Study on nanoparticle additives in multiphase systems (liquid, polymer) are of immense interest in developing new product applications. Critical challenges for nanoparticle additives include their synthesis, formulation and characterization. These challenges are addressed in three application areas: nanofluids for engine lubrication, ultrathin nanocomposites for optical devices, and nanoparticle size distribution characterization. Nanoparticle additives in oligomer mixtures can be used to develop extended temperature range motor oils. A model system includes poly(α-olefin) based oligomers with a modest fraction of poly(dimethylsiloxane) oligomers along with graphite as nanoparticle additive. Partition coefficients of each oligomer are determined since the oligomer mixture phase separated at temperatures less than -15 °C. Also, the surface of graphite additive is quantitatively analyzed and modified via silanization for each oligomer. Thus, upon separation of the oligomer mixture, each functionalized graphite additive migrates to its preferred oligomers and forms a uniform dispersion. Similarly, nanoparticle additives in polymer matrices can be used to develop new low haze ultrathin film optical coatings. A model system included an acrylate monomer as the continuous phase with monodisperse or bidisperse mixtures of silica nanoparticles deposited on glass and polycarbonate substrates. Surface (root mean squared roughness, Wenzel’s contact angle) and optical properties (haze) of these self assembled experimental surfaces were compared to simulated surface structures. Manipulating the size ratios of silica nanoparticle mixtures varied the average surface roughness and the height distributions, producing multimodal structures with different packing fractions. In both nanofluid and nanocomposite applications, nanoparticle additives tend to aggregate/agglomerate depending on various factors including the state of nanoparticles (powder, dispersion). A set of well-characterized ceria and titania nanoparticle products from commercial sources along with in-lab synthesized nanoparticles were studied via fractal theory. Fractal coefficients were obtained through two-dimensional images (from electron microscopy) and particle size distributions (from electron microscopy and dynamic light scattering). For some arbitrary collections of aggregated nanoparticle materials, the fractal coefficients via two-dimensional images correlated well to the average primary particle size. This complementary tool could be used along with conventional nanoparticle characterization techniques when not much is known about the nanoparticle surfaces to characterize agglomeration or aggregation phenomena.

Les activités de production des hydrocarbures sont fortement dépendantes du comportement thermodynamique des fluides produits. La précipitation d'asphaltènes, entités qui constituent les principaux composants de la fraction la plus lourde et la plus polaire du pétrole, peut conduire à la formation d'un dépôt solide. Nous avons mis en oeuvre et évalué plusieurs méthodologies expérimentales appliquées à la détermination des diagrammes de phase de fluides asphalténiques dans les conditions de haute pression et haute température. Nous avons mis au point une technique utilisant un résonateur à cristal de quartz (RCQ), capable d'identifier les conditions thermodynamiques de changement de phase, sous haute pression, dans des fluides avec une teneur faible en asphaltènes. Les données obtenues avec le RCQ ont été validées par filtration isobare et par microscopie haute pression (MHP). Les effets sur la floculation de l'ajout de gaz, des conditions thermodynamiques imposées au fluide et de la vitesse de dépressurisation ont été étudiés expérimentalement à l'aide des trois techniques susmentionnées. Les résultats obtenus par MHP sur différentes live oils suggèrent l'existence de quatre types de comportement de fluides lors d'une dépressurisation isotherme, avec dans certains cas l'apparition d'un équilibre liquide-liquide dans des conditions de températures et de pressions élevées. Enfin, nous avons établi, avec la caractérisation physico-chimique des asphaltènes obtenus (nC7) à partir des huiles mortes, que la différence d'aromaticité entre cette fraction et celle de son huile d'origine, pouvait être un indicateur utile afin d'anticiper un possible phénomène de précipitation. / Oil production activities are strongly dependent on the phase behavior of produced fluids. The flocculation of asphaltenes, the major components of the heaviest and most polar fraction of crude oil, can lead to solids formation in several steps of oil production. In this thesis, we evaluated several methodologies applied for asphaltenes phase behavior assessment under high-pressure conditions. Among the methodologies, we had developed an apparatus based on the quartz crystal resonator (QCR), able to identify thermodynamic conditions of phase changes in pressurized fluids containing low asphaltenes content. The data obtained with the QCR were validated by isobaric filtration and high pressure microscopy (HPM) tests. Applying the three aforementioned techniques, the influence of gas addition, kinetic factors, thermodynamic conditions and the influence of depressurization rate on the onset of asphaltenes flocculation were studied. Live oils were evaluated by the HPM technique. The results from HPM suggest the existence of four phase behavior patterns for isothermal depressurization experiments, highlighting the existence of a liquid-liquid equilibrium at elevated temperatures and pressures. The physico-chemical characterization of asphaltenes extracted with n-heptane from dead oil suggests that the difference of aromaticity between this fraction and its referred oils could be a parameter to indicate possible problems of asphaltenes flocculation during the oil production.

