes be zero. When there is a clear energetic preference for either LDL or HDL for all pressures and temperatures, then there is insufficient competition between the two liquid structures and no anomalies occur. From the simple models it also follows that anomalies can occur without the presence of a LLPT and vice versa. It remains therefore unclear if water has a LLPT that ends in a liquid-liquid critical point (LLCP), a hypothesis that was first proposed based on simulations of the ST2 water model. We confirm the existence of a LLCP in this model using finite size scaling and the Challa-Landau-Binder parameter, and show that the LLPT is not a liquid-crystal transition, as has recently been suggested. Previous research has indicated the possible existence of a LLCP in liquid silica. We perform a detailed analysis of two different silica models (WAC and BKS) at temperatures much lower than was previously simulated. Within the accessible temperature range we find no LLCP in either model, although in the case of WAC potential it is closely approached. We compare our results with those obtained for other tetrahedral liquids and conclude that insufficient "stiffness" in the Si-O-Si bond angle might be responsible for the absence of a LLCP.

The aim of this thesis is to study the structural and thermodynamical properties of polymers at liquid/liquid interfaces by means of multiscale molecular dynamics simulations. This thesis is presented in alternative format, and the results, consisting of three journal articles, are divided into two main parts. The first part of the thesis looks at the structural and dynamical changes as well as the thermodynamic stability of polymers of varying topology (linear and star-shaped) at interfaces by performing molecular dynamics simulations on model systems. It was found that homopolymers are attracted to the interface in both good and poor solvent conditions making them a surface active molecule, despite not being amphiphilic. In most cases changing polymer topology had only a minor effect on the desorption free energy. A noticeable dependence on polymer topology is only seen for relatively high molecular weight polymers at the interface. Examining separately the enthalpic and entropic components of the desorption free energy suggests that its largest contribution is the decrease in the interfacial free energy caused by the adsorption of the polymer at the interface. Furthermore, we propose a simple method to qualitatively predict the trend of the interfacial free energy as a function of the polymer molecular weight. In terms of the dynamics of a linear polymer, the scaling behaviour of the polymer confined between two liquids did not follow that predicted for polymers adsorbed onsolid or soft surfaces such as lipid bilayers. Additionally, the results show that in the diffusive regime the polymer behaves like in bulk solution following the Zimm model and with the hydrodynamic interactions dominating its dynamics. Further simulations carried out when the liquid interface is sandwiched between two solid walls show that when the confinement is a few times larger than the blob size the Rouse dynamics is recovered. The second part of the thesis focuses on optimizing the MARTINI coarse-grained (CG) Model, which retains certain chemical properties of molecules, to reproduce solubility of polymers, in specific polyethylene oxide (PEO), in both polar and non-polar solvents. Performing molecular dynamics simulations using this CG model will then enable us to study the properties PEO in octanol/water and hexane/water systems with increased length and timescales not accessible by atomistic simulations. The MARTINI CG method (Marrink et al., J. Phys. Chem. B, 2007, 111, 7812) is based on developing the optimal Lennard-Jones parameters to reproduce the partition free energy between water (polar solvent) and octanol (apolar solvent). Here we test the MARTINI CG method when modelling the partitioning properties of PEO, with increasing molecular weight between solvents of different polarity by comparing the results with atomistic simulation. We show that using simply the free energy of transfer from water to octanol to obtain the force parameters does not guarantee the transferability of the model to other solvents. Instead one needs to match the solvation (or hydration) free energies to ensure that the polymer has the correct polarity. We propose a simple method to select the Lennard-Jones parameter to match the solvation free energies for different beads. We also show that, even when the partition coefficient of the monomer is correct, even for modestly high molecular weight of the polymer the predicted partitioning properties could be wrong.