No description available.

This thesis was concerned with the proof of concept for mid-grade, 250-500oC, industrial waste heat recovery using a thermally regenerative electrochemical system. Proposed thermally regenerative electrochemical systems are limited to high operating temperatures (> 900oC) and suffer from poor conversion efficiencies (< 20%). As such, a single chamber design that is free of moving parts was presented in this work. The concept for this novel regenerative system relies on gravity and a liquid medium to convey dissolved sodium hydride in a hydride-borohydride solution from cold to hot regions in a continuous circuit. Such a liquid transport medium could allow for operation below 500oC while stabilizing the hydride from thermal decomposition. Investigations on this system were carried out using a custom pressure differential thermal analyzer that was able to operate above temperatures of 700oC and pressures of 2.2MPa. The results of the experiments provided valuable information concerning the phase diagrams of various hydride-borohydride mixtures. The eutectic composition of the NaH-KBH4 system was found to be 43 mole% NaH. The corresponding eutectic temperature (503oC) was determined using the differential cooling curves. Appreciable NaH decomposition was noticed in mixtures above 59.0 mole% NaH. Mixtures up to 42.5 mole% KH in KBH4 were also investigated. The eutectic composition of the KH-KBH4 binary system was determined by extrapolating the liquidus curve to intersect the solidus curve. The KH-KBH4 eutectic temperature was found to be 390oC at 66 mole% KH. The experimental work successfully demonstrates that thermally unstable hydrides can be obtained in the liquid phase below their melting points, under moderate pressures, when mixed with alkali borohydrides. This significantly lowers the achievable operating temperature of the thermally regenerative electrochemical systems currently proposed. The use of the single chamber design with a hydride-borohydride liquid medium offers numerous advantages including: reduced maintenance, reduced operating temperature, reduced system weight, reduced parasitic losses, increased voltage, and increased reliability. The viability for mid-grade industrial waste heat recovery requires construction of a prototype which optimizes power outputs and explores the hydrodynamic transport of material. / Thesis (Master, Mining Engineering) -- Queen's University, 2009-09-24 14:33:22.627

The flow of solid liquid mixtures (slurries) has attracted much attention in research work because of its importance to industry. Prediction of pressure losses associated with slurry flow helps pipe designers select the correct pipe sizes for optimum energy consumption, equipment sizing and reliable operation of the pipeline networks. Many workers developed empirical correlations, but due to the randomness of the problem they seem of limited use in design applications because they do not contain an assessment except by trial and error, which is costly. The existence of more than one particle size poses more complexities to the slurry flow problem but it is in need in practical applications. The aims of this work are justified under the light of the observations on the state of the art in slurry transport. An experimental program is designed to highlight the effects of this problem through a predetermined set of test runs. The variables are grouped to optimise the number of experiments and to remove the effect of dimensions on the prediction method The test rig is built to serve the aims of this exercise and test runs conducted, results grouped and discussed for polyfractional slurries. A mathematical model is developed in the form of an empirical correlation. Statistical tests are employed to verify the goodness of fit. Finally, conclusions and recommendations for further work are listed.

Doctor of Philosophy / Department of Chemistry / Paul E. Smith / Kirkwood Buff (KB) theory is one of the most important theories of solutions. The theory can relate integrals over radial (pair) distribution functions (rdfs) in the grand canonical ensemble to common thermodynamic properties. An inversion of the KB theory has been proposed by Ben-Naim and this has led to the wide spread popularity of KB theory. The idea of the KB inversion procedure is to calculate KB integrals from available thermodynamic properties. The KB theory can be used to validate the force field (ff) parameters used in molecular dynamics simulations. We have tested a series of small molecule ff parameters using KB theory that consists of both atom centered partial atomic charges and extra charge sites. The results indicate that using extra charge sites, derived from QM calculations, does not necessarily provide a more accurate representation of condensed phase properties. A further study aimed at an ongoing project of deriving new biomolecular ff parameters based on KB theory, has developed ff parameters for esters in order to represent the ester conjugation of the phospholipid molecule. The models were further tested against experimental properties. Preferential solvation (PS) is an important concept of solution mixtures that can be described using KB theory. The difference between local composition and bulk composition in solution mixtures leads to the concept of PS. A generalized explanation based on local mole fractions was derived by Ben-Naim using KB theory. However, the original expressions have been modified over years. Here, we propose a new approach based on local volume fractions to explore PS in binary and ternary solution mixtures. Experimental and simulation data were used to examine different approaches to PS. A relationship between the rdf and the triplet distribution function can be obtained using the Kirkwood Superposition Approximation (KSA). A combination of Fluctuation Solution Theory and experimental rdfs are used to examine the KSA at a series of state points for pure water. The accuracy of several other approximate relationships between the pair and triplet correlation functions was also investigated and are in good agreement for regions of the phase diagram where the compressibility is small.

No description available.

Gravity on Earth limits the study of the properties of pure fluids near critical point because they become stratified under their own weight. Near the critical point, all thermodynamic properties either diverge or converge and the heating and cooling cause instabilities of the convective flow as a consequence of the expansibility divergence. In order to study boiling, fluctuation and phase separation processes near the critical point of pure fluids without the influence of the Earth's gravity, a number of experiments were performed in the weightlessness of Mir space station. The experimental setup called ALICE II instrument was designed to suppress sedimentation and buoyancy-driven flow. Another set of experiments were carried out on Earth using a carefully density matched system of deuterated methanolcycloxexane to observe critical fluctuations directly. The set of experiments performed on board of Mir space station studied boiling and wetting film dynamics during evaporation near the critical point of two pure fluids (sulfur hexafluoride and carbon dioxide) using a defocused grid method. The specially designed cell containing the pure fluid was heated and, as a result, a low contrast line appeared on the wetting film that corresponded to a sharp change in the thickness of the film. A large mechanical response was observed in response to the cell heating and we present quantitative results about the receding contact lines. It is found that the vapor recoil force is responsible for the receding contact line. Local density fluctuations were observed by illuminating a cylindrical cell filled with the pure fluid near its liquid- gas critical point and recorded using a microscope and a video recorder. Microscopic fluctuations were analyzed both in sulfur hexafluoride and in a binary mixture of methanol cyclohexane. Using image processing techniques, we were able to estimate the properties of the fluid from the recorded images showing fluctuations of the transmitted and scattered light. We found that the histogram of an image can be fitted to a Gaussian relationship and by determining its width we were able to estimate the position of the critical point. The characteristic length of the fluctuations corresponding to the maximum of the radial average of the power spectrum was also estimated. The power law growth for the early stage of the phase separation was determined for two different temperature quenches in pure fluid and these results are in agreement with other experimental results and computational simulations.

