Spin systems with low dimensionality and geometrical frustration have attracted interest because of the possible emergence of novel magnetic phases at low temperatures by suppressing conventional magnetic order, and allow for a novel spin-disordered ground state, such as quantum spin liquid and glass without any apparent structural disorder. In this thesis, we have discussed magnetic and dielectric measurements on the quasi-two-dimensional triangular antiferromagnet NiGa2S3.85, in order to investigate its magnetic state and dielectric property at low temperatures. In the measurement of susceptibility In the measurement of susceptibility £q(T), we found that the freezing temperature is near 6 K. This suggests that the sample with the sulfur deficiency should be close to the stoichiometric NiGa2S3.85. Under 7 T magnetic filed ZFC(zero-field-cooling) and FC(field-cooling) still bifurcate indicating more magnetic order state than spin-liquid. Temperature-dependent dielectric measurement shows an interesting colossal enhancement of dielectric constant with frequency dispersion and is ascribed to the interfacial polarization (termed as Maxwell-Wagner relaxation) at the interface between adjacent layers. Temperature-dependent dielectric measurement under applied magnetic field (up to 9 T) shows negligible magnetodielectric behavior because of the sample is not magneto resistive.

The goal of the present study is to elucidate the modulatory effect of lipid compositions on phospholipase A2 (PLA2) activity. Sphingomyelin (SM) incorporation inhibited catalytic activity and membrane-damaging activity of native and mutated PLA2 toward egg yolk phosphatidylcholine (EYPC) vesicles. The inhibitory effects were through the reduction of membrane fluidity and modulation of the mode of membrane binding of PLA2 at water/lipid interface. The modulated effect of SM depended on inherent structural elements of PLA2. Moreover, cholesterol (Chol) incorporation into EYPC/egg yolk sphingomyelin (EYSM) vesicles relieved the inhibitory effect of sphingomyelin on PLA2 activity via lipid domain formation by SM and Chol. The effects on the interactive mode of PLA2 with phospholipids induced by the physical state changes of membrane bilayers abolished the inhibition of SM on catalytic activity and membrane-damaging activity of PLA2. Additionally, quercetin incorporation increased PLA2 activity and membrane-damaging activity toward EYPC/SM vesicles via its raft-making effect. Quercetin incorporation reduced PLA2 activity and membrane-damaging activity toward EYPC/SM/Chol vesicles via its raft-breaking effect. Membrane-inserted quercetin affected on membrane structure and membrane-bound mode of PLA2 to modulate PLA2 interfacial activity and membrane-damaging activity. Finally, studies on the effects of phosphatidylserine (PS) content on the sensitivity of lipid vesicles mimicking inner and outer plasma membrane toward PLA2 activity revealed that the membrane-binding mode adopted by PLA2 depended on the lipid composition. The effects of PS content on the extent of lipid domain formation and the conformation of PLA2 adopted at water-lipid interface modulate PLA2 catalytic activity. Collectively, these results indicate that lipid composition modulates PLA2 activity via its effects on membrane structure and membrane-bound mode of PLA2

Two-phase liquid-gas flow has a wide variety of applications in space, including active thermal control systems, high-power communications satellites, heat pumps and space nuclear reactors. Two-phase systems have many potential advantages over current single-phase systems due to reductions in system size, weight and power consumption. The mechanisms of pressure drop, heat transfer coefficients, void fractions, and flow regimes must be well understood under microgravity conditions in order to design reliable two-phase systems. The main objective of this present research is to develop a new mathematical model that can accurately predict the annular two-phase friction pressure drop to optimize the design of two-phase systems. The two-phase flow tests were conducted aboard the NASA KC-135 aircraft by the Interphase Transport Phenomena (ITP) group from Texas A&M University. The two-phase flow pressure drops were measured across a single transparent test section 12.7 mm ID and 1.63 m long in annular regimes under microgravity conditions during two flight campaigns. Different from previous work, this was the first time both the void fraction and the film thickness were measured under microgravity conditions. The empirical correlations for the interfacial friction factor and void fraction were developed from 57 experimental data using a linear least squares regression technique. The annular two-phase friction pressure drop can be predicted by the new mathematical model requiring only knowledge of the length and diameter of the tube, liquid and vapor mass flow rates, and properties of the working fluid. In addition, the new mathematical model was validated using Foster-Miller & ITP data collected over twelve flights aboard the KC-135 with working fluid R-12 (77 data points), Sundstrand data collected aboard the KC-135 with working fluid R-114 (43 data points) and Zhao and Rezkallah data aboard the KC-135 with working fluid water and air (43 data points). Compared with the LockhartMartinelli model, Wheeler model, Chen model and homogeneous model, the new mathematical model is the optimal model for predicting the two-phase friction pressure drop in annular regimes. The majority of the data falls within +-20% of the proposed correlation and the average error is 12%.

