Dissertations / Theses on the topic 'Liquid dielectrics'

A new model for the complex dielectric constant, ε, of aqueous ammonia (NH4OH) has been developed based on laboratory measurements in the frequency range between 2-8.5 GHz for ammonia concentrations of 0-8.5 %NH3/volume and temperatures between 277-297 K. The new model has been validated for temperatures up to 313 K, but may be consistently extrapolated up to 475 K and ammonia concentrations up to 20 %NH3/volume. The model fits 60.26 % of all laboratory measurements within 2σ uncertainty. The new model is identical to the Meissner and Wentz (2004) model of the complex dielectric constant of pure water, but it contains a correction for dissolved ammonia. A description of the experimental setups, uncertainties associated with the laboratory measurements, the model fitting process, the new model, and its application to approximating jovian cloud opacity for NASA's Juno mission to Jupiter are provided.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Kerr electro-optic technique has been used to measure the electric field distribution in high voltage stressed dielectric liquids, where the difference between refractive indices for light polarized parallel and perpendicular to the local electric field is a function of the electric field intensity. For transformer oil, the most widely-used insulating liquids in power apparatus and high voltage technology, Kerr effect is very weak due to its low Kerr constant. Previous Kerr measurements have been using ac modulation technique, which is only applicable to dc steady-state electric field mapping while various instabilities develop in liquid under long-term high voltage application. The use of the high-sensitivity CCD camera as optical detector makes it possible to capture the weak Kerr effect in high voltage stressed transformer oil. The first part of this thesis is to demonstrate the reliability and evaluate the sensitivity of the measurements for various cases with identical electrodes under pulsed excitation with insignificant flow effects. After the validation and optimization of the experimental setup, measurements are taken to record the time evolution of electric field distributions in transformer oil stressed by high voltage pulses, from which the dynamics of space charge development can be obtained. Correlation between space charge distribution pattern and impulse breakdown voltage is examined. Hypothetically, bipolar homo-charge injection with reduced electric field at both electrodes may allow higher voltage operation without insulation failure, since electrical breakdown usually initiates at the electrode-dielectric interfaces. It is shown that the hypothesis is testable and correct only under specific circumstances. Besides, fractal-like kinetics for electrode charge injection is identified from the measurement data, which enriches the knowledge on ionic conduction in liquids by offering an experimentally-determined boundary condition to the numerical model. Physical mechanisms based on formative steps of adsorption-reaction-desorption reveal possible connections between geometrical characteristics of electrode surfaces and fractal-like kinetics of charge injection. The second part of this thesis focuses on the fluctuations in the detected light intensity in Kerr measurements. Up to now, within an experimentally-determined valid range of high voltage pulse duration, the strategy to reduce fluctuation has been taking multiple measurements and then averaging the results. For very short impulses, it is found that the light intensities near the rough surfaces of electrodes both fluctuate in repeated measurements and vary spatially in a single measurement. The major cause is electrostriction which brings disturbances into optical detection. The calculated spatial variation has a strong nonlinear dependence on the applied voltage, which generates a precursory indicator of the electrical breakdown initiation. This result may have potential applications in non-destructive breakdown test and inclusion detection in dielectric liquids. When the applied voltage is dc or ac, signatures of turbulent electroconvection in transformer oil are identified from the Kerr measurement data. It is found that when the applied dc voltage is high enough, compared with the results in the absence of high voltage, the optical scintillation index and image entropy exhibit substantial enhancement and reduction respectively, which are interpreted as temporal and spatial signatures of turbulence. Under low-frequency ac high voltages, spectral and correlation analyses also indicate that there exist interacting flow and charge processes in the gap. This also clarifies the meaning of dc steady state and the requirement on ac modulation frequency in Kerr measurements.
by Xuewei Zhang.
Ph. D.

The delivery of tunable millimetre-wave components at 60GHz is of research and development interests with the advent of 5G era. Among applications such as high-data-rate wireless communications, high-precision automotive radars and hand-gesture sensing, variable phase shifters are vital components for antenna arrays to steer an electromagnetic beam without mechanical movement. However, present microwave technology has limited scope in meeting more and more stringent requirements in wavefront phase control and device performance for those cutting-edge applications in the millimetre-wavelength range. Although some existing microwave switchable techniques (such as RF MEMS and solid-state p-i-n diodes) can offer ultra-fast speed for phase modulation, their binary beam-steering nature is resolution-limited and thereby degrades the beam-scanning performance. In response to this, continuously-tunable phase shifting can be realised by using tunable dielectric materials such as ferroelectric BST and liquid crystals (LCs). BST thin films can offer relatively fast switching and modest tunability. However, the increased dielectric loss beyond 10GHz impedes their implementation for higher frequency applications. By comparison, liquid crystals (LCs) have drawn attention in recent years because of their continuous tunability as well as low losses especially at millimetre-wavebands. The principle of shifting the phase continuously is based on the shape anisotropy of LC molecules for variable polarizabilities and hence tunable dielectric constants, which allows wave speed to be controlled with ease by a low-frequency field of only up to 10V. However, LC-based tunable delay lines are not well established in the frequency regime of 60GHz-90GHz because of the limited status of LC microwave technology in which most of the LC based devices have been designed for below 40GHz. It is the aim of this PhD research to bridge the gap and address future societal needs based on our group's focus and experience in developing cutting-edge LC-based agile microwave components. In this work, a liquid crystal (LC) based 0-180˚continuously-variable phase shifter is developed with insertion loss less than -4.4dB and return loss below -15dB across a wide spectrum from 54GHz to 67GHz. The device is driven by a 0-10V AC bias and structured in a novel enclosed coplanar waveguide (ECPW) including an enclosed ground plate in the design, which significantly reduces the instability due to floating effects of the transmission line. This structure screens out interference and stray modes, allowing resonance-free quasi-TEM wave propagation up to 90GHz. The tunable ECPW is optimised by competing spatial volume distribution of the millimetre-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics and minimising the total of dielectric volumetric loss and metal surface loss for a fixed phase-tuning range. A variety of influences affecting the actual device performance are studied, experimented and optimised. Fabricated prototypes exhibit wideband low-loss performance and 0-π continuous tuning with low power consumptions and high linearity compared with the state-of-the-arts. Potentially, the ECPW-fed phased antenna array will be incorporated with advanced beam-forming algorithms to develop compact beam-steering systems of improved performances and targeted for ultra-high-data-rate wireless communications, inter-satellite communications, current road safety improvement, futuristic autonomous driving, and other smart devices such as the hand-gesture recognition.

Dissertation (Ph.D.) -- Worcester Polytechnic Institute.
Keywords: random-field interactions; radio frequency field heating; modulation calorimetry technique; heat capacity; aerosil; nematic; isotropic; phase transitions Includes bibliographical references.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Includes bibliographical references.
by Steven Marc Gasworth.
Ph.D.

Protein electrical properties have been studied using dielectric relaxation measurements throughout the past century. These measurements have advanced both the theory and practice of liquid dielectric spectroscopy and have contributed to understanding of protein structure and function. In this dissertation, the relationship between permittivity measurements and underlying molecular mechanisms is explored. Also presented is a method to take molecular structures from the Protein Data Bank and subsequently estimate the charge distribution and dielectric relaxation properties of the proteins in solution. This process enables screening of target compounds for analysis by dielectric spectroscopy as well as better interpretation of protein relaxation data. For charge estimation, the shifted pKa values for amino acid residues are calculated using Poisson-Boltzmann solutions of the protein electrostatics over varying pH conditions. The estimated internal permittivity and estimated dipole moments through shifted pKa values are then calculated. Molecular dynamics simulations are additionally used to refine and approximate the solution-state conformation of the proteins. These calculations and simulations are verified with laboratory experiments over a large pH and frequency range (40 Hz to 110 MHz). The measurement apparatus is improved over previous designs by controlling temperature and limiting the electrode polarization effect through electrode surface preparation and adjustment of the cell's physical dimensions. The techniques developed in this dissertation can be used to analyze a wide variety of molecular phenomena experimentally and computationally, as demonstrated through various interactions amongst avidin, biotin, biotin-labeled and unlabeled bovine serum albumin, beta-lactoglobulin, and hen-lysozyme.