This thesis reports light-scattering experiments and visual investigations close to the critical point, in the solvophobic systems, 3-methylpyridine (3MP) + heavy water (D2O) + sodium bromide (NaBr) and methyl ethyl ketone (MEK) + water (W) + secondary butyl alcohol (sBA). The system 3MP + D2O + NaBr was chosen in order to throw more light on the reported crossover from mean-field to Ising-type of critical behaviour shown by this system and to investigate the existence of a mean-field tricritical point in it at an NaBr weight fraction of X = 0.1700, two issues that have been the subject of an intense scientific debate in recent years. The system MEK + W + sBA is the result of our search for a system, other than, the well known 3-methylpyridine (3MP) + water (W) + heavy water (HW) + potassium iodide (KI), in which a quadruple critical point (QCP) can potentially be realized. In addition to this the thesis provides exhaustive details regarding the design, fabrication, and characterization, of a microkelvin thermostat in which a temperature stability of the order of a few microkelvin is achievable despite its relatively simple thermal design. The thesis is organized into 6 Chapters. Chapter 1 provides an introduction to the field of critical phenomena in liquid mixtures. The critical phenomena observed in various systems such as simple fluids, ionic fluids, polymer blends and polymer solutions, and micellar and microemulsion systems, are discussed in brief. Particular attention has been paid to the investigations by various researchers, into, the crossover from Ising to mean-field critical behaviour in electrolyte and polymer solutions, and in amphiphilic systems. Recent theoretical attempts at modeling ionic criticality have also been cited and summarized. A brief discussion on the various types of special critical points and multicritical points that are observed in multicomponent liquid mixtures and other condensed matter systems has been provided. The appealing possiblity of the presence of multicritical points in ionic fluids leading to crossover behaviour is also discussed. The chapter ends with a statement on the goals of this thesis. Chapter 2 describes the instrumentation and other aspects of the experimental techniques used for the light-scattering studies reported in this thesis. Details about the thermal instrumentation such as the water bath and the silicone-oil bath used for the visual investigation experiments and the metal thermostat used for the light-scattering experiments have been provided. The important design considerations relating to the achievement of a high degree of temperature stability (Formula) have been elucidated clearly. The modifications made to the design of the light-scattering thermostat, that enables achievement of a temperature stability of ± 2.5 mK at temperatures 19 ≤ T ≤ 24°C has been discussed. A section has been devoted to the description of the calibration of the temperature sensors we used in our experiments. The light-scattering instrumentation has been discussed in depth. The difficulties associated with the light-scattering techniques when it is used as a tool to study critical phenomena have been detailed. This is followed by a description of the method we used in correcting our light-scattering data for double-scattering effects. A description of the sample cells used for visual investigations and light-scattering experiments along with the sample filling and cleaning procedures followed by us has been described. Chapter 3 deals with the first of the three important problems discussed in this thesis. The chapter is aimed at investigating the crossover behaviour of the solvo-phobic system 3-methylpyridine (3MP)+ water (H2O) + sodium bromide (NaBr), by means of light-scattering studies on the strongly motivated and non-trivial system of 3-methylpyridine (3MP) + heavywater (D2O) + sodium bromide (NaBr). The replacement of H2O by D2O in 3MP + D2O + NaBr, is expected to accentuate the crossover behaviour reportedly displayed by 3MP + H2O + NaBr, and thereby, provide conclusive evidence regarding the existence or otherwise of a crossover between the Ising- and the mean-field-types of critical behaviour in this system. The chapter begins with a detailed literature survey on the topic of the crossover behaviour shown by the system 3MP + H2O + NaBr. We also provide a survey of the effect of the iso-topic H→D substitution on the critical behaviour of binary and quasibinary systems. Through an argument based on small-angle neutron scattering (SANS) studies and the Kirkwood-Buff integrals (KBIs), a strong and cogent motivation is established, which proves that, if the reported crossover behaviour in 3MP + H2O + NaBr is assumed to be correct, then the system 3MP + D2O + NaBr should display not just the same crossover behaviour as shown by the undeuterated system 3MP + H2O + NaBr, but, in addition, also a more pronounced dependence of the crossover temperature on the concentration of NaBr in the mixture than that seen in 3MP + H2O + NaBr. This approach to understand the crossover behaviour of 3MP + H2O + NaBr, has not been used by any of the previous investigators. The coexistence curve data for the system 3MP + D2O + NaBr are obtained at six different values of the NaBr weight fractions viz. X = 0, 0.0250, 0.0800, 0.1200, 0.1500, and 0.1800. The closed-loop immiscibility loop obtained for X = 0, agrees well with the reported phase diagram for 3MP + D2O in the literature. A comparison between the lower-critical lines obtained for the deuterated and the undeuterated system has been provided. Within error bars, no perceptible dip was observed in the critical line at X = 0.1700 in the case of the system 3MP + D2O + NaBr. Hence, our study does not indicate the presence of a mean-field tricritical point that has been reported at X = 0.1700 in the system 3MP + H2O + NaBr. A large section of Chapter 3 is devoted to the results and discussions of our extensive light-scattering experiments on the system 3MP + D2O + NaBr. The experiments were performed on 13 different samples of 3MP + D2O + NaBr with NaBr weight fractions in the range of 0 ≤ X ≤ 0.1900. The choice of the X values were guided by the NaBr concentrations at which earlier investigators have done light-scattering experiments on the system 3MP + H2O + NaBr. Detailed light-scattering experiments reveal that the system 3MP + D2O + NaBr shows a simple Ising-type critical behaviour with γ ' 1.24 and ν ' 0.63 over the entire