It is an important issue for manufacturing and operation to formulate reliability about the effects of the moisture absorption and IR reflow parameters on IC packages. Two problems, the warpage of the thin IC package, and characterizing the adhesion features of IC package¡¦s interface, are studied in this dissertation. In a thin IC package, the CTE and CHE mismatch between materials are primarily attributed to the warpage which occurs when the package is being mounted on a PCB. The existence of defects in the corresponding interfaces can gradually degrade the interfacial adhesion when IC package is exposed to the high temperature and humidity. In this dissertation, the stability equations for the warpage in a thin IC package without the solder balls being subjected to hygrothermal loading, by modeling it as an initially perfect/imperfect composite plate, is developed. The analytical closed-form solutions are found and used to compute not only the critical moisture content but also the warpage occurrence before the critical loads are reached. The hygrothermal buckling phenomenon is checked by shadow moiré whole-field maps with different moisture content. The results indirectly indicate that the thin PBGA package has little imperfection. For characterizing the adhesion features of IC package¡¦s interface, the fuzzy controller is used to stabilize multiple performance characteristics, i.e., the moisture weight gain and adhesion strength, for the button shear test specimen. Parameters design, although based on the Taguchi method, can optimize the performance characteristic through the setting of process parameters and can reduce the sensitivity of the system performance to sources of variation. The control rules of the fuzzy controller were formed using the author¡¦s experience and knowledge of IC packaging process. The control parameters to be tuned were the membership functions. Therefore, the controller¡¦s performance depended on the membership functions. The fuzzy controller combined Taguchi parameter design, which makes the control performance insensitive to the operating condition change and noise, was used to determine the membership functions.

Inorganic-polymer hybrid materials have a high potential to enable major advances in material performance in a wide range of applications. This research focuses on characterizing and tailoring the physics and chemistry of inorganic-polymer interfaces in fabricating high-performance zeolite-polymer mixed-matrix membranes for energy-efficient gas separations. In addition, the topic of novel metal nanoparticle-coated polymer microspheres for optical applications is treated in the Appendix. In zeolite/polymer mixed-matrix membranes, interfacial adhesion and interactions between dope components (zeolite, polymer and solution) play a crucial role in determining interfacial morphology and particle dispersion. The overarching goal is to develop accurate and robust tools for evaluating adhesion and interactions at zeolite-polymer and zeolite-zeolite interfaces in mixed-matrix membrane systems. This knowledge will be used ultimately for selecting proper materials and predicting their performance. This project has two specific goals: (1) development of an AFM methodology for characterizing interfacial interactions and (2) characterization of the mechanical, thermal, and structural properties of zeolite-polymer composites and their correlation to the zeolite-polymer interface and membrane performance. The research successfully developed an AFM methodology to determine interfacial interactions, and these were shown to correlate well with polymer composite properties. The medium effect on interactions between components was studied. We found that the interactions between two hydrophilic silica surfaces in pure liquid (water or NMP) were described qualitatively by the DLVO theory. However, the interactions in NMP-water mixtures were shown to involve non-DLVO forces arising from bridging of NMP macroclusters on the hydrophilic silica surfaces. The mechanism by which nanostructured zeolite surfaces enhanced in zeolite-polymer interfacial adhesion was demonstrated to be reduced entropy penalties for polymer adsorption and increased contact area. ¡¡¡¡¡¡Metal nanoparticle (NP)-coated polymer microspheres have attracted intense interest due to diverse applications in medical imaging and biomolecular sensing. The goal of this project is to develop a facile preparation method of metal-coated polymer beads by controlling metal-polymer interactions. We developed and optimized a novel solvent-controlled, combined swelling-heteroaggregation (CSH) technique. The mechanism governing metal-polymer interaction in the fabrication was determined to be solvent-controlled heteroaggregation and entanglement of NPs with polymer, and the optical properties of the metal/polymer composite beads were shown to make them useful for scattering contrast agent for biomedical imaging and SERS (Surface-Enhanced Raman Scattering) substrates.

