Dissertations / Theses on the topic 'Binary mixture'

Flammability is an important factor of safe practices for handling and storage of liquid mixtures and for the evaluation of the precise level of risk. Flash point is a major property used to determine the fire and explosion hazards of a liquid, and it is defined as the minimum temperature at which the vapor present over the liquid at equilibrium forms a flammable mixture when mixed with air. Experimental tests for the complete composition range of a mixture are time consuming, whereas a mixture flash point can be estimated using a computational method and available information. The information needed for mixture flash point predictions are flashpoints, vapor pressures, and activity coefficients as functions of temperature for each mixture component. Generally, sufficient experimental data are unavailable and other ways of determining the basic information are needed. A procedure to evaluate the flash point of binary mixtures is proposed, which provides techniques that can be used to estimate a parameter that is needed for binary mixture flash point evaluations. Minimum flash point behavior (MFPB) is exhibited when the flash point of the mixture is below the flash points of the individual components of the mixture. The identification of this behavior is critical, because a hazardous situation results from taking the lowest component flash point value as the mixture flash point. Flash point predictions were performed for 14 binary mixtures using various Gex models for the activity coefficients. Quantum chemical calculations and UNIFAC, a theoretical model that does not require experimental binary interaction parameters, are employed in the mixture flash point predictions, which are validated with experimental data. MFPB is successfully predicted using the UNIFAC model when there are insufficient vapor liquid data. The identification of inherent safety principles that can be applied to the flammability of binary liquid mixtures is also studied. The effect on the flash point values of three binary mixtures in which octane is the solute is investigated to apply the inherent safety concept.

Thesis (Ph.D. in Biostatistics) -- University of Colorado Denver, 2007.
Typescript. Includes bibliographical references (leaves 70-71). Free to UCD affiliates. Online version available via ProQuest Digital Dissertations;

Increasing concern about the rapid escalation of environmental pollution has led to strong legislation to ensure, for example, that the emission of pollutants from vehicles and industries is controlled to an acceptable level. As a consequence, there has been a rapid expansion of research into developing more efficient and low-cost gas monitoring systems. Currently, commercial solid-state atmospheric gas detection systems are based on one sensor for each gas, while research systems are an array of sensors for the detection of multiple gases. In this research, techniques are developed whereby more than one gas is detected using a single resistive gas sensor. A novel modulated temperature technique was used to enhance the selectivity of the resistive SnO2 gas sensor. Fast Fourier transforms was used to extract the Fourier coefficients. These in turn were used as input to neural networks for training and subsequently for prediction purposes. The result has shown that a single doped SnO2 resistive microsensor can be used to classify binary gas mixture in air. The research objectives have been fulfilled in that a novel way in detecting the components and the concentration level of a binary gas mixture was developed. Additionally, a low-cost low-power intelligent gas monitoring system was designed. This included the design of a novel temperature/thermometer circuit.

Model-H is used to describe structures found in the phase separation in films of binary liquid mixture that have a surface that is free to deform and also may energetically prefer one of the components. The film rests on a solid smooth substrate that has no preference for any component. On the one hand the study focuses on static aspects by investigating steady states that are characterised by their concentration and film height profiles. A large variety of such states are systematically analysed by numerically constructing bifurcation diagrams in dependence of a number of control parameters. The numerical method used is based on minimising the free energy functional at given constraints within a finite element method for a variable domain shape. The structure of the bifurcation diagrams is related to the symmetry properties of the individual solutions on the various branches. On the other hand the full time dependent model-H is linearised about selected steady states, in particular, the laterally invariant, i.e.\ layered states. The resulting dispersion relations are discussed and related to the corresponding bifurcation points of the steady states. In general, the results do well agree and confirm each other. The described analysis is performed for a number of important cases whose comparison allows us to gain an advanced understanding of the system behaviour: We distinguish the critical and off-critical case that correspond to zero and non-zero mean concentration, respectively. In the critical case the investigation focuses on (i) flat films without surface bias, (ii) flat films with surface bias, (iii) height-modulated films without surface bias, and (iv) height-modulated films with surface bias. Each case is analysed for several mean film heights and (if applicable) energetic bias at the free surface using the lateral domain size as main control parameter. Linear stability analyses of layered films and symmetry considerations are used to understand the structures of the determined bifurcation diagrams. For off-critical mixtures our study is more restricted. There we consider height-modulated films without and with surface bias for several mean film heights and (if applicable) energetic bias employing the mean concentration as main control parameter.

The temperature dependence of the refractive index and the density of aqueous binary mixtures of water and ethyl alcohol (C₂H₅OH) were measured by using a modified Michelson interferometer and a narrow glass capillary tube over the temperature range of 278≤T≤353 K for solutions of 100, 75,65, 50, 25, 10 and 0 volume percent ethyl alcohol. The temperature was cycled over both increasing and decreasing directions to explore hysteresis in the cycling. The data are discussed and compared with the Lorentz-Lorenz (LL) formula. A more accurate formula which fits the experimental data better than the LL relation was derived. An attempt was made to determine the nature of the solvent-solute interaction through any changes that were found in the refractive index for He-Ne laser light and IR diode signals and to analyze the refractive index and density results to test the accuracy of the available mixing rules in predicting the refractive index values and the density of binary systems. Conductivity measurements (d. c.) over the temperature range 278≤T≤353 K of aqueous solutions of NaCl at various concentrations were made and used to establish transport properties of ions in solution. The dynamical properties of the electrolytes were used to establish the nature of hydrogen bonding in aqueous binary mixture systems. Rate equations for ion formation and recombination were used to establish the temperature ranges in which hydrogen bonding dominated in forming polymeric species. From experimental data on the binary mixtures with water, a better understanding of water in its different functions and aggregation is possible. The water molecule itself and its response to the environment are understood when suitable studies are made of the forces in the system. In this work, some qualitative aspects of the interactions and dynamics of the water molecule have been investigated. Classical molecular dynamics simulations were tried to explain some of the thermodynamical properties of the water molecule.

The Drosophila larva is a suitable model to study olfaction due to its numerical simplicity. The peripheral olfactory system consists of just 21 pairs of olfactory sensory neurons (OSNs), each expressing one, or at most two classes of olfactory receptors (ORs) that define the receptive range of the OSN. Larvae produce robust behaviours to many odours and are easily genetically manipulated. Unlike audition, relatively little is known regarding olfaction due to its complex nature - most odours exist as multimolecular units that vary in their identity and structure, concentrations and proportions. Until recently, most olfactory research has focused on the processing of simple odours, which does not realistically model real-world odours. Presented here is one of the first in situ investigations of odour mixture processing in the Drosophila melanogaster larva. Processing of odour mixtures was explored using both electrophysiological recordings of the peripheral olfactory system and behavioural assays at the output of the system, and the effects of various factors on responses were also explored. w1118 larvae in which all OSNs were functional, and larvae with only a single class of OSN (using the Gal4-UAS expression system) were studied. At the peripheral level, mixture responses were never entirely transformed from the components, and were always as large as or greater than the response to the strongest component, and therefore the neuron was either 'seeing' just one or more than one of the components, respectively. Mixture responses across all OSNs were always additive, hypoadditive or partially suppressive, and there were no instances of synergistic or fully suppressive responses. Peripheral mixture responses were both OR- and component-dependent, as the same mixture was represented differently across OSNs. At the behavioural level, mixture responses were mostly additive, partially and fully suppressive and therefore not always predictable from the components. Interestingly, responses of larvae with only a single class of OSN were mostly predictable as there was no complexity of processing arising from the combinatorial code. When all OSNs were functional and the combinatorial code appropriately activated, mixture responses were more complex and unpredictable. Associative conditioning experiments revealed that larvae were unable to identify components from within a mixture, providing evidence that, at least at the behavioural level, mixture responses were probably synthetic, and therefore likely that interactions between the components occurred at some point along the processing pathway. Mixtures were often dominated by the component inducing the largest firing rate, and carbon chain length and vapour pressure influenced, to some degree, which component dominated. The nature of mixture responses were affected by concentration which is consistent with a model of receptor competition - at low concentrations mixture responses were additive, whilst at high concentrations responses were reduced compared to an additive response. In contrast, prior experience had little effect on peripheral responses to pure odours and mixtures, although rapid adaptation was observed during exposure. Exposure did have an effect on subsequent behavioural responses to pure odours and mixtures, providing evidence of central effects of adaptation. The data presented here provides evidence that mixture processing is extremely complex, with many factors influencing and affecting the way that the system responds to mixtures. This data reveals an unexpected complexity in a numerically simple system and with such'simple' complex odours, and indicates the likelihood of more complex responses when all OSNs are functional.

In this study, efforts ensued to increase our knowledge of fluidization and gasification behavior of Geldart A particles using CFD. An extensive Eulerian-Eulerian numerical study was executed and simulations were compared and validated with experiments conducted at Utah State University. In order to improve numerical predictions using an Eulerian-Eulerian model, drag models were assessed to determine if they were suitable for fine particles classified as Geldart A. The results proved that if static regions of mass in fluidized beds are neglected, most drag models work well with Geldart A particles. The most reliable drag model for both single and binary mixtures was proved to be the Gidaspow-blend model. In order to capture the overshoot of pressure in homogeneous fluidization regions, a new modeling technique was proposed that modified the definition of the critical velocity in the Ergun correlation. The new modeling technique showed promising results for predicting fluidization behavior of fine particles. The fluidization behavior of three different mixtures of coal and poplar wood were studied. Although results indicated good mixing characteristics for all mixtures, there was a tendency for better mixing with higher percentages of poplar wood. In this study, efforts continued to model co-gasification of coal and biomass. Comparing the coal gasification of large (Geldart B) and fine (Geldart A) particles showed that using finer particles had a pronounced effect on gas yields where CO mass fraction increased, although H2 and CH4 mass fraction slightly decreased. The gas yields of coal gasification with fine particles were also compared using three different gasification agents. Modeling the co-gasification of coal-switchgrass of both fine particles of Geldart A and larger particles of Geldart B showed that there is not a synergetic effect in terms of gas yields of H2 and CH4. The gas yields of CO, however, showed a significant increase during co-gasification. The effects of gasification temperature on gas yields were also investigated.
Ph. D.