NaBr concentration range 0 ≤ X ≤ 0.1900. The crossover behaviour is predominantly nonmonotonic, and the crossover is completed well outside the critical domain. An analysis in terms of the effective susceptibility exponent (γeff) showed that the crossover behaviour is nonmonotonic for 0 ≤ X ≤ 0.1793 and tends to become monotonic for X > 0.1793. The correlation length amplitude, ξo, has a value of (Formula) for 0.0250 < X ≤ 0.1900, whereas for (Formula). Since isotopic H—> D substitution is not expected to change the critical behaviour of the system, our results shows that the system 3MP + H2O + NaBr should exhibit universal Ising-type critical behaviour that is typical for aqueous solutions. Our search for a new system in which a quadruple critical point (QCP) could possibly be realized forms the subject matter of the Chapter 4 of the thesis. The system methyl ethyl ketone (MEK) + water (W) + secondary butyl alcohol (sBA) is identified as a very promising candidate-system for this purpose. The chapter begins with a brief survey of the various types of multicritical points and special critical points realizable in multicomponent liquid mixtures. The importance of investigating special critical points such as the QCP is motivated. A detailed coexistence surface for MEK + W + sBA was developed by generating the coexistence curves corresponding to five different, but onstant, values of MEK weight fractions XM = 0.0500, 0.1000, 0.1750, 0.2300, and 0.3000, respectively. The complete isobaric coexistence surface (at 1 atm) for the system MEK + W + sBA was visualized in the form of a prismatic phase diagram. The surface is found to display a tunnel-like appearance in the MEK weight fraction range of 0.0500 ≤ XM ≤ 0.1750, with the tunnel being the narrowest at the point (XM,XW,XSBA) = (0.1750, 0.5801, 0.2449), where, xw and XSBA are, respectively, the weight fractions of water and sBA in the mixture. An analysis of the order parameter data showed that MEK + W + sBA shows near Ising-type of critical behaviour near their upper critical solution temperatures, TU's. It was seen that the critical temperature Tc shows a low drift with time (Formula)/day and that the tunnel-like portion in the phase diagram of MEK + W + sBA was very symmetric. These two features make (MEK + W + sBA) a considerably more promising system than (3MP + W + HW + KI )for the realization of the QCP. It may be recalled that 3MP + W + HW + KI is the only system in which QCP studies have been reported so far in literature. The light-scattering investigations in MEK + W + sBA near the lower critical solution temperatures TL are described next. We corrected our light-scattering data for both turbidity as well as double-scattering effects. Our experiments revealed that (MEK + W + sBA) shows near three-dimensional-Ising type of critical behaviour at the lower critical solution temperatures, with the susceptibility exponent (γ) in the range of 1.217 ≤ γ ≤ 1.246. The correlation length amplitudes (ξo) and the critical exponent (ν) of the correlation length (ξ) were in the ranges of 3.536 ≤ ξo ≤ 4.611 A and 0.619 ≤ ν ≤ 0.633, respectively. An analysis in terms of the effective susceptibility exponent (γeff) results in the interesting result, namely that, the critical behaviour of (MEK + W + sBA ) is of the Ising-type for MEK concentrations in the ranges of 0.1000 ≤ XM ≤ 0.1250 and XM ≥ 0.3000; but, for the intermediate range of 0.1750 < XM < 0.3000, the system shows a tendency towards mean-field type of critical behaviour. This behaviour is interesting because both the constituent binary systems of the ternary system (MEK + W + sBA), namely, (MEK + W) and (W + sBA) show Ising-type of critical behaviour. Chapter 5 discusses another crucial objective of this thesis, namely, the fabrication and characterization of a microkelvin thermostat, which has been built for the purpose of performing light-scattering studies exceptionally close to the critical temperature. At the outset, the need for a temperature stability of the order of a few microkelvin for performing reliable critical point phenomena experiments very close to the critical point, is justified and demonstrated. This is followed by an in-depth account of the thermal design of the thermostat and the electronic circuitry used in the temperature controller. The variations in the ambient temperature and the stability of the bridge excitation source are identified and demonstrated to be crucial factors that affect the long-term temperature stability of the thermostat. A simple compensation scheme to nullify the effects of ambient temprature variations on the controller performance is suggested. It is demonstrated that the thermostat gives a temperature stability of (Formula) and ±60−90 µK for 7 − 14 h over a broad range of 25 − 103 °C. A detailed profile of thermal gradients within the sample recess is provided. It is shown that the parameter ∆Teff [i.e., the difference between the maximum (minimum if ∆Teff has a negative value) temperature within the sample recess and the temperature just outside the sample recess] is a more relevant parameter than ∆T (i.e., the temperature difference between the inner and the outer stages) in understanding the behaviour of multistage thermostats. The most important result that emerges from our study is that the thermal gradients and the transient response of the controller, can both be tuned by varying ∆Teff (or by varying ∆T). The best horizontal and vertical thermal gradient performance observed within our thermostat were 250 and 100 µK/mm, respectively, which are observed for a ∆Teff = 4.46 mK. The transient response of the controller is almost invariant for ∆Teff > 0 but it shows a dramatic decrease of almost 50% when ∆Teff < 0. It is seen that, the limit ∆Teff →>• 0, provides the best operating conditions of the thermostat from the standpoints of temperature stability, transient response and gradient performance. An error analysis relevant to the circuitry used by us is provided at the end of the chapter, which clearly indicates the efficacy of the compensations scheme proposed by us to nullify the effects of ambient temperature variations. Chapter 6 summarizes the important results obtained in this thesis. It also presents a range of open problems that need to be explored further in order to fully understand the results that are reported in this thesis, especially, regarding the type of crossover behaviour seen in the systems 3MP + D2O + NaBr and MEK + W + sBA.