Die Dissertation verfolgt das Ziel, das Sedimentationsverhalten kolloidaler Suspensionen in Abhängigkeit von der Partikelkonzentration und den Partikelwechselwirkungen zu untersuchen und die Grenzen einer Sedimentationsanalyse im Zentrifugalkraftfeld auszuarbeiten. Um Effekte der Partikelagglomeration von den anderen Einflussfaktoren unterscheiden zu können, wurde besonderes Augenmerk auf die Gewährleistung der Suspensionsstabilität und deren messtechnischen Nachweis gerichtet. Im Submikrometerbereich gewinnen die zwischen den einzelnen Partikeln wirkenden nicht-hydrodynamischen Kräfte gegenüber Trägheits- oder Feldkräften an Bedeutung und können diese sogar dominieren. Infolgedessen ist der Zustand einer kolloidalen Suspension nicht mehr allein über die Partikelgrößenverteilung und die Partikelkonzentration definiert, sondern gleichfalls abhängig von den bestehenden Grenzflächeneigenschaften, die wiederum von solchen Eigenschaften der kontinuierlichen Phase wie pH-Wert oder Elektrolytgehalt abhängen. Im Zentrum der experimentellen Arbeiten stand die Untersuchung des Einflusses der Partikelkonzentration auf das Sedimentationsverhalten feinster Partikelsysteme. In der Literatur existiert keine einheitliche Beschreibung des Konzentrationseinflusses. In der Dissertation wurde die Suspensionsstabilität von Siliziumdioxid-Suspensionen gezielt beeinflusst, um deren Einfluss auf das Sedimentationsverhalten zu bewerten. Es wurde gezeigt, dass nur für instabile Suspensionen die erwartete Sinkgeschwindigkeitsüberhöhung existiert. Es wurde aber auch gezeigt, dass die bei unterschiedlichen Drehzahlen erhaltenen Sinkgeschwindigkeiten nicht über das Beschleunigungsvielfache skaliert werden können. Weiterhin wurde demonstriert, dass in solchen Systemen eine komplexe Abhängigkeit vom Feststoffgehalt existiert, weil die Koagulationsgeschwindigkeit auch von der Partikelkonzentration abhängt. Als geeignetes Kriterium zur Bewertung des Agglomerationszustandes monodisperser Partikelsysteme konnte die Breite der Sinkgeschwindigkeitsverteilung nachgewiesen werden. In Ergänzung zu den im Zusammenhang mit der Partikelkoagulation instabiler Suspensionen führen insbesondere bei elektrostatisch stabilisierten Partikelsystemen die mit der elektrochemischen Doppelschicht verbundenen Wechselwirkungen zu einer Beeinflussung der Suspensionsstruktur und folglich zu einer Beeinflussung hydrodynamischer Phänomene. Das wird in den bekannten Modellen nicht berücksichtigt und in der vorgelegten Arbeit am Sedimentationsverhalten monodisperser Partikelsysteme bei verschiedenen Elektrolytgehalten der kontinuierlichen Phase untersucht. Zu diesem Zweck wurden aus einer konzentrierten Suspension von 200 nm Partikeln und dem ihr zugehörigen Zentrifugat Suspensionsproben unterschiedlichen Feststoffgehaltes zubereitet. Mit einem Potenzansatz, wie er bereits von Richardson und Zaki für die Sedimentation von Mikrometerpartikeln verwendet wurde, konnte der experimentell bestimmte Zusammenhang zwischen der Sinkgeschwindigkeit und der Suspensionsporosität beschrieben werden. Dabei ist die Sedimentationsbehinderung umso ausgeprägter, je kleiner der Elektrolytgehalt, d.h. je ausgedehnter die Doppelschichtdicke ist. Die stark mit dem Elektrolytgehalt korrelierenden Werte für den Exponenten dieses Ansatzes liegen zwischen 5 und 10 im Gegensatz zu Richardson und Zaki von 4,65. Untersuchungen zum Konzentrationseinfluss mit gröberen Partikeln in elektrolytarmen Lösungsmitteln bestätigten die gegenüber dem Mikrometerbereich stärkere Sedimentationsbehinderung elektrostatisch stabilisierter kolloidaler Suspensionen. Zusätzlich zu den wissenschaftlichen Untersuchungen erfolgte die Konstruktion einer einfachen und robusten Sedimentationszelle mit optischer Messwerterfassung. Es wurde die Funktionstüchtigkeit eines zuverlässigen, partikelgrößenselektiven Messgerät z.B. für Industrielabore zur Optimierung von Sedimentationsprozessen demonstriert. / The sedimentation of stabilized suspensions strongly depends on the particle concentration. Even for dilute systems the decrease of the settling velocity compared to that of isolated particles is quite significant. This is primarily due to hydrodynamic interactions (HI), which are long-range interaction, since disturbances in the flow field decline reciprocally with the distance from the surface. The sedimentation of colloidal particles is additionally affected by the electric double layer surrounding them. The double layer leads to electro-viscous effects as well as to electrostatic repulsion between neighboring particles. Both phenomena can amplify the hydrodynamic hindrance to considerable extent. In this dissertation thesis an experimental study on the influence of double layer thickness on the sedimentation of charged colloidal particles is presented. Investigations were carried out using an optical centrifuge, in which the sedimentation velocity of monosized sub-micrometer silica particles were studied at different particle concentration and varying ionic strength. The results are discussed with regard to the applicability of theoretical models and (semi-)empirical approximations. Richardson and Zaki had determined a power law exponent of 4.65 for hard sphere systems in the 100 micrometer range. In the experimental work for sub-micrometer particles the exponent was determined between 5 (low double layer thickness at high electrolyte concentration) and 10 (high double layer thickness at low electrolyte concentration). Additionally a simple and robust device for gravitational sedimentation analysis by optical signal sensing was designed. It enables industrial application for the optimization of sedimentation processes.

