Dissertations / Theses on the topic 'Liquid dielectrics. Liquids'

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.

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

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.

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.

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

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: 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.

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.

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

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. 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) Kurad, D.; Jeschke, G.; Marsh, D. Lipid Membrane Polarity Profiles by High-Field EPR. Biophys. J. 2003, 85 (2), 1025–1033. https://doi.org/10.1016/S0006-3495(03)74541-X. (6) Marsh, D. Polarity and Permeation Profiles in Lipid Membranes. Proc. Natl. Acad. Sci. U. S. A. 2001, 98 (14), 7777–7782. https://doi.org/10.1073/pnas.131023798. (7) Huang, H.; McIntosh, A. L.; Atshaves, B. P.; Ohno-Iwashita, Y.; Kier, A. B.; Schroeder, F. 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. Fluorescent Probes Used to Monitor Membrane Interfacial Polarity. Chem. Phys. Lipids 1999, 101 (1), 57–64. https://doi.org/10.1016/S0009- 3084(99)00055-9. (12) 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. (13) Fumagalli, L.; Ferrari, G.; Sampietro, M.; Gomila, G. Dielectric-Constant Measurement of Thin Insulating Films at Low Frequency by Nanoscale Capacitance Microscopy. Appl. Phys. Lett. 2007, 91 (24), 15–18. https://doi.org/10.1063/1.2821119. (14) Gomila, G.; Toset, J.; Fumagalli, L. Nanoscale Capacitance Microscopy of Thin Dielectric Films. J. Appl. Phys. 2008, 104 (2). https://doi.org/10.1063/1.2957069. (15) Fumagalli, L.; Gramse, G.; Esteban-Ferrer, D.; Edwards, M. A.; Gomila, G. Quantifying the Dielectric Constant of Thick Insulators Using Electrostatic Force Microscopy. Appl. Phys. Lett. 2010, 96 (18), 88–91. https://doi.org/10.1063/1.3427362. (16) Fumagalli, L.; Ferrari, G.; Sampietro, M.; Casuso, I.; Martínez, E.; Samitier, J.; Gomila, G. Nanoscale Capacitance Imaging with Attofarad Resolution Using Ac Current Sensing Atomic Force Microscopy. Nanotechnology 2006, 17 (18), 4581–4587. https://doi.org/10.1088/0957-4484/17/18/009. (17) Gramse, G.; Schönhals, A.; Kienberger, F. Nanoscale Dipole Dynamics of Protein Membranes Studied by Broadband Dielectric Microscopy. Nanoscale 2019, 11 (10), 4303–4309. https://doi.org/10.1039/c8nr05880f. (18) Knapp, H. F.; Mesquida, P.; Stemmer, A. Imaging the Surface Potential of Active Purple Membrane. Surf. Interface Anal. 2002, 33, 108–112. https://doi.org/10.1002/sia.1172. (19) Gramse, G.; Casuso, I.; Toset, J.; Fumagalli, L.; Gomila, G. Quantitative Dielectric Constant Measurement of Thin Films by DC Electrostatic Force Microscopy. Nanotechnology 2009, 20 (39). https://doi.org/10.1088/0957-4484/20/39/395702. (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. Dielectric Constant of Flagellin Proteins Measured by Scanning Dielectric Microscopy. Nanoscale 2018, 10 (40), 19188–19194. https://doi.org/10.1039/c8nr06190d. (28) Gramse, G.; Edwards, M. A.; Fumagalli, L.; Gomila, G. Dynamic Electrostatic Force Microscopy in Liquid Media. Appl. Phys. Lett. 2012, 101 (21). https://doi.org/10.1063/1.4768164. (29) Gramse, G.; Dols-Perez, A.; Edwards, M. A.; Fumagalli, L.; Gomila, G. Nanoscale Measurement of the Dielectric Constant of Supported Lipid Bilayers in Aqueous Solutions with Electrostatic Force Microscopy. Biophys. J. 2013, 104 (6), 1257–1262. https://doi.org/10.1016/j.bpj.2013.02.011. (30) Millán, R.; Checa, M.; Fumagalli, L.; Gomila, G. Mapping the Capacitance of Self- Assembled Monolayers at Metal/Electrolyte Interfaces at the Nanoscale by In-Liquid Scanning Dielectric Microscopy. Nanoscale 2020, 12 (40), 20658–20668. https://doi.org/10.1039/d0nr05723a. (31) Di Muzio, M.; Millan-Solsona, R.; Borrell, J. H.; Fumagalli, L.; Gomila, G. Cholesterol Effect on the Specific Capacitance of Submicrometric DOPC Bilayer Patches Measured by In-Liquid Scanning Dielectric Microscopy. Langmuir 2020, 36 (43), 12963–12972. https://doi.org/10.1021/acs.langmuir.0c02251. (32) Di Muzio, M.; Millán, R.; Gomila, G. Electrical Properties and Lamellarity of Single Liposomes Measured by In-Liquid SDM. [in Prep. (33) 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. (34) 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. (35) 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. (36) 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. (37) 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. (38) 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. (39) 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. (40) Casuso, I.; Fumagalli, L.; Gomila, G.; Padrós, E. Nondestructive Thickness Measurement of Biological Layers at the Nanoscale by Simultaneous Topography and Capacitance Imaging. Appl. Phys. Lett. 2007, 91 (6), 063111–063113. https://doi.org/10.1063/1.2767979. (41) Kyndiah, A.; Checa, M.; Leonardi, F.; Millan-Solsona, R.; Di Muzio, M.; Tanwar, S.; Fumagalli, L.; Mas-Torrent, M.; Gomila, G. Nanoscale Mapping of the Conductivity and Interfacial Capacitance of an Electrolyte-Gated Organic Field-Effect Transistor under Operation. Adv. Funct. Mater. 2020, 2008032, 1–8. https://doi.org/10.1002/adfm.202008032. (42) Lubrano, C.; Matrone, G. M.; Iaconis, G.; Santoro, F. New Frontiers for Selective Biosensing with Biomembrane-Based Organic Transistors. ACS Nano 2020, 14 (10), 12271–12280. https://doi.org/10.1021/acsnano.0c07053.
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.