Exfoliated graphite was used as a substrate for adsorption of argon and methane. Adsorption experiments were conducted for both equal parts mixtures of argon and methane and for each gas species independently. The purpose of this was to compare mixture adsorption to single component adsorption and to investigate theoretical predictions concerning the kinetics of adsorption made by Burde and Calbi.6 In particular, time to reach pressure equilibrium of a single dose at a constant temperature for the equal parts mixture was compared to time of adsorption for each species by itself. It was shown that mixture adsorption is a much more complex and time consuming process than single component adsorption and requires a much longer amount of time to reach equilibrium. Information about the composition evolution of the mixture during the times when pressure was going toward equilibrium was obtained using a quadrupole mass spectrometer. Evidence for initial higher rate of adsorption for the weaker binding energy species (argon) was found as well as overall composition change which clearly indicated a higher coverage of methane on the graphite sample by the time equilibration was reached. Effective specific surface area of graphite for both argon and methane was also determined using the Point-B method.2

The focus of this project is to find a suitable method to determine the mixing ratio inbinary fluid mixtures in continuous-flow microfluidic systems because of thedifficulties in doing so for mixtures containing compressible fluids. Refractive indexand relative static permittivity are both properties that could be suitable, but methodsmeasuring the refractive index scales badly for microsystems. A microfluidic chip for measuring capacitance was placed on a PCB together with amixing structure with strain-relieved fluid and electrical interfaces. This PCB was builtinto a rig with two piston pumps and a backpressure regulator to makemeasurements of the relative static permittivity of air, ethanol, methanol, acetonitrile,liquid and gaseous carbon dioxide, as well as of several mixtures of ethanol andcarbon dioxide using a Network Analyzer. Several other measuring techniques were tried, but the Network Analyzer wassuperior in accuracy, stability and frequency range. It produced values within 4% ofthe theoretical, and the discrepancy could be explained by the approximations in theparallel plate capacitor formula, the capacitance contributions of the external parts ofthe system and surface roughness. The Network Analyzer is a good tool to determinethe mixing ratio in binary fluid mixtures in continuous-flow microfluidic systems.

Detailed sensitivity numerical studies have shown that the mesh cell-size may have a drastic effect on the modelling of circulating fluidized bed with small particles. Typically, the cell-size must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Hence, the Euler-Euler numerical simulations of industrial processes are generally performed with grids too coarse to allow the prediction of the local segregation effects. Appropriate modelling, which takes into account the influence of unresolved structures, have been already proposed for monodisperse simulations. In this work, the influence of unresolved structures on a binary mixture of particles is investigated and models are proposed to account for those effect on bidisperse simulations of bidisperse gas-solid fluidized bed. To achieve this goal, Euler-Euler reference simulations are performed with grid refinement up to reach a mesh independent solution. Such kind of numerical simulation is very expensive and is restricted to very simple configurations. In this work, the configuration consists of a 3D periodical circulating fluidized bed, that could represent the established zone of an industrial circulating fluidized bed. In parallel, a filtered approach is developed where the unknown terms, called sub-grid contributions, appear. They correspond to the difference between filtered terms, which are calculated with the reference results then filtered, and resolved contributions, calculated with the filtered fields. Then spatial filters can be applied to reference simulation results to measure each sub-grid contribution appearing in the theoretical filtered approach. A budget analysis is carried out to understand and model the sub-grid term. The analysis of the filtered momentum equation shows that the resolved fluid-particle drag and inter-particle collision are overestimating the momentum transfer effects. The analysis of the budget of the filtered random kinetic energy shows that the resolved production by the mean shear and by the mean particle relative motion are underestimating the filtered ones. Functional models are proposed for the subgrid contributions of the drag and the inter-particle collision.

Master of Science
Department of Civil Engineering
Kyle Riding
Corrosion of reinforcing steel is one of the most common and serious causes of reinforced concrete deterioration. While corrosion is normally inhibited by a passive layer that develops around the reinforcing steel due to the high pH environment of the surrounding concrete, chlorides will break down this protective layer, leading to reinforcement corrosion. Decreasing the diffusivity of the concrete would slow the ingress of chlorides into concrete, and is one of the most economical ways to increase the concrete service life. Optimized concrete mixtures blending portland cement and supplementary cementing materials (SCMs) have become popular throughout the construction industry as a method of improving both fresh and long-term concrete properties such as workability, strength and porosity. It has been shown that use of Class F fly ash, silica fume and ground granulated blast furnace slag (GGBFS) in binary concrete mixture blends can result in a significant reduction in concrete diffusivity. This study investigates the ability of Class C fly ash and ternary concrete mixture blends to also aid in diffusivity reduction. In order to study the effect of incorporation of SCMs into concrete, mixtures containing Class C and Class F fly ash, silica fume and GGBFS were tested following the ASTM C 1556 procedures to measure the concrete’s apparent chloride diffusivity. Structure life cycles were modeled using the measured apparent chloride diffusivities with two finite-difference based life-cycle analysis software packages. To determine whether a correlation between diffusivity and deterioration due to freezing and thawing exists, samples were also tested for their ability to resist deterioration from freezing and thawing cycles using a modified ASTM C 666 Procedure B test. Results show that the use of Class C fly ash yields some service life improvements as compared to the portland cement control mixtures, while ternary mixture blends performed significantly better than the control mixture and equal to or better than the binary SCM mixtures tested. Freeze-thaw tests showed all mixtures to be equally resistant to deterioration due to freezing and thawing.

My dissertation is an investigation into the basic Physics of phase separation fronts. Such phase-separation fronts occur in many practical applications, like the formation of immersion precipitation membranes, Temperature induced phase-separation of polymeric blends, or the formation of steel. Despite the fact that these phenomena are ubiquitous no generally acceptable theory of phase-separation front exists. I believe the reason lies in the complexity of many of these material systems where a large number of physical effects (like phase-separation, crystallization, hydrodynamics, etc) cooperate to generate these structures. As a Physicist, I was driven to develop an understanding of these systems, and we choose to start our investigation with the simplest system that would incorporate a phase-separation front. So we initially limited our study to systems with a purely diffusive dynamics. The phase-separation front is induced by a control-parameter front that is a simple step function advancing with a prescribed velocity. We investigated these systems numerically using a lattice Boltzmann method and also investigated them analytically as much as possible. Starting from a one-dimensional front moving with a constant velocity we then extended the complexity of the systems by increasing the number of dimensions, examining a variable front velocity, and finally by including hydrodynamics.

This thesis, which contains fourteen chapters in two parts, presents theoretical and computer simulation studies of dynamics in supercooled liquids and thermotropic liquid crystals. These two apparently diverse physical systems are unified by a startling similarity in their complex slow dynamics. Part I consists of six chapters on supercooled liquids while Part II comprises seven chapters on thermotropic liquid crystals. The fourteenth chapter provides a concluding note. Part I starts with an introduction to supercooled liquids given in chapter 1. This chapter discusses basic features of supercooled liquids and the glass transition and portrays some of the theoretical frameworks and formalisms that are widely recognized to have contributed to our present understanding. Chapter 2 introduces a new model of binary mixture in order to study dynamics across the supercooled regime. The system consists of an equimolar mixture of the Lennard-Jones spheres and the Gay-Berne ellipsoids of revolution, and thus one of its components has orientational degrees of freedom (ODOF). A decoupling between trans-lational diffusion and rotational diffusion is found to occur below a temperature where the second rank orientational correlation time starts showing a steady deviation from the Arrhenius temperature behavior. At low temperatures, the optical Kerr effect (OKE) signal derived from the system shows a short-to-intermediate time power law decay with a very weak dependence on temperature, if at all, of the power law exponent as has been observed experimentally. At the lowest temperature investigated, jump motion is found to occur in both the translational and orientational degrees of freedom. Chapter 3 studies how the binary mixture, introduced in the previous chapter, explores its underlying potential energy landscape. The study reveals correlations between the decoupling phenomena, observed almost universally in supercooled molecular liquids, and the manner of exploration of the energy landscape of the system. A significant deviation from the Debye model of rotational diffusion in the dynamics of ODOF is found to begin at a temperature at which the average inherent structure energy of the system starts falling as the temperature decreases. Further, the coupling between rotational diffusion and translational diffusion breaks down at a still lower temperature, where a change occurs in the temperature dependence of the average inherent structure energy. Chapters 4-6 describe analytical and numerical approaches to solve kinetic models of glassy dynamics for various observables. The β process is modeled as a thermally activated event in a two-level system and the a process is described as a β relaxation mediated cooperative transition in a double-well. The model resembles a landscape picture, conceived by Stillinger [Science 267, 1935 (1995)], where the a process is assumed to involve a concerted series of the β processes, the latter being identified as elementary relaxations involving transitions between contiguous basins. For suitable choice of parameter values, the model could reproduce many of the experimentally observed features of anomalous heat capacity behavior during a temperature cycle through the glass transition as described in chapter 4. The overshoot of the heat capacity during the heating scan that marks the glass transition is found to be caused by a delayed energy relaxation. Chapter 5 shows that the model can also predict a frequency dependent heat capacity that reflects the two-step relaxation behavior. The high-frequency peak in the heat capacity spectra appears with considerably larger amplitude than the low-frequency peak, the latter being due to the a relaxation. The model, when simplified with a modified description of the a process that involves an irreversible escape from a metabasin, can be solved analytically for the relaxation time. This version of the model captures salient features of the structural relaxation in glassy systems as described in chapter 6. In Part II, thermotropic liquid crystals are studied in molecular dynamics simulations using primarily the family of the Gay-Berne model systems. To start with, chapter 7 provides a brief introduction to thermotropic liquid crystals, especially from the perspective of the issues discussed in the following chapters. This chapter ends up with a detail description of the family of the Gay-Berne models. Chapter 8 demonstrates that a model system for calamitic liquid crystal (comprising rod-like molecules) could capture the short-to-intermediate time power law decay in the OKE signal near the isotropic-nematic (I-N) phase transition as observed experimentally. The single-particle second rank orientational time correlation function (OTCF) for the model liquid crystalline system is also found to sustain a power law decay regime in the isotropic phase near the I-N transition. On transit across the I-N phase boundary, two power law decay regimes, separated by a plateau, emerge giving rise to a step-like feature in the single-particle second rank OTCF. When the time evolution of the rotational non-Gaussian parameter is monitored as a diagnostic of spatially heterogeneous dynamics, a dominant peak is found to appear following a shoulder at short times, signaling the growth of pseudonematic domains. These observations are compared with those relevant ones obtained for the supercooled binary mixture, as discussed in chapter 2, in the spirit of the analogy suggested recently by Fayer and coworkers [J. Chem. Phys. 118, 9303 (2003)]. In chapter 9, orientational dynamics across the I-N transition are investigated in a variety of model systems of thermotropic liquid crystals. A model discotic system that consists of disc-like molecules as well as a lattice system have been considered in the quest of a universal short-to-intermediate time power law decay in orientational relaxation, if any. A surprisingly general power law decay at short to intermediate times in orientational relaxation is observed in all these systems. While the power law decay of the OKE signal has been recently observed experimentally in calamitic systems near the I-N phase boundary and in the nematic phase by Fayer and coworkers [J. Chem. Phys. 116, 6339 (2002), J. Phys. Chem. B 109, 6514 (2005)], the prediction for the discotic system can be tested in experiments. Chapter 10 presents the energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals by determining the inherent structures of a family of one-component Gay-Berne model systems. This study throws light on the interplay between the orientational order and the translational order in the mesophases the systems exhibit. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures. The inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the I-N transition and this breakdown is found to occur at a temperature below which the system explores increasingly deeper potential energy minima. There exists a remarkable similarity in the manner of exploration of the potential energy landscape between the Gay-Berne systems studied here and the well known Kob-Andersen binary mixture reported previously [Nature, 393, 554 (1998)]. In search of a dynamical signature of the coupling between orientational order and translational order, anisotropic translational diffusion in the nematic phase has been investigated in the Gay-Berne model systems as described in chapter 11. The translational diffusion coefficient parallel to the director D// is found to first increase and then decrease as the temperature drops through the nematic phase. This reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. The non-monotonic temperature behavior of D// can thus be viewed from an energy landscape analysis as a dynamical signature of the coupling between orientational and translational order at the microscopic level. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion. Chapter 12 investigates the validity of the Debye model of rotational diffusion near the I-N phase boundary with a molecular dynamics simulation study of a Gay-Berne model system for calamitic liquid crystals. The Debye model is found to break down near the I-N phase transition. The breakdown, unlike the one observed in supercooled molecular liquids where a jump diffusion model is often invoked, is attributed to the growth of orientational pair correlation. A mode-coupling theory analysis is provided in support of the explanation. Chapter 13 presents a molecular dynamics study of a binary mixture of prolate ellipsoids of revolution with different aspect ratios interacting with each other through a generalized Gay-Berne potential. Such a study allows to investigate directly the aspect ratio dependence of the dynamical behavior. In the concluding note, chapter 14 starts with a brief summary of the outcome of the thesis and ends up with suggestion of a few relevant problems that may prove worthwhile to be addressed in future.