La cristallisation de la cire dans les huiles pétrolières est un processus qui se produit à la suite de changements dans les conditions de pression et de température dans lesquelles ils sont sur le gisement, et qui diminuent progressivement le long de ses processus de production, transport et de stockage. Sa précipitation et son dépôt sur les surfaces intérieures des pipelines nécessitent la mise en œuvre des techniques de guérison ou d'amélioration des propriétés des fluides, afin de réduire les pertes causées par leur accumulation, qui dans certains cas pourrait complètement paralyser le production d'une plante. L'étude du processus de précipitation des paraffines est basée sur la détermination des conditions de pression et de température dans lesquelles il se produit, et la caractérisation des phases coexistent en équilibre. Parmi les principales limites de ce processus, nous trouvons de la disponibilité et de la conception des appareils expérimentaux qui permettent la détection des températures de fusion finissantes et la séparation de phases sous pression, et le développement des méthodes chromatographiques pour l'identification et la quantification des paraffines lourdes. Le développement de modèles thermodynamiques qui décrivent le processus de précipitation des paraffines sont l'un des principaux outils pour l'anticipation et la prévention des processus de cristallisation des cires. Son efficacité dans l'estimation des conditions dans lesquelles les cristaux commencent à apparaître, ainsi que la quantité totale de solides qui pourrait être formée, dépendent de la conception des techniques expérimentales qui reproduisent les conditions réelles d'opération, et de recueillir des informations fiables du comportement de phase dans des mélanges des hydrocarbures. Dans ce travail de recherche s'est développé une méthodologie complète pour la détection et filtration des cristaux dans une gamme s'étendant à partir des conditions normales jusqu'à 800 bars et une méthode chromatographique d’haute température qui ont permis d'effectuer une évaluation du comportement de phase en fonction de la composition, la pression et la température, ainsi que l'identification et la quantification des paraffines. Le comportement de phase des mélanges de paraffines étudiés indiquent que les variations de pression et de température ont une grande influence sur la cristallisation des cires: les processus de compression isotherme refroidissement isobare diminuent la solubilité des cires et entraîner non seulement dans une augmentation de la quantité de solides précipités, mais dans une variante de sa nature. De plus, l'augmentation de la pression du système provoque une augmentation linéaire des températures de changement de phase des mélanges étudiés. Pour sa part, les différences de composition des mélanges étudiés ont généré des différences significatives dans leur température de changement de phase, mais pas dans la quantité de matières solides cristallisées. En général, des mélanges enrichis en paraffines lourdes ont produit une augmentation de leur WAT. Les résultats obtenus ont montré que l'effet prédominant sur le processus de cristallisation des cires correspond à la diminution de la température du système, ce qui conduit à la formation de quantités importantes de déchets solides. De plus, elles sont consistant avec le comportement de phase des mélanges de cires synthétiques, ce qui permet de conclure que la méthode expérimentale développé, constitué par le couplage de la technique de détection et de séparation de phase avec chromatographie en phase gazeuse à haute température, représente outil précis et fiable pour l'étude des processus de précipitation de la paraffine dans des conditions réelles d'opération, et qui a surmonté les limites expérimentales typiques de ces analyses. / The wax crystallization in oil fluids is a process that occurs as a result of changes in pressure and temperature conditions found in the site, and gradually decreasing along the production process, transport and storage thereof. Precipitation and deposition on the inner surfaces of pipelines require the implementation of healing techniques or to improve the properties of fluids, in order to reduce losses caused by their accumulation, which in some cases could come to a complete standstill production plant. The study of paraffin precipitation process is based on determining the pressure and temperature conditions in which it occurs, and the characterization of the phases coexist in equilibrium. The main constraints of this process, we found the availability and experimental design devices that allow detection of the onset temperatures of crystals and phase separation at high pressure and the development of chromatographic methods for the identification and quantification of paraffins high molecular weight. The development of thermodynamic models describing the precipitation of paraffins is one of the main tools for anticipating and preventing wax crystallization process. Its effectiveness in estimating the conditions that will start appearing crystals and the