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.

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

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.

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.

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.

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.

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.

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.

Dans les travaux de recherche développés durant cette thèse, le concept de convection d’origine diélectrophorétique dans les liquides diélectriques confinés, telle qu’obtenue par application de champs électriques non uniformes et non intenses, est proposé et étudié. Dans un premier temps, les ingrédients théoriques de l’électrohydrodynamique sont présentés, puis les propriétés du couplage multiphysique entre mécanique des fluides, thermique et électrostatique sont mises en évidence. On peut démontrer qu’un couple d’origine diélectrophorétique est présent dès le régime conductif dès lors qu’un champ électrique non-uniforme est imposé. En conséquence, la possibilité de mettre un liquide diélectrique en mouvement, en imposant des champs électriques modestes en microgravité, est concevable en régimes conductif et de couches limites. Dans cette thèse, on étudie la convection ThermoElectroHydroDynamique (TEHD) d’un fluide diélectrique, en cavité différentiellement chauffée et soumise à un gradient de potentiel électrique produit par une paire d’électrodes. Deux configurations d'électrodes sont proposées : des électrodes planes partielles et des électrodes triangulaires. Une analyse en ordres de grandeur et une étude numérique sont développées afin d'étudier les transferts de chaleur convectifs induits par la flottabilité d’origine diélectrophoretique. Les lois d’échelle et les résultats numériques montrent qu'une amélioration sensible des transferts thermiques est possible grâce à l’utilisation d’un champ électrique non intense, non uniforme, sans qu'il soit nécessaire de recourir à des régimes instables. En outre, une approche expérimentale est également développée, réintroduisant la gravité et par conséquent la flottabilité d’origine thermique. De l'huile silicone est confinée dans une cavité ménagée au sein d’un bloc de plexiglas et scellée par une paire d'électrodes. Celles-ci sont connectées, pour l’une, à un amplificateur AC, pour l’autre, à la masse. Toutes deux sont maintenues à des températures différentes et constantes. Le champ de vitesse en régime permanent est mesuré par PIV à l’aide de traceurs fluorescents et l'effet du couple de rotation diélectrophorétique sur l’écoulement est détecté. En comparant avec les simulations numériques, des tendances similaires sont observées pour chaque configuration d'électrodes. Enfin, la température est mesurée à différentes localisations sur le banc expérimental pour la configuration basée sur les électrodes planes partielles. En présence de gravité, l'augmentation du transfert de chaleur, attendue avec la présence de champs électriques non uniformes, n'est pas particulièrement prononcée dès lors que l'écoulement est dominé par la flottabilité d’origine thermique
In this thesis, the concept of steady-state dielectrophoretic-induced convection in confined dielectric liquids, by means of non-uniform non-intense electric fields, is introduced and investigated. First, theoretical foundations of electrohydrodynamics are presented and a multiphysics coupling between fluids mechanics, heat transfers, and electrostatics is made evident. It is shown that a dielectrophoretic (DEP) torque arises at leading order provided that a non-uniform electric field is imposed. Thus, in microgravity conditions, the possibility of setting a dielectric liquid in motion, even with a modest electric field intensity, is shown to be finally conceivable in conductive regime as well as in boundary layer regime. In this work, steady ThermoElectroHydroDynamic (TEHD) convection is investigated for the case of a dielectric liquid confined in a differentially-heated square cavity, submitted to an electric potential gradient imposed from an electrode pair. Two electrode configurations, that generate the required non-uniform electric fields, are proposed: a partial planar electrode pair and a triangular electrode pair. Scaling analysis and a numerical study are developed in order to investigate dielectrophoretic-induced convective heat transfers. The scaling laws and the numerical results show that a significant enhancement of heat transfers is made possible from the use of a non-intense non-uniform electric field, with no need for giving rise to unstable regimes. An experimental approach is also considered, reintroducing gravity and buoyancy-driven convection. Silicon oil is confined in a cavity, formed in a Plexiglas block, and sealed by a pair of electrodes, one of them is connected to a high voltage AC amplifier while the other one is grounded. Both electrodes are kept at different but constant temperatures. By means of PIV imaging of fluorescent tracers, the velocity field in steady-state is measured and processed, and the effect of the imposed DEP torque on the whole flow is made evident. In comparison with numerical simulations, similar tendencies can be observed relative to each electrode configuration. Finally, the temperature is measured at different locations on the experimental bench for the configuration based on partial electrodes. In presence of gravity, heat transfer enhancement, expected from the application of a non-uniform electric field, is not particularly pronounced since the flow is dominated by thermal buoyancy