Orientadores: Júlio Roberto Bartoli, Marcos Akira D'Ávila
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: O presente trabalho estudou a preparação e caracterização de híbridos de polímero-argila, tendo a poli(acrilonitrila-butadieno-estireno) (ABS) como matriz polimérica e duas argilas montmorilonitas organofílicas (MMTO) distintas e sua mistura binária 1:1 como fases dispersas. O objetivo foi avaliar os efeitos das variáveis: tipo de argila e processo nas propriedades físicas dos híbridos de ABS/MMTO. A seleção das argilas MMTO comerciais (Cloisite 30B e Cloisite 20A) baseou-se nas possíveis afinidades químicas de cada uma delas com as distintas fases do terpolímero ABS. Na preparação dos híbridos através do processo de intercalação no estado fundido, em extrusora com rosca-dupla co-rotacional, foi investigado o efeito do torque da rosca (ou tempo de residência na extrusora), na dispersão das argilas na matriz ABS. Os compostos obtidos foram caracterizados através de análises de difração de raios-X, termogravimetria, ensaios de tração uniaxial e resistência ao impacto, flamabilidade e análises reológicas do fundido em regime permanente e oscilatório em altas e baixas taxas de cisalhamento. A difração de raios-X indicou que os híbridos obtidos apresentavam estruturas intercaladas, que proporcionaram aumento nos módulos de elasticidade por tração e por cisalhamento (armazenamento e perda). As análises reológicas dos híbridos ABS mostram o surgimento de um caráter pseudo-sólido, em especial para os híbridos contendo a MMTO com maior afinidade química (Cloisite 30B) à fase SAN do terpolímero. Este comportamento indicaria uma provável dispersão em escala nanométrica da Cloisite 30B nos híbridos ABS, seja como único componente na fase dispersa ou na sua mistura binária com a Cloisite 20A. Este resultado caracterizaria os materiais obtidos como nanocompósitos. Melhorias significativas nas propriedades mecânicas de tração também foram verificadas nos híbridos a base de Cloisite 30B. Já os ensaios de rigidez ao impacto e as análises de estabilidade térmica não apresentaram resultados satisfatórios. Entretanto a adição de MMTO eliminou o gotejamento de material incandescente apresentado pelo ABS durante a queima (norma UL 94 HB). A utilização de um menor torque na rosca, ou seja, maior tempo de residência dos híbridos na extrusora, parece favorecer a dispersão/intercalação das argilas na matriz de ABS. Entretanto, o efeito deste fator foi confundido com variações na concentração nominal de argila
Abstract: This work studied the preparation and characterization of hybrids of polymer-clay, where the polymeric matrix was the poly(acrylonitrile-butadiene-styrene) (ABS) and two different organically modified montmorillonite (OMMT) and their mixture (1:1) were used as dispersed phase. The aim was evaluate the effect of kind of clay and process parameters on physical properties of ABS/OMMT hybrids. Two grades of commercial OMMT organoclay (Cloisite 20A and Cloisite 30B) were investigated, with distinct chemical affinities according to terpolymer phases, and a binary mixture of these clays. The hybrids were prepared by melt intercalation process, on a co-rotating twin-screw extruder, the effect of screw torque (or residence time on extruder) on clay dispersion in the polymeric matrix was investigated. The hybrids were characterized by analysis of X-ray diffraction, thermogravimetry, mechanical properties (uniaxial tensile and impact strength), flammability, and rheological analysis in steady and oscillatory states, at high and low shear rates. The X-ray diffractions indicated that the ABS hybrids present an intercalated structure, which improved the tensile elastic modulus and shear modulus (storage and loss). The rheological analysis of ABS hybrids shows the emergence of a pseudo-solid character, especially to the hybrids containing the OMMT with higher chemical affinity (Cloisite 30B) to SAN phase of the terpolymer. This behavior would indicate a probable nanometric scale dispersion of the Cloisite 30B on the hybrids of ABS, even in the single form or in a binary mixture, likely characterizing them as nanocomposites. Significant improvements in the tensile mechanical properties were also verified on the hybrids based on Cloisite 30B. Nevertheless the impact strength and thermal stability analysis did not show satisfactory results. The flammability test (UL 94 HB standard) of ABS hybrids showed a non-dripping effect of incandescent material during burning. The use of a lower screw torque, higher residence time of the hybrids on extruder, seems to favor clay dispersion/intercalation on the ABS matrix, however, the effect of this factor was confounded with some variations in the organoclay nominal content
Mestrado
Ciencia e Tecnologia de Materiais
Mestre em Engenharia Química

Orientadores: Julio Roberto Bartoli, Humberto Gracher Riella
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Este trabalho apresenta um estudo sobre a relação entre estrutura e propriedades de híbridos de montmorilonitas organicamente modificadas (MMTO) e terpolímero de acrilonitrila-butadieno-estireno (ABS), compatibilizados com o copolímero de estirenoetileno- butadieno-estireno (SEBS) ou de estireno-butadieno-estireno (SBS) preparados via intercalação no estado fundido em extrusora de rosca-dupla. Quatro formulações de híbridos foram propostas segundo um planejamento fatorial de experimentos 22 para estudar o efeito dos fatores compatibilizante (SEBS e SBS) e composição da MMTO (Cloisite 30B e mistura Cloisite 30B+Cloisite 20A (1:1)). A mistura binária de argilas foi proposta para verificar a viabilidade em balancear o caráter hidrofílico e hidrofóbico dos surfactantes destes dois tipos de argilas. As etapas de processamento foram: 1) Preparação de quatro concentrados na proporção mássica de 49,5: 40: 10: 0,5 de ABS/argila/compatibilizante/antioxidante em misturador interno; 2) Diluição para 4% em massa de MMTO; 3) extrusão do composto; 4) Granulação em moinho e moldagem por injeção dos corpos de prova. O efeito destes fatores e suas interações foram avaliados através de análises de difração de raios-X (DRX), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), termogravimetria (TGA), calorimetria diferencial de varredura (DSC), ensaios de tração uniaxial, resistência ao impacto, flamabilidade e análises reológicas do fundido em regime permanente e oscilatório em altas e baixas taxas de cisalhamento. As análises de DRX e de MET indicaram que os híbridos apresentaram estruturas intercaladas (ABS/20A30B/SEBS) e parcialmente esfoliadas (ABS/30B/SBS), essencialmente na fase SAN dos híbridos. As análises por MEV mostraram morfologias distintas da superfície de fratura na tração para os híbridos com SBS e SEBS sendo o SEBS caracterizado por uma fratura dúctil. As análises reológicas dos híbridos mostraram o surgimento de um caráter pseudo-sólido, com aumento significativo nos módulos de armazenamento e na viscosidade complexa, em especial para os híbridos com SBS. Este comportamento revela uma provável dispersão em escala nanométrica das argilas nos híbridos ABS, seja na forma simples ou mistura binária de MMTO. A resistência ao impacto, de todos os híbridos, foi significativamente reduzida devido às micro ou nano partículas de argila que podem atuar como defeitos aumentando aconcentração das tensões localizadas. Melhorias significativas nas propriedades mecânicas de tração quanto ao módulo de elasticidade foram verificadas nos híbridos com SBS em relação ao ABS de referência, por sua vez os híbridos com SEBS mostraram um expressivo comportamento dúctil. No ensaio de flamabilidade na horizontal (norma UL 94 HB) verificou-se uma supressão do gotejamento de material incandescente durante a queima dos híbridos contendo SBS, gotejamento observado nos híbridos com SEBS e no ABS de referência, este comportamento favorável é provavelmente devido à viscosidade do híbrido fundido SBS ser o dobro do SEBS. O estudo da cinética de degradação termo-oxidativa dos híbridos mostrou que a energia de ativação dos híbridos compatibilizados com SEBS é significativamente maior do que os híbridos com SBS, provavelmente devido à hidrogenação do butadieno no SEBS que melhora a sua estabilidade térmica. O grau de dispersão obtido pelas argilas permite designar estes híbridos como nanocompósitos de ABS
Abstract: The present work, shows a study about the relationship between structure and properties of hybrids of organically modified montmorillonites (MMTO) and terpolymer of acrylonitrile-butadiene-styrene (ABS), compatibilized with styrene-ethylene-butadienestyrene (SEBS) or styrene-butadiene-styrene (SBS) prepared by melt blending process. Four formulations of hybrids were proposed in a 22 factorial design of experiments to study the effect of factors compatibilizer (SEBS and SBS) and composition of OMMT (Cloisite 30B and Cloisite 30B + Cloisite 20A mixture (1:1)). The binary mixture of clay was proposed to verify the feasibility of balancing the hydrophobic and hydrophilic character of surfactants these two types of clays. The processing steps were: 1) Preparation of four masterbatches in mass ratio of 49,5: 40: 10:0,5 of ABS/clay/compatibilizer/antioxidant in an internal mixer; 2) Dilution to 4% by weight of OMMT; 3) Extrusion of the compound; 4) Granulation in mill and injection molding of test specimens. The effect of these factors and their interactions were evaluated through analysis of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry (TGA), differential scanning calorimetry (DSC), uniaxial tensile tests, impact strength, flammability and rheological analysis at high and low shear rates. The analyses of XRD and TEM showed that hybrids had structures intercaled (ABS/20A30B/SEBS) and partially exfoliated (ABS/30B/SBS) essentially in the SAN phase of the hybrids. The analyses by SEM showed different morphologies of the fracture surface in tensile for hybrids with SBS and SEBS, being the SEBS characterized by a ductile fracture. The analyses rheological of hybrids showed the appearance of a pseudo-solid behavior, with a significant increase in storage modulus and complex viscosity, in particular for hybrids with SBS. This behavior reveals a probable dispersion in nano scale of clays in hybrids ABS, either as single or binary mixture of MMTO. The impact strength of all hybrids were significantly reduced due to micro or nano clay particles that can act as defects increasing the concentration of localized stresses. The mechanical properties showed positive results of tensile as so elastic modulus observed in hybrids with SBS in relation to pristine ABS, while hybrids with SEBS showed a significant ductile behavior. In horizontal flammability test (UL 94 HB) verified a suppression of dripping of incandescent material during the burning of hybrids containing SBS, drip observed in hybrids with SEBS and pristine ABS reference, this behavior is probably due to the viscosity of hybrid melted SBS be the double of SEBS. The study of the kinetics of thermo-oxidative degradation of hybrids showed that the activation energy of the hybrid compatibilized with SEBS is significantly greater than the hybrids with SBS, probably due to hydrogenation of the butadiene on SEBS which improves their thermal stability. The degree of dispersion obtained by clays allows to designate these hybrids how nanocomposites ABS
Mestrado
Ciencia e Tecnologia de Materiais
Mestre em Engenharia Química