total amount of solid that could be formed, depends on the design of experimental techniques to reproduce the real operating conditions, and gather reliable information of phase behavior in mixtures hydrocarbon. In the present investigation a complete methodology for detecting and filtering crystals in a range extending to 800 bar normal conditions and a high temperature chromatographic method that allowed to carry out the assessment phase behavior developed in Depending on the composition, pressure and temperature as well as the identification and quantification of heavy paraffins. Phase behavior of mixtures of paraffins studied indicates that changes in pressure and temperature have a great influence on the crystallization of waxes: isothermal compression processes isobaric cooling and decrease the solubility of the wax and result not only in an increase in the amount of precipitated solids but in a variation of the nature thereof. Additionally, increasing the system pressure generated an increase in temperature of the phase change mixtures studied. For its part, the differences in composition of the mixtures studied generated significant differences in their phase change temperature but not in the amount of solid crystallized. In general, enriching the mixture to heavy paraffins produced an increase in their respective WAT. The results obtained showed that the predominant effect in the wax crystallization process corresponds to the temperature decrease of systems, leading to the formation of large quantities of solid waste. Also, these are consistent with the phase behavior of mixtures of synthetic waxes, which allows to conclude that the experimental methodology developed, consisting of the coupling and detection techniques phase separation gas chromatography with high temperature, represents accurate and reliable tool for the study of paraffin precipitation process in real operating conditions, and who overcame the typical experimental limitations of these analyzes.

Thermo-responsive homopolymer poly(N-isopropylacrylamide), is a widely studied and used polymer. Our recent observations on thermal behavior of aqueous solutions of this polymer requires a short overview of existing results in order to understand the formation of different phases, both stable and unstable with the addition of hydrophilic Ionic liquids (ILs) 1-Butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-Butyl-3-methylimidazolium acetate ([BMIM][OAc]) and 1-Butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) to the system. PNIPAM is soluble in cold water due to its inter- and intramolecular hydrogen bonding but phase separates upon heating at T > 32 , which is its lower critical solution temperature (LCST). PNIPAM exists in an expanded coil like conformation in water below its LCST which gives a transparent homogenous solution but at T > LCST it undergoes hydrophobic collapse marked by cloudiness of solution and conformational change from coil to globule state. All aqueous PNIPAM solutions undergo phase separation or cloud point transition at T > 32 , regardless of the molar mass of the polymer. Room temperature Ionic liquids (ILs) are unique designer fluids because of the novel physico-chemical properties arising from their structure, which have tremendous implications in the field of IL as solvents or co-solvents for polymeric solutes. During recent years a number of different imidazolium based ILs have also been tested for solubilization and stabilization of proteins as well as polymers due to hydrogen bond formation of the IL ions. Recent studies have shown that certain imidazolium based ILs can decrease the LCST of PNIPAM aqueous solution by hydrophobic collapse/aggregation of the PNIPAM chains, as well as some can induce an upper critical solution temperature (UCST) behavior of PNIPAM in neat IL solution. Even so, experimental studies of such phase transition/ instability of thermoresponsive polymer-IL systems has been a challenging task. In this research we have explored the critical solution temperature (CST) type phase behavior of multicomponent systems i.e. PNIPAM in solution media of water, neat IL and aqueous solutions of IL. The overall fundamental challenge is to understand how the interactions among the components control both structure and dynamics of PNIPAM network in solution. For example the disruption of hydrogen bonding or desolvation interactions between blocks of a PNIPAM molecule and solvent molecules in aqueous mixtures that lead to a LCST type transition at higher temperatures. Interestingly, it was found in our case that PNIPAM shows both LCST and UCST-type phase transition in some aqueous solutions of hydrophilic IL [BMIM][BF4]. It was found for the first time that this IL can influence the LCST type behavior of PNIPAM in aqueous solutions based on our visual and experimental cloud point (CP) observations. In our experiments the effect of the ILs [BMIM][BF4] and [BMIM][OAc] is qualitatively similar to influence of Kosmotropic salts on the LCST of aqueous PNIPAM solutions as predicted by the Hofmeister series.