The structure and physicochemical properties of biomembranes are fundamental for the functioning of cells, and many pathologies have been associated with their alteration (cancer, neurodegenerations, obesity, etc.) 1, 2. For this reason, biomembranes have been the subject of intensive research. Yet, there is still limited knowledge of biomembranes, which show a heterogeneous structure at the nanoscale that is naturally present in cells, and determines many of the phenomena occurring through them at the molecular level 3, 4. Due to their prominent role in Electrophysiology, electrical properties are among the more relevant physical properties of biomembranes. Most often, attention is paid to biomembranes' conduction properties, and the role played in them by ionic channels. However, biomembranes' dielectric properties are also of central interest in bioelectric phenomena, and a powerful reporter of membranes' composition, which can be exploited to develop label-free mapping methods. Yet, most of the available techniques have addressed the dielectric membrane properties in bulk solutions and at the level of single cells (micrometers), thus lacking spatial resolution. In other cases, they make use of exogenous labels, as in the case of spin paramagnetic resonance 5, 6 and fluorescence microscopy 7, 8, 9, 10, 11. In recent years, the Nanoscale Bioelectric Characterization group at IBEC, as well as other groups, have developed some Scanning Probe Microscopies (SPMs) based techniques to attempt the dielectrical characterization at the nanoscale 12, 13, 14, 15, 16 and applied them to biomembranes 17, 18, 19, 20, 21 and other biosystems 22, 12, 23, 24, 25, 26, 27. Initially, these techniques were implemented to be operated in air environment, but lately they were also extended to liquid environment 28, 29. The implementation of in-liquid Scanning Dielectric Microscopy (SDM) paved the way to the accurate dielectric characterization of biomembranes at the nanoscale, in their physiological environment and in a label-free way 28, 29. In-liquid SDM is based on measuring the electrostatic force acting on a nanometric probe under application of a modulated voltage between the tip and a conductive substrate, on top of which the sample is sitting. As compared to the standard SDM in air, operation in liquid environment requires several modifications. In terms of set-up, one needs to apply frequencies above the dielectric relaxation frequency of the electrolyte. Significant changes are also necessary for the modelling part 30. This work of thesis takes advantage of the latest developments of in-liquid SDM to characterize the dielectric properties of heterogeneous model and natural purified membranes systems in liquid. In this framework, new knowledge has been gained about imaging in liquid conditions with SDM, e.g. about the prominent electrostatic finite size effect and different models have been tested and optimized for the analysis of the measurements. First, I focused on characterizing mono- and bicomponent planar supported bilayer lipid mixtures containing cholesterol, providing a first proof-of-concept of the label-free mapping capabilities of the technique in liquid media, extending earlier work done in air on nanoparticles 12. This study allowed gaining information on the composition of sub- micrometric membrane domains in liquid environment 31 and to provide reliable values of the intrinsic dielectric properties of DOPC and DOPC/cholesterol compositions, about which there was some debate in the literature. The low values obtained are responsible for membranes’ low permeability to ions, in agreement with previous studies on monocomponent biomembranes 29. Our results allow speculating on fundamental properties of lipid bilayers like viscosity and hydration of cholesterol-containing layers. Afterwards, we extended the methods to deal with more complex biomembrane 3D structures, such as liposomes 32. Liposomes with few hundred nanometers in height have been successfully imaged by in-liquid SDM, showing a sensitivity comparable to the one for flat biomembranes only a few nanometers thin. Once again, the dielectric properties of the liposomes’ membrane were precisely extracted, this time in a more natural configuration of the biomembrane. This study also highlighted the technique’s sub- surface capabilities in the liquid environment, demonstrated earlier only in air measurements 33, 34, 35, 36, 37, 38, 39. This capability enabled to obtain in a label-free way the lamellarity of liposomes, a crucial parameter in liposomes technology. The developed methodology has the potential to be used to screen a myriad of different compositions of liposomes (shell and core), since in-liquid SDM was shown to be sensitive to the dielectric properties of the membrane but also to the conductivity of the medium inside the liposomes. This accomplishment was essential to evaluate its future application to living cells and constitutes one of the main achievements of this work. During the thesis, I also draw my attention to the dielectric characterization of natural purified membranes in liquid environment. As a test example, we focused on the case of the purple membrane (PM), which had previously been studied in air environment 40, 20, 19. PMs are constituted by the protein bacteriorhodopsin (BR) arranged in a crystal lattice, and lipids in a ratio 10:1 lipids:proteins. However, an unsolved uncertainty in determining the real topography of supported PM patches in the liquid environment, which can also display a concave surface, made the dielectric quantification problematic, and further explorations will be necessary to provide reliable values of the permittivity of these layers in liquid media. In summary, the objective and common thread connecting all the chapters of this work has been implementing and demonstrating the capabilities of in-liquid SDM in the dielectric characterization of bio-membranes, model and natural systems, with nanoscale spatial resolution. I believe that this work laid the ground for elucidating the structure and dielectric properties of more complex membranes systems and their associated electric phenomena, e.g. conduction. Preliminary studies of the cell membrane directly on living neuroblastoma cells, in low concentration MOPS buffer, were carried out in collaboration with Maria Elena Piersimoni, PhD student at Imperial College, London. The group is now collaborating with experts in the field and trying to develop new algorithms, fundamental to extend the methods to living cells. In addition to the main objective of my thesis, I also participated in a side project concerning the in-liquid SDM characterization of an operative EGOFET transistor 41, crucial for optimizing the devices and gain a better understanding of the transduction mechanism with biological entities. One of the newest frontiers of such technology is indeed to use supported lipid bilayers for bio-sensing purposes 42. References: (1) Lauwers, E.; Goodchild, R.; Verstreken, P. Membrane Lipids in Presynaptic Function and Disease. Neuron 2016, 90 (1), 11–25. https://doi.org/10.1016/j.neuron.2016.02.033. (2) Ashrafuzzaman, M., Tuszynski, J. 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Use of Dansyl-Cholestanol as a Probe of Cholesterol Behavior in Membranes of Living Cells. J. Lipid Res. 2010, 51 (5), 1157–1172. https://doi.org/10.1194/jlr.M003244. (8) Parasassi, T.; De Stasio, G.; Ravagnan, G.; Rusch, R. M.; Gratton, E. Quantitation of Lipid Phases in Phospholipid Vesicles by the Generalized Polarization of Laurdan Fluorescence. Biophys. J. 1991, 60 (1), 179–189. https://doi.org/10.1016/S0006- 3495(91)82041-0. (9) Signore G., Abbonato G., Storti B., Stöckl M., Subramaniam V., B. R. Imaging the Static Dielectric Constant in Vitro and in Living Cells by a Bioconjugable GFP Chromophore Analog. ChemComm 2013, 49 (1723). https://doi.org/10.1039/b000000x. (10) Demchenko, A. P.; Mély, Y.; Duportail, G.; Klymchenko, A. S. Monitoring Biophysical Properties of Lipid Membranes by Environment-Sensitive Fluorescent Probes. Biophys. J. 2009, 96 (9), 3461–3470. https://doi.org/10.1016/j.bpj.2009.02.012. (11) Epand, R. M.; Kraayenhof, R. 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(20) Fumagalli, L.; Ferrari, G.; Sampietro, M.; Gomila, G. Quantitative Nanoscale Dielectric Microscopy of Single-Layer Supported Biomembranes. Nano Lett. 2009, 9 (4), 1604– 1608. https://doi.org/10.1021/nl803851u. (21) Dols-Perez, A.; Gramse, G.; Caló, A.; Gomila, G.; Fumagalli, L. Nanoscale Electric Polarizability of Ultrathin Biolayers on Insulating Substrates by Electrostatic Force Microscopy. Nanoscale 2015, 7, 18327–18336. https://doi.org/10.1039/x0xx00000x. (22) Cuervo, A.; Dans, P. D.; Carrascosa, J. L.; Orozco, M.; Gomila, G.; Fumagalli, L. Direct Measurement of the Dielectric Polarization Properties of DNA. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (35). https://doi.org/10.1073/pnas.1405702111. (23) Biagi, M. C.; Fabregas, R.; Gramse, G.; Van Der Hofstadt, M.; Juárez, A.; Kienberger, F.; Fumagalli, L.; Gomila, G. Nanoscale Electric Permittivity of Single Bacterial Cells at Gigahertz Frequencies by Scanning Microwave Microscopy. ACS Nano 2016, 10 (1), 280–288. https://doi.org/10.1021/acsnano.5b04279. (24) Esteban-Ferrer, D.; Edwards, M. A.; Fumagalli, L.; Juárez, A.; Gomila, G. Electric Polarization Properties of Single Bacteria Measured with Electrostatic Force Microscopy. ACS Nano 2014, 8 (10), 9843–9849. https://doi.org/10.1021/nn5041476. (25) Van Der Hofstadt, M.; Fabregas, R.; Millan-Solsona, R.; Juarez, A.; Fumagalli, L.; Gomila, G. Internal Hydration Properties of Single Bacterial Endospores Probed by Electrostatic Force Microscopy. ACS Nano 2016, 10 (12), 11327–11336. https://doi.org/10.1021/acsnano.6b06578. (26) Checa, M.; Millan-Solsona, R.; Blanco, N.; Torrents, E.; Fabregas, R.; Gomila, G. Mapping the Dielectric Constant of a Single Bacterial Cell at the Nanoscale with Scanning Dielectric Force Volume Microscopy. Nanoscale 2019, 11 (43), 20809–20819. https://doi.org/10.1039/c9nr07659j. (27) Lozano, H.; Fabregas, R.; Blanco-Cabra, N.; Millán-Solsona, R.; Torrents, E.; Fumagalli, L.; Gomila, G. 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La estructura y propiedades fisicoquímicas de las biomembranas son fundamentales para el funcionamiento de las células, y muchas patologías (cáncer, neurodegeneraciones, obesidad, etc.) 1, 2 se han asociado a su alteración . Por este motivo, las biomembranas han sido objeto de intensas investigaciones. Sin embargo, todavía existe un conocimiento limitado de las biomembranas, que muestran una estructura heterogénea a la nanoescala, que en realidad son las que están presentes de forma natural en las células y determinan muchos de los fenómenos que ocurren a través de ellas a nivel molecular 3, 4. Las propiedades eléctricas, debido a su papel destacado en la electrofisiología, se encuentran entre las propiedades físicas más relevantes de las biomembranas. La mayoría de las veces se presta atención a las propiedades de conducción de las biomembranas y al papel que juegan en ellas los canales iónicos. Sin embargo, las propiedades dieléctricas de la biomembrana también son de interés central en los fenómenos bioeléctricos y, también, pueden considerarse como un poderoso indicador de la composición de la biomembrana, que puede aprovecharse para desarrollar métodos de mapeo sin marcadores. Este trabajo de tesis aprovecha los últimos desarrollos de microscopía dieléctrica de sonda de barrido (SDM) en líquido para caracterizar las propiedades dieléctricas de sistemas de membranas de modelo heterogéneo y membranas naturales purificadas en líquido. En este trabajo, se han obtenido nuevos conocimientos sobre la técnica de SDM en líquido, como por ejemplo sobre el prominente efecto electrostático de tamaño finito. También se han probado y optimizado diferentes modelos para el análisis de las medidas. Primero, nos concentramos en caracterizar mezclas de bicapa lipídicas soportadas mono y bicomponente que contienen colesterol, proporcionando una primera prueba de concepto de las capacidades de mapeo sin etiqueta de la técnica en líquido y ampliando el trabajo realizado anteriormente en aire sobre nanopartículas 5. Posteriormente, ampliamos los métodos para tratar con estructuras 3D de biomembranas más complejas, como los liposomas 6. Mediante SDM en liquído, se han obtenido imágenes de liposomas de unas pocas docenas de nanómetros de altura. Una vez más, se extrajeron con precisión las propiedades dieléctricas de la biomembrana de los liposomas, esta vez en una configuración más natural de la biomembrana. Este estudio también destacó las capacidades subsuperficiales de la técnica en líquido, demostradas anteriormente solo en medidas de aire 7, 8, 9, 10, 11, 12, 13, y permitió obtener de forma ‘label-free’ la lamelaridad de los liposomas, un parámetro crucial en esta tecnología. Este trabajo sentó las bases para dilucidar la estructura y las propiedades dieléctricas de sistemas de membranas más complejos, incluidas células vivas, y sus fenómenos eléctricos asociados, como por ejemplo la conducción. References: (1) Lauwers, E.; Goodchild, R.; Verstreken, P. Membrane Lipids in Presynaptic Function and Disease. Neuron 2016, 90 (1), 11–25. https://doi.org/10.1016/j.neuron.2016.02.033. (2) Ashrafuzzaman, M., Tuszynski, J. Membrane-Related Diseases, Springer-V.; Springer- Verlag Berlin Heidelberg 2012, 2012. (3) Mueller, P.; Rudin, D. O. Resting and Action Potentials in Experimental Bimolecular Lipid Membranes. J. Theor. Biol. 1968, 18 (2), 222–258. https://doi.org/10.1016/0022- 5193(68)90163-x. (4) Hodgkin, A. L.; Huxley, A. F. A Quantitative Description of Membrane Current and Its Application to Conduction and Excitation in Nerve. J Physiol. 1952, 117, 500–544. https://doi.org/10.1109/ICCCT2.2017.7972284. (5) Fumagalli, L.; Esteban-Ferrer, D.; Cuervo, A.; Carrascosa, J. L.; Gomila, G. Label-Free Identification of Single Dielectric Nanoparticles and Viruses with Ultraweak Polarization Forces. Nat. Mater. 2012, 11 (9), 808–816. https://doi.org/10.1038/nmat3369. (6) Di Muzio, M.; Millán, R.; Gomila, G. Electrical Properties and Lamellarity of Single Liposomes Measured by In-Liquid SDM. [in Prep. (7) Fumagalli, L.; Esfandiar, A.; Fabregas, R.; Hu, S.; Ares, P.; Janardanan, A.; Yang, Q.; Radha, B.; Taniguchi, T.; Watanabe, K.; et al. Anomalously Low Dielectric Constant of Confined Water. Science (80-. ). 2018, 360 (6395), 1339–1342. https://doi.org/10.1126/science.aat4191. (8) Fabregas, R.; Gomila, G. Dielectric Nanotomography Based on Electrostatic Force Microscopy: A Numerical Analysis. J. Appl. Phys. 2020, 127 (2). https://doi.org/10.1063/1.5122984. (9) Castañeda-Uribe, O. A.; Reifenberger, R.; Raman, A.; Avila, A. Depth-Sensitive Subsurface Imaging of Polymer Nanocomposites Using Second Harmonic Kelvin Probe Force Microscopy. ACS Nano 2015, 9 (3), 2938–2947. https://doi.org/10.1021/nn507019c. (10) Riedel, C.; Alegra, A.; Schwartz, G. A.; Arinero, R.; Colmenero, J.; Senz, J. J. On the Use of Electrostatic Force Microscopy as a Quantitative Subsurface Characterization Technique: A Numerical Study. Appl. Phys. Lett. 2011, 99 (2), 99–101. https://doi.org/10.1063/1.3608161. (11) Zhao, M.; Gu, X.; Lowther, S. E.; Park, C.; Jean, Y. C.; Nguyen, T. Subsurface Characterization of Carbon Nanotubes in Polymer Composites via Quantitative Electric Force Microscopy. Nanotechnology 2010, 21 (22). https://doi.org/10.1088/0957- 4484/21/22/225702. (12) Cadena, M. J.; Misiego, R.; Smith, K. C.; Avila, A.; Pipes, B.; Reifenberger, R.; Raman, A. Sub-Surface Imaging of Carbon Nanotube-Polymer Composites Using Dynamic AFM Methods. Nanotechnology 2013, 24 (13). https://doi.org/10.1088/0957- 4484/24/13/135706. (13) Alekseev, A.; Chen, D.; Tkalya, E. E.; Ghislandi, M. G.; Syurik, Y.; Ageev, O.; Loos, J.; De With, G. Local Organization of Graphene Network inside Graphene/Polymer Composites. Adv. Funct. Mater. 2012, 22 (6), 1311–1318. https://doi.org/10.1002/adfm.201101796.