Pevaporation is a method for separating volatile components from liquid mixtures at ambient temperatures. The paint processing industry uses Hansen solubility parameters (HSP) to indicate polymer solubility. The potential of this method to predict solvent-polymer affinity was investigated for screening potential membrane materials for the pervaporation of a model solution containing linalool and linalyl acetate (major components of lavender essential oil), in ethanol. Published HSP values were collated for various polymers, and statistically analysed to determine variations in HSP values for polymer species. An investigation of published research into pervaporation of organic/organic binary solutions separated by homogeneous membranes indicated that the solvent whose HSP value was closest to that of the polymer would preferentially permeate. This relationship did not always hold for halogenated solvents or aqueous/organic solutions. Conflicting literature regarding the relationship between solvent uptake by polymers and HSP relative energy differences was resolved using a logarithmic relationship between these two parameters. The following membranes were selected, using their HSP to indicate their potential to interact with lavender oil components: Polyamide (PA: 26.9 micro;m), Polycarbonate (PC: 20.5 micro;m), Poly(ether imide) (PEI: 29.2 micro;m), Poly(ether sulphone) (PES: 27.6 micro;m), Polyethylene (HDPE: 10 micro;m, LDPE: 13-30 micro;m), Polyimide (PI: 30.0 micro;m), Poly(methyl methacrylate) (PMMA: 50 micro;m), Polypropylene (PP: 15.9 micro;m), and Poly(tetrafluoro ethylene) (PTFE: 26.7 micro;m). The HSP (dispersive, polar hydrogen bonding components) for each membrane were calculated using the mean value obtained from swelling experiments, group contribution (calculated using Hoftyzer-Van Krevelen, Hoy and Beerbower methods), refractive indices (dispersive component), dielectric constants (polar component), and published HSP values. Pervaporation experiments investigated the effect of membrane thickness, process temperature, permeate pressure, impinging jet heights, feed flow rates and concentrations, and pre-soaking the membrane; on flow rate and selectivity in a polyethylene membrane. Membrane thickness was the dominant factor in membrane selectivity; the thinnest membranes (11.3-14.8 micro;m) had much poorer selectivity than membranes gt;24.7 micro;m. Temperatures between 22-34ordm;C, permeate pressure lt;10 kPa, impinging jet heights between 0.36-3.36 mm, feed flow rates between 541-1328 mL/min and concentrations between 1.78-6.01 % v/v of linalool and linalyl acetate in ethanol did not significantly affect selectivity. Flow rates increased with operating temperature, permeate pressure, and impinging jet heights. However, feed flow rate and concentration had no effect on membrane flux rate. Pre-soaking the membrane reduced the time to reach steady-state. Selected membranes were further investigated under standard operating conditions (permeate temperature 30ordm;C, permeate pressure lt;10 kPa, impinging jet height 1.36 mm, feed flow rate 804 mL/min and feed concentration of 5% v/v of linalool and linalyl acetate in ethanol). PMMA completely disintegrated in feed solution, and PC was too brittle to make an effective homogeneous membrane. PA, PC, PEI and PTFE had the highest efficiency (selectivity x flow rate) in their homogeneous form. However, PEI, PI and PTFE had the greatest selectivity, thus further trials should be done to improve stability and flow rates through these membranes. Pervaporation selectivity did not always follow trends predicted by HSP. Although polymers such as PA, PEI, PES, and PI preferentially permeated linalool as predicted, PC, PP and PTFE did not preferentially permeate linalyl acetate. This may have been due to the difference in size and diffusivity of these molecules (linalyl acetate, the larger molecule, did not follow the sorption selectivity predictions), or reliability of literature HSP values and those calculated by group contribution. This research shows that HSP is a good screening method for pervaporation membranes, especially where the molecules being separated are of comparable size. Polymers that have HSP close to the desired component and not to other components tend to have the best selectivity and flux characteristics. However, diffusion is an important factor, and is not completely accounted for by HSP. Recommendations for further research include: carrying out pervaporation analyses of selected polymers using pure lavender essential oil; modifying polymers to form asymmetric or composite membranes with improved permeation characteristics; and potential use of thin channel inverse gas chromatography to determine a more accurate HSP which includes diffusivity.

