Les systèmes diphasiques à pompage capillaire sont couramment utilisés pour contrôler la température de l'électronique embarquée. Ces systèmes sont fiables et performants, mais ils présentent certaines limites associées essentiellement à la vaporisation dans le milieu poreux (limite capillaire, limite d'ébullition). Une façon d'étendre leurs performances en termes de longueur de transport de la chaleur et d'intensification des transferts serait de les coupler avec un système mécaniquement actif. Un des moyens pour réaliser cela est d'utiliser les forces électro-hydro-dynamiques (EHD) se développant dans le fluide lorsqu'on applique un champ électrique. Les travaux proposés sont une contribution à la compréhension de l'interaction entre une interface liquide-vapeur et un champ électrique afin de déterminer quels sont les mécanismes qui dans ces conditions contrôlent le pompage et le transfert de chaleur. La première partie se focalise sur l'étude expérimentale d'une interface liquide-vapeur sous un champ électrique avec ou sans flux de chaleur dans une configuration très académique (deux électrodes planes et verticales) tout en étant proche de ce qui se passe dans une cannelure de caloducs par exemple. L'objectif est d'observer, de quantifier et d'analyser les effets (forces, structures, instabilités) se développant sur l'interface. Une analyse a ensuite été menée à partir de modèles 1D et 2D. Nous avons ainsi pu vérifier que parmi l'ensemble des forces s'exerçant sur l'interface, la force diélectrophorétique est celle qui contrôle sa position et sa forme avec ou sans vaporisation. On a montré cependant qu'il existait des effets de couplage avec la conduction électrique dans le liquide pouvant sensiblement agir sur la courbure de l'interface. Enfin, les résultats en vaporisation ont confirmé que le champ électrique, en donnant des moyens de contrôle de la position et de la structure de l'interface de vaporisation, peut être effectivement mis à profit pour une intensification des transferts de chaleur proches d'une paroi chauffée. Dans un dernier volet, les travaux se sont concentrés sur la mise en mouvement d'un liquide diélectrique en mettant à profit le régime de conduction. Une étude expérimentale permettant d'étudier l'influence des différents paramètres (géométrie des électrodes, distance inter électrodes, nombre de modules) a été réalisée dans les fluides HFE-7000 et HFE-7100. Les résultats ont montré une faible reproductibilité des performances de la pompe pour ces fluides suggérant une forte sensibilité des phénomènes à l'état de surface des électrodes et aux régimes parasites d'injection de charge. / Two-phase systems based on the capillary pumping are widely used for electronics cooling. These systems are reliable and efficient, but the maximum heat load is given by the porous medium characteristics (pore size and conductivity) and the fluid properties. The use of an additional source of energy to actively control the heat transport and the heat transfers is a way to extend the performance. Electro-hydrodynamic forces (EHD) could fulfill this objective. This work proposed a contribution to the understanding of the interaction between a liquid-vapor interface and an electric field in order to determine which mechanisms control the pumping and heat transfer. The first part focused on the experimental study of a liquid-vapor interface under an electric field with or without heat flux in a very academic configuration while being close to the operating conditions of the vaporization in a groove of a heat pipe for example. The objective was to observe, quantify and analyze the effects (forces, structures, instabilities) developing on the interface. On top of that, analysis based on 1D and 2D models were made. We found that the dielectrophoretic force mainly controlled the position and the shape of the interface with or without vaporization. However, some effects of coupling with the electrical conduction in the liquid were proved to substantially modify the interface curvature. Finally, the results confirmed that the electric field can effectively be used to the heat transfer enhancement close to a heated wall. In a final section, the work is related to the pumping of a dielectric liquid based on the conduction regime. An experimental study was carried out in HFE-7000 and HFE-7100 fluids to investigate the role of different parameters (electrode geometry, inter-electrode distance, number of modules). For these fluids, the repeatability of results was not satisfactorily suggesting a high sensitivity of the phenomena according to the surface state of the electrodes and parasitic charge injection.

Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 % reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 % over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 % reduction of the driving electric field) as well as in the maximum actuation strain (250 %). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation. / Die Palette von elektro-mechanischen Aktuatoren, basierend auf dem Prinzip weicher dehnbarer Kondensatoren, scheint besonders für Anwendungen in der Medizin und für biomimetische Applikationen unbegrenzt. Diese Wandler zeichnen sich sowohl durch hohe Reversibilität bei großer mechanischer Deformation als auch durch ihre Flexibilität aus, wobei die mechanischen Deformationen durch elektrische Felder induziert werden. Die Notwendigkeit von hoher elektrischer Spannung zur Erzeugung dieser mechanischen Deformationen verzögert jedoch die technisch einfache und breite Markteinführung dieser Technologie. Diesem Problem kann durch eine gezielte Materialmodifikation begegnet werden. Eine Modifikation hat das Ziel, die relative Permittivität zu erhöhen, wobei die Flexibilität und die hohe elektrische Durchbruchsfeldstärke beibehalten werden sollten. Durch eine Materialmodifikation kann die Energiedichte des Materials bedeutend erhöht und somit die notwendige Betriebsspannung des Aktuators herabgesetzt werden. Eine Verbesserung der funktionalen Materialeigenschaften kann durch die Verwendung von Nanokompositen erzielt werden, welche die fundamentalen Eigenschaften der Nanopartikel, d.h. ein gutes Verhältnis von Oberfläche zu Volumen nutzen, um eine gezielte makroskopische Materialmodifikation zu bewirken. Diese Arbeit behandelt die Anwendung innovativer Strategien für die Erzeugung von Nanomaterialien mit hoher Permittivität. Die so erzeugten Materialien und deren relevante Aktuatorkenngrößen werden durch elektrische und mechanische Experimente vollständig erfasst. Mittels der klassischen Mischansätze zur Erzeugung von Kompositmaterialen mit hoher Permittivität konnte durch nichtleitendes Titaniumdioxid TiO2 (Rutile) in einem Thermoplastischen-Block-Co-Polymer SEBS (poly-styrene-co-ethylene-cobutylene-co-styrene) die Permittivität bereits um 370 % erhöht und die elektrische Energiedichte um 570 % gesteigert werden. Diese Veränderungen führten jedoch zu einem signifikanten Anstieg der Steifigkeit des Materials. Aufgrund der positiven Rückkopplung von elektrischen und mechanischen Eigenschaften des Kompositmaterials ermöglicht bereits dieser einfache Ansatz eine Verbesserung der Aktuation, bei einer 27 %-igen Reduktion der Aktuatorbetriebsspannung. Eine direkte Verwendung von leitfähigen Nanopartikeln kann ebenso zu einem Anstieg der relativen Permittivität beitragen, wobei jedoch die Leitfähigkeit dieser Nanopartikel bedeutende Wechselwirkungen verursacht, welche somit die Energiedichte des Materials negativ beeinflusst und die praktische Verwendung dieses Kompositsystems ausschließt. Als ein völlig neuer Ansatz zur Steigerung der relativen Permittivität und Energiedichte und abweichend vom klassischen Mischverfahren, wird die Herstellung eines "Molekularen Komposits", basierend auf einem chemischen Propfverfahren, präsentiert. In diesem Ansatz wird ein π-konjugiertes leitfähiges Polymer (PANI) an die Hauptkette des Elastomers der Polymermatrix gebunden. Die daraus resultierende Ladungsverteilung entlang der Elastomerhauptkette bewirkt eine 470 %-ige Steigerung der Permittivität des "Molekularen Komposits" im Vergleich zur Permittivität des unbehandelten Elastomermaterials. Aufgrund der Verkapselung der chemischen Bindungen der PANI-Kette entstehen kaum negative Rückwirkungen auf die elektrischen und mechanischen Eigenschaften des so erzeugten Komposits. Diese Materialeigenschaften resultieren in einem signifikanten Anstieg der Energiedichte des Materials. Das mittels dieses Verfahrens erzeugte Komposit zeigt sowohl eine Steigerung der Sensitivität der elektromechanischen Antwort (Reduktion des elektrischen Felds um 83 %) als auch eine bedeutende Steigerung der maximalen Aktuation (250 %). Die Ergebnisse und Ideen dieser Arbeit stellen einen wesentlichen Sprung im Verständnis zur Permittivitätssteigerung in Polymermaterialien dar und werden deshalb in der Erforschung und Entwicklung von Elastomeraktuatoren Beachtung finden.