Experimental investigation and theoretical analysis of an electromagnetic flowmeter designed for use with dielectric liquids has been carried out. An extensive survey of the industrial users of flowmeters has been made, involving the participation of over 47 companies, which provides information about the current industrial use, attitudes and attributes of electromagnetic and other types of flowmeters. The design of the flowmeter is mainly concerned with overcoming the charge noise that is associated with the flow of dielectric liquids so as to effectively detect the weak flow signal. It is shown that the working of the flowmeter depends heavily on the design of the eddy current free electrostatic shield. The result of the mathematical analysis of the design is a simplified formula for predicting the sensitivity of the meter. It is adjusted to take account of such factors as end-effects and electrical properties of the flow conduit of the meter. Experimental results show that not only an induction flowmeter based on Faraday's principle is possible but also the measured values of the flow signal closely matches those obtained from the formula. It is suggested that the formula can be generalised to include moderately conducting liquids which is supported by results achieved from experiments on water. Finally, recommendations for future work are put forward for further improvement of the design.

Les recherches sur des attogrammes (1 attogramme = 10 -18 gramme) et zeptogrammes (1 zeptogramme = 10-21 gramme) de matière offrent la possibilité de mettre en évidence la transition entre la nanoscience et la physique des molécules, ouvrant la porte à des questions fondamentales en physique de la matière molle, comme par exemple ‘’Quelle est la quantité minimale de matière nécessaire pour ‘‘définir’’ les propriétés des matériaux ?’’. Les propriétés électriques et diélectriques des matériaux, à cette échelle, sont étudiées par la spectroscopie diélectrique. Cette technique offre une large gamme de fréquence, pour mesurer les propriétés diélectriques des matériaux, couvrant plus de 10 ordres de grandeur et allant de 10-3 à 10+7 Hz. Cette technique assure une caractérisation précise d’une grande diversité des phénomènes physiques qui se déroulent à des échelles de longueur et de temps différents, tels que: les transitions des phases, les fluctuations de densité, les fluctuations moléculaires, le transport des charges, etc. Les mesures à l’échelle des attogrammes et zeptogrammes nécessitent l’utilisation des cellules ayant des dimensions nanométriques. Basé sur le concept d’utiliser des nano-conteneurs comme des cellules expérimentales, un développement expérimental a été mis en évidence, dans cette thèse, permettant d’étudier la dynamique moléculaire et les transitions des phases des matériaux polymères, allant jusqu’au zeptogrammes de matière. Cette approche permet de cristalliser des très petites quantités des matériaux sous l’application d’un champ électrique élevé, dans le but d’induire une cohérence macroscopique des fonctions moléculaires. Cela peut donner lieu à des nouvelles propriétés des matériaux, qui n’existent pas dans le cas des matériaux en masse
Dielectric investigations on attograms (1 attogram = 10 -18 gram) and zeptograms of matter (1 zeptogram = 10 -21 gram) offer the possibility of exploring the transition between nanoscience and molecule physics, opening the door for fundamental questions in soft-matter physics, such as for instance “What is the minimum amount of matter necessary to “define” the material properties?”. The electric and dielectric properties of materials at this level are investigated by Broadband Dielectric Spectroscopy. This technique provides an extraordinary broad frequency range, for measuring dielectric properties of matter, covering more than 10 orders of magnitude, typically from 10-3 to 10+7Hz. It ensures a precise characterization of large diversity of physical phenomena taking place at different length and time scales such as: phase transitions, density fluctuations, molecular fluctuations, charge transport processes, etc. Measurements on the scale of attograms and zeptograms require sample cells having all three dimensions on the nanometric length-scale. Based on the concept of employing nanocontainers as experimental cells, a novel experimental development allowing investigations on molecular dynamics and phase transitions of polymeric materials down to the level of zeptograms is demonstrated in the present PhD study. This approach enables one to crystallize tiny amounts of matter under high electric fields with the goal of inducing a macroscopic coherence of molecular functionalities. This could give rise to new material properties, not naturally available in the case of bulk materials

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.
"September 2007."
Includes bibliographical references (leaves 99-100).
Three ionization chambers with different geometries have been constructed and filled with dielectric liquids for detection of fast neutrons. The three dielectric liquids studied were Tetramethylsilane (TMS), Tetramethylpentane (TMP), and Isooctane, which each have intrinsic properties that make them attractive for fast neutron detection. Their electronic properties are similar to those of condensed noble gases, but they don't require cryogenic temperatures to maintain liquid phase. However, like condensed noble gases, they do require a high level of purity. A stainless steel purification system was constructed to purify the liquids and the purity was monitored by an ionization chamber with a 241Am source inside. The three liquid detectors were exposed to 250keV x-rays from an orthovoltage x-ray tube and neutrons (1.4-12MeV) from a 1-Ci 239Pu-Be source. Experimental data show that an ionization chamber filled with dielectric liquid is capable of detecting fast neutrons in pulse mode. While chamber 1, chamber 2, and chamber 3 (filled with TMS) did not respond to the Pu-Be source, chamber 3 (filled with TMP and Isooctane) successfully detected the presence of neutrons. Data also show that the chambers could not detect gamma rays from 1[mu]Ci Co-60 and Cs-137 check sources. In addition, the chambers could detect 250 keV x-rays in current mode, but not pulse mode. These results present positive implications for the gamma-blindness of the dielectric liquids studied.
by Erin M. Boyd.
S.M.