Nach einer kurzen technischen Beschreibung der Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW und der verwendeten Messtechnik werden die theoretischen Grundlagen zur Modellierung der Kondensation von Dampf in einer Wasserströmung erläutert. Dabei gehen die Autoren besonders auf die Auswahl geeigneter Modelle zur Beschreibung des Wärmeübergangs und der Zwischenphasengrenzfläche im Druckbereich zwischen 10 und 65 bar detailliert ein. Außerdem werden verschiedene Drift-Flux-Modelle auf ihre Tauglichkeit anhand von experimentellen Daten geprüft. Da Veränderungen thermodynamischer und strömungstechnischer Parameter hauptsächlich in axialer Richtung stattfinden, wurden diese Modelle in einen eindimensionalen Code eingebettet, mit dem der Strömungsverlauf entlang einer vertikalen Rohrleitung mit einer Länge von 8 m und einem Nenndurchmesser von 200 mm berechnet werden kann. Anschließend werden Aufbau und Funktion dieses Programms vorgestellt. Nachfolgend vergleichen die Autoren experimentelle und berechnete Strömungsverläufe bei der Kondensation von Dampf sowohl in einer unterkühlten Wasserströmung als auch nahe der Siedetemperatur. Dabei wird der Einfluss wichtiger Randbedingungen, wie z.B. Druck oder Primärblasengröße, auf die Kondensationsintensität analysiert. Eine Einschätzung der Fehlerbanden für die experimentellen Daten, die verwendeten Gittersensoren und die numerische Simulation schließen den Bericht ab.