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.

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

A variety of waveguide structures have been analysed for the measurement of the complex dielectric permittivity of liquids. Mode matching techniques are im- plemented to solve the forward problem of computing the scattering parameters for a sample of known permittivity filling a rectangular metal waveguide. Three different sample geometries are used. In the first, the liquid and the sample holder completely fill the waveguide cross section. As a result, only the dominant waveguide modes are matched across the discontinuity interface and an exact an- alytical relation between the S parameters and permittivity can be written. The second and third configurations are concentric cylinders and rectangles respec- tively, partially filling a metal waveguide, hence higher order modes are taken into account in the formulation. For the partially filled rectangular sample, a generalised scattering matrix method to obtain the overall scattering parameters due to the several discontinuity regions. Iterative methods are then introduced to solve the inverse problem of recover- ing the unknown permittivity from simulated or measured scattering parameters. For the partially filled waveguides, because an exact analytical relation does not exist, objective( error) functions are defined and minimized. The partially filled rectangular sample case is extended to obtain the resonant frequency and qual- ity factor of a dielectric loaded resonant cavity, and the results compared to the approximation normally used for the cavity perturbation technique. Finally, a rectangular dielectric waveguide method for liquid measurements was developed. This method has a treatment similar to the well known free space tech- niques. It has a distinct advantage of relaxing the strict requirements of sample dimension associated with metal waveguides, especially at higher frequencies.

This thesis is concerned with the development of a prototype electromagnetic flowmeter for dielectric liquids. A initial prototype flowmeter is tested in laboratory conditions with a liquid of low conductivity, the conclusion of these initial tests being that the stability of the flowmeter is below that required for its design applications. This lack of stability is a problem reported on several occasions in similar projects involving electromagnetic flowmeters for dielectric liquids. Therefore the main body of the work is spent investigating the causes of instability and trying to redress the necessary problems in order that a viable working prototype is developed. Problems of thermal instability, electrostatic and electromagnetic shielding are addressed along with the causes and effects of all the major noise and unwanted signals experienced in such a system. A new prototype is developed incorporating stability driven improvements. This new design is rigorously tested and assessed. The stability of the meter is considered with respect to its flow related output. Several parameters of operational stability are given in the examples considered. A final assessment is then made of the flowmeters baseline performance and a account of any remaining instability is given with respect to the issue developed throughout the thesis. The conclusions indicate that the electromagnetic flowmeter for dielectric fluids does produce a linear output based on Faraday's law of induction. They also indicate that the instability experienced previously can be broken into its constituent parts and each contributor accounted for and reduced, working towards the ideal totally stable flowmeter.

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.

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.

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.