The unique features of flexoelectric and dielectric effects are investigated, and exploited for a variety of functions, in a wide range of helicoidal liquid crystal systems, including non-chiral, cholesteric and blue phases. Electrooptic techniques are developed to measure flexoelectric parameters in non-chiral and cholesteric liquid crystals using twisted nematic and Grandjean geometries respectively. A crystal rotation method, and using a lock-in amplifier, is used to enable the measurement of a very small e/K of 0.011 C/N^-1m^-1. Enhancement in chiral-flexoelectric switching is demonstrated theoretically in liquid crystals with negative dielectric anisotropy and in systems in which the pitch is constrained to be other than the natural pitch. A methodological framework for inducing stable Uniform Lying Helix alignment is developed based on weak homeotropic alignment conditions and a method to bias the helicoidal axis orientation; a series of approaches within this framework are demonstrated, including nano-grooved interfaces, periodic boundaries conditions, in-plane fields, and mould-templated micro-channels. The latter approach is potentially commercially viable for sub-millisecond electrooptic technology. The contribution to a cholesteric material's effective dielectric permittivity of flexoelectric polarization is formulated, and an ability to switch a cholesteric between Grandjean and lying-helix configurations based on the dispersion in the flexoelectric polarization and resultant relaxation in dielectric properties is demonstrated. The flexoelectric contribution to dielectric permittivity is exploited to enable switching in bistable reflective displays and alignment of the Uniform Lying Helix. The existence of a flexoelectric contribution to Kerr switching in blue phases is demonstrated, and a semi-empirical model for the effect is developed. The effect is the first known example of a non-polar flexoelectrooptic effect. Independent flexoelectric and dielectric contributions to Kerr switching in blue phases are measured experimentally by measuring the induced birefringence as a function of driving frequency in flexoelectric- and dielectric-dominated wide-temperature-range blue phase materials.

Les charges électriques présentes naturellement aux interfaces liquide/solide ou qui se développent dans les liquides de façon contrôlée ou non-désirée sont sources, d’une part, de nombreuses applications (micro-pompages, laboratoires sur puce, super-condensateurs…), et d’autre part de risques industriels (inflammations, explosions…). Ceci nécessite une quantification aussi précise que possible des valeurs et des répartitions de ces charges dans les milieux diélectriques liquides. Les techniques de mesure actuelles sont soit non-résolutives, les réponses mesurées sur l’ensemble de l’éprouvette permettant de déduire des informations sur les charges et les processus associés de manière indirecte (au travers de modèles), soit limitées en termes de sensibilité et/ou de résolution. Par exemple, le modèle de la double couche électrique, proposé par Stern en 1924 et complètement accepté par la communauté scientifique depuis, n’a encore jamais été confirmé expérimentalement, notamment en raison du manque de résolution et de sensibilité des méthodes existantes.Plusieurs techniques ont été développées depuis 1980 pour mesurer de façon directe et non-destructive les charges électriques dans les isolants solides. Parmi ces méthodes, celles basées sur l’application de stimuli thermiques de faible amplitude ont montré les meilleures sensibilités et les meilleures performances pour la mesure des charges près des interfaces. L’application de ces techniques aux liquides est une voie de recherche à explorer afin de répondre aux questionnements scientifiques et applicatifs évoqués. Ce travail étudie, aussi bien du point de vue théorique qu’expérimental, l’application du principe de l’onde thermique à la mesure de charges électriques dans les liquides isolants. La double couche électrique, qui s’établit au niveau des parois liquide/solide, est utilisée comme objet d’étude. Plusieurs liquides diélectriques sont concernés : cyclohexane à l’état liquide et solide, huile minérale pure et additivée et huile silicone.À travers des simulations numériques, les réponses électriques susceptibles d’être issus de l’application de stimuli thermiques de quelques degrés à des liquides isolants sont calculées, en considérant la couche diffuse présente à l’interface avec les parois. L’influence de différents paramètres de la double couche électrique sur les signaux simulés est étudiée. Les effets de la thermo-convection sont quantifiés en particulier et des critères permettant de les identifier dans les réponses électriques sont établis.Des résultats expérimentaux, obtenus avec une installation de mesure conçue et réalisée spécialement pour les liquides, montrent que les réponses issues de l’application d’onde thermique de faibles amplitudes à des liquides isolants sont bien mesurables. Leur analyse détaillée permet de conclure que ces réponses proviennent bien des charges de la double couche électrique. La contribution probable aux signaux mesurés non seulement de la couche diffuse, mais également de la couche compacte, est mise en évidence. Les résultats permettent de conclure que les méthodes à stimuli thermique sont applicables aux liquides diélectriques. La poursuite de leur développement devrait aboutir à des mises en œuvres expérimentales avec des résolutions et des sensibilités adaptées à l’étude des charges et des champs électriques aux interfaces et dans le volume de ces matériaux
The electrical charges naturally present at liquid/solid interfaces or which develop in liquids in a controlled or undesired way are at the origin both of numerous applications (micro-pumps, lab-on-a-chip, super-capacitors) and of industrial risks (inflammations, explosions). This requires the most precise possible quantification of the values and distributions of these charges in liquid dielectric media. The present measurement techniques are either non-resolutive, as the responses measured on the entire specimen allow to deduce information about the charges and the associated processes indirectly (through models), or limited in terms of sensitivity and resolution. For example, the electrical double layer model, proposed by Stern in 1924 and fully accepted by the scientific community since then, has not been confirmed experimentally yet, in particular due to the lack of resolution and sensitivity of the existing methods.Several techniques have been developed since 1980 to measure directly and non-destructively the electrical charges in solid insulators. Among these methods, those based on the application of low-amplitude thermal stimuli have shown high sensitivity and performance for the measurement of loads near interfaces. The application of these techniques to liquids is a research path to be explored in order to answer the above scientific and applicative questions. This work studies, both from theoretical and experimental points of view, the application of the thermal step principle to the measurement of electrical charges in insulating liquids. The electrical double layer, which sets up at the level of the liquid/solid walls, is used as object of the study. Several dielectric liquids are concerned: cyclohexane in liquid and solid state, pure and additive mineral oil and silicone oil.Through numerical simulations, electrical responses expected from the application of thermal stimuli of several degrees to insulating liquids are calculated, considering the diffuse layer present at the interface with the walls. The influence of different parameters of the electrical double layer on the simulated signals is studied. In particular, the effects of thermo-convection are quantified and criteria to identify them in the electrical responses are established.Experimental results, obtained with a measuring installation designed and built specifically for liquids, prove that the responses resulting from the application of low-amplitude thermal steps to insulating liquids are well measurable. Their detailed analysis leads to the conclusion that these responses are indeed due to charges from the electrical double layer. The probable contribution to the measured signals not only of the diffuse layer, but also of the compact layer, is highlighted. The results allow to conclude that thermal stimuli methods are applicable to dielectric liquids. Their further development should lead to experimental implementations with resolutions and sensitivities adapted to the study of electric charges and fields at the interfaces and in the volume of these materials

Polymer Dispersed Liquid Crystals (PDLCs) are attracting considerable attention for new optical displays. This thesis describes the synthesis of PDLC materials, fabrication of cells and study of their optical and dielectric behaviour. This work includes two areas of research. Predominantly it is an investigation of the properties of PDLCs prepared using Polymerisation Phase Separation (PIPS) by UV irradiation of mutually soluble liquid crystal (LC) and pre-polymer materials, developed for use in PDLC systems. A limited study of liquid crystal gels completes the thesis. We demonstrate that the electro-optical response of a PDLC is due to alignment of the LC phase, illustrated by comparison of the dielectric behaviour of the PDLC and LC in an aligning field. It is evident from this work that there is solubility of the LC component in the polymer that forms the continuous phase. Therefore, only at higher concentrations of the LC component (above 30%) will the PDLC be formed, and in such materials, the continuous phase contains dissolved LC material. Variation of experimental conditions under which samples are prepared, by changing the composition, temperature of cure and the presence of aligning fields, leads to modifications in the structure and properties of PDLCs, which are investigated. Techniques to study the dielectric, electro-optic and optical properties have been applied to the range of samples prepared. Such studies give information on the alignment of the LC phase in a PDLC in directing electric fields. It is demonstrated that dielectric relaxation spectroscopy (DRS) provides direct information on the macroscopic orientation and voltage induced changes in the alignment of gels produced in the presence and absence of electric fields. Our studies show that DRS, in combination with optical techniques, provides a powerful means for studying the alignment of LC molecules in PDLCs and gels.