In this thesis detailed investigations of the phase behavior of poly(n-alkyl methacrylate-b-methyl methacrylate) diblock copolymers and its influence on the wettability of the polymer surfaces were carried out. For this investigation two polymethacrylic systems differing only in the alkyl rest of one block: poly(pentyl methacrylate-b-methyl methacrylate) and poly(propyl methacrylate-b-methyl methacrylate) have been chosen in order to prove how this substituent affects the phase behavior of whole system. The PnAlkMA-b-PMMA diblock copolymers in a wide range of molar masses, and with varied block length ratios were synthesized by living anionic polymerization. The syntheses were carried out in tetrahydrofuran (THF), at –78 °C, by using sec-buthyllithium as initiator, in the presence of lithium chloride (LiCl). Under these conditions highly syndiotactic products, rr ~ 0.82, with very narrow molar mass distribution, Mw/Mn ~ 1.1, were obtained. The phase behavior of PnAlkMA-b-PMMA diblock copolymers in bulk was investigated by means of DSC and SAXS measurements. The DSC analysis revealed that the PPMA-b-PMMA with weight fractions of PPMA, fPPMA, from 0.28 up to 0.86 showed two separate Tg’s, indicative of a phase separated system. However, by comparing the Tg’s of the diblock copolymers with the Tg’s of the corresponding homopolymers we found that in a few cases, mostly for samples with the high molar masses, they were slightly shifted. This finding pointed out the existence of two mixed phases, and hence partial miscibility between the both blocks was assumed. The SAXS patterns reflected for most diblock copolymers lamellae morphologies even in the case of very asymmetric composition, for instance with volume fraction of PPMA, 0.86 It was assumed that this behavior is caused by the chemical similarity of both blocks as well as by the differences in their molar volumes. The SAXS findings were further confirmed by the AFM measurements on the cutted “bulk” samples. From the solubility concept of Van Krevelen we obtained that the interaction parameter of PPMA-b-PMMA is rather low, 0.065, compared to the other well-known diblock copolymers. The calculated spinodals are characterized by a high asymmetry. The investigation of the phase behavior of PPMA-b-PMMA in thin films showed that the morphology as well as the topography of the thin films were strongly affected by the film thickness, when the films were prepared from a non-selective solvent (THF) onto silicon wafers. Well-recognizable nanostructures with long-range order were mainly found in thin films of diblock copolymers with high molar masses, above 100,000 g/mol, and with a high amount of PPMA. The lateral domain spacing obtained for these films from AFM corresponded well with that found in bulk. The study of the influence of the thermal as well as vapor annealing on the morphology and topography of the thin films provided additional information about the phase behavior of PPMA-b-PMMA diblock copolymers in thin films. Finally, the wettability of the investigated PPMA-b-PMMA surfaces was established by means of contact angle measurements. The measured contact angles were in most cases even on nicely nanostructured surfaces very similar to the contact angle of PPMA, indicating preferential segregation of PPMA to the film surface. Additional XPS measurements also showed an enrichment of the PPMA at the surface, independent of the morphology observed by AFM, and thereby confirmed the ADSA finding. In the next part of this work, investigations of the phase behavior of PPrMA-b-PMMA diblock copolymers were presented. In the contrary to the previous system the PPrMA-b-PMMA showed mostly a single Tg, which was further found to be depend on the weight fraction of PPrMA, fPPrMA. The SAXS data revealed that the PPrMA-b-PMMA diblock copolymers were phase separated in bulk, however the obtained scattering patterns exhibited mostly broad, not-well discernible higher-order peaks. Nevertheless, it was possible to identify the formed morphologies and depending on the volume fraction of PPrMA, hexagonally packed cylinders and