This thesis reports the results of light-scattering measurements and visual investigations of critical phenomena in the complex mixture 1-propanol (1P) + water (W) + potassium chloride (KCl) which has a special critical point (or a special thermodynamic state) known as the double critical point (DCP). The main theme of the thesis is the critical behavior on approaching a special critical point (i.e., the DCP) in a complex or associating mixture in contrast with that in simple, nonassociating mixtures. The asymptotic critical behavior in complex or associating fluids, such as polymer solutions and blends, ionic and nonionic micellar solutions, microemulsions, aqueous and nonaqueous electrolyte solutions, protein solutions, etc., is now commonly accepted to belong to the 3D-Ising universality class. However, the temperature range of the asymptotic regime in these fluids, with universal behavior, has a nonuniversal width and is, in general, smaller than that in simple or nonassociating fluids. In complex mixtures, which are made up of relatively large molecules or particle clusters of mesoscopic range, the coupling between the conventional correlation length of the critical fluctuations ( ξ) and an additional length scale associated with the mesoscale structures (ξD) is known to modify the approach towards the universal nonclassical critical behavior near their critical points. Nevertheless, the generality of this approach needs to be confirmed. There are also instances of a pure classical or close to classical behavior being observed in the critical domain of complex mixtures, although recent experimental results contradict the earlier observations. Therefore, further experimental evidences than that presently available are necessary before one can say how far the analogy between simple and complex fluids can be pushed. Variations in the effective dielectric constant of a mixture have been known to affect the critical behavior. Furthermore, we anticipate the presence of special critical points in complex mixtures to cause nontrivial modifications in the approach towards the universal asymptotic critical behavior. Special thermodynamic states are characterized by critical fluctuations with exceptionally large correlation length, and are displayed by multicomponent liquid mixtures, in which there are a multitude of thermodynamic paths by which a critical point can be approached, and offers rich information about the critical phenomena. These issues are being addressed in this research work. This thesis is organized into 7 Chapters. Chapter 1 begins with an account of the historical development of the field of critical point phenomena with a brief introduction to critical phenomena in simple fluids. Critical phenomena observed in various complex systems such as aqueous and nonaqueous ionic fluids, polymer solutions and blends, micellar and microemulsion systems, etc., are discussed, with particular attention to investigations into crossover from Ising to mean-field critical behavior observed in these systems, which are relevant to the present work. Theoretical attempts at modeling ionic criticality are cited and summarized. This is followed by a discussion of re-entrant phase transitions in multicomponent liquid systems. An account of the various types of special critical points, such as double critical point, critical double point, critical inflection point, quadruple critical point, etc., highlighting the critical behavior on approaching these special critical points, and some of the models of reentrant miscibility are briefly given. The Chapter ends with a statement on the goals of the present research work. Chapter 2 describes the instrumentation developed and the data acquisition procedures adopted for the study. Details of the thermostats and precision temperature controllers used for visual and light-scattering measurements are provided. The important design considerations relating to the achievement of a high degree of temperature stability (~ ±1 mK in the range 293-383 K) are elucidated clearly. The temperature sensors used in the present experiments and their calibration procedures are discussed. The light-scattering instrumentation is discussed in depth. The problems associated with the light-scattering techniques when it is used to study critical point phenomena, and the strategies adopted to overcome them are discussed. The sample cells used for visual investigations and light- scattering experiments, along with the procedure adopted for cleaning and filling of sample cells are also described. Chapter 3 essentially deals with the characterization of the system 1P + W + KCl. It begins with a brief introduction to the critical behavior in complex mixtures, and the motivation behind choosing the present system. The phase behavior in the present mixture, the generation of the coexistence curves and the line of critical points in the mixture, and the method used for preparation of the samples are described. The criticality of the samples is judged by the equal volume phase separation criterion through visual investigations. Addition of a small amount of salt (i.e., KCl) to the 1P + W solution induces phase separation in the mixture as a result of a salting-out process. Decreasing the salt concentration has the same effect as that of increasing pressure on the liquid-liquid demixing of this mixture. Therefore, KCl may be considered as an appropriate field variable analogous to pressure in this mixture. The mixture 1P + W + KCl exhibits reentrant phase transitions and has an array of lower (TL) and upper (TU) critical solution temperatures. It is found that the line of TL’s and TU’s, known as the line of critical points, merge (TU - TL = ΔT → 0) to form a special thermodynamic state known as the DCP. The DCP is approached as close as 509 mK (i.e., ΔT ~ 509 mK) in this work. An analysis of the critical line shows that it is roughly parabolic in shape, which is in consonance with the predictions of the lattice models and the Landau-Ginzburg theory of phase transition. In addition to the presence of a special critical point, various structure probing techniques like small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), etc., indicate the presence of large-scale density inhomogeneities or clusters in 1P + W solution and its augmentation on adding small amount of KCl. Therefore, the present mixture provides a unique possibility to investigate the combined effects of molecular structuring as well as a special critical point on the critical behavior. Only a section of the coexistence surface of the mixture could be generated, owing to various experimental limitations and other problems inherent to the system. This limited further studies on the coexistence curves in the mixture. Chapter 4 reports the critical behavior of osmotic susceptibility in the present mixture. The behavior of the susceptibility exponent is deduced from static light-scattering measurements, on approaching the lower critical solution temperatures (TL’s) along different experimental paths by varying t [ =| (T - T TL)/ TL|] from the lower one-phase region. The light-scattering data analysis emphasizes the need for correction-to-scaling terms for a proper description of the data over the investigated t range. Renormalization of the critical exponents is observed as the critical line is approached along certain special paths. Experimental evidence for the doubling of the extended scaling exponent Δ1 near the DCP is shown. There is no signature of Fisher renormalization in the values of the critical exponents. The data analysis yields very large magnitudes for the correction amplitudes A1 and A2, with the first-correction amplitude A1 being negative, signifying a nonmonotonic crossover behavior of the susceptibility exponent in the mixture. The magnitudes of the correction amplitudes are observed to increase gradually as TL approaches the DCP. The increasing need for extended scaling in the neighborhood of special critical points has been noted earlier in several aqueous electrolyte solutions, in polymer-solvent systems, etc. However, the magnitudes of the correction amplitudes were not as large as that in the present case. Analysis of the effective susceptibility exponent γeff in