Dissertação para obtenção do grau de mestre em Engenharia de Materiais
The main purpose of this work was to realize an exhaustive study on the molecular mobility of a glass-forming liquid and evaluate the influence of thermal treatment in the phase transformations undergone by the material. It was also our goal to investigate it response when subjected to confinement in nano-porous inorganic materials. The liquid selected, Triton X100, is characterized by a high dielectric response and a high tendency to crystallize by coming from both molten and glassy states. However, it is possible to find the conditions under which crystallization is avoided and the material enters in the supercooled liquid state. This allowed us to study the molecular mobility in the liquid, supercooled liquid, glassy states and as well as the crystallization and investigate temperature driven phase transformations. To get a further insight in the crystallization behaviour, isothermal crystallization at different temperatures and from both glassy and molten states was promoted and monitored in real-time by Dielectric Spectroscopy Relaxation. This study gave information about the influence of the crystallization on the remaining amorphous phase. Motivated by the recent knowledge that molecular mobility and phases transformations can be significantly altered when a glass-forming liquid is confined in the nanometer scale, the molecular dynamics of the Triton X100 was evaluated when confined in mesoporous materials (SBA-15 and MCM-41; pore size, respectively, 5.7 and 3.4 nm). This study revealed that the confinement in SBA-15 is an effective strategy to avoid the crystallization of the Triton X100 independently of the thermal history. Dielectric Spectroscopy Relaxation (DRS) was the main technique used to obtain detailed information about the molecular mobility in a wide range of frequencies (10-2 – 106 Hz). As complementary techniques Differential Scanning Calorimetric (DSC) and polarized Optical Microscopy (POM) were used. Some of the results have been published in the Journal of Physical Chemistry B 2011, 115, (43), 12336-12347.

Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: phase transitions; quenched random disorder; liquid crystals; dielectric spectroscopy; calorimetry. Includes bibliographical references (leaves 78-83).

Arrays of microelectrodes were used to apply forces to dielectric (soda lime glass) spheres in a thin (200 micrometer thick) layer of a dielectric liquid polymer (EOPN 8021). The microelectrodes were fabricated using standard photolithographic methods of evaporating and electroplating gold onto a glass substrate. The objective is to use the electric body forces in the sphere and the electric surface tractions on the sphere to position the spheres in a microscale pattern, in this case a square array in-plane. Three sizes of spheres were used: 30, 90, and 170 microns in diameter. The 30 micron spheres formed clusters associated with the regions of highest electric energy density, whereas single 90 micron spheres were located at the regions of highest electric energy density. The 170 micron spheres generally did not form patterns. The experiments indicated that free charges, either in the volume of the sphere and/or on the sphere surface, significantly influence the motion of the sphere. A finite element analysis was performed to study the electro-fluid mechanics. The liquid velocity and streamlines were plotted, and the force resultants due to the liquid acting on the sphere were calculated. Also, the electric body force and surface tractions resultants were calculated. In general, the forces on the sphere and the liquid velocity are in agreement with the experimental results.

A variety of methods have been reviewed for obtaining parallel or perpendicular alignment in liquid-crystal cells. Some of these methods have been selected and developed and were used in polarised spectroscopy, dielectric and electro-optic studies. Also, novel dielectric and electro-optic cells were constructed for use over a range of temperature. Dielectric response of thin layers of E7 and E8 (eutectic mixture liquid-crystals) have been measured in the frequency range (12 Hz-100 kHz) and over a range of temperature (183-337K). Dielectric spectra were also obtained for supercooled E7 and E8 in the Hz and kHz range. When the measuring electric field was parallel to the nematic director, one loss peak (low-frequency relaxation process) was observed for E7 and for E8, that exhibits a Debye-type behaviour in the supercooled systems. When the measuring electric field was perpendicular to the nematic director, two resolved dielectric processes have been observed. The phase transitions, effective molecular polarisabilities, anisotropy of polarisabilities and order parameters of three liquid crystal homologs (5CB, 6CB, and 7CB), 60CB and three eutectic nematic mixtures E7, E8, and E607 were calculated using optical and density data measured at several temperatures. The order parameters calculated using the different methods of Vuks, Neugebauer, Saupe-Maier, and Palffy-Muhoray are nearly the same for the liquid crystals considered in the present study. Also, the interrelationship between density and refractive index and the molecular structure of these liquid crystals were established. Accurate dielectric and dipole results of a range of liquid-crystal forming molecules at several temperatures have reported. The role of the cyano-end group, biphenyl core, and flexible tail in molecular association, were investigated using the dielectric method for some molecules which have a structural relationship to the nematogens. Analysis of the dielectric data for solution of the liquid-crystals indicated a high molecular association, comparable to that observed in the nematic or isotropic phases. Electro-optic Kerr effect were investigated for some alkyl cyanobiphenyls, their nematic mixtures and the eutectic mixture liquid-crystals E7 and E8 in the isotropic phase and solution. The Kerr constant of these liquid crystals found to be very high at the nematic-isotropic transition temperatures as the molecules are expected to be highly ordered close to phase transition temperatures. Dynamic Kerr effect behaviour and transient molecular reorientation were also observed in thin layers of some alkyl cyanobiphenyls. Dichroic ratio R and order parameters of solutions containing some azo and anthraquinone dyes in the nematic solvent (E7 and E8), were investigated by the measurement of the intensity of the absorption bands in the visible region of parallel aligned samples. The effective factors on the dichroic ratio of the dyes dissolved in the nematic solvents were determined and discussed.

The submitted thesis describes characteristics and use of ferroelectric materials which find their utilization in electrotechnical and electronics industry. The thesis is mainly aimed at their behaviour in the electrical field at various intensity. The method using an osciloscope is selected for measuring. For the main measuring in part of this thesis was produced experimental wafer with five samples which were subsequently mesuared. The VEE PRO program was used for creating of collecting datas for histeresis loop and it’s functionality was checked on wafer with five examples in measuring. During this measuring was also measured electric tension dependence of components of complex permittivity.

Ces travaux de thèse ont porté sur des matériaux constitués de dispersions de particules colloïdales nanométriques, issues d'un matériau ferroélectrique, dans un cristal liquide chiral à phase smectique ferroélectrique. Ils ont pour but d'étudier les effets occasionnés par ces dispersions sur les propriétés du nanocolloïde, notamment celles liées à leur ferroélectricité. Cette étude a montré que les comportements mésomorphes et ferroélectriques de ces matériaux sont conservés. Une baisse de polarisation spontanée ainsi qu'un recul des températures des transitions ont été mis en évidence pour des faibles concentrations en NPs. Une "transition" de ces comportements a été observée pour une concentration critique au-delà de laquelle les particules s'agrègent pour former des amas au sein du milieu cristal liquide. Nous nous sommes intéressés ensuite à deux modes de relaxation diélectriques. Le premier lié aux mouvements de distorsions de l'hélice dans la phase ferroélectrique, le second aux mouvements de compression des couches smectiques de part et d'autre de la transition ferroélectrique-paraélectrique. Les comportements observés semblent être gouvernés par les modifications des propriétés visco-élastiques des nanocolloïdes, occasionnés par l'intercalation des nanoparticules entre les couches smectiques
The present thesis work concerns materials made of dispersions of nanometric colloidal particles, from a bulk ferroelectric material, dispersed within a chiral smectic phase of a ferroelectric liquid crystal. The goal of this work is to study the effect of the dispersed nanoparticles over the nanocolloïd properties, specially the ones related to ferroelectricity. This study showed no change over mesomorphic and ferroelectric behavior of the materials. A decrease in spontaneous polarization and phase transition temperatures was found for low nanoparticle concentrations. A "transition" of these behaviors was observed for a critical concentration, beyond which, nanoparticles aggregate and form clusters inside the liquid crystal matrix. Afterwards, we have studied two dielectric relaxation modes. The first one related to distorsions of the helix in the ferroelectric phase and the second one to the compression movements of the smectic layers around the ferroelectric-paralectric transition. The observed behaviors seem to be due to modifications of the visco-elastic properties of nanocolloids, produced by intercalation of nanoparticles between the smectic layers

Um novo método de medida (SAM -Spectral Analysis Method) mostra que, devído a um erro sistemático tradicionalmente desprezado, os valores medidos de polarização espontânea do cristal líquido ZLI-3654 (Merck) não seguem o que é previsto pela teoria de Landau das transições contínuas. Porém, a variação da susceptibilidade elétrica relativa com a temperatura proporcional à (T Tc) IND.-1, onde Te é a temperatura onde ocorre o máximo da susceptibilidade ...... está de acordo com o modelo de Landau. A resposta em freqüência da constante dielétrica mostra que, a fim de minimizar a corrente iônica, as medidas de polarização elétrica devem ser realizadas em frequências acima de 20 Hz. Por sua vez, os valores dos ângulos de fase dos harmônicos da polarização, obtidos pelo novo método, indicam que a intensidade do campo elétrico aplicado deve ser inferior a 1, 1 x 10 IND.6 Vrms/m (em 23Hz) para que não ocorram instabilidades elctrohidrodinâmicas, Finalmente, o ajuste das amplitudes dos harmônicos da polarização elétrica obtidos pelo SAM aos parâmetros da equação de Landau-Kalatnikov mostra um bom acordo dos valores medidos com o modelo, em contraste com os valores de polarização espontânea, A solução da equação de equilíbrio, levando em consideração os parâmetros ajustados, mostra como seriam os valores da polarização espontânea sem os erros sistemáticos.
A new proposed measurement method (SAM - Spectral Analysis Method) shows that, due a traditionally neglected systematic error, the values of the measured spontaneous polarization cf the ferroeleotric liquid crystal ZLI-3654 (Merck) doesn\'t follow what is predicted by the Landau theory of continuous transition. In contrast, the decay of the relative electric susceptibility with the temperature (T) - proportional to (T Tc)-l, where Tc is at the maximum of the susceptibility - is in good agreement with the Landau model. The frequency response of the dielectric constant shows that the measurements of the electric polarization of the sample must be done at frequencies hígher than 20Hz to avoid the actíons of the ionic currents. The phase values of the electric polarization harmonics obtained by the SAM indicates that the electric field must be lower thau 1,1 x l06Vrms/m (at 23Hz) to avoid electrohydrodynamic instabilities, Finally, the fitting of the amplitudes of the electric polarization harmonics obtained by the SAM to the parameters of the Landau-Kalatnikov equation shows a good agreement with the model, in contrast with the spontaneous polarization measurements. The solution of the Landau model, considering the fitted parameters, predicts how should be the spontaneous polarization values without the systematic errors.