Due to increasing problems with bacterial resistance development, there is a growing need for identifying new types of antibiotics. Antimicrobial peptides constitute an interesting group of substances for this purpose, since they are believed to act mainly by disrupting the bacterial membrane, which is a fast and non-specific mechanism. In order to understand the details on this action simplified phospholipid model membranes based on liposomes, monolayers and bilayers, were employed in this thesis. By in situ ellipsometry studies on supported lipid bilayers in combination with leakage from liposomes it was found that peptide-induced membrane rupture to a great extent is related to peptide adsorption. The peptide activity and mechanism of action is highly dependent on peptide properties such as length, topology, charge, and hydrophobicity. Electrostatic interactions are crucial for peptide adsorption, whereas α-helix formation is of less importance, demonstrated by the dominating peptide conformation being random coil both in absence and presence of membranes, as investigated by circular dichroism. Comparable effects were observed in both mono- and bilayer systems, showing that formation of transmembrane structures is no prerequisite for membrane rupture by complement-derived peptides. Electrochemical studies on these peptides further demonstrated that hydrophobic interactions facilitate peptide penetration into the membrane, causing defects in close proximity to the peptides, while strong electrostatic interactions arrest the peptide in the headgroup region. Increasing the peptide hydrophobicity, by e.g., tryptophan end-tagging, also increases salt resistance. Good correlations were found between model membrane investigations and antibacterial activity towards both Gram-negative and Gram-positive bacteria, showing that membrane rupture is a key mechanism of action for the peptides investigated. In addition, for all peptides investigated cell toxicity is low.

Lightly cross-linked polyelectrolyte microgels are materials with interesting properties for a range of applications. For instance, the volume of these particles can be drastically changed in response to pH, ionic strength, temperature, or the concentration of specific ions and metabolites. In addition, microgel particles can bind substantial amounts of oppositely charged substances, such as proteins and peptides, and release them upon changes in the external environment. Consequently, microgels have potential in catalysis, photonics, biomaterials, and not at least, as protective and stimuli-sensitive carriers for protein and peptide drugs. In this thesis, the interaction between anionic microgels and cationic peptides was investigated by monitoring microgel deswelling and reswelling in response to peptide binding and release using micromanipulator-assisted light microscopy. In addition, peptide distribution in microgels was analyzed with confocal laser scanning microscopy and peptide uptake determined with solution depletion measurements. The aim of the thesis was to clarify how parameters such as peptide size, charge density, pH, ionic strength and hydrophobicity influences the peptide binding to, distribution in and release from, polyelectrolyte microgels. Results obtained in this thesis show that electrostatic attraction is a prerequisite for interaction to occur although non-electrostatic contributions are responsible the finer details of the interactions. The size and charge density of the interacting peptides play a major role, as large and highly charged peptides are restricted to enter and interact with the microgel core, thus displaying a surface-confined distribution. The peptide-microgel interaction strength is highly reflected in the probability of peptides to be detached from the gel network. For instance, reducing the electrostatic interactions by adding salt induces significant peptide release of sufficiently small and moderately charged peptides, whereas longer and more highly charged peptides is retained in the microgel network due to the strong interaction, insufficient salt screening, and gel network pore size restriction. Decreasing the charge density of microgel network and/or peptides increases the probability for peptide detachment tremendously. To summarize, interactions occurring in oppositely charged microgel-peptide systems can be tuned by varying parameters such as charge density and peptide size and through this, the peptide uptake, distribution and release can be controlled to alter the performance of microgels in peptide drug delivery.