This thesis, which contains fourteen chapters in two parts, presents theoretical and computer simulation studies of dynamics in supercooled liquids and thermotropic liquid crystals. These two apparently diverse physical systems are unified by a startling similarity in their complex slow dynamics. Part I consists of six chapters on supercooled liquids while Part II comprises seven chapters on thermotropic liquid crystals. The fourteenth chapter provides a concluding note. Part I starts with an introduction to supercooled liquids given in chapter 1. This chapter discusses basic features of supercooled liquids and the glass transition and portrays some of the theoretical frameworks and formalisms that are widely recognized to have contributed to our present understanding. Chapter 2 introduces a new model of binary mixture in order to study dynamics across the supercooled regime. The system consists of an equimolar mixture of the Lennard-Jones spheres and the Gay-Berne ellipsoids of revolution, and thus one of its components has orientational degrees of freedom (ODOF). A decoupling between trans-lational diffusion and rotational diffusion is found to occur below a temperature where the second rank orientational correlation time starts showing a steady deviation from the Arrhenius temperature behavior. At low temperatures, the optical Kerr effect (OKE) signal derived from the system shows a short-to-intermediate time power law decay with a very weak dependence on temperature, if at all, of the power law exponent as has been observed experimentally. At the lowest temperature investigated, jump motion is found to occur in both the translational and orientational degrees of freedom. Chapter 3 studies how the binary mixture, introduced in the previous chapter, explores its underlying potential energy landscape. The study reveals correlations between the decoupling phenomena, observed almost universally in supercooled molecular liquids, and the manner of exploration of the energy landscape of the system. A significant deviation from the Debye model of rotational diffusion in the dynamics of ODOF is found to begin at a temperature at which the average inherent structure energy of the system starts falling as the temperature decreases. Further, the coupling between rotational diffusion and translational diffusion breaks down at a still lower temperature, where a change occurs in the temperature dependence of the average inherent structure energy. Chapters 4-6 describe analytical and numerical approaches to solve kinetic models of glassy dynamics for various observables. The β process is modeled as a thermally activated event in a two-level system and the a process is described as a β relaxation mediated cooperative transition in a double-well. The model resembles a landscape picture, conceived by Stillinger [Science 267, 1935 (1995)], where the a process is assumed to involve a concerted series of the β processes, the latter being identified as elementary relaxations involving transitions between contiguous basins. For suitable choice of parameter values, the model could reproduce many of the experimentally observed features of anomalous heat capacity behavior during a temperature cycle through the glass transition as described in chapter 4. The overshoot of the heat capacity during the heating scan that marks the glass transition is found to be caused by a delayed energy relaxation. Chapter 5 shows that the model can also predict a frequency dependent heat capacity that reflects the two-step relaxation behavior. The high-frequency peak in the heat capacity spectra appears with considerably larger amplitude than the low-frequency peak, the latter being due to the a relaxation. The model, when simplified with a modified description of the a process that involves an irreversible escape from a metabasin, can be solved analytically for the relaxation time. This version of the model captures salient features of the structural relaxation in glassy systems as described in chapter 6. In Part II, thermotropic liquid crystals are studied in molecular dynamics simulations using primarily the family of the Gay-Berne model systems. To start with, chapter 7 provides a brief introduction to thermotropic liquid crystals, especially from the perspective of the issues discussed in the following chapters. This chapter ends up with a detail description of the family of the Gay-Berne models. Chapter 8 demonstrates that a model system for calamitic liquid crystal (comprising rod-like molecules) could capture the short-to-intermediate time power law decay in the OKE signal near the isotropic-nematic (I-N) phase transition as observed experimentally. The single-particle second rank orientational time correlation function (OTCF) for the model liquid crystalline system is also found to sustain a power law decay regime in the isotropic phase near the I-N transition. On transit across the I-N phase boundary, two power law decay regimes, separated by a plateau, emerge giving rise to a step-like feature in the single-particle second rank OTCF. When the time evolution of the rotational non-Gaussian parameter is monitored as a diagnostic of spatially heterogeneous dynamics, a dominant peak is found to appear following a shoulder at short times, signaling the growth of pseudonematic domains. These observations are compared with those relevant ones obtained for the supercooled binary mixture, as discussed in chapter 2, in the spirit of the analogy suggested recently by Fayer and coworkers [J. Chem. Phys. 118, 9303 (2003)]. In chapter 9, orientational dynamics across the I-N transition are investigated in a variety of model systems of thermotropic liquid crystals. A model discotic system that consists of disc-like molecules as well as a lattice system have been considered in the quest of a universal short-to-intermediate time power law decay in orientational relaxation, if any. A surprisingly general power law decay at short to intermediate times in orientational relaxation is observed in all these systems. While the power law decay of the OKE signal has been recently observed experimentally in calamitic systems near the I-N phase boundary and in the nematic phase by Fayer and coworkers [J. Chem. Phys. 116, 6339 (2002), J. Phys. Chem. B 109, 6514 (2005)], the prediction for the discotic system can be tested in experiments. Chapter 10 presents the energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals by determining the inherent structures of a family of one-component Gay-Berne model systems. This study throws light on the interplay between the orientational order and the translational order in the mesophases the systems exhibit. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures. The inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the I-N transition and this breakdown is found to occur at a temperature below which the system explores increasingly deeper potential energy minima. There exists a remarkable similarity in the manner of exploration of the potential energy landscape between the Gay-Berne systems studied here and the well known Kob-Andersen binary mixture reported previously [Nature, 393, 554 (1998)]. In search of a dynamical signature of the coupling between orientational order and translational order, anisotropic translational diffusion in the nematic phase has been investigated in the Gay-Berne model systems as described in chapter 11. The translational diffusion coefficient parallel to the director D// is found to first increase and then decrease as the temperature drops through the nematic phase. This reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. The non-monotonic temperature behavior of D// can thus be viewed from an energy landscape analysis as a dynamical signature of the coupling between orientational and translational order at the microscopic level. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion. Chapter 12 investigates the validity of the Debye model of rotational diffusion near the I-N phase boundary with a molecular dynamics simulation study of a Gay-Berne model system for calamitic liquid crystals. The Debye model is found to break down near the I-N phase transition. The breakdown, unlike the one observed in supercooled molecular liquids where a jump diffusion model is often invoked, is attributed to the growth of orientational pair correlation. A mode-coupling theory analysis is provided in support of the explanation. Chapter 13 presents a molecular dynamics study of a binary mixture of prolate ellipsoids of revolution with different aspect ratios interacting with each other through a generalized Gay-Berne potential. Such a study allows to investigate directly the aspect ratio dependence of the dynamical behavior. In the concluding note, chapter 14 starts with a brief summary of the outcome of the thesis and ends up with suggestion of a few relevant problems that may prove worthwhile to be addressed in future.

In this study, a two phase investigation of the hydraulic conductivity parameters of silty soils was performed. In the first phase, double-ring infiltrometer tests were used to measure infiltration rates in-situ at two sites in the Piedmont physiographic province of Georgia. The efficacy of predicting saturated hydraulic conductivity for Piedmont soils via published soil surveys from the National Resource Conservation Service and pedotransfer functions was then investigated. Work focused on the development of a consistent test methodology for soils (sandy, to silts and clays) in the Piedmont, and the final test method utilized being the constant head test, using a double-ring infiltrometer with Mariotte tubes to maintain the head. In the second phase of the investigation, laboratory based measurements of the saturated hydraulic conductivity of binary mixtures of fine sand and nonplastic silt were performed to investigate the effects of particle mixtures on hydraulic conductivity. The materials used were ASTM 100/200 sand and Sil-Co-Sil 40 non-plastic silt, chosen based on the ratio of the mean particle diameters. Significant effort was invested in the development and comparison of methodologies to produce uniform specimens of the binary mixtures for hydraulic conductivity testing, with the final being modified dry tubing. Two fixed densities were used to investigate the effects of particle packing on the hydraulic conductivity of binary mixtures, with critical fines contents chosen to ensure the finer particles primarily filled the pore volume of the coarse particles. Incremental fines contents, by mass, up to this theoretical fines content were tested. The measured saturated hydraulic conductivity was evaluated in terms of fines content, global and intergranular void ratio, and confining stress. Models for predicting extreme void ratios and saturated hydraulic conductivity of binary mixtures were also investigated.