Samples of copper, iron and graphite, commonly used as tool and workpiece electrodes in the electro-discharge machining process are subjected to single electrical discharges by breakdown of the paraffin liquid in which they are immersed. The discharge currents and durations used are typical of the repetitive discharges used in EDM. The electrode morphologies, resulting from the erosive action of the discharges, are examined using both optical and electron microscopy. The results of these examinations are related to single discharge erosion data derived from performance figures of commercial EDM equipment. It is concluded that the anode is heated by a plasma discharge which expands with time. During the discharge cathode material is evaporated by cathode spots which differ in character for thermionic and nonthermionic materials. Molten anode and cathode material is evacuated after the discharge by a fall in pressure within a bubble of vapour which surrounds the electrodes during the discharge. Graphite electrodes are eroded by sublimation during the discharge. A novel proposal for the relation between micro-cratering of iron cathodes and the plasma diameter is proposed and tested.

Dizertační práce je zaměřena na studium elektrických a dielektrických vlastností iontových kapalin. Iontové kapaliny mohou nacházet uplatnění v široké škále aplikací, především pak v elektrotechnice. Teoretická část se věnuje popisu základních vlastností iontových kapalin a možností jejich uplatnění v kondenzátorech a elektrochemických senzorech plynů. Experimentální část se věnuje použitým metodám charakterizace vlastností iontových kapalin, jsou zde popsány teoretické poznatky o dielektrické spektroskopii včetně metod stanovení fyzikálních vlastností a vyhodnocení experimentálních dat. Experimentální část je rozdělena na dvě základní části. První se věnuje studiu iontových kapalin pro použití jako elektrolytu v kondenzátorech, druhá část se věnuje studiu vlastností připravených experimentálních senzorů na NO2, zejména vlivem vlastností iontových kapalin na sledované parametry senzoru.

Success in geotechnical analysis, design, and construction invariably requires that we have proper knowledge and understanding of (1) the strength, (2) the fluid flow properties, and (3) the stress-deformation behavior of the earth materials. These important engineering properties are primarily determined by the components and structure of a soil, which also dictate the soilâ s responses in an electromagnetic field. As a nondestructive technique, the electromagnetic property measurement offers a promising approach to characterize earth materials and identify the effects of changes in environments. However, despite many investigations in the last several decades, the relationship between the frequency-dependent electromagnetic properties of soils and their components and structure are still not well understood. Hence, estimation of engineering properties of a soil in a quantitative way from electromagnetic measurements can be uncertain. In this research several tasks have been accomplished: (1) Development of a physically based model that provides a means of investigating the coupled effects of important polarization mechanisms on soil electromagnetic properties, and a means of relating the electromagnetic properties of a soil to its fines content, clay mineralogy, anisotropy, degree of flocculation and pore fluid chemistry; (2) Proposal of a practically applicable method to determine the volumetric water content, specific surface area and pore fluid salt concentration simultaneously from the dielectric spectrum; (3) Deduction of the wide-frequency electromagnetic properties of a soil by measuring its responses to a step pulse voltage using time domain reflectometry (TDR); (4) Establishment of the relationships between the specific surface area and compressibility, residual shear strength and hydraulic conductivity. This study establishes a framework for quantifying soil engineering properties from their electromagnetic properties. If properly determined and interpreted, the electromagnetic properties can also provide insights into the causes of soil property changes over time and can be very useful in studying the effects of biological factors in geotechnical engineering, a field that may offer great potential for future advances.
Ph. D.

Self-assembly of nanomaterials over macroscopic dimensions and development of novel nano-electromechanical systems (NEMS) hold great promise for numerous nanotech applications. However, it has always been a great challenge to find a general route for controlled self-assembly of nanomaterials and generating electromechanical response at the nanoscale level. This work indicates that self-organized anisotropic nematic liquid crystals (LC) can be exploited for nanotemplating purposes to pattern carbon nanotubes (CNTs) and Quantum dots (QDs) over a macroscopic dimension. The pattern formed by the CNTs or QDs can be controlled by applying external electric and magnetic fields, developing novel nano-electromechanical and nano-magnetomechanical systems. Self-organizing nematic liquid crystals (LC) impart their orientational order onto dispersed carbon nanotubes (CNTs) and obtain CNT-self-assembly on a macroscopic dimension. The nanotubes-long axis, being coupled to the nematic director, enables orientational manipulation via the LC nematic reorientation. Electric field induced director rotation of a nematic LC+CNT system is of potential interest due to its possible application as a nano-electromechanical system. Electric field and temperature dependence of dielectric properties of an LC+CNT composite system have been investigated to understand the principles governing CNT-assembly mediated by the LC. In the LC+CNT nematic phase, the dielectric relaxation on removing the applied field follows a single exponential decay, exhibiting a faster decay response than the pure LC above a threshold field. Due to a strong LC-CNT anchoring energy and structural symmetry matching, CNT long axis follows the director field, possessing enhanced dielectric anisotropy of the LC media. This strong anchoring energy stabilizes local pseudo-nematic domains, resulting in nonzero dielectric anisotropy in the isotropic LC phase. These anisotropic domains respond to external electric fields and show intrinsic frequency response. The presence of these domains makes the isotropic phase electric field-responsive, giving rise to a large dielectric hysteresis effect. These polarized domains maintain local directors, and do not relax back to the original state on switching the field off, showing non-volatile electromechanical memory effect. Assembling quantum dots (QDs) into nanoscale configurations over macroscopic dimensions is an important goal to realizing their electro-optical potential. In this work, we present a detailed study of a pentylcyanobiphenyl liquid crystal (LC) and a CdS QD colloidal dispersion by probing the dielectric property  and relaxation as a function of an applied ac-electric field Eac. In principle, dispersing QDs in a nematic LC medium can direct the dots to align in nearly one-dimensional chain-like structures along the nematic director and these assemblies of QDs can be directed by external electric fields. In a uniform planar aligned cell, the Fréedericksz switching of the LC+QDs appears as a two-step process with the same initial switching field as the bulk but with the final value larger than that for an aligned bulk LC. The relaxation of  immediately following the removal of Eac follows a single-exponential decay to its original value that is slower than the bulk but becomes progressively faster with increasing Eac, eventually saturating. These results suggest that the arrangement of the QDs is mediated by the LC.

Progress in the fields of wearable computing, soft robotics and bio hybrid engineering depend on new classes of soft multifunctional materials that match the mechanical properties of soft biological tissue and possess high toughness, while having metal-like electrical and thermal properties.

Ce travail est une analyse de la structure des panaches Électrohydrodynamiques plans également appelés jets Électrohydrodynamiques en géométrie plane. Il a pour objectif de proposer une description la plus précise possible de l'écoulement, d'apporter une meilleure compréhension des phénomènes physiques notamment à l'aide de modèles simples et de quantifier la force électrique. Le chapitre I est une étude bibliographique qui propose un résumé des principales connaissances sur la structure de deux écoulements très similaires aux jets EHD : les jets classiques et les panaches thermiques. Le chapitre II est consacré à la présentation du montage expérimental, ainsi qu'à la méthodologie expérimentale utilisée dans cette étude. La qualité des mesures obtenues grâce à la méthode de vélocimétrie par images de particule y est discutée ; les problèmes de non corrélation, de convergence statistique des résultats y sont par exemple abordés. L'analyse des champs de vitesse permet de mettre en évidence la structure des panaches et de proposer une classification des jets EHD. Le chapitre III est consacré à l'étude de la force électrique dans les panaches EHD. L'actionneur utilisé pour produire le jet plan est de type lame-plan. Trois méthodes indirectes ont été utilisées pour estimer la force à partir du champ de vitesse. La première méthode appelée méthode intégrale classique calcule la force par intégration volumique de l'équation de Navier-Stokes. La deuxième méthode appelée méthode RANS intégrale estime la force à partir de chacun des termes de l'équation RANS en utilisant une décomposition de la vitesse en valeur moyenne et fluctuation. Enfin, la force est également calculée selon une troisième méthode basée sur une modélisation simplifiée de l'écoulement inspirée des travaux de Malraison et Atten. Dans le dernier chapitre, l'étude est étendue à un écoulement électroconvectif de type jet de paroi électrique. Il est généré par un actionneur à barrière diélectrique. L'étude est faite avec deux types des liquides diélectriques différents. Comme pour le jet plan, l'analyse des champs de vitesse permet de définir les structures de l'écoulement mais également de calculer l'intensité de la force produite
This work is related to the analysis of the structure of electrohydrodynamic plane plumes also called electrohydrodynamic jets in plane geometry. The aim of this work is to provide a more precise description and a better understanding of its physical phenomenon and to quantify the electric force using the simple models. Chapter I is a literature review which provides a summary of two flows with the structure very similar to EHD jets: classic jets and thermal plumes. Chapter II is devoted to the presentation of the experimental setup and method used in this study. The quality of the measurements obtained by the method of Particle Image Velocimetry is discussed; problems of non correlation and statistical convergence of the results are also discussed. The analysis of velocity fields allows us to identify the structure and propose a classification of the EHD plumes. Chapter III is devoted to the study of the electric force in the EHD plumes. The actuator used to produce the plane jet is a blade plane device. Three indirect methods were used to estimate the force from the velocity field. The first classical method called integral method calculates the force by volumetric integration of Navier-Stokes equations. The second method called RANS integral method estimates the force from each term of RANS equation using the average and fluctuating velocity components. Finally, the force is also calculated using a third approach with a simplified flow model based on the work of Malraison and Atten. In the last chapter, the study is extended to one type of électroconvectif flow: the electrical wall jet. It is generated by a dielectric barrier actuator. The study is carried out with two different dielectric liquids. As is the case with plane jet, the analysis of velocity fields is used to define the flow structures and calculate the force produced