We are developing a novel classical over-the barrier model for electron transfer from an in nitely thin conducting disc to a point charge projectile to model multiple electron capture in e.g. keV collisions of atomic ions with poly-cyclic aromatic hydrocarbons (PAHs). In its nal form, the present model will incorporate the polarization of the PAH molecules due to the active electron and the point charge projectile at a general angle of incidence. This will drastically improve the description of the potential barrier in comparisons with simpler versions of the model where the nite size and polarizability of the target molecule is neglected or treated in an averaged fashion. In this work we arrive at expressions for the electrostatic potential energy barrier experienced by the active electron in the two spatial orientations where the point charge projectile is located along the normal symmetry axis and in the tangent plane of the disc. Applied to coronene (C24H12) such barriers compare better with high level density functional theory (DFT) calculations than with the results from the simpler versions of the classical over-the-barrier models for atomic and spherical cluster targets. These results thus strongly supports the conducting disc approximation of PAHs. Finally we discuss the nal steps in the model development and possible extensions of the model to include less symmetric elliptical discs or spherical caps.

With the continuous growth of non-linear power electronic components and the increasing penetration of the distributed generation (DG), the potential for degradation in the power quality of the existing grid exists. There are concerns that the total harmonic distortion (THD) could reach unacceptable levels of 5% or higher. Moreover, there is additional potential of the presence of amplified harmonic components in the power network grid when the harmonic frequencies align with the resonant frequencies that are being injected by power electronic components of the DG. The above conditions could increase the electrical stresses on the insulation system of the power system components, and in particular, cable terminations are a concern. Standard cable terminations are designed to operate under power frequency in the power system network and their service life is considered accordingly. The research work aims to provide an understanding of the performance of the stress grading (SG) system of a commercial cable termination when the voltage waveform is distorted due to the presence of harmonics and when the high frequency and high dV/dt voltage waveforms are present from a typical power electronic drive. An aging experiment was performed for over a 600 hour time period using the pulse width modulated (PWM) high-voltage generator to quantify the impact of high frequency stress on SG system of cable termination. Furthermore, the cable termination was tested under power frequency, distorted voltage waveforms composed of fundamental and low order harmonics using an experiment setup that generate distorted voltage waveforms. Diagnostic techniques such as surface potential distribution measurements and surface temperature monitoring are used to analyze the termination performance. The surface tangential field is calculated based on the gradient of the termination surface potential as measured with an electrostatic voltmeter. The study shows that distorted voltage waveforms with high frequency and high dV/dt components, increase the electric field, resistive heating, and surface temperature rise in the terminations that use the field-dependent SG materials. The rise of electric field by as high as 27.1% and surface temperature rise of as high as 17C demonstrates the severity on the cable terminations. Such electric field enhancements for a period of time have a potential to initiate partial discharge that could lead to degradation of the termination. Moreover, surface temperature rise of 17 deg C could reduce the allowable ampacity of the cable conductor, reduce the short circuit levels, and reduce the feeder loading limits. The field-dependent electrical conductivity (σ(E,T)), permittivity (ε), and the temperature dependencies of (σ(E,T) and ε) have strong impact to degrade the electrical and thermal properties of the termination due to stress from the non-sinusoidal distorted voltage waveform. In order to minimize the surface temperature rise from the hotspot and electrical stress enhancement that eventually lead to insulation degradation and failure, the following recommendations are made for a suitable SG design for a termination to handle the severe voltage stress: Apply the capacitively graded termination in the grid where the distortion levels are low. Under the increased total harmonic distortion levels and HF components, resistively grading with higher degree of nonlinearity (achieved through the use of ZnO filler) is beneficial. The utilities could take preventive maintenance on medium voltage power cable accessories to prevent the termination failure before it actually occurs. Researchers could focus to resolve and minimize the rising power quality issues when the distribution generations are operated, improve the power electronic converters, and provide cost-effective harmonic filter solutions for harmonic mitigation.