terms of t indicate that, for the TL far away from the DCP, γeff displays a nonmonotonic crossover from its single limit 3D Ising value (~ 1.24) towards its mean-field value with increase in t. While for that closest to the DCP, γeff displays a sharp, nonmonotonic crossover from its nearly doubled 3D-Ising value (~ 2.39) towards its nearly doubled mean-field value (~ 1.84) with increase in t. For the in-between TL’s, the limiting value of γeff in the asymptotic as well as nonasymptotic regimes gradually increases towards the DCP. The renormalized Ising regime extends over a relatively larger t range for the TL closest to the DCP, and a trend towards shrinkage in the renormalized Ising regime is observed as TL shifts away from the DCP. Nevertheless, the crossover behavior to the mean-field limit extends well beyond t > 10¯2 for the TL’s studied. The crossover behavior is discussed in terms of the emergence of a new lengthscale ξD associated with the enhanced ion-induced clustering seen in the mixture, as revealed by various structure probing techniques, while the observed unique trend in the crossover is discussed in terms of the varying influence of the DCP on the critical behavior along the TL line. The discussion is extended to explain the observed critical behavior in various re-entrant systems having other special critical points. The extended renormalized Ising regime towards the DCP is also reflected in a decrease in the correlation length amplitude (ξ0) as TL approaches the DCP. It is observed that the first-correction amplitude A1 corresponding to fit using two correction terms becomes more negative as TL approaches the DCP, implying an increase in the value of the parameter ū of the crossover model [by Anisimov et al., Phys. Rev. Lett. 75, 3146 (1995)] as the DCP is approached. This increase in reflected in a trend towards a relatively sharp crossover behavior of γeff as TL shifts towards the DCP, i.e., towards the high temperature critical points. The significance of the field variable tUL in understanding different aspects of reentrant phase transitions is manifested in the present system as well. Analysis of the data in terms of tUL led to the retrieval of universal values of the exponents for all TL’s. The effective susceptibility exponent as a function of tUL displays a nonmonotonic crossover from its asymptotic 3D-Ising value towards a value slightly lower than its nonasymptotic mean-field value of 1. The limited (TL _ T) range restricted such a behavior of the effective exponent (in terms of t as well as tUL) for the lowest TL. This feature of the effective susceptibility exponent is interpreted in terms of the possibility of a nonmonotonic crossover to the mean-field value from lower values in the nonasymptotic, high tUL region, as foreseen earlier in micellar systems. The effective susceptibility exponent in terms of tUL also indicates an increase in the sharpness of crossover towards the high temperature TL’s. An increase in the sharpness of crossover with polymer chain length has been observed in polymer solutions. Therefore, our results suggest the need for further composition and temperature-dependent study of molecular structuring in the present mixture. There is also a large decrease in the dielectric constant of the mixture towards the high temperature TL’s. In Chapter 5 the light-scattering measurements are performed on approaching the DCP along the line of the upper critical solution temperatures (i.e., TU’s), by varying t [ = (T - TU )/ TU ] from the high temperature one-phase region in the mixture. A trend towards shrinkage in the simple scaling region is observed as TU shifts away from the DCP. Such a trend was not visible in the data analysis of the TL’s using the correction terms, due to the varying (TL - T) ranges. The light-scattering data analysis substantiates the existence of a nonmonotonic crossover behavior of the susceptibility exponent in the mixture. As with the TL’s, for the TU closest to the DCP, γeff displays a nonmonotonic crossover from its 3D-Ising value towards its nearly doubled mean-field value with increase in t. While for that far away from the DCP, γeff displays a nonmonotonic crossover from its single limit Ising value towards a value slightly lower than its mean-field value of 1 with increase in t. The limited (TL – T) range restricted such a behavior of γeff for the TL far away from the DCP, This feature of γeff in the nonasymptotic, high t region is yet again interpreted in terms of the possibility of a nonmonotonic crossover to the mean-field value from below. Unlike TL’s, the crossover behavior in the present case is pronounced and more sharp for all TU’s. However, the variation in the width of the renormalized Ising regime on approaching the DCP along the TU line is quite similar to that observed along the TL line. The crossover behavior is attributed to the strong ion-induced structuring seen in the mixture, while the observed trend in the crossover as TU shifts towards/away from the DCP is attributed to the varying influence of the DCP. The influence of the DCP on the critical behavior along the TU (or TL) line decreases as TU (or TL) shifts away from the DCP. Our observations indicate an increase in the sharpness of crossover as the critical temperature shifts from TL towards TU, or in other words, as the critical point shifts towards higher temperatures. SANS measurements on the present mixture indicate no difference in the growth of mesoscale clusters in the lower and upper one-phase regions in the mixture. Hence, the observed increase in the sharpness of crossover towards the TU’s is very puzzling. The dielectric constant of the major constituent (i.e., water, ~ 62 %) of the present mixture decreases from around 80 to 63 as the critical temperature shifts from TL towards TU. Therefore, our results suggest the need to look at the crossover phenomena probably from two perspectives, namely, the solvent or dielectric effect and the clustering effect. The increase in the sharpness of the crossover behavior on approaching the high temperature critical points is probably related to the macroscopic property of the mixture, i.e., to the decrease in the dielectric constant of the mixture, while the actual nonmonotonic character of the crossover behavior is related to the microscopic property of the mixture, i.e., to the clustering effects, the extent of which determines the width of the asymptotic critical domain. However, this conclusion is somewhat subtle and calls for rigorous theoretical and experimental efforts to unravel the exact dependence of the crossover behavior on the dielectric constant. Analysis using the field variable tUL in lieu of the conventional variable t led to the retrieval of unique, universal exponents for all TU’s irrespective of the ΔT value. For all TU’s, the effective susceptibility exponent in terms of tUL displays a nonmonotonic crossover from its asymptotic 3D-Ising value towards a value slightly lower than its nonasymptotic mean-field value of 1, as that observed in the t analysis of the effective exponent for the TU far away from the DCP. Like with the TL’s, the crossover behavior extends over nearly the same tUL range for the TU’s studied. However, the crossover is again sharper when compared to the TL’s. Chapter 6 reports light-scattering measurements (by heating as well as cooling) on a non phase-separating 1P + W + KCl mixture in the vicinity of the DCP. The results indicate that despite the lack of phase-separation or critical points, critical-phenomena-like fluctuations can still occur in homogeneous mixtures if they reside in some other direction than temperature or composition (like, pressure or salt concentration) of the phase diagram. Unlike earlier studies on non phase-separating mixtures, our results indicate a crossover behavior of the effective susceptibility exponent, in addition to the power-law behavior. Chapter 7 sums up the major findings of the work reported in this thesis. It also presents a range of open problems that need to be explored further in order to fully understand the results that are reported in this thesis, especially, regarding the exact dependence of dielectric constant of the mixture on the character of the crossover behavior.