In this dissertation, liquid crystal (LC) materials and devices are investigated in order to meet the challenges for photonics and displays applications. We have studied three kinds of liquid crystal materials: positive dielectric anisotropic LCs, negative dielectric anisotropic LCs, and dual- frequency LCs. For the positive dielectric anisotropic LCs, we have developed some high birefringence isothiocyanato tolane LC compounds with birefringence ~0.4, and super high birefringence isothiocyanato biphenyl-bistolane LC compounds with birefringence as high as ~0.7. Moreover, we have studied the photostability of several high birefringence LC compounds, mixtures, and LC alignment layers in order to determine the failure mechanism concerning the lifetime of LC devices. Although cyano and isothiocyanato LC compounds have similar absorption peaks, the isothiocyanato compounds are more stable than their cyano counterparts under the same illumination conditions. This ultraviolet-durable performance of isothiocyanato compounds originates from its molecular structure and the delocalized electron distribution. We have investigated the alignment performance of negative dielectric anisotropic LCs in homeotropic (vertical aligned, VA) LC cell. Some (2,3) laterally difluorinated biphenyls, terphenyls and tolanes are selected for this study. Due to the strong repulsive force between LCs and alignment layer, (2,3) laterally difluorinated terphenyls and tolanes do not align well in a VA cell resulting in a poor contrast ratio for the LC panel. We have developed a novel method to suppress the light leakage at dark state. By doping positive [Delta][epsilon] or non-polar LC compounds/mixtures into the host negative LC mixtures, the repulsive force is reduced and the cell exhibits an excellent dark state. In addition, these dopants increase the birefringence and reduce the viscosity of the host LCs which leads to a faster response time. Dual-frequency liquid crystal exhibits a unique feature that its dielectric anisotropy changes from positive to negative when we increase the operating frequency. Submillisecond response time can be achieved by switching the frequency of a biased voltage, rather than switching the voltage at a given frequency. In this dissertation, we investigate the dielectric heating effect of dual-frequency LCs. Because the absorption peak of imaginary dielectric constant occurs at high frequency region (~ MHz), there is a heat generated when the LC cell is operated at a high frequency voltage. To measure the transient temperature change of the LC inside the cell, we have developed a non-contact method by utilizing the temperature-dependent birefringence property of the LC. Most importantly, we have formulated a new dual-frequency LC mixture which greatly reduces the dielectric heating effect while maintaining good physical properties. Another achievement in this thesis is that we have developed a polarization independent phase modulator by using a negative dielectric anisotropic LC gel. With ~20 % of polymer mixed in the LC host, the LC forms polymer network which, in turn, exerts a strong anchoring force to the neighboring LC molecules. As a result, the operating voltage increases but the response time is significantly decreased. On the phase shift point of view, our homeotropic LC gel has ~0.08 [pi] phase shift, which is 2X larger than the previous nano-sized polymer-dispersed liquid crystal droplets. Moreover, it is free from light scattering and requires a lower operating voltage. In conclusion, this dissertation provides solutions to improve the performance of LC devices both in photonics and displays applications. These will have great impacts in defense and display systems such as optical phased array, LCD TVs, projectors, and LCD monitors.
Ph.D.
Other
Optics and Photonics
Optics

Blue phase liquid crystals (BPLCs) have a delicate lattice structure existing between chiral nematic and isotropic phases, with a stable temperature range of about 2 K. But due to short coherent length, these self-assembled nano-structured BPLCs have a fast response time. In the past three decades, the application of BPLC has been rather limited because of its narrow temperature range. In 2002, Kikuchi et al. developed a polymer stabilization method to extend the blue-phase temperature range to more than 60 K. This opens a new gateway for display and photonic applications. In this dissertation, I investigate the material properties of polymer-stabilized BPLCs. According the Gerber's model, the Kerr constant of a BPLC is linearly proportional to the dielectric anisotropy of the LC host. Therefore, in the frequency domain, the relaxation of the Kerr constant follows the same trend as the dielectric relaxation of the host LC. I have carried out experiments to validate the theoretical predictions, and proposed a model called extended Cole-Cole model to describe the relaxation of the Kerr constant. On the other hand, because of the linear relationship, the Kerr constant should have the same sign as the dielectric anisotropy of the LC host; that is, a positive or negative Kerr constant results from positive or negative host LCs, respectively. BPLCs with a positive Kerr constant have been studied extensively, but there has been no study on negative polymer-stabilized BPLCs. Therefore, I have prepared a BPLC mixture using a negative dielectric anisotropy LC host and investigated its electro-optic properties. I have demonstrated that indeed the induced birefringence and Kerr constant are of negative sign. Due to the fast response time of BPLCs, color sequential display is made possible without color breakup. By removing the spatial color filters, the optical efficiency and resolution density are both tripled. With other advantages such as alignment free and wide viewing angle, polymer-stabilized BPLC is emerging as a promising candidate for next-generation displays. However, the optical efficiency of the BPLC cell is relatively low and the operating voltage is quite high using conventional in-plane-switching electrodes. I have proposed several device structures for improving the optical efficiency of transmissive BPLC cells. Significant improvement in transmittance is achieved by using enhanced protrusion electrodes, and a 100% transmittance is achievable using complementary enhanced protrusion electrode structure. For a conventional transmissive blue phase LCD, although it has superb performances indoor, when exposed to strong sunlight the displayed images could be washed out, leading to a degraded contrast ratio and readability. To overcome the sunlight readability problem, a common approach is to adaptively boost the backlight intensity, but the tradeoff is in the increased power consumption. Here, I have proposed a transflective blue phase LCD where the backlight is turned on in dark surroundings while ambient light is used to illuminate the displayed images in bright surroundings. Therefore, a good contrast ratio is preserved even for a strong ambient. I have proposed two transflective blue phase LCD structures, both of which have single cell gap, single gamma driving, reasonably wide view angle, low power consumption, and high optical efficiency. Among all the 3D technologies, integral imaging is an attractive approach due to its high efficiency and real image depth. However, the optimum observation distance should be adjusted as the displayed image depth changes. This requires a fast focal length change of an adaptive lens array. BPLC adaptive lenses are a good candidate because of their intrinsic fast response time. I have proposed several BPLC lens structures which are polarization independent and exhibit a parabolic phase profile in addition to fast response time. To meet the low power consumption requirement set by Energy Star, high optical efficiency is among the top lists of next-generation LCDs. In this dissertation, I have demonstrated some new device structures for improving the optical efficiency of a polymer-stabilized BPLC transmissive display and proposed sunlight readable transflective blue-phase LCDs by utilizing ambient light to reduce the power consumption. Moreover, we have proposed several blue-phase LC adaptive lenses for high efficiency 3D displays.
Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics

Electrohydrodynamic (EHD) pumping of single and two-phase media is attractive for terrestrial and outer space applications since it is non-mechanical, lightweight, and involves no moving parts. In addition to pure pumping purposes, EHD pumps are also used for the enhancement of heat transfer, as an increase in mass transport often translates to an augmentation of the heat transfer. Applications, for example, include two-phase heat exchangers, heat pipes, and capillary pumping loops. In this research, EHD induction pumping of liquid film in annular horizontal and vertical configurations is investigated. A non-dimensional analytical model accounting for electric shear stress existing only at the liquid/vapor interface is developed for attraction and repulsion pumping modes. The effects of all involved parameters including the external load (i.e. pressure gradient) and gravitational force on the nondimensional interfacial velocity are presented. A non-dimensional stability analysis of EHD induction pumping of liquid film in a vertical annular configuration in the presence of external load for repulsion mode is carried out. A general non-dimensional stability criterion is presented. Stability maps are introduced allowing classification of pump operation as stable or unstable based on the input operating parameters. An advanced numerical model accounting for the charges induced throughout the bulk of the fluid due to the temperature gradient for EHD induction pumping of liquid film in a vertical annular configuration is derived. A non-dimensional parametric study including the effects of external load is carried out for different entrance temperature profiles and in the presence of Joule heating. Finally, a non-dimensional theoretical model is developed to investigate and to understand the EHD conduction phenomenon in electrode geometries capable of generating a net flow. It is shown that with minimal drag electrode design, the EHD conduction phenomenon is capable of providing a net flow. The theoretical model is further extended to study the effect of EHD conduction phenomenon for a two-phase flow (i.e. a stratified liquid/ vapor medium). The numerical results presented confirm the concept of liquid film net flow generation with the EHD conduction mechanism.