<p>The aim of the present investigation is to increase theunderstanding of the role played by the solvent in inhibitingor enhancing crystal growth. Drowning-out crystallizationexperiments has been performed by the controlled addition ofwater or ethanol water mixtures to a saturated solution ofbenzoic acid in ethanol-water mixtures. Crystal habitcontrolling factors have been identified.Seededcrystallization experiments have been carried out to evaluatethe effect of solvent composition on crystal habit at constantsupersaturation. The solubility of benzoic acid inethanol-water mixtures at the working temperatures has beendetermined.</p><p>Electro-zone sensing determinations and microscopicmeasurements are used to characterize the final crystallineproduct. It has been found that the shape of the benzoic acidcrystals grown from ethanol-water solutions ranges from needlesto platelets. Platy particles possess a predominant basal plane(001), bound by (010) and (100) faces, while needles aredeveloped along the b-axis. Long needle-shaped particles havebeen produced at low initial bulk concentration and highethanol concentration in the feed. Small platelets are obtainedat high initial bulk concentrations and high waterconcentration in the feed.</p><p>The effect of solvent composition on the growth rate hasbeen evaluated at constant supersaturation. Seed crystals arecharacterized by image analysis measurement both before andafter each experiment. Length and width dimensions have beenmeasured on the particle silhouette. The growth rate, thesolid-liquid interfacial energy and the surface entropy factorfor the (010) faces (length dimension) and (100) faces (widthdimension) have been estimated. The interfacial energy andsurface entropy factor decreases in the direction of increasingethanol concentration due to increasing solubility.</p><p>The results suggest that at low ethanol concentration(xEtOH<60%) growth proceeds by screw dislocation mechanism,and adsorption of ethanol molecules may reduce the growth rate.As the ethanol concentration increases above a critical value(xEtOH ≥60%), the growth mechanism shifts to surfacenucleation and the growth rate increases with increasingethanol concentration. It has been suggested that the observedeffect of the solvent composition on crystal habit is theresult of two conflicting effects here referred as the kineticand interfacial energy effects. High interactions of the pairethanol-benzoic acid seem to be responsible of the growthretardation (kinetic effect) exerted by the solvent. On theother hand, increased ethanol concentration leads to reduceinterfacial energy and increasing surface nucleation whichmight contribute to enhance growth kinetics.</p><p><b>Keywords:</b>drowning-out crystallisation, solventcomposition, benzoic acid, solubility, crystal growth,interfacial energy, surface entropy factor, growth mechanism,crystal shape distribution.</p>

<p>Admixtures like reactants and byproducts are solublenon-crystallizing compounds that can be present in industrialsolutions and affect crystallization of the main substance.This thesis provides experimental and molecular modellingresults on the influence of admixtures on crystal nucleation ofvanillin (VAN). Seven admixtures: acetovanillone (AVA),ethylvanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxy-acetophenone (HAP), 4-hydroxy-benzaldehyde (HBA), andvanillic acid (VAC) have been used in this study. Classicalnucleation theory is used as the basis to establish arelationship between experimental induction time andsupersaturation, nucleation temperature, and interfacialenergy. A novel multicell device is designed, constructed, andused to increase the experimental efficiency in thedetermination of induction times by using 15 nucleation cellsof small volumes simultaneously. In spite of the largevariation observed in the experiments, the solid-liquidinterfacial energy for each VAN-admixture system can beestimated with an acceptable statistical confidence. At 1 mole% admixture concentration, the interfacial energy is increasedin the presence of GUA, GUE, and HBA, while it becomes lower inthe presence of the other admixtures. As the admixtureconcentration increases from 1 to 10 mole %, the interfacialenergy also increases. The interfacial energies obtained are inthe range 7-10 mJ m^-2. Influence of admixtures on metastable zone widthand crystal aspect ratio of VAN is also presented. Theexperimental results show that the admixtures studied arepotential modifiers of the nucleation of VAN. Molecularmodelling by the program Cerius2 is used to identify the likelycrystal growth faces. Two approaches, the surface adsorptionand the lattice integration method, are applied to estimatequantitatively the admixture-crystal interaction energy on thedominating crystal faces of VAN,<i>i.e</i>., {0 0 1} and {1 0 0}. However, a simple and clearcorrelation between the experimental values of interfacialenergy and the calculated interaction energies cannot beidentified. A qualitative structural analysis reveals a certainrelationship between the molecular structure of admixtures andtheir effect on nucleation. The determination of the influenceof admixtures on nucleation is still a challenge. However, themolecular and crystal structural approach used in this thesiscan lead to an improved fundamental understanding ofcrystallization processes. Keywords: Crystallization,nucleation, vanillin, admixtures, additives, impurities,induction time, interfacial energy, molecular modelling,interaction energy.</p>

The thermoelectric effect was discovered well over a century ago, yet performance has not shown improvement until recent years. Prior work has shown that the thermoelectric effect can be enhanced by the use of microscale pieces of thermoelectric material. Conventional assembly techniques are inadequate to deal with parts of this size, making it necessary to find a suitable alternative before these devices can be made economically. Capillary self-assembly is a promising alternative to conventional techniques. This method employs the use of preparing substrates with areas of favorable surface tension to place and align parts. Still, many obstacles have to be overcome to adapt this process for use of constructing thermoelectric coolers. The goal of this work is to overcome these obstacles and assess the viability of self-assembly for fabricating these devices. In effort to make the method more effective a process for creating more uniform deposits of solder is also assessed. This work shows that microscale thermoelectric elements can be assembled into functional thermoelectric devices using self-assembly techniques through the assembly of coolers in experimental work.