Biomass energy is increasingly used to reduce the dependence on fossil fuels and reduce the impact of greenhouse gas emissions on global warming. Fluidized bed gasification converts solid biomass into gaseous fuels that can be used for combustion or liquid fuels synthesis. The efficiency of biomass gasification is directly affected by the fluidized bed hydrodynamics. For example, the solids recirculation rate through the system is an important parameter that affects the heat and mass transfer rates. In this study, a cold model of a dual fluidized bed (DFB) biomass gasification plant was designed using scaling laws, and was constructed to investigate the hydrodynamics of industrial DFBs. A DFB consists of a bubbling fluidized bed (BFB), where biomass is gasified to produce syngas, and a circulating fluidized bed (CFB) where the residues of gasification are combusted. The investigation was divided into Phase I and II. In Phase I, an operational map was developed for the CFB to define operational boundaries for steady state operation of the plant. An empirical model was developed to predict the solids mass flow rate out of the CFB riser, which is an empirical function of the exit opening width, the CFB diameter, and a newly introduced aerodynamic factor. The correlation coefficient, R2 for the empirical function was 0.8327. The aerodynamic factor accounts for the particle inertia and clustering effects at the exit of the CFB riser. Results from Phase I also showed that increasing the fluidizing velocities increased the solids circulation rate and affected the pressure drop over various points in the CFB plant due to redistribution of solids with the system. A critical assessment was performed on published correlations found in the literature to determine how accurately they predicted the hydrodynamics in the CFB riser. By comparing predicted and experimental results, the correlations were found to be inaccurate for the conditions and configuration of the CFB tested in this study. For example, the solids velocity was not accurately predicted by published correlations due to unaccounted particle clustering effects. The main issue with the published correlations was a lack of generality, so that the correlations only applied for predicting fluidizing behaviour in the equipment they were developed in. In Phase II, an operational map was developed for the DFB, which incorporated both the CFB and the BFB. Experiments with a binary mixture representing sand and char in an industrial gasifier showed a blocking effect in the connecting chute between the CFB and BFB by the material representing char, which was larger and less dense than the material representing sand. A computational fluid dynamics (CFD) based design tool for modelling the cold model CFB cyclone was developed and validated by comparing the predicted and experimental cyclone pressure drop. The correlation coefficient for the CFD pressure drop prediction was 0.7755. The design tool contained information about the grid resolution and the time step required for modelling the cyclone accurately.

The photocatalytic oxidation of trichloroethylene (TCE), ethylene. ethane and toluene on TiO2, Pt/TiO2 and Ag/TiO2 were investigated in a dedicated reactor set-up operated at room temperature and ambient pressure condition. The gas phase experiments were carried out for both single and binary mixtures of these chemicals to identify the role of Pt and Ag metallisation in the photocatalytic oxidation of different contaminants. In a single contaminant system, the presence of Pt enhanced the oxidation of ethylene, ethane and toluene but detrimental to the oxidation of TCE. In the oxidation of ethylene, Pt enhanced the oxidation by acting as catalyst and as electron sink. However, in ethane oxidation, the enhancement was solely associated to the ability of Pt to act as electron sink. The detrimental effect observed in TCE oxidation was attributed to Pt and Cl interaction, which formed a persistent inorganic chlorine species decreasing the overall Pt/TiO2 photocatalyst performance. Interestingly, Ag did not show any significant effect to the oxidation of any single system degradation. In binary system degradation, where TCE and another organic compound either ethylene, ethane or toluene were degraded simultaneously, Pt always caused a detrimental effect due to its strong interaction with Cl. However, the presence of Ag and Cl gives a more synergetic effect. Ag was found to provide sites to temporarily trap chlorine radicals as AgCl. Under illumination, electrons transferred from Cl to Ag forming chlorine radicals that could react with the surface contaminant enhancing its breakdown and mineralization.

碩士
中原大學
化學工程研究所
97
In the presence of electric field, two commercial nanofiltration membranes, DL and NF-270, were used to separate the binary salt mixture, solution and solution. Parameters such as Donnan potential, pore radius and reflection coefficient were used to analyze the performance of filtrating two salts mixture solution, solution and solution. The results of rejection of these two mixture solutions agree with the Donnan potential. Higher Donnan potential means higher exclusion to ions from membrane. Membrane in solution has higher Donnan potential than in solution. Also, better performances of rejection in every ion of solution than solution are observed. In addition, both membranes appears the same results. Results of Electro-Nanofiltration show that the rejections of cation are lower under the addition of electric field into the process. This is caused by the ionic mobility of cation in the direction toward the permeate side. On the other hand, there was higher rejection of anions by the force toward feed side from the application of electric field. In separation of single valence with positive and negative ion, rejection of anion raise with stronger electric field, in the meanwhile rejection of cation decrease sharply. So heighten electric field will separate positive and negative single valence ions well. In separation of the same positive or negative ions but different valence, the weaker electric field is needed. Different separation performances of same ion between in single and binary salt mixture are observed. Heighten the strength of electric field is able to eliminate this difference, and ion rejections will reach almost 90%.

博士
國立中興大學
物理學系所
97
This report discusses the behavior of the intruded particles in a group of background particles which are agitated by external force. The intruded particles population is minority and have larger size than the background particles and also different in mass. The main researches for the last 30 years mostly focused on systems in which the vibrated direction is parallel to gravitational field. Some reports found the so called Brazil Nut Effect(BNE) [32] that the larger particles always accumulate on the top layer after agitation.And also the larger particles may sink to bottom (Reverse BNE) [41] if the size ratio and mass ratio are selected appropriately. By the Molecular dynamics (MD) simulation, this report found the similar phenomenon of BNE in the 2 dimensional granular systems in the absence from gravitational field. The intruder in the system migrates either to the center or the edge of the cluster of the background particles. Since this system has negligible influence by gravity and the interstitial fluid, it may be an easier and important way to understand the mechanisms of particles segregation. Furthermore, it can be approximately realized by horizontal shaken experiment in gravitational field. With the aids of simulation and experiment, this report suggests a mechanism for migration of an intruder in the shaking granular bed. The mechanism suggests that the migration of the intruder is due to the competition between the collision frequency and the inertia of the intruder. Since the collision frequency and the inertia is proportional to the size and the mass respectively, that explain why the size ratio and mass ratio become the main control parameters in particles migration. This mechanism also explains well the results in the system shaken in two dimensions.

A model describing the one-dimensional heat transfer and solute redistribution during a planar solidification of a binary mixture in a finite medium, insulated and nonpermeable at one boundary, and subject to thermal boundary conditions of the first, second, third and fourth kind at the other boundary is developed. The temperature and concentration fields were obtained by both, approximate analytical and numerical techniques. Approximate analytical solutions consist of using a modified Karman-Pohlhausen integral technique and Biot's variational method (only for the first domain of the temperature field in the liquid domain). An implicit finite difference method was employed to obtain the temperature and concentration fields numerically. The Mullins-Sekerka stability criterion was used to analyze the stability of the planar interface. The results indicate that the solute concentration at the interface is not constant but increases with time due to increased solute rejection from the ice matrix as the nonpermeable wall slows the interface motion, and the fusion temperature will be depressed because of the solute build-up at the interface. Application of the stability criterion to the freezing of saline water indicates that almost for any practical freezing rate the planar interface was unstable. This represents an indictment of the planar freezing model and indicates the tendency for aqueous solutions to freeze dendritically. It was found that for lower initial solute concentrations and/or heat fluxes, the instability will be reached in longer times.

碩士
國立臺灣科技大學
機械工程系
94
In this study, flow boiling of 2-propanol/water and ethanol/heptane mixtures in microdiffuser is investigated under isothermal heating condition. The mole fractions of 2-propanol in water tested are 0 (pure water), 0.015, 0.1, 0.3, 0.5, 0.69 (azeotropic point), 0.9, and 1 (pure 2-propanol). The mole fractions of ethanol in heptane tested are 0 (pure heptane), 0.1, 0.3, 0.64 (azeotropic point), 0.9, and 1 (pure ethanol). The half angle of the microdiffuser is 25o, while the inlet width, depth, and length are 60 �慆, 200 �慆, and 1200 �慆, respectively. A syringe pump is used to deliver the mixtures and the flow rates are set to 0.03 ml/min and 0.09 ml/min. There are three boiling regime identified: slug flow, annular flow, and mist flow. In 2-propanol/water mixture, slug flow regime is observed at mole fraction x ≤ 0.3 and the zone of slug regime are diminished as the mole fraction increases. In ethanol/heptane mixture, slug flow regime is not observed in microdiffuser because of smaller surface tension. In 2-propanol/water mixture, the vapor eruption is observed at the start of boiling and mist eruption is observed at annular flow/mist flow transition as the flow rate rises. At fixed flow rate, the pressure in the microdiffuser initially decreased with temperature because of the changing fluid properties, and then the pressure will sharply rise as phase changing begins. In 2-propanol/water with single phase flow, when mole fraction x < 0.3, the pressure rises with mole fraction increasing. When mole fraction x > 0.3, the pressure reduces with mole fraction increasing. In ethanol/hptane with single phase flow, the pressure rises with mole fraction increasing. The void fraction could be estimated by experimental results. Using Martinelli parameter calculates two phase frictional multiplier. The results show that the deceleration pressure drop in microdiffuser do not make influence to total pressure. In micro scale, the frictional pressure drop dominates the total pressure in microdiffuser.