The thesis entitled “Novel Redox Responsive Cationic Lipids, Lipopolymers, Glycolipids and Phospholipid-Cationic Lipid Mixtures: Syntheses, Aggregation and Gene Transfection Properties” elucidates the design, synthesis, aggregation and gene transfection properties of novel cholesterol based cationic lipids with ferrocene as the redox moiety, polyethylenimine based ferrocenylated lipopolymers and cholesterol based non-ionic glycolipids. The thesis also discusses the cationic phospholipid-cationic lipid mixtures as superior gene transfection agents. The work has been divided into six chapters. Chapter 1. Introduction Part A. Various Cholesterol based Systems for Applications as Biomaterials Liposomes composed of cationic lipids have become popular gene delivery vehicles. A great deal of research is being pursued to make efficient vectors by varying their molecular architecture. Cholesterol being ubiquitous component in most of the animal cell membranes is increasingly being used as a hydrophobic segment of synthetic cationic lipids. In this chapter we describe various cholesterol based cationic lipids and focus on the effect of modifying various structural segments like linker and the headgroup of the cationic lipids on gene transfection efficiency with a special emphasis on the importance of ether linkage between cholesteryl backbone and the polar headgroup. Interaction of cationic cholesteryl lipids with dipalmitylphosphatidycholine membranes is also discussed here. Apart from cholesterol being an attractive scaffold in the drug/gene delivery vehicles, certain cholesteryl derivatives have also been shown to be attractive room temperature liquid-crystalline materials. Part B. Diverse Applications of Ferrocene Derivatives This chapter gives a brief overview of ferrocene chemistry followed by description of major applications of ferrocenyl derivatives in a variety of fields like catalysis, materials chemistry, electrochemical sensors, medicinal chemistry etc. We discuss the use of ferrocene as an electrochemical and redox active switch to achieve control over supramolecular aggregation. It also reviews ferrocene based amphiphiles including surfactants, lipids and polymers with an emphasis on the role of ferrocene over aggregate formation and their utilization in biological applications. Chapter 2: Optimization of Redox Active Alkyl-Ferrocene Modified Polyethylenimines for Efficacious Gene Delivery in Serum 1a-c, n = 6, P8-C6-F1, P8-C6-F2, P8-C6-F3 2a-c, n = 11, P8-C11-F1 P8-C11-F2, P8-C11-F3 % ferrocene grafting, F1 = 15%, F2 = 25% and F3 = 50% Figure 1. Structure of the alkyl-ferrocene modified 800 Da Branched Polyethylenimine. In this chapter we present six new lipopolymers based on low molecular weight polyethylenimines (BPEI 800 Da) which are hydrophobically modified using ferrocene terminated alkyl tails of variable lengths. The effects of degree of grafting, spacer length and redox state of ferrocene in the lipopolymer on the self assembly properties were investigated in detail by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and zeta potential measurements. The assemblies displayed a redox induced increase in the size of the aggregates. The coliposomes comprising of the lipopolymer and a helper lipid 1,2-Dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) showed excellent gene delivery capability in serum containing environment in two cancer cell lines (HeLa, U251 cells). Optimized formulations showed remarkably higher transfection activity than BPEI 25 KDa and even better than commercial Lipofectamine 2000 as evidenced from luciferase activity and EGFP expression analysis. Oxidation of ferrocene in lipopolymers led to reduced levels of gene transfection which was also followed by cellular internalization of fluorescently labeled pDNA using confocal microscopy. Cytotoxicity assay revealed no obvious toxicity for the lipopolyplexes in the range of optimized transfection levels. Overall, we have exploited the redox activity of ferrocene in PEI based polymeric gene carriers for trenchant control over gene transfection potential. RLU/mg protein HeLa Cells Figure 2. Maximum transfection efficacies of optimized redox lipopolymer/DOPE formulations by (A) Luciferase Assay and (B) Flow cytometry (GFP expression). Chapter 3. Membranes derived from Redox-active Cholesterol based Cationic Lipids and their Interactions with DNA and Phospholipid Membranes Figure 3. Molecular structures of the electroactive cholesterol based monomeric and gemini lipids. This chapter describes the synthesis and aggregation properties of two series of redox-active ferrocene containing monomeric and gemini cationic lipids with cholesterol as a hydrophobic domain. These cationic lipids are modified at their headgroup region using ferrocene terminated alkyl chains of differing length. All the four cationic lipids formed stable suspensions in water. Aggregation behavior of these cationic lipids in aqueous suspensions in their unoxidized and oxidized state was studied using TEM, DLS, zeta potential measurements and XRD studies. Cationic lipids with ferrocene in natural, reduced state were found form bigger sized vesicles which upon oxidation became smaller aggregates with increased zeta potential. XRD results indicate the existence of nice lamellar arrangements of the lipid bilayers. Thermotropic phase transition behavior of DPPC membranes incorporated with cationic ferrocene lipids was also studied using differential scanning calorimetry. Finally, we assayed pDNA (plasmid DNA) binding ability of all the four cationic lipids using ethidium bromide intercalation assay where all the cationic lipid formulations showed excellent DNA binding capability. In the experiments involving SDS-induced release of DNA, we observed that redox-active monomeric lipids (3a-b) were found to be more efficient in facilitating the release of DNA from the liposome-DNA complex in the presence of negatively charged SDS micelles than their gemini counterparts (4a-b). Chapter 4. Redox-responsive Gene Delivery by Ferrocene containing Cationic Cholesteryl Lipids in Serum This chapter describes the transfection efficacy of redox-active monomeric and gemini cationic lipids with cholesterol backbone. The transfection efficiency of all the lipids could be tuned by changing the oxidation state of the ferrocene moiety. Gene transfection capability was assayed