lamellae were detected. The PPrMA-b-PMMA is characterized by a significantly lower value of the interaction parameter, 0.022, than the PPMA-b-PMMA system. This difference clearly reflects the weakening of the interactions between the components with decrease of the length of the alkyl side chain. The thin films of PPrMA-b-PMMA diblock copolymers appeared mostly smooth and featureless, independent of the film thickness. From the contact angle and XPS measurements we obtained, that unlike the PPMA-b-PMMA, both components were always present on the top of the surface. / In der vorliegenden Arbeit wurden Untersuchungen zum Entmischungsverhalten von Poly(n-alkylmethacrylat-b-methylmethacrylat) Diblockcopolymeren und deren Einfluss auf die Benetzbarkeit der Polymeroberflächen dargestellt. Diese Untersuchungen wurden anhand der Poly(pentylmethacrylat-b-methylmethacrylat) und Poly(propylmethacrylat-b-methylmethacrylat) durchgeführt. Die Diblockcopolymere in einem weiten Molmassenbereich, mit enger Molmassenverteilung, abgestuften Zusammensetzung wurden erfolgreich mittels anionischer Polymerization synthetisiert. Die Synthese erfolgte in THF bei (-78 °C) in Gegenwart von Lithiumchlorid. Als Initiator wurde sec. Butyllithium genutzt. Das Phasenverhalten der Diblockcopolymere im Festkörper wurde mittels DSC und SAXS untersucht. Für die meiste PPMA-b-PMMA Diblockcopolymere wurden mittels DSC zwei getrennte Tg gefunden, die aber im Vergleich zu den Tg von den entsprechenden Homopolymeren leicht verschoben waren. Es wurde also eine partielle Mischbarkeit der Blöcke festgestellt. Mittels SAXS-Untersuchungen wurde für die Mehrzahl der Diblckcopolymere in einem weiten Zusammensetzungsbereich bis zum 0.86 Volumenanteil von PPMA, eine lamellare Anordnung beobachten. Diese Befunde wurden nachfolgend mit AFM–Untersuchungen an dünnen Polymerfolien bestätigt. Das mit der Mean-Filed-Methode berechnete Phasendiagramm zeigte eine Asymmetrie, die durch die Unterschiede in den molaren Volumina des Blöckes verursacht war. Es wurde aber eine gute Übereinstimmung mit der experimentell erhaltenen Daten gefunden. Der berechnete für das System Wechselwirkungsparameter beträgt 0,065. Die AFM-Untersuchungen zum Entmischungsverhalten in dünnen Filmen haben gezeigt, dass die Topographie als auch Morphologie des Films war von der Filmdicke beeinflusst. Die Polymerfilme wurden mittels dipcoating der Si-Wafer präpariert. Dazu wurden Polymerlösungen in THF verwendet. Reguläre Nanostrukturen, deren Abstände mit dem im Festkörper gefundenen sehr gut übereinstimmten, wurden bei den Proben mit höherem Anteil von PPMA erhalten. Es wurden auch der Einfluss der Temperatur und der Dampfbehandlung auf die Morphologie und Topographie des Films untersucht. Die Benetzbarkeit der untersuchte PPMA-b-PMMA Filme wurde mit der Kontaktwinkelmessungen (ADSA) bestimmt. Als Messflüssigkeit wurde Milipore Wasser genutzt. Für die Mehrzahl der Diblockcopolymere wurden Kontaktwinkel im Bereich um 95° ermitteln, unabhängig von der Zusammensetzung der Diblockcopolymere und der vorhandenen Nanostruktur. Dies entspricht dem Kontaktwinkel von PPMA Homopolymer. Die Benetzbarkeit der PPMA-b-PMMA Filme wurde also durch die Oberflächensegregation des Niedrigenergieblocks (PPMA) bestimmt. Dies wurde danach durch zusätzliche XPS Messungen bestätigt. Im Vergleich zu PPMA-b-PMMA, die nachfolgend untersuchte PPrMA-b-PMMA Diblockcopolymere wiesen eine höhere Tendenz zur Mischbarkeit auf. Anhand der DSC–Untersuchungen wurde hier vorübergehend eine Misch-Tg gefunden. Nur bei der Probe mit symmetrischer Zusammensetzung wurden zwei getrennte Tg beobachtet. Die Streukurven von diesem System waren sehr schwach ausgeprägt. Dadurch die Indizierung der vorhandenen Morphologien war nicht eindeutlich. Der berechnete Wechselwirkungsparameter beträgt 0,022. Bei den AFM-Untersuchungen zum Entmischungsverhalten in dünnen PPrMA-b-PMMA Filmen wurden entweder keine oder sehr schwach geordnete Nanostruktur gefunden. Im Gegensatz zu dem vorherigen System, die Benetzbarkeit der PPrMA-b-PMMA Filme war durch die Zusammensetzung der Diblockcopolymere bedingt.

