Dissertations / Theses on the topic 'Dielectric liquids'

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.

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.

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.

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.

La recherche et le développement sur les matériaux semi-conducteurs ont permis de transformer la technologie des dispositifs électroniques de puissance, avec une densité de puissance, des performances thermiques et un dimensionnement plus compacts. Ils permettent aux appareils de fonctionner à des tensions, températures et fréquences de commutation plus élevées dans les modules de puissance. Pourtant, ces développements ne sont pas suivis de la même manière par d’autres éléments, tels que les encapsulants.Avec un matériau d'encapsulation récent, à savoir un gel de silicone, la température maximale de fonctionnement ne peut pas dépasser 200 ° C alors que les dispositifs à semi-conducteurs WBG sont très supérieurs (par exemple, du SiC à 500 ° C). Il s’agit là d’un obstacle majeur car il joue un rôle important dans la protection mécanique et électrique d’un module de puissance. Dans ce travail, nous proposons des liquides diélectriques comme agent d’encapsulation alternatif pouvant avoir une performance thermique supérieure au gel de silicone. Les caractérisations diélectriques de plusieurs candidats ont été effectuées dans le cadre d’une cellule d’essai spécialement conçue, capable de chauffer à haute température dans un environnement contenant de l’azote afin d’éviter les risques d’incendie et d’oxydation. Nous avons mesuré la conductivité de liquides soumis à une variation de température en appliquant une spectroscopie de champ alternatif dans une large plage de mobilité fréquentielle et ionique sous une variation de polarité inverse en courant continu. Nous étudions l'influence de la température et de la pression sur les pannes avec des champs quasi uniformes et divergents, ainsi que des décharges partielles, aussi bien dans les liquides que dans les substrats céramiques noyés dans des liquides, afin de démontrer leurs applications dans les modules de puissance. Des modèles numériques ont également été développés par simplification à partir des résultats de spectroscopie diélectrique afin d'estimer et d'observer la distribution de champ à un point triple critique.Enfin, nous présentons une comparaison de candidats liquides et de gel de silicone pour montrer leurs avantages et leurs inconvénients pour les applications d’électronique de puissance à haute température. Néanmoins, ces travaux ne couvrent pas tous les aspects fondamentaux et d’applications tels que le vieillissement thermique, la capacité de refroidissement des liquides, etc., ces résultats ont établi une bonne base pour les liquides diélectriques dans les applications à haute température
Todays, power electronics cover wide range of applications in our daily life, starting from household appliances, communications, transportation systems up to harsh and extreme environment as in oil and gas exploration and the deep space missions. The main deliveries of power electronics are energy efficiency, compact size, reliability, long durability. Improving power electronics will surely mean to deal with materials, the packaging system, switching technologies, heat dissipation, dielectric properties, thermal stability etc. It was since the first arc-mercury rectifying in traction system, and then reshaped by the discovery of classical semiconductor (Si based) and ultimately the wide bandgap semiconductor materials, such as SiC, GaN and carbon based (diamond). They have superior thermal and dielectric properties compared to previous classical semiconductor technologies (Ge, Si and GaAs), and allow devices to operate at higher voltage, temperature and switching frequency in power modules. Unfortunately, these developments are not equally followed by other parts within, such as encapsulant.Despite their key roles to provide mechanical and electrical protection inside a power module, silicone gel as major encapsulant is limited to 200°C, which is far below devices (e.g. SiC at 500°C). Encapsulant came from polymerization and curing process of silicone liquids mixture and transforms into gel. They worked very well when assembly with classical SC devices, but not with WBG SC. Thus, it is necessary to solve this thermal related issue by improving silicone gel or start looking for other type of encapsulant with better thermal performance such as dielectric liquid or gas.Dielectric liquids have been used as insulating medium for high voltage (HV) applications for decades. Their excellent self-healing and arc quenching properties were used in the HV circuit breaker applications even though nowadays replaced by gas. Their low viscosity allow the fluid flow to exchange heat from internal source yielding effective cooling system as in power transformers. Other industries use dielectric liquids as heat transfer liquid at much higher temperature range compare to those in HV applications. Of course as heat transfer liquids, their dielectric properties are out of considerations. Nevertheless, having this wide range of applications spectrum, dielectric liquids seem rather promising and potential as alternative encapsulant. Some questions then aroused such as how are their electrical properties at high temperature (HT) approx. 400°C, are their dielectric properties stable at HT and can they contribute to cooling of devices inside power module.This work presents the initial study of dielectric liquids for HT power electronics module applications. We demonstrated the electrical characterization of several dielectric liquids under influence of temperature such as dielectric spectroscopy and ion mobility measurement, partial discharge, streamers and breakdown. Interesting physical phenomena such as liquid motions due to EHD and natural thermal convection were observed during experiments. Comparison among liquids are showed to indicate the most convenient. In term of application, conditions were adapted and simplified to replicate as those in power module when we performed characterizations to actual ceramic substrates under quasi-uniform to highly divergent electric field with AC, DC and impulse voltage. Many fundamental behaviours of liquids have been confirmed and evidenced at HT range. Governing parameters for electrical properties such as breakdown, charge injection etc. were affirmed.While not all aspects of encapsulant requirement in term of HT are covered, this work has established essential basis for electrical properties of dielectric liquids. Further works are required to fully assess their compatibility as alternative encapsulant, such as thermal ageing process, cooling contribution, complete modelling, etc