in terms of EGFP expression using pEGFP-C3 plasmid DNA in three cancer cell lines of different origin, namely Caco-2, HEK293T and HeLa in the presence of serum. Figure 4. Effect of oxidation state of ferrocene on maximum transfection efficacies of monomeric and gemini lipids in three different cell lines (Caco-2, HEK 293T and HeLa). Cationic liposomal formulations with ferrocene in its reduced state were observed to be potent transfectants reaching the EGFP expression levels even better than commercial lipofectamine 2000 in the presence of serum as evidenced by flow cytometry. EGFP expression was further substantiated using fluorescence microscopy studies. All liposomal formulations containing oxidized ferrocene displayed diminished levels of gene expression and interestingly, these results were consistent for each formulation in all the three cell lines. Assessment of EGFP expression mediated by both reduced and oxidized ferrocene containing formulations was also undertaken following cellular internalization of labelled pDNA using confocal microscopy and flow cytometry. Lipoplexes derived from different liposomal formulations with reduced and oxidized ferrocene were characterised using TEM, AFM, zeta potential and DLS measurements. Overall, we demonstrate here controlled gene transfection levels using redox driven, transfection efficient cationic monomeric and gemini lipids. Chapter 5: Synthesis of ‘Click Chemistry’ Mediated Glycolipids: Their Aggregation Properties and Interaction with DPPC Membranes This chapter describes the synthesis and aggregation properties of cholesterol based glycolipids along with their interaction with a model phosphatidylcholine membranes. Three series of non-ionic glycolipids with hydrophobic cholesterol backbone and various monosaccharide and disaccharide sugars as the hydrophilic polar domain have been synthesized. These were conjugated to the cholesteryl backbone via oligooxyethylene spacers of different lengths (n = 1, 3 and 4) using Cu (I) catalyzed Huisgen [3+2] cycloaddition, which is popularly known as „Click Chemistry‟. All the synthetic glycolipids (5a-d, 6a-d and 7a-d) formed vesicular aggregates in aqueous medium as confirmed by TEM and DLS. XRD studies with the cast films of lipids revealed that the bilayer width increased with increase in the length of oligoethylene spacer unit that has been incorporated between the hydrophobic and hydrophilic domains. Also, within the same series containing a particular oligoethylene unit, bilayer widths were found to be more for the lipids containing disaccharides as their headgroup than monosaccharides. Figure 5. Molecular structures of various cholesterol-based glycolipids. Calorimetry studies of the coaggregates containing naturally occurring 1, 2-dipalmitoylphosphatidylcholine (DPPC) and various mol-% of each of the glycolipids revealed that more than 30 mol-% of glycolipids are required to completely abolish the phase transition of DPPC membranes. These results were further supported by fluorescence anisotropy measurements of the co-aggregates using 1, 6-diphenylhexatriene (DPH) as a probe. Fluorescence anisotropy of the neat vesicles revealed that 9a and 9c were more rigid than DPPC vesicles in the solid-like gel phase, while the glycolipids with longer oxyethylene spacers (n = 3 and 4) were less rigid than the DPPC vesicles. Chapter 6. Hydrophobic Moiety Decides the Synergistic Increase in Transfection Efficiency in Cationic Phospholipid/Cationic Lipid mixtures This chapter describes the effect of inclusion of cationic lipid/cationic gemini lipids into the membranes of a cationic phospholipid on the gene delivery efficiency across HeLa and HEK293T cell lines. Although all the three cationic lipids have the same quaternary ammonium moiety as their headgroup, they differ from each other in terms of their hydrophobic moiety and in the number of cationic headgroups. Chol-N is a cholesterol based monocationic lipid, while 2C14-N and 2C14N-5-N2C14N are monomeric and gemini cationic lipids respectively with pseudoglycerol backbone consisting of tetradecyl (n-C14H29) chains. Each of the three cationic lipids under the current investigation, namely, Chol-N, 2C14-N and 2C14N-5-N2C14N were added in different ratios to EtDMoPC and the resultant mixed membranes were studied for the biophysical characterization and gene delivery efficacies. Figure 6. Molecular structures of cationic lipids used in this study. All the formulations were characterized using dynamic light scattering and zeta potential measurements to obtain their hydrodynamic diameters and surface charge properties respectively. Their DNA binding ability was also studied by measuring changes in zeta potential and gel electrophoresis of the lipoplexes formed by the coliposomal formulations and pDNA at different Lipid/DNA weight ratios. The gene delivery efficacies of various formulations were studied in terms of EGFP expression using pEGFP-C3 plasmid DNA in two different cell lines, namely HeLa and HEK293T. In the absence of serum we found that the formulation (EtDMoPC+2C14N-5-N2C14N) showed better transfection efficiency than the individual lipids. However, in the case of others, i.e., (EtDMoPC+Chol-N) and (EtDMoPC+2C14-N) formulations, there was a slight decrease in transfection efficiency compared to the individual lipids. In the presence of serum, the formulations (EtDMoPC+2C14-N) and (EtDMoPC+2C14N-5-N2C14N) showed significantly higher transfection efficacies compared to their individual lipids. Fusion assay using labelled cationic lipid formulations and unlabelled anionic liposomes revealed that lipoplexes prepared from EtDMoPC+ 2C14-N and EtDMoPC+ 2C14N-5-N2C14 exhibited much higher fusogenicity as compared to the lipoplexes prepared using EtDMoPC+Chol-N as well as the individual lipids. Thus, the liposome formulations which showed better transfection activity fused more readily with the anionic liposomes than did the formulations with poorer activity. Overall, we found that the hydrophobic domain of the cationic lipid/cationic gemini lipid that is added to cationic phospholipid has an important role on the transfection efficiency of the mixed formulations. Additionally the cytotoxicity studies revealed that each of these formulations was not significantly toxic making them viable for applications in vivo. (For structural formula pl see the abstract pdf file)