Localized heating leads to generation of thermal Hotspots that affect performance and reliability of an Integrated Circuit(IC). Functional workloads determine the locations and temperature of hotspots on a die. Programs are classified into phases based on program execution profile. During a phase, spatial power dissipation pattern of an application remains unchanged. In this thesis, we present a systematic approach for developing a synthetic workload from a functional workload to create worst case temperature of a target hotspot in 2D and 3D IC. These synthetic workload are designed to create thermal stress patterns, which would help in characterizing the thermal characteristics of micro architecture to worst case temperature transient which is an important problem in Industry. Our approach is based on the observation that, worst case temperature at a particular location in 2 D IC is determined not only by the current activity in that region, but also by the past activities in the surrounding regions. Therefore, if the surrounding areas were “pre-heated” with a different workload, then the target region may become hotter due to slower rate of lateral heat dissipation Similarly in case of 3D IC, the workload applied to each of the dies in 3D IC keeps on changing continuously, thus the hotspot could be found in any of the stacked layers. Thus the creation of localized hotspot at a particular location in a stacked 3D IC layer depends not only on the present activity at that location but also on the previous activity in the surrounding region and also on the activity of layers below it. Accordingly, (i) we develop a wavelet-based canonical spatio-temporal heat dissipation model for program traces, and use (ii) a novel Integer Linear Programming (ILP) formulation to rearrange program phases to generate target worst case hotspot temperature in 2D and 3D IC. We apply this formulation to target another well-known problem of (iii) maximizing temperature between a pair of co-ordinates in an IC. Experimental results show that by taking the spatio-temporal effect into account and with dynamic phase change behavior, we could raise temperature of a hotspot higher than what is possible otherwise. ICs are often tested at worst-case system operating conditions to assure that, all ICs shipped will function properly in the end system. Thus hotspot temperature maximization is an important in design verification and testing.

The main objective of this research was to exploit the interrelations between the rheological behavior and nano-microstructure of complex fluids in solving two state-of-the-art problems, one in the field of biomedical engineering: controlling the amount and characteristics of bioaerosol droplets generated during coughing, and the other in the bitumen-heavy oil industry: characterizing the nano-microstructure of asphaltene particles in bitumen and heavy oil from their rheological behavior. For the first problem, effect of viscoelastic and surface properties of artificial mucus simulant gels on the size distribution and amount of airborne bioaerosol droplets generated during simulated coughing were investigated. The results revealed that suppressing the generation of bioaerosol droplets and/or reducing the number of emitted droplets to a minimum during coughing are practically achievable through modulation of mucus viscoelastic properties. While variation of surface tension did not show any change in the droplet size distribution, an increase in particle size was observed as the samples changed from elastic solid type to viscoelastic type to viscous fluid type samples. This knowledge will help in the development of a new class of drugs being developed at the University of Alberta, aimed at controlling the transmission of airborne epidemic diseases by modifying the viscoelastic properties of mucus. For the second problem, studies of viscoelastic behavior of Athabasca bitumen (Alberta) and Maya crude (Mexico) oil samples, along with their Nano-filtered and chemically separated-plus-reconstituted samples were performed. The results revealed that the rheological behaviors of the bitumen-heavy oil samples are governed by their multiphase nature. The rheological behavior of all feeds, permeates and retentate samples followed a single master curve over the entire temperature interval, consistent with that of a slurry comprising a Newtonian liquid plus a dispersed solid comprising non-interacting hard spheres. The behavior of asphaltenes in the reconstituted samples, however, was found to be significantly different from that in nanofiltered samples. The information about the characteristics and behaviors of asphaltenes obtained in this study will help better understand the asphaltene structures, and support the effort to determine solutions for numerous asphaltene-related industrial problems. In the long run, this knowledge will help to create more efficient extraction and upgrading processes for bitumen and heavy oils. / Thermo Fluids