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Two experimental studies of the natural convection characteristics of heated protrusions immersed in dielectric liquids were conducted. the first study used a three by three array of simulated 20 pin dual-in-line chips which were made from aluminum blocks with full heaters. The second set of experiments used a three by three array of thermal evaluation devices mounted on an alumina substrate. The devices were 8.9 mm square chips which contained resistors and a type of temperature sensing transistor. Both studies used an insulated Plexiglas enclosure with a top mounted heat exchanger maintained at a constant 10 degrees C. Each array was mounted on a Plexiglass substrate, and spacers were used to vary the horizontal distance from the components to the enclosure wall. Five separate enclosure widths were used, with a maximum spacing of 40 mm. The vertically oriented aluminum blocks were tested with FC-71 and power levels ranging from 0.115 W/chip to 2.9 W/chip. The non-dimensional data obtained was used to develop an empirical correlation which predicts Nusselt number as a function of Rayleigh number and enclosure width. The correlation was accurate to within 4% of the array averaged data, and the maximum uncertainty in the Nusselt number was 7.4%. The actual electronic components were tested with FC-71, FC-43 and FC-75. Power levels ranged from 0.34 W/chip to 1.48 W/chip. Again, the data obtained was used to develop a Nusselt number correlation. In this case a better correlation of the data was achieved using Grashof number and enclosure width. The correlation is accurate to within 2% of the array averaged data. The maximum Nusselt number uncertainty was 4.7%

Dissertação para obtenção do Grau de Doutor em Química Sustentável
Ionic liquids (ILs) are promising materials which have been used in a wide range of applications. However, their major limitation is their physical state. In order to address this challenge, a self-supported IL-based material was developed by combining gelatine with an IL, originating a quasi-solid material named Ion Jelly (IJ). This is a light flexible material, dimensionally stable, with promising properties to develop safe and highly conductive electrolytes. This thesis is focused on the characterization of IJ films based on different ILs. The conductive mechanisms of IJ materials were studied using dielectric relaxation spectroscopy (DRS) in the frequency range 10-1−106 Hz. The study was complemented by differential scanning calorimetry (DSC) and pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy. A glass transition was detected by DSC for all materials allowing to classify them as glass formers. From dielectric measurements, transport properties such as mobility and diffusion coefficients were extracted. Moreover, it was found that the diffusion coefficients and mobility are similar for the IL and IJ, especially for the IL EMIMDCA. Since for BMIMDCA, those properties significantly change upon hydration, the influence of water content [0.4 - 30% (w/w)] was also studied for the ILs. In particular for BMPyrDCA with 30% water, it was analyzed the reorientational polarization by the complex permittivity and electric modulus, from which three different processes were identified: a secondary relaxation with Arrhenian temperature dependence, the process that is believed to be behind the dynamic glass transition and the mobility of charge carriers. An application of the IJs was successfully explored with a chemoresistive gas sensor made up by different IJs as active layer, which is an electronic nose formed by an array of such sensors. The performance of this e-nose revealed its ability to correctly detect eight common volatile solvents.