This thesis presents the investigation of the liquid crystal (LC) - particle suspensions. Particles from nano- to micro-size, spherical to two-dimensional shapes, with different functionality are dispersed into nematic and smectic phases. The aim is to create ordered nanoparticle (NP) assemblies and thereby modify the common properties of the liquid crystal, such as dielectric anisotropy and electro-optical, revealing any interaction between particles and LC properties. It is found that for concentrations (>0.5vol%), the ferroelectric NPs have increased the sensitivity of the nematic liquid crystal to the electric field through electro-optical responses, which is seen by an enhancement in the dielectric anisotropy. This could be induced by the coupling of the electrical dipole moments in the spherical NPs with the LC director field. The electro-optical properties of the chiral smectic (SmC*) phase (tilt angle Θ, switching time τ_s and spontaneous polarisation P_s) are found to be independent of the concentration and sizes of the doped NPs. The relaxation frequency f_R of the Goldstone mode is faster in the ferroelectric NPs suspensions of 2.0vol% compared to the paraelectric NPs. In the graphene oxide (GO) - nematic LC (5CB) suspensions, the small GO sizes of mean size 560 nm are more easily dispersible than larger flakes of 2.8 micro metre mean size. As the GO concentration is increased, each of the threshold voltage and splay elastic constant dramatically increases, reaching saturation at ≈1.0wt%. The field driven switching-on time is practically not affected, while the purely elastically driven switching-off time is strongly sped-up. Interestingly, thermotropic and lyotropic LC phases are exhibited in the GO-5CB suspensions when heating the thermotropic liquid crystal into its isotropic phase. The isotropic phase of 5CB acts as a solvent for the GO particles, forming a lyotropic nematic phase with largely reduced birefringence. It is found that the nematic to isotropic phase transition is shifted toward higher temperature for the GO-5CB system compared to the BaTiO3-5CB system. Dispersions of different sizes of GO flakes are prepared in isotropic and nematic fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature range (25-60 ℃) and frequency range (100 Hz-2 MHz). The mixtures containing GO flakes were found to exhibit varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. The relaxation frequencies in the isotropic media were lower compared to the nematic medium. Relaxation frequencies (~10 kHz) are observed in the GO-isotropic media, which are reduced as the size of the GO flakes are decreased, are anticipated to be inherited from GO flakes. However, the fast relaxations (~100 kHz) that are observed in the nematic suspensions could imply strongly slowed down molecular relaxation modes of the nematogenic molecules. Finally, the phase diagram of lyotropic LC as a function of the lateral dimensions of the GO flakes, their concentration, geometrical confinement configuration and solvent polarity was investigated. Polarising optical microscopy was used to determine isotropic-biphasic-nematic phase evolution. The confinement volume and geometry of the sample relative to the GO size are shown to be vital to the observation of the lyotropic phase. GO LCs have the potential for a range of applications from display technologies to conductive fibres. The confinement related LC phase transition is critical toward their applications. It is also found that the stability of the LC phase is higher for the solvent of higher dielectric constant.

L'objectif de ce travail est de développer et d’étudier une nouvelle classe de fluidesintelligents à base de dispersions colloïdales de carbone, sensibles à un stimulus externe pour desapplications de conversion et stockage d’énergie. Ces stimuli sont de différentes natures : vibrationmécanique, mouvement humain, variation de pression ou écoulement d'un solvant, et peuventaltérer les structures de tels systèmes. Ceci induit une modification de la structure locale desparticules et par conséquent des propriétés diélectriques et électriques. Habituellement, lessuspensions de matériaux carbonés sont étudiées au repos ou séchées. Toutefois, comprendre leurcomportement en flux est essentiel pour de nouvelles applications où ces matériaux sont exploitésdans des conditions dynamiques telle que le stockage d'énergie électrochimique assisté par flux(FAES). Par exemple, les matériaux à base de graphène jouent désormais un rôle important dans lesnouvelles technologies énergétiques. Ils sont utilisés comme additifs conducteurs dans lesassemblages d'électrodes, mais en raison de leur forme anisotrope spécifique, ils permettentégalement d’obtenir des fluides diélectriques sous écoulement.Les cristaux liquides d'oxyde de graphène, en tant que matériau souple électrostrictif, sont étudiéspour la récupération d'énergie mécanique, ainsi que des dispersions de noir de carbone pour lestockage d'énergie.Les propriétés diélectriques et électriques de ces dispersions fluides dans des conditions statiques etdynamiques sont mesurées et analysées. Enfin, l’effet de l’écoulement sur l’orientation et laréorganisation locale des particules et leur comportement diélectrique et électrique sont examinés
The aim of this work is to develop and study a new class of smart fluids made of colloidalcarbon-based dispersions, which are sensitive to an external stimulus for energy storage orconversion applications. The effect of an external input, such as mechanical vibration, humanmotion, variable pressure, flowing of a solvent, can alter the structures of such systems.Consequently these changes induce modifications of the dielectric and electrical properties. Usually,the suspensions of carbon materials are investigated at rest or dried. However, their flow behavior iscritical when new technologies, which exploit these materials in dynamic conditions such as FAES(Flow-Assisted Electrochemical Energy Storage) are considered. For example, graphene-basedmaterials are now playing a significant role in energy materials. They act as conductive additives inelectrode assemblies, but due to their specific anisotropic shape they also provide a new route toachieve dielectric liquid media.In details, Graphene Oxide liquid crystals as electrostrictive soft material for mechanical energyharvesting and Carbon black dispersions as percolated flowable electrodes for capacitive energystorage are investigated.In particular, the dielectric and electrical properties of these flowable dispersions are studied understatic and dynamic conditions. The effect of the flow-rate on the local orientation and reorganizationof the particles and their related dielectric and electrical behavior are examined