This thesis is mainly concerned with some important properties of complex fluids, and how these properties are influenced by structures in the nano/mesoscopic scale. Short-range assembly of the constituent molecules results in an amazing variety of phase behavior in these systems. Liquid-liquid phase transitions, or transitions from a homogeneous(mixed) phase to an immiscible phase (two-phase coexistence), are the outcome of a competition between entropy and short-ranged attractive forces, and form an important part of this thesis. A rich phase behavior is uncovered by a detailed study of liquid-liquid phase transitions in a mixture of ethanol(E) and water(W), induced by the addition of ammonium sulfate(AS) ions (E and W are otherwise completely soluble in each other). This is the main motivation for choosing this system. Furthermore, experimental evidence of the presence of supramolecular association in alcohol-water mixtures [J.-H. Guo et al., Phys. Rev Lett, 91, 15401(2003)] enhances our interest to study the phase behavior in more detail. The presence of a critical point, at which there is a second order phase transition, is quite common in complex fluids. An issue which has been the subject of extensive scientific research in recent years is the influence of nano/mesoscopic structure on the critical behavior of these fluids corresponds to the Ising universality class. However, the approach to the asymptotic regime is governed by a competition between the correlation length of critical concentration fluctuations and the additional length scale arising due to structuring., which results in a crossover from the universal Ising behavior to the mean-field behavior, sometimes within the critical domain. This phenomenon of crossover criticality is presently explored in the E + W + AS system. A significant portion of the thesis presents explorations on the critical behavior in the vicinity of special critical points (SCP), which are formed by the coalescence of two or more critical points. Recentrant liquid-liquid phase transitions observed in the E + W + AS system, furnishes an unique opportunity for the realization of three SCPs – the double critical point(DCP) and the critical double point(CDP) formed by the merger of two critical points , and a critical inflection point(CIP), formed by the merger of three critical points. A CIP had not been experimentally realized prior to the studies presented in this thesis. Apart from the above studies investigations are also carried out on the conformational changes of a technologically important conducting polymer, polyethylene dioxythiophene doped with polystyrene suflonate (PEDOT-PSS), in various solvents. The electrical and optical properties of the polymer films get enhanced when solution processed with specific solvents. The experiments presented in this thesis are directed at unraveling the role of conformational modifications in the electrical and optical properties of these systems. The experimental techniques that were employed in the present studies are: Laser light scattering, small-angle X-ray scattering(SAXS) measurements and visual observations. The eoexistence surface of the system E + W + AS was determined by visual observations. Laser light scattering measurements were conducted to study the critical behavior of osmotic susceptibility (xr) of E + W + As, whereas SAXS studies were conducted to ascertain the existence, and quantify the spatial extent of the additional length scale in the two systems investigated. The main objectives of this research were: (i) to study the phase behavior of the ternary mixture E + W + AS at atmospheric pressure; (ii) to check the existence of crossover from 3-D Ising to mean-field critical behavior while moving away from Tc in this system; (iii) to determine the nature (monotonic or nonmonotonic) of crossover; (iv) to provide some insight into the origin of this crossover behavior in terms of an additional length scale characteristic of the system; (v) to understand the evolution of the critical behavior in the proximity of CDP, and DCP; (vi) to experimentally realize the CIP; and (vii) to investigate the presence of solvent-induced conformational changes in conducting polymer.

No description available.

Environmentally benign alternatives for solvents and catalysts are essential for the development of sustainable chemical processes. Toward this end, we focused our research on the design of novel solvents and catalysts that reduce the environmental impact of these important materials. In this research, we develop switchable and tunable systems that couple reaction and separation to ease the processing requirements for product isolation and catalyst recovery. The switchable solvents use a ¡°switch¡± to transition from non-volatile, polar, aprotic solvents to volatile gases that can be easily separated. This allows us to facilitate reactions within the solvent and then enable easy separation through activation of the switch. We have used these materials for numerous reaction applications, including difficult reactions involving highly immiscible compounds. We also extended the work to acid-catalyzed reactions, in which we can avoid wasteful neutralization processes that are often associated with homogeneous acid catalysis. The tunable solvents use carbon dioxide pressure to ¡°tune¡± into desired solvent properties. We enable this through the dissolution of carbon dioxide into organic solvents, which generates gas-expanded liquids with solvent properties highly dependent on the carbon dioxide pressure. We can use this effect to couple homogeneous reaction with heterogeneous separation, allowing for recovery of expensive catalysts and ligands. In this work, we assess the possibilities of using liquid polyethylene glycol in the tunable systems, studying the phase behavior and industrial applications.