Ba(Zr0.1Ce0.7Y0.2)O3-£_ (BZCY) shows high proton conductivity as well as high chemical stability over a wide range of solid oxide fuel cell (SOFC) operating conditions. Sm0.5Sr0.5CoO3-£_ (SSC) cathode deposited by electrostatic spray deposition (ESD) on SOFC half cell obtained via tape-casting shows porous and reticular microstructure, and the SOFC single cell consists of substrate/ BZCY+NiO/ BZCY/ SSC. The electrolyte thickness decrease from 22 £gm, 20 £gm, 17.6 £gm to 15.1 £gm after sintering as the content of carbon pore former in the corresponding anode functional layer increased from 0.0 wt.%, 5.0 wt.%, 10.0 wt.% to 15.0 wt.%, and the maximum power density of corresponding cells at 700¢J varies from 476.89 mW/cm2, 713.34 mW/cm2, 862.50 mW/cm2 to 706.89 mW/cm2, respectively.

First, one of the purposes of this thesis is to estimate the complete crosstalk effects including the package and the pads on the surface acoustic wave (SAW) substrate. A new approach based on finite-difference time-domain (FDTD) with equivalent current source method is applied. Two kinds of patterns of one-port SAW resonators with the same package structure and inter-digital transducer (IDT) design are studied. Verification with the measurement results shows that our method is able to obtain good agreement and be used to observe the influence from the SAW pattern. Second, the equivalent current source method is extended to model the excitation of human-body¡¦s electrostatic discharge (ESD) situations. The efficiencies of sacrificial electrodes are also discussed. Finally, a novel sacrificial electrode with fractal to protect SAW devices from ESD break is proposed. Comparing with traditional electrode, the simulation results show that fractal can improve the protective efficiency greatly. Finally, a novel analysis model that can be used to analyze and optimize the impedance of an RFID transponder integrated circuit (IC) which uses backscatter encoding based on simultaneously maintaining the BER of the reader and maximizing the received power of the transponder IC is proposed. The analysis method utilizes mapping from signal constellation of the backscattered signal to the Smith chart to relate the two parameters. Given the system specification and characteristics of the reader and transponder antennas, the optimum impedances of transponder IC for binary communication system can be easily designed by using this model.

This thesis presents analysis, design, implementation, and testing of electrostatically actuated MEMS microvalves. The microvalves are specifically designed for lab-on-a-chip applications to achieve leakage ratios below 0.1 at pressure levels in the order of 101 kPa. For this purpose, two different microvalves are presented in the study. In the proposed designs, electrostatic actuation scheme is utilized to operate the microvalves in normally open and normally closed modes. Characterization of normally open microvalves show that, microvalves with radii ranging between 250

This thesis studies the formation of mobile and surface-bound electric charges in nonpolar liquids. Unlike aqueous media with their natural abundance of charged species, liquids of low dielectric constant do not readily accommodate charges, but can do so in the presence of certain surfactant additives. Surfactant-mediated charging in nonpolar oils has long been exploited industrially, but the underlying charging mechanisms are far from understood. The present work seeks clarification by comparing the effect of ionic and nonionic surfactants on the conductivity of nonpolar solutions and the electrophoretically observable surface charge of suspended polymer particles. Both types of surfactant are found to generate mobile ions in solution as well as particle charge; and in the more surprising case of nonionic surfactants, the occurrence of particle charge and screening ions is confirmed independently by measurements of the electrostatic particle interaction energy. A systematic variation of the particle material and functionalization, the residual water content, and the surfactant concentration above and below the critical micelle concentration provides insights about the possible charging pathways. Reverse surfactant micelles are explored not only as charging agents, but also as reactors and templates for the synthesis of novel nanogels with promise for drug delivery. Synthesis via copper-free Click chemistry is shown to allow for better control of the particle size than a more conventional polymerization scheme, while avoiding metal catalysts and free radicals that are considered hazardous for most biomedical applications.