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / In the process of purification of biodiesel is of extreme importance washing methyl or ethyl ester rich- phase, since in conventional processes there is a great amount of water. During the washing is extracted primarily excess alcohol. Composition data for the washing process of biodiesel is still scarce in the literature and the study of liquid-liquid equilibrium provides the means to develop equipment and to optimize the extraction processes. Thus the main goal of this work is to determine equilibrium data for three different ternary systems: water - methanol - soybean biodiesel; corn biodiesel â methanol â water; methanol - coconut biodiesel - water at 20  C and 40  C. The experiments were carried out in equilibrium cells where the temperature was kept constant by thermostat control. The experimental determination was made by the method of densimetry. The consistency of data obtained for the tie lines was verified by correlations. It was verified by the ternary graphs, little influence of temperature on the systems studied. The equilibrium data were correlated liquid-liquid models for the activity coefficient NRTL, UNIQUAC and UNIFAC and proved quite satisfactory. / No processo de purificaÃÃo do biodiesel, a lavagem da fase rica em metil ou etil Ãster à de extrema importÃncia, visto que nos processos convencionais hà um grande gasto de Ãgua. Durante a lavagem à extraÃdo principalmente Ãlcool em excesso. Dados de composiÃÃes para a lavagem de biodiesel ainda sÃo escassos na literatura e o estudo do equilÃbrio lÃquido-lÃquido pode fornecer meios para o desenvolvimento de equipamentos e otimizaÃÃo dos processos de extraÃÃo. Dessa forma, o principal objetivo dessa dissertaÃÃo foi determinar dados de equilÃbrio lÃquido- lÃquido para os sistemas ternÃrios contendo biodiesel de soja + metanol + Ãgua, biodiesel de milho + metanol e Ãgua e biodiesel de coco + metanol + Ãgua, a 20 ÂC e 40 ÂC. Os experimentos foram feitos em cÃlulas de equilÃbrio mantendo a temperatura constante. A determinaÃÃo experimental das misturas ternÃrias foi feita pelos mÃtodos de titulaÃÃo e densimetria. A consistÃncia dos dados das linhas de amarraÃÃo foi verificada pelas correlaÃÃes de Othmer-Tobias e Hand. Verificou-se por meio de grÃficos ternÃrios, pouca influÃncia da temperatura sobre os sistemas estudados. Os dados de equilÃbrio lÃquido-lÃquido foram correlacionados pelos modelos para coeficiente de atividade NRTL, UNIQUAC e UNIFAC e mostraram-se bastante satisfatÃrios.

Orientador: Martin Aznar / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T20:46:38Z (GMT). No. of bitstreams: 1 Cunha_EvelynVilmaCaravazi_M.pdf: 1619492 bytes, checksum: 1e4afeecf37b0da40904e4da5be5eb20 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho são determinados experimentalmente dados de equilíbrio líquido ¿ líquido dos sistemas de duas fases aquosas, água + PEG 8000 + sulfato de magnésio e água + PEG 8000 + sulfato de sódio, nas temperaturas de 25 e 50ºC. As composições de ambas as fases em equilíbrio foram obtidas por gravimetria, utilizando a técnica de liofilização (freeze-drying) para a determinação da quantidade de água e a calcinação em forno mufla para quantificação de PEG, sendo que a composição de sal foi obtida por diferença de massa. Os dados assim obtidos foram modelados através dos modelos NRTL e UNIFAC para o cálculo do coeficiente de atividade. O modelo NRTL, com a estimação de novos parâmetros de interação energética entre as espécies envolvidas, apresentou excelentes resultados de correlação, com baixos desvios entre as composições experimentais e as calculadas. O modelo UNIFAC, que é basicamente preditivo, foi capaz de representar satisfatoriamente os sistemas estudados com alguns grupos funcionais e parâmetros de interação existentes na literatura e outros estimados a partir dos dados experimentais obtidos nesse trabalho / Abstract: In this work, experimental data of the liquid-liquid equilibrium for the aqueous twophase systems water + PEG8000 + magnesium sulfate and water + PEG8000 + sodium sulfate were determined at 25 e 50°C. The compositions of both equilibrium phases were obtained by a gravimetric method, using the lyofilization (freeze-drying) technique for the water determination and the calcination in a muffle furnace for the PEG determination; in this way the salt was determined by mass difference. The experimental data were modeled by the NRTL and UNIFAC models for the activity coefficient. The NRTL model, with new energy interaction parameters, showed excellent correlation results, with low deviations between experimental and calculated compositions. The UNIFAC model, which is a predictive one, was able to represent the studied systems with some energy interaction parameters form the literature and others estimated from the experimental data determined in this work / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Orientador: Elias Basile Tambourgi / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-04T03:58:27Z (GMT). No. of bitstreams: 1 Leite_PatriciaBernardi_D.pdf: 