Tese de mestrado em Física (Física Estatística e Matéria Condensada), Universidade de Lisboa, Faculdade de Ciências, 2020
Fenómenos de sincronização estão presentes em muitos sistemas naturais e artificiais, e são o fenómeno chave no estudo de alguns destes sistemas. E possível observar fenómenos de sincronização em ecologia, por exemplo nas oscilações de presa e predador; na etologia com a sincronização de coros de sapos e do piscar de pirilampos; na fisiologia, na sincronização de ritmos biológicos, como o ciclo circadiano e alguns ciclos hormonais; na matéria condensada, na sincronização de osciladores de spin Hall; e em tantos outros sistemas. A compreensão de fenómenos de sincronização, e o estudo de modelos de sincronização são, portanto, campos bastante ativos atualmente. Estabelecemos um modelo de trabalho para estudar o fenómeno de sincronização. Primeiro estudamos o modelo de Kuramoto, um modelo usado para estudar sincronização desde 1975. Este modelo consiste num sistema de equações diferencias, não lineares e autónomas, que regem a evolução da fase de cada oscilador que modelam. Kuramoto introduziu alguns resultados analíticos sobre o modelo e desde então ele tem sido cada vez mais usado e novas técnicas foram desenvolvidas. A outra base do nosso modelo de trabalho são as partículas brownianas, ou seja, partículas que por estarem imersas num fluído têm um movimento aleatório dentro dele. O estudo das partículas Brownianas também já tem muita história existindo uma grande quantidade de resultados teóricos e experimentais sobre elas. Usamos alguns dos resultados teóricos mais conhecidos para validarmos o código que usamos para este trabalho. Neste trabalho utilizamos o LAMMPS, uma biblioteca em C++ para desenvolver algoritmos de dinâmica molecular e modelos coarse-grained. e tivemos que implementar de raiz a interação de Kuramoto para as nossas partículas. Esta biblioteca permite realizar simulações moleculares em paralelo e o nosso código passou em todos os testes teoricos. O nosso objectivo era estudar como se dava a sincronização de uma mistura de osciladores, que interagiam com os seus vizinhos e que se deslocavam no espaço como partículas Brownianas. Assim, modificamos o modelo de Kuramoto para aplicá-lo a uma mistura binária de partículas Brownianas. A interação de sincronização dessa mistura binária pode ser modelada de várias maneiras e estudamos dois modelos diferentes. No Modelo I, dividimos os osciladores em dois grupos onde partículas semelhantes tinham uma constante de acoplamento positiva, o que leva a que a fase desses osciladores evolua para que fiquem com uma diferença de fase de 0. Se os osciladores fossem de dois tipos diferentes as partículas tinham uma constante de acoplamento negativa, o que conduz a uma diferença de fase de π. Chamamos a este modelo o modelo de osciladores repulsivos visto que os osciladores de tipos diferentes tendem a ficar com a fase desfasada por π. Estávamos interessados em controlar a sincronização e em saber se era possível acelerá-la, retardá-la ou até mesmo impedi-la. Para isso estudamos neste modelo o papel de diferentes constantes de acoplamento, de diferentes percentagens para a mistura de osciladores, de diferentes densidades do sistema de osciladores, e verificamos que apesar de ser impossível impedi-la é possível acelerá-la e retardá-la. O Modelo II consiste numa mistura de osciladores onde um tipo de oscilador possui uma constante de acoplamento negativa em todas as suas interações, sendo estes denominados osciladores “contrariados”, ˜ e o outro tipo possui acoplamento positivo com osciladores semelhantes e acoplamento negativo com o outro tipo. Com este modelo foi possível impedir a sincronização de partículas e estudamos o efeito da quantidade de osciladores contrariados e também o papel da constante de acoplamento negativo. Este resultado é interessante devido às possíveis aplicações em situações onde a sincronização é um fenómeno indesejado, como a sincronização do disparo dos neurónios num paciente com epilepsia ou Parkinson. Estendemos ainda ambas as modificações ao modelo de Kuramoto para partículas brownianas ativas, de forma semelhante ao modelo contínuo de Vicsek, para conectar este modelo a alguns fenómenos que podem ser observados na natureza. O modelo de Vicsek foi extensamente usado na caracterização de fenómenos de deslocação colectivos. Com ele é possível explicar e prever as trajetórias observadas nos voos de conjuntos de pássaros ou no deslocamento de cardumes. O uso do modelo de Kuramoto como interação entre as partículas ativas permitiu observar alguns dos fenómenos previstos por Vicsek, como os engarrafamentos, onde as colisões das partículas geram aglomerados, e permitiu nos colocar questões sobre possíveis trabalhos próximos. Foi possível observar que a velocidade de propulsão das partículas contribui para o processo de sincronização, confirmando a importância da capacidade de mistura entre os osciladores para que a sincronização se processe mais rápido.
Synchronization phenomena have been studied for a long time and are present in many natural and artificial systems. They are the key phenomena in areas like biology, neurosciences and condensed matter physics. In our work we try to understand the synchronization behaviour of a binary mixture of moving oscillators. We established a working framework to model synchronization phenomena, implementing the Kuramoto model and with this framework we confirmed some of the theoretical results of this theory. We used a computational library to perform Langevin dynamics and then modified the Kuramoto model to apply it to a binary mixture of Brownian particles. The synchronization interaction of this binary mixture can be modeled in numerous ways, thus we studied two different models. In Model I we split our oscillators into two groups where similar particles had a positive coupling constant, which lead them to phase lock with phase difference 0, and two different particles had a negative coupling constant, which lead them to phase lock with a phase difference of π. Model II consists of a mixture of oscillators where one type of oscillators has a negative coupling constant in all its interactions, these being called contrarian oscillators, and the other type has a positive coupling with similar oscillators and a negative coupling with the other type. We also applied model I to active Brownian particles, in a similar way to the continuous Vicsek model, to connect this model to some phenomena that can be observed in nature. We explored a broad range of parameters for these models. We looked at different splits of the mixture, from 5% to 95%, at different coupling constant ranges, but we considered that all oscillators have the same internal phase frequency and that the range of interaction is constant. Model I enhances synchronization for particles of both groups, allowing control over the synchronization behaviour by changing the interaction strength and the mixture split percentage. Model II can enhance synchronization for the contrarians, which would not synchronize if they were left alone, and can suppress synchronization for both oscillator groups if their interaction is strong enough. The ability for the oscillators to move and exchange neighbours increases the synchronization speed, as was observed when active Brownian particles were used.

碩士
長庚大學
化工與材料工程學系
99
The main purpose of this study is to use ZnO and TiO2 for photocatalytic degradation of a binary mixture of methylene blue (MB) and rhodamine B (RhB). The optimal TiO2 and ZnO dosages and pH values were determined. The adsorption results demonstrated that 80% decolorization of MB was achieved at pH 10 due to adsorption of MB on TiO2. Additionally, 20% declorization of MB was achieved at pH 10 due to adsorption of MB on ZnO. However, no adsorption of MB on TiO2 and ZnO was found at pH 4 and 7. Moreover, less than 10% decolorization of RhB due to adsorption of RhB on TiO2 and ZnO was observed at pH 4, 7, and 10. The experimental results for degradation of single dye (10ppm) demonstrated that the optimal photocatalyst dosages of TiO2 and ZnO are 0.5g/L. Using TiO2, 98.6% decolorization of MB was achieved at pH 7 and 75.5% decolorization of RhB was achieved at pH 10.Moreover, 97.2% decolorization of MB and 80.1% decolorization of RhB was achieved using ZnO with pH 10. The experimental results for degradation of binary dye mixture with a weight ratio of MB to RhB of 5:5 indicated that 75.7% decolorization of MB, 80.3% decolorization of RhB and 43.6% mineralization were achieved at pH 10 with a ZnO dosage of 0.5 g/L, as measured after 120 min. However, 87.3% decolorization of MB, 78.3% decolorization of RhB and 10.7% mineralization were achieved at pH 10 with a TiO2 dosage of 0.5 g/L, as measured after 120 min.

Addition of acids to foods allows for enhanced food safety. Acids are the primary form of defense against microbial contamination in refrigerated foods, while use of acids in conjunction with heat or high hydrostatic pressure processing lowers energy usage resulting in cost reduction. However, addition of acids to food or beverage formulations often reduces palatability due to higher sourness and this has limited the food industry's ability to better utilize them as preservatives. This study was aimed at gaining a better understanding of sourness suppression and its underlying mechanisms so that such limitations might be ultimately overcome. This work was divided into three parts dealing with the suppression of the sourness of citric, lactic and malic acids, as perceived by a trained sensory panel in a) binary mixtures with sugars, b) binary mixtures with salts and c) tertiary mixtures. The results of the first part showed that suppression was not mediated by sugar molarity or weight, but was significantly influenced by its perceived sweetness intensity in most cases. Sucrose and fructose were more effective than glucose in suppressing acid sourness and the data supported a separate receptor site/mechanism for glucose. Suppression was thought to have both central and peripheral components. In binary acid-salt mixtures sodium acetate (NaAc) affected the most sourness reduction, along with the largest concurrent pH increase (above 4.4). Sodium chloride (NaCl) mixtures showed significant suppression without a pH increase. Sodium gluconate (NaGluc) mixtures showed moderate suppression with citric and malic acids with pH increases remaining below 4.4, but showed little effect on lactic acid sourness. Saltiness appeared to drive suppression only in the case of NaCl, while pH change was responsible for reduction of sourness with NaAc and NaGluc. The tertiary trials indicated that a two-component multiple masker was more effective when its components stimulated different (as opposed to similar) receptors/receptor mechanisms in the taste system, irrespective of taste quality. Furthermore, a two-component masker was more effective than each component alone, and both components of a two-component masker did not have to be effective individually for them to function together as an effective multiple masker.
Graduation date: 2002

碩士
國立中山大學
應用數學系研究所
102
In this work, D-optimal designs for binary response models in mixture experiments are discussed. This kind of model setting occurs in many chemical experiments. Under the linear logit link, D-optimal designs for binary response models with two explanatory variables on the rst quadrant as the design space have been investigated by Sitter and Torsney (1995) and Haines et al. (2007). 　　We first provide an approach to obtain an essentially complete class of designs with reduced number of optimal supports, then the D-optimal designs may also be obtained with more insights on the structure appeared there. It is helpful for the search of D-optimal designs on the other design spaces with more restrictions. Later under the design space with constraints due to the mixture restriction, we obtain the D-optimal designs for binary response models under the linear logit link in a mixture design space.

碩士
國立東華大學
應用物理研究所
96
Our goal is to study the change of a binary mixture system within polymers. In experiments, we measure the heat capacity of 2,6-lutidine with water by TAM, and the critical exponent of heat capacity is found to be 0.09. When we put the PAA into the mixed solvent, and a becomes very small. In computer simulations, we find out that the critical exponent nu of Ising systems with polymers become 0.44, independent of the polymer concentration and polymer length. From the simulation results we find that in Ising systems with polymers is smaller than that in pure Ising system. We also find that the critical temperature increases linearly with polymer concentration.

碩士
中原大學
物理研究所
98
This research focuses on physical properties of binary mixtures containing a major positive liquid crystal and a minor negative one. The physical characteristics investigated include the phase-transition temperature, birefringence, dielectric anisotropy, and the rotational viscosity. In addition, the response times of the devices made of various mixtures with distinct content ratios have also been studied. Many material and device properties of the binary mixture can be tunable by changing the compositional ratio of the two liquid-crystal components. The experimental results show that the phase-transition temperatures are altered when the major liquid crystal is blended with the negative liquid crystal. The changes include the decrease in the melting point, increase in the clearing point, and, in turn, the wider range of the mesophase. The birefringence of the binary liquid crystal decreases with increasing concentration of the negative-liquid-crystal component because the birefringence of the negative dielectric anisotropy is less than that of the positive one. The physical properties of the binary substance, such as the dielectric anisotropy and rotational viscosity, change at various temperatures. Furthermore, the response time of the blend rises exponentially with the increase in concentration of the liquid crystal with negative dielectric anisotropy.