博士
國立成功大學
微電子工程研究所
103
GaN-based high-electron mobility transistors (HEMTs) have gained much attention for their applications in high-power, high-frequency, and high-temperature devices due to their wide bandgap, high breakdown voltage, and high saturated electron velocity. However, AlGaN/GaN HEMTs still have surface/interface-related problems, including high gate leakage current, collapse in drain current, and low gate voltage swing, which may limit corresponding applications. An alternative structure, namely, a metal–insulator/oxide–semiconductor (MIS/MOS), was incorporated on GaN-based devices using a thin insulator film between the gate electrode and the semiconductor. The use of insulators, including SiO2, SiN, and Al2O3 as gate dielectrics, have shown that these problems could be alleviated, but with a significant decrease in device transconductance and a large shift in threshold voltage. These problems can be overcome using a dielectric with high permittivity. MOSHEMTs with high-κgate dielectrics could translate into a more efficient modulation; thus, a small decrease in device transconductance and a slight increase in threshold voltage could be expected in AlGaN/GaN MOSHEMTs. LPD technique provides a simple, low-cost, less complex, and reliable method to obtain large area oxide thin films at low temperature. Several different materials, including TiO2, Ba-doped TiO2, and ZrO2, were deposited and analyzed by XPS, XRD, etc. The demonstrated MOSHEMTs with high-κ gate dielectrics show higher maximum gate bias with a higher drain current density, higher breakdown voltage, and lower gate leakage current density, as compared with the conventional HEMT. Furthermore, the properties of the LPD-TiO2 film deposited on (NH4)2Sx-treated AlGaAs were also investigated. In addition, TiO2 films prepared via the sol–gel solution process were deposited on n-type In0.53Ga0.47As to realize the enhancement-mode (E-mode) In0.53Ga0.47As MOSFET. This indicates that the sol–gel processed TiO2 as a gate dielectric was suitable for E-mode In0.53Ga0.47As MOSFET applications.

博士
國立成功大學
微電子工程研究所碩博士班
101
The high-k materials were deposited on GaN and AlGaN/GaN MOSHEMTs were fabricated with high-k gate dielectrics. Liquid-phase-deposition (LPD) is a simple, low-cost method. It works without complicated equipments or any assisting energy source, and can be used at low temperature. The relatively low deposition temperature effectively avoids thermal strain and defects. Several different high-k materials, including TiO2, STO, and ZrO2, were deposited on GaN and analyzed by XPS, SEM, etc. By using a high-k material as a gate dielectric, the decrease of transconductance and the tunneling current can be overcome by maintaining high gate-to-source capacitance and oxide thickness. TiO2 and STO both have quite high dielectric constant (〉60). The MOSHEMTs using these 2 kinds of oxides show lower leakage current and larger breakdown voltage, compared with the counterpart HEMTs. There is no obviously change of transconductance and threshold voltage in the MOSHEMTs. The LPD oxides also improve surface states, and reduce influences from interface scattering. However, the bandgap of these two oxides is low, and this leads to the larger leakage current. To overcome this problem, ZrO2 was also deposited, due to its high dielectric constant (〉20) and high bandgap (〉6eV). It's demonstrated that the gate leakage current and breakdown characteristics can be improved in the AlGaN/GaN MOSJEMTs with 2 nm-thick ZrO2 show The high current and high voltage for high power applications of AlGaN/GaN HEMT usually cause strong self-heating effects related to power dissipation problems. This problem can be overcome by using SiC substrate. In the final chapter, the HEMTs using SiC substrate and Si substrate were compared, and the HEMTs using SiC substrate show the better performance. In the HEMT with gate width of 1.2 mm, the maximum PAE is 38.4% and output power is 981 mW.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη στοχαστικών μοντέλων εκκενώσεων σε υγρά διηλεκτρικά και κατ’επέκταση η εξομοίωση τους σε υπολογιστή για να συγκριθούν ποιοτικά με μετρήσεις σε πραγματικές συνθήκες. Αρχικά περιγράψαμε βασικές έννοιες που χρησιμοποιούμε, όπως εκκένωση, τάση διάσπασης, ηλεκτρική αντοχή, απώλειες κ.α με σκοπό να είναι κατανοητή πλήρως η εργασία. Ύστερα αναλύσαμε τα φυσικά μοντέλα που υπάρχουν και πάνω στα οποία στηρίζονται τα στοχαστικά μοντέλα που μελετήσαμε. Αναλύσαμε το μοντέλο της φυσαλίδας και την συμπεριφορά των φυσαλίδων στις εκκενώσεις στα υγρά διηλεκτρικά. Επίσης μιλήσαμε για το μοντέλο μικροδιάσπασης καθώς και το μοντέλο ιονισμού. Στη συνέχεια περιγράψαμε τον τρόπο με τον οποίο γίνεται η διάδοση της εκκένωσης μέσα σε ένα υγρό διηλεκτρικό. Αρχικά μιλήσαμε για την έννοια της ηλεκτρονικής στιβάδας και για το πώς αυτή δημιουργείται. εν συνεχεία αναλύσαμε της βασικότατες έννοιες του streamer (αρνητικό και θετικό) καθώς και του leader και περιγράψαμε τους τρόπους δημιουργίας τους, διάδοσης τους και την σχέση που έχουν μεταξύ τους. Τελειώνοντας το θεωρητικό κομμάτι αυτής της διπλωματικής εργασίας αναλύσαμε τα βασικά υπάρχοντα θεωρητικά μοντέλα. Συγκεκριμένα αναλύσαμε το μοντέλο Niemeyer-Pietronero-Wiesmann, εν συνεχεία περιγράψαμε τις βασικές αρχές του μοντέλου FFC (Field Fluctuation Model). Έπειτα αναλύσαμε το μοντέλο Biller και τις εξισώσεις που το διέπουν. Τέλος παρουσιάσαμε και το μοντέλο Δανίκα αναπτύχθηκε το 1996 στο Δημοκρίτειο Πανεπιστήμιο Θράκης. Στη συνέχεια παρουσιάσαμε το μοντέλο εξομοίωσης με το οποία ασχοληθήκαμε και την βασική ιδέα πάνω στην οποία στηριχθήκαμε. Επίσης περιγράψαμε τις παραμέτρους του προγράμματος και τις παραδοχές που κάναμε. Τέλος αναλύσαμε τις βασικές συναρτήσεις που χρησιμοποιήθηκαν για την εξομοίωση του μοντέλου. Επιπρόσθετα δώσαμε τα αποτελέσματα, με πίνακες και γραφικές παραστάσεις, αρχικά για ομογενές πεδίο και μετά για μή ομογενές πεδίου (ακίδα-πλάκα). Επίσης παρουσιάσαμε τα αποτελέσματα κρατώντας διαφορετικές παραμέτρους σταθερούς όπως το συντελεστή γήρανσης και το μήκος του διακένου, με σκοπό να μελετήσουμε ποιοτικά την συμπεριφορά του μοντέλου μας υπό διαφορετικές συνθήκες. Τέλος κάναμε αναλυτικό σχολιασμό τον αποτελεσμάτων των εξομοιώσεων και σύγκριση των με πειραματικές μετρήσεις. Έγινε ακόμα περαιτέρω σχολιασμός για τις πιθανές αστοχίες που μπορεί να εμφανίσει το μοντέλο μας.
The purpose of the current diploma research is the study on the stochastic models of discharge in liquid dielectrics and furthermore the simulation of these models with computer software in order to compare the simulated results with the laboratory results. Firstly we describe the basic theory that we used, for example the discharge voltage, the breakdown voltage, the electric strength and the power loss. The purpose of this description is the diploma research to be easy read. Afterwards we analyzed the physical models that exist which on them are based the stochastic models that we are going to discuss. We analyzed the bubble model and the behavior of the bubbles when a discharge happens in liquid dielectrics. Also we discussed for the model of microexplosion and the model of ionize. Furthermore we described the way that is done the discharge phenomenon inside the dielectric gap. Firstly we analyzed the meaning of the electronic pile and the way that she is formed. Continuously we described the Streamer (negative and positive) and the leader and we described the ways of their creation according with the relationship both of them have. Also we talked about the basic theoretical stochastic models that already exist. In especial we analyzed the Niemeyer-Pietronero-Wiesmann and also we described the basic principles of the model FFC (Field Fluctuation Model). After that we analyzed the model Biller and the equation on which this model is based. Continuously we introduced the model Danika. Furthermore we introduced the model of simulation that we made and the basic idea on which we are based on. Also we described the parameters of the program and the assumptions that we made. Finally we analyzed the basic functions of the program that we used during the simulation of the program. Additionally we introduced the results that we have, with result tables and graphics, firstly for homogeneous field and then for inhomogeneous field. Also we introduced the results with different parameters as guide, like the growth factor and the gap space, in order to have a qualitative analysis of the behavior of the model into different circumstances. Finally we commented thoroughly the results of the simulation and we compare of the results with the laboratories. Also we made further discussion on the possible failure that the program may have.