6148337 bytes, checksum: f4db900db28f697e2c296bf0ea5251a1 (MD5) Previous issue date: 2005 / Resumo: : A enzima glicose-6-fosfato desidrogenase (G6PDH) pode ser obtida de origem animal, vegetal ou microbiana, como no caso da levedura Saccharomyces cerevisiae. Esta enzima apresenta grande importância para a sobrevida celular uma vez que participa da regulação do ciclo das pentoses sendo responsável pela manutenção de um nível adequado de NADPH nas células. A deficiência de glicose-6-fosfato desidrogenase (G6PDH) em seres humanos é considerada a mais importante enzimopatia diagnosticada. A deficiência desta enzima favorece a ruptura de membrana dos glóbulos vermelhos (hemácias ou eritrócitos) levando à anemia hemolítica. Nesse trabalho, estudou-se as condições de extração da enzima G6PDH através do uso da técnica de extração líquido-líquido por micelas reservas de tensoativos aniônicos (AOT) e catiônicos (CTAB). Planejamentos estatísticos específicos para casa sistema analisado foram empregados. As variáveis estudadas foram pH, concentração do tensoativo e temperatura. Estudou-se, também uma microcoluna agitada por campânulas pulsadas, visando promover um eficiente contato entre as fases através de uma agitação suave, aumentando assim o tempo de contato entre as fases no interior da microcoluna e também evitando a desnaturação da enzima. As porcentagens de recuperação da enzima para estes sistemas variaram de nulos a 5,10% utilizando AOT e de nulos a 14,04% cin CTAB. No entanto, observou-se diminuição na atividade catalítica da enzima ...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital / Abstract: The enzime glucose-6-phosphate dehydrogenase (G6PDH) it can be obtained of animal origin, vegetable or microbial, as in the case of the yeast Saccharomyces cerevisiae. This enzymes presents great importance for the cellular survival once it participates in the regulation of the cycle of the pentosys being responsible for the support of an appropriate level of NADPH in the cells. The deficiency of the glucose-6-phosphate dehydrogenase (G¨PDH) in human being the most important diagnosed enzymepatic is considered. The deficiency of this enzyme favors the rupture of the membrane of the red globules (hemacys or erythrocytes), taking to the hemolytic anemia. In this work, it was studies the conditions of extraction of the enzyme G6PDH by extraction on reserved micelles utilizing a anionic surfactant (AOT) and cationic surfactant (CTAB). Specific statical design for each analyzed system were used. The studied variables were: pH, concentration of the surfactant and temperature. It was studied, also, a microcolumn agitated by pulsed caps, due to promote an efficient contact between the phases in the column and also to avoid the enzyme denaturation and the loss of main proteins properties. The percentages of recovery of the enzyme of these system varied of 0 to 5,10% using AOT and of 0to 14,04% with CTAB. However, decrease was observed in the catalytic activity of the enzyme ...Note: The complete abstract is available with the full electronic digital thesis or dissertations / Doutorado / Sistemas de Processos Quimicos e Informatica / Doutor em Engenharia Química

Nematic liquid crystals are mesogenic materials that are popular working materials for optical displays. There has been an increased interest in bistable liquid crystal devices which support two optically distinct stable equilibria. These devices typically exploit a complex geometry or anchoring conditions, which often induces defects in the equilibria. There remains a great deal to be understood about the structure of the defects and how they stabilize multiple equilibria in modern devices. This thesis focuses on four problems: the first three explore the effect of confinement and defects on nematic equilibria in simple geometries, with the aim of exploring multistability in these geometries; the fourth problem concerns the fine structure of point defects, essential for future modelling of nematic equilibria in more complex geometries. Firstly, we study nematic liquid crystals confined to two-dimensional rectangular wells using the Oseen-Frank theory. Secondly, we study equilibria within a semi-infinite rectangular domain with weak tangential anchoring on the surfaces. Thirdly, we study nematic equilibria within two-dimensional annuli. We derive explicit expressions for the director fields and free energies of equilibria within these geometries and discuss the stability of the predicted states. These three problems are motivated by the experimental work on colloidal nematic liquid crystals, which we interpret in the context of our results. Finally, we study the fine structure and stability of the radial hedgehog defect in the Landau-de Gennes theory with a sixth order bulk potential, relevant to the observability of global biaxial phases in a model with higher order potential terms.