The thesis presents detailed results of theoretical analyses based on extensive computer simulation studies with an aim to explore, quantify whenever possible, and understand structure and dynamics of polymers and proteins in several complex solvents. In order to make the Thesis coherent, we also study certain aspects of binary mixtures. Based on the phenomena studied, the thesis has been divided into four major parts: I. Dynamics of biological water: Distance dependent variation of dielectric constants in aqueous protein solutions II. Temperature dependent study of structural transformations in aqueous binary mixtures III. Conformation and dynamics of polymers in solution: Role of aqueous binary mixtures IV. Conformational change and unfolding dynamics of proteins: Role of sol-vent environment The above mentioned four parts have further been divided into thirteen chapters. In the following we provide a brief chapter-wise outline of the thesis. Part I consists of two chapters, where we focus on the study of dynamics of biological water and distance dependent variation of static and dynamic proper-ties (including dielectric constant) of water near different proteins. To start with, chapter 1 provides an introduction to the structure and dynamics of biological water. Here we discuss different experimental studies; including dielectric relaxation, NMR and salvation dynamics those explore the bimolecular hydration dynamics in great detail. We also discuss the wide range of computer simulation and theoretical studies that have been carried out to understand the dynamical behaviour of biological water. In chapter 2, we present our molecular dynamics simulation study to ex-plore the distance dependent static and dynamic behaviour of biological water near four different protein surfaces. Proteins are known to have large permanent dipole moments that can influence structure and dynamics of even distant water molecules. Therefore, distance dependence of polarization punctuation can provide important insight into the nature of biological water. We explore these aspects by studying aqueous solutions of four different proteins of different char-acteristics and varying sizes. We find that the calculated dielectric constants of the systems show a noticeable increment in all the cases compared to that of neat water. Total dipole moment auto time correlation function of water is found to be sensitive to the nature of the protein. We also define and calculate the effective dielectric constant of successive layers and find that the layer adjacent to protein always has significantly lower value (∼ 50). However, progressive layers exhibit successive increment of dielectric constant, finally reaching a value close to that of bulk 4–5 layers away. Theoretical analysis providing simple method for calculation of shellwise local dielectric constant and implication of these findings are elaborately discussed in this chapter. Part II deals with the temperature dependent study of aqueous DMSO and ethanol solutions and consists of three chapters. Chapter 3 provides a general introduction to the non-ideality (deviation from Raoult’s law) encountered in different binary mixtures. We discuss different theoretical models for treatment of binary mixtures. Finally we provide a systematic study about the non-ideality observed in aqueous binary mixtures. Here we discuss the anomalies observed in such systems and carry out a brief survey on the existing ideas of structural transformations associated with the solvation of a foreign molecule in water. In chapter 4, we discuss the results of temperature dependent study of struc-tural and dynamic properties of aqueous dimethyl sulfoxide (DMSO) mixture. It is now well-known that aqueous DMSO mixture exhibits signature of perco-lation driven structural aggregation at a mole fraction range xDMSO ≈ 0.15. We study the structural and dynamical change in this binary mixture below and above the percolation threshold along with decreasing temperature. Significant change in the molecular structure of DMSO as well as that of water is observed above the percolation threshold at a lower temperature, particularly at 200K. The structural arrangement of the DMSO molecules is found to be progressively more ordered with increasing DMSO concentration and decreasing temperature. On the other hand, water structure is found to be significantly deviated from tetrahedral arrangement in presence of DMSO clusters even at low temperature. The dynamics of water is also found to be considerably affected with increase of concentration and lowering of temperature. Similar phenomenon is observed for another amphiphilic molecule, ethanol, and has been discussed in chapter 5. Aqueous ethanol mixture is a widely studied solvent, both experimentally and using computer simulations. All the studies indicate several distinct salvation regimes. In recent molecular dynamics simulation studies, the reason for formation of micro-aggregates of ethanol is again attributed to percolation driven structural transformation. We carry out a temperature dependent study of water-ethanol binary mixture, particularly at low ethanol concentration to understand the molecular origin of such structural transformation. We find that the structural arrangement of ethanol as well as water molecules is similarly affected as that of DMSO with lowering of temperature. However, dynamics of water molecules in aqueous ethanol solution is found to be marginally affected, unlike the case of aqueous DMSO solution. We discuss the microscopic reason for such behaviour in a detailed manner. In Part III, we discuss the dynamics of linear polymer chains in different aqueous binary mixtures. Here we have three chapters. In chapter 6, we carry out a brief survey of the existing theories of polymers in solution. We discuss the quality of solvents depending on the preferred interactions between the polymer and the solvent or the polymer with its own. We also discuss the celebrated Flory-Huggins theory. We derive the expression of free energy of the Flory-Huggins theory in terms of the volume fraction of monomer and solvent molecules. In chapter 7, we discuss the results of our study of polymer dynamics in aqueous DMSO solution. We find that at a mole fraction 0.05 of DMSO (xDMSO ≈ 0.05) in aqueous solution, a linear polymer chain of intermediate length (n=30) adopts collapsed conformation as the most stable conformational state. The same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations in neat water. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the polymer is found to be as large as 17 %. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behaviour to emerge near xDMSO ≈ 0.15 that is attributed to the percolation driven structural aggregation of DMSO that lowers the relative concentration of the DMSO molecules in the hydration layer. In chapter 8, we carry out similar study of linear polymer chain in water– ethanol binary mixture. In this case also, we find a sudden collapse of the poly-merat xEtOH ≈ 0.05. Since ethanol molecules are known to form micro-aggregates in this concentration range, stability of collapsed state of polymer at this con-centration is anticipated to be correlated to this phenomenon. In fact, a purely hydrophobic polymer chain, in its collapsed form is anticipated to assist in the formation of spanning cluster comprised of hydrophobic ethyl groups at this concentration range thereby facilitating the percolation transition. We discuss these prospects in this chapter. Part IV deals with the solvent sensitivity to the conformational change and unfolding dynamics of protein. Part IV consists of five chapters. In chapter 9, we develop an understanding of protein folding and unfolding dynamics by discussing the fundamental theories developed in the last few decades. We also discuss the major role of solvents in stabilizing or destabilizing the native, ordered state. In chapter 10, we present a detailed study of unfolding of a small protein, chicken villin headpiece (HP36) in water-ethanol binary mixture, using molecular dynamics simulations. The prime objective of this work is to explore the sensitivity of protein dynamics towards increasing concentration of the cosolvent and unravel essential features of intermediates formed in the unfolding path-way. In water–ethanol binary mixtures, HP36 is found to unfold partially, under ambient conditions, that otherwise requires temperature as high as ∼ 600K to denature in pure aqueous solvent. The study unravels certain interesting aspects about the pathway of unfolding, guided by the formation of unique intermediates. Unfolding is initiated by the separation of hydrophoic core comprising three phenylalanine residues (Phe7, Phe11, Phe18). This separation initiates the melting of the helix2 of the protein. However, with an increase of cosolvent concentration different partially unfolded intermediates are found to be formed. We attribute the emergence of such partially unfolded states to the preferential solvation of hydrophobic residues by the ethyl groups of ethanol. We explore and subsequently quantify the detailed dynamics of unfolding in water-ethanol that appear to be more complex and sensitive to solvent composition. With an aim to develop a general understanding of the role of water–ethanol binary mixture in facilitating anomalous conformational dynamics of proteins, we carry out combined theoretical and experimental studies to explore detailed structural change of a larger protein, Myoglobin with increasing ethanol concentration. These studies are described in chapter 11. In agreement with our pre-vious observations, we identify in this case two well-defined structural regimes, one at xEtOH ≈ 0.05 and the other at xEtOH ≈ 0.25, characterized by formation of distinct partially folded conformations and separated by a unique partially unfolded intermediate state at xEtOH ≈ 0.15. We also find non-monotonic com-position dependence of (i) radius of gyration (ii) long range contact order (iii) residue specific solvent accessible surface area of tryptophan (iv) circular dichro-ism spectra and UV-absorption peaks. Multiple structural transformations, well-known in water-ethanol binary mixture, appear to have considerably stronger effects on the conformation and dynamics of protein Myoglobin. In chapter 12, we explore the free energy surface of unfolding pathway through umbrella sampling, for the small globular alpha-helical protein chicken-villin headpiece (HP36) in three different solvent conditions (water, xDMSO ≈ 0.15 and xDMSO ≈ 0.3). Recently established as a facilitator of helix melting, DMSO is found to be a good denaturant for HP36 and at a mole fraction of xDMSO ≈ 0.3, complete melting of the protein is ensured. The unfolding proceeds through initial separation or melting of the same aggregated hydrophobic core that com-prises three phenylalanine residues (Phe7, Phe11 and Phe18) accompanied by simultaneous melting of the helix2. Unfolding is found to be a multistage process involving crossing of three consecutive minima and two barriers at the initial stage. At a molecular level, Phe18 is observed to reorient itself towards other hy-drophobic grooves to stabilize the intermediate states. We identify the configuration of intermediates in all the solvent conditions which are found to be unique for the corresponding minima with similar structural arrangement. Consider-able softening of the barriers is observed with increasing DMSO concentration. Higher concentration of DMSO tunes the unfolding pathway by destabilizing the third minimum and stabilizing the second one, indicating the development of solvent modified, less rugged pathway. Chapter 13 provides a detailed microscopic mechanism of DMSO induced unfolding of HP36. We analyze the free energy contours of the protein HP36, obtained from molecular dynamics simulation in xDMSO ≈ 0.15 and xDMSO ≈ 0.3. The most probable intermediates obtained from the free energy contours are found to be similar to those obtained from umbrella sampling which again sup-ports the fact that the melting proceeds through formation of a series of unique intermediates. We characterize the preferential hydrophobic salvation of the hydrophobic core that drives the melting of secondary structure, by calculating time dependent radial distribution function and identifying the formation of strong orientation order between methyl groups of DMSO and phenyl alanine residues. Finally we employ Kramer’s rate equation to calculate the rate of bar-rier crossing that reveals significantly faster rate of unfolding with increasing DMSO concentration that is in agreement with simulation results. Whenever possible, we have discussed the scope of future work at the end of each chapter.

The thesis presents detailed results of theoretical analyses based on extensive computer simulation studies with an aim to explore, quantify whenever possible, and understand structure and dynamics of polymers and proteins in several complex solvents. In order to make the Thesis coherent, we also study certain aspects of binary mixtures. Based on the phenomena studied, the thesis has been divided into four major parts: I. Dynamics of biological water: Distance dependent variation of dielectric constants in aqueous protein solutions II. Temperature dependent study of structural transformations in aqueous binary mixtures III. Conformation and dynamics of polymers in solution: Role of aqueous binary mixtures IV. Conformational change and unfolding dynamics of proteins: Role of sol-vent environment The above mentioned four parts have further been divided into thirteen chapters. In the following we provide a brief chapter-wise outline of the thesis. Part I consists of two chapters, where we focus on the study of dynamics of biological water and distance dependent variation of static and dynamic proper-ties (including dielectric constant) of water near different proteins. To start with, chapter 1 provides an introduction to the structure and dynamics of biological water. Here we discuss different experimental studies; including dielectric relaxation, NMR and salvation dynamics those explore the bimolecular hydration dynamics in great detail. We also discuss the wide range of computer simulation and theoretical studies that have been carried out to understand the dynamical behaviour of biological water. In chapter 2, we present our molecular dynamics simulation study to ex-plore the distance dependent static and dynamic behaviour of biological water near four different protein surfaces. Proteins are known to have large permanent dipole moments that can influence structure and dynamics of even distant water molecules. Therefore, distance dependence of polarization punctuation can provide important insight into the nature of biological water. We explore these aspects by studying aqueous solutions of four different proteins of different char-acteristics and varying sizes. We find that the calculated dielectric constants of the systems show a noticeable increment in all the cases compared to that of neat water. Total dipole moment auto time correlation function of water is found to be sensitive to the nature of the protein. We also define and calculate the effective dielectric constant of successive layers and find that the layer adjacent to protein always has significantly lower value (∼ 50). However, progressive layers exhibit successive increment of dielectric constant, finally reaching a value close to that of bulk 4–5 layers away. Theoretical analysis providing simple method for calculation of shellwise local dielectric constant and implication of these findings are elaborately discussed in this chapter. Part II deals with the temperature dependent study of aqueous DMSO and ethanol solutions and consists of three chapters. Chapter 3 provides a general introduction to the non-ideality (deviation from Raoult’s law) encountered in different binary mixtures. We discuss different theoretical models for treatment of binary mixtures. Finally we provide a systematic study about the non-ideality observed in aqueous binary mixtures. Here we discuss the anomalies observed in such systems and carry out a brief survey on the existing ideas of structural transformations associated with the solvation of a foreign molecule in water. In chapter 4, we discuss the results of temperature dependent study of struc-tural and dynamic properties of aqueous dimethyl sulfoxide (DMSO) mixture. It is now well-known that aqueous DMSO mixture exhibits signature of perco-lation driven structural aggregation at a mole fraction range xDMSO ≈ 0.15. We study the structural and dynamical change in this binary mixture below and above the percolation threshold along with decreasing temperature. Significant change in the molecular structure of DMSO as well as that of water is observed above the percolation threshold at a lower temperature, particularly at 200K. The structural arrangement of the DMSO molecules is found to be progressively more ordered with increasing DMSO concentration and decreasing temperature. On the other hand, water structure is found to be significantly deviated from tetrahedral arrangement in presence of DMSO clusters even at low temperature. The dynamics of water is also found to be considerably affected with increase of concentration and lowering of temperature. Similar phenomenon is observed for another amphiphilic molecule, ethanol, and has been discussed in chapter 5. Aqueous ethanol mixture is a widely studied solvent, both experimentally and using computer simulations. All the studies indicate several distinct salvation regimes. In recent molecular dynamics simulation studies, the reason for formation of micro-aggregates of ethanol is again attributed to percolation driven structural transformation. We carry out a temperature dependent study of water-ethanol binary mixture, particularly at low ethanol concentration to understand the molecular origin of such structural transformation. We find that the structural arrangement of ethanol as well as water molecules is similarly affected as that of DMSO with lowering of temperature. However, dynamics of water molecules in aqueous ethanol solution is found to be marginally affected, unlike the case of aqueous DMSO solution. We discuss the microscopic reason for such behaviour in a detailed manner. In Part III, we discuss the dynamics of linear polymer chains in different aqueous binary mixtures. Here we have three chapters. In chapter 6, we carry out a brief survey of the existing theories of polymers in solution. We discuss the quality of solvents depending on the preferred interactions between the polymer and the solvent or the polymer with its own. We also discuss the celebrated Flory-Huggins theory. We derive the expression of free energy of the Flory-Huggins theory in terms of the volume fraction of monomer and solvent molecules. In chapter 7, we discuss the results of our study of polymer dynamics in aqueous DMSO solution. We find that at a mole fraction 0.05 of DMSO (xDMSO ≈ 0.05) in aqueous solution, a linear polymer chain of intermediate length (n=30) adopts collapsed conformation as the most stable conformational state. The same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations in neat water. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the polymer is found to be as large as 17 %. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behaviour to emerge near xDMSO ≈ 0.15 that is attributed to the percolation driven structural aggregation of DMSO that lowers the relative concentration of the DMSO molecules in the hydration layer. In chapter 8, we carry out similar study of linear polymer chain in water– ethanol binary mixture. In this case also, we find a sudden collapse of the poly-merat xEtOH ≈ 0.05. Since ethanol molecules are known to form micro-aggregates in this concentration range, stability of collapsed state of polymer at this con-centration is anticipated to be correlated to this phenomenon. In fact, a purely hydrophobic polymer chain, in its collapsed form is anticipated to assist in the formation of spanning cluster comprised of hydrophobic ethyl groups at this concentration range thereby facilitating the percolation transition. We discuss these prospects in this chapter. Part IV deals with the solvent sensitivity to the conformational change and unfolding dynamics of protein. Part IV consists of five chapters. In chapter 9, we develop an understanding of protein folding and unfolding dynamics by discussing the fundamental theories developed in the last few decades. We also discuss the major role of solvents in stabilizing or destabilizing the native, ordered state. In chapter 10, we present a detailed study of unfolding of a small protein, chicken villin headpiece (HP36) in water-ethanol binary mixture, using molecular dynamics simulations. The prime objective of this work is to explore the sensitivity of protein dynamics towards increasing concentration of the cosolvent and unravel essential features of intermediates formed in the unfolding path-way. In water–ethanol binary mixtures, HP36 is found to unfold partially, under ambient conditions, that otherwise requires temperature as high as ∼ 600K to denature in pure aqueous solvent. The study unravels certain interesting aspects about the pathway of unfolding, guided by the formation of unique intermediates. Unfolding is initiated by the separation of hydrophoic core comprising three phenylalanine residues (Phe7, Phe11, Phe18). This separation initiates the melting of the helix2 of the protein. However, with an increase of cosolvent concentration different partially unfolded intermediates are found to be formed. We attribute the emergence of such partially unfolded states to the preferential solvation of hydrophobic residues by the ethyl groups of ethanol. We explore and subsequently quantify the detailed dynamics of unfolding in water-ethanol that appear to be more complex and sensitive to solvent composition. With an aim to develop a general understanding of the role of water–ethanol binary mixture in facilitating anomalous conformational dynamics of proteins, we carry out combined theoretical and experimental studies to explore detailed structural change of a larger protein, Myoglobin with increasing ethanol concentration. These studies are described in chapter 11. In agreement with our pre-vious observations, we identify in this case two well-defined structural regimes, one at xEtOH ≈ 0.05 and the other at xEtOH ≈ 0.25, characterized by formation of distinct partially folded conformations and separated by a unique partially unfolded intermediate state at xEtOH ≈ 0.15. We also find non-monotonic com-position dependence of (i) radius of gyration (ii) long range contact order (iii) residue specific solvent accessible surface area of tryptophan (iv) circular dichro-ism spectra and UV-absorption peaks. Multiple structural transformations, well-known in water-ethanol binary mixture, appear to have considerably stronger effects on the conformation and dynamics of protein Myoglobin. In chapter 12, we explore the free energy surface of unfolding pathway through umbrella sampling, for the small globular alpha-helical protein chicken-villin headpiece (HP36) in three different solvent conditions (water, xDMSO ≈ 0.15 and xDMSO ≈ 0.3). Recently established as a facilitator of helix melting, DMSO is found to be a good denaturant for HP36 and at a mole fraction of xDMSO ≈ 0.3, complete melting of the protein is ensured. The unfolding proceeds through initial separation or melting of the same aggregated hydrophobic core that com-prises three phenylalanine residues (Phe7, Phe11 and Phe18) accompanied by simultaneous melting of the helix2. Unfolding is found to be a multistage process involving crossing of three consecutive minima and two barriers at the initial stage. At a molecular level, Phe18 is observed to reorient itself towards other hy-drophobic grooves to stabilize the intermediate states. We identify the configuration of intermediates in all the solvent conditions which are found to be unique for the corresponding minima with similar structural arrangement. Consider-able softening of the barriers is observed with increasing DMSO concentration. Higher concentration of DMSO tunes the unfolding pathway by destabilizing the third minimum and stabilizing the second one, indicating the development of solvent modified, less rugged pathway. Chapter 13 provides a detailed microscopic mechanism of DMSO induced unfolding of HP36. We analyze the free energy contours of the protein HP36, obtained from molecular dynamics simulation in xDMSO ≈ 0.15 and xDMSO ≈ 0.3. The most probable intermediates obtained from the free energy contours are found to be similar to those obtained from umbrella sampling which again sup-ports the fact that the melting proceeds through formation of a series of unique intermediates. We characterize the preferential hydrophobic salvation of the hydrophobic core that drives the melting of secondary structure, by calculating time dependent radial distribution function and identifying the formation of strong orientation order between methyl groups of DMSO and phenyl alanine residues. Finally we employ Kramer’s rate equation to calculate the rate of bar-rier crossing that reveals significantly faster rate of unfolding with increasing DMSO concentration that is in agreement with simulation results. Whenever possible, we have discussed the scope of future work at the end of each chapter.

碩士
明志科技大學
化學工程研究所
100
This study reports on the synthesis and the physical properties of ionic liquid of 1-isoalkyl-3-methylimidazolium bromide [i-Cnmim][Br], (n＝3,4,5)。The values of density, refractive index , viscosity and conductivity at temperature range from 298.15 to 338.15 K were measured and reported for the 1-isoalkyl-3-methylimidazolium bromide ionic liquid。Empirical correlations were proposed to represent the present experimental data。The density, refractive index and viscosity values decrease with increasing temperature。The density and refractive index values decrease with the increases in the length of the alkyl chain in the imidazolium cation。The viscosity value increase with increasing in the length of the alkyl chain in the imidazolium cation 。The conductivity values increase with increasing temperature。 In the study，densities , refractive index and viscosity of the 1-isoalkyl-3-methylimidazolium bromide, in water ,methanol , ethanol ,1-propanol and 1-butanol at a temperature range from 298.15 to 338.15 K and atmospheric pressure were measured over the whole composition range。Excess molar volumes , refractive index deviations and viscosity deviations for the binary systems were calculated 。These results were fitted to a Redlich-kister equation to determine the fitting parameters and the root mean square deviations。

碩士
國立交通大學
光電科技學程
106
The purpose of this study is to investigate the phase behaviors and dielectric properties of binary liquid crysta(LC) mixtures. The research contents include positive liquid crystal (CYLC01)mixed negative liquid crystal (MLC-6608), negative liquid crystal (MLC-6608) and positive liquid crystal (CB7CB)Liquid crystal hybrid dual-frequency rod-like liquid crystal (HEF-951800), a total of three combinations, respectively, with the doping concentration and phase transition behavior and dielectric properties of the correlation. The experimental results show that: 1. When the positive and negative rod-shaped liquid crystals are mixed, the phase transition temperature has a linear relationship with the concentration ratio of the negative rod-shaped liquid crystal doped. 2. Negative rod-shaped liquid crystal and positive curved liquid crystal when mixed, will produce a new NTB phase, when the positive curved liquid crystal is greater than the proportion of negative liquid crystal rod-shaped, because of immiscibility and delamination phenomenon. When the positive curved liquid crystal and the dual-frequency liquid crystal are mixed, the phase transition temperature has a linear relationship with the positive liquid crystal doped ratio, and under the applied voltage, the dielectric relaxation phenomenon will be more obvious.