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 liquides ioniques (LIs) sont des sels à faible température de fusion (plus petit 100 °C). Ils disposent généralement de bonnes stabilités thermique et chimique ainsi qu’une haute conductivité ionique. Ces propriétés les rendent par exemple intéressants en tant que lubrifiant, électrolyte ou additif en sciences des polymères. Dans le cadre de cette thèse, les liquides ioniques sont proposés comme alternative aux problématiques d’accumulation de charges au sein d’un isolant composite à base époxy pour postes sous enveloppe métallique (PSEM) sous haute tension en courant continu (HVDC). Une augmentation des phénomènes de conduction électrique est recherchée afin d’évacuer les charges accumulées en surface de l’isolant au cours de son utilisation. L’influence de l’addition de LI sur les mécanismes de polymérisation et sur les propriétés finales du réseau époxy et a été évaluée avec et sans durcisseur anhydride et en présence d’un liquide ionique à cation phosphonium et anion phosphinate, connu comme réactif et amorceur de la polymérisation des polyépoxydes. Les mécanismes de polymérisation ont été déterminés par résonance magnétique nucléaire (RMN) et analyse calorimétrique différentielle (DSC), les réseaux et leur microstructure par analyse mécanique dynamique (DMA), et leur morphologie par microscopie électronique (SEM ou TEM). Enfin, les propriétés diélectriques et mécanismes de conduction ont été étudiés par spectroscopie diélectrique et mesures de conductivité DC et discutés en fonction des architectures des différents réseaux
Ionic liquids (Ils) are salts exhibiting a low melting temperature (minus 100 °C). They display interesting properties such as good thermal and chemical stabilities and a high ionic conductivity. For example, these properties make them attractive as lubricant, electrolyte or additive in polymer science. In this thesis, ionic liquids are proposed as a solution for charge accumulation occurring in epoxy based insulators of gas insulated substations (GIS), under high voltage direct current (HVDC). An increase of conduction phenomenon is researched in order to reduce charge accumulation on the surface of insulators during their service. The influence of the addition of IL on the polymerisation of the epoxy network and its properties has been evaluated with and without a conventional anhydride hardener, using a phosphonium based IL, known as reactive and initiator of the epoxy polymerisation. Polymerisation mechanisms were identified by nuclear magnetic resonance (NMR) in liquid phase and differential scanning calorimetry (DSC), the networks and their microstructure by dynamic mechanical analysis (DMA), and their morphology by electronic microscopy (SEM or TEM). Finally, dielectric properties were studied by broadband dielectric spectroscopy and DC conductivity measurements and were discussed in function of the architecture of the different networks

Il y a à l'heure actuelle un grand besoin en systèmes et composants agiles pour les dispositifs front-end RF. Dans cette thèse, deux approches innovantes sont développées pour la conception de tels dispositifs RF. Dans un premier temps, un mécanisme de reconfiguration micro-mécanique est développé. Cette approche vise à contrôler la hauteur d'un gap d'air inséré dans le substrat de composants microrubans afin d'en modifier les dimensions électriques. Les choix de conception et la fabrication d'un déphaseur à ligne micro-ruban ainsi que d'une antenne accordable en fréquence sont discutés. Une solution d'actionnement piézoélectrique basse tension (+/- 30 V) est retenue. La figure de mérite obtenue dans le cas du déphaseur atteint jusqu'à 313 °/dB ce qui dépasse l'état de l'art en matière de déphasage analogique. Dans le cas de l'antenne, le potentiel d'agilité en fréquence atteint 35 % autour d'une fréquence centrale de 55 GHz. Contrairement aux solutions classiques à base de semiconducteurs ou de RF-MEMS, ce mécanisme de reconfiguration n'impacte pas les performances de l'antenne dont l'efficacité de rayonnement est proche de 94 %. Dans un second temps, c'est un mécanisme micro-fluidique qui est étudié. L'agilité en fréquence d'antennes est créée par l'écoulement successif de liquides de permittivités différentes dans des micro-canaux intégrés au substrat. L'accord en fréquence atteint alors la très large ampleur de 51 % pour une fréquence centrale de 22 GHz. Cette étude s'accompagne de la recherche et caractérisation diélectrique de plusieurs fluides dans l'optique d'augmenter aussi bien la plage d'accord en fréquence que les performances de rayonnement des antennes
As wireless networks evolve, the frequency bands they exploit multiply. Frequency multiplexing, beamforming and tracking, networks interoperability, those mutations increase the need for agility and tunability in the RF-front end systems. In this thesis, two innovative approaches for the design of tunable RF components are studied. First, a micro-mechanical reconfiguration mechanism is developed. This approach means to control the height of an air gap within the substrate of microstrip components in order to control their electrical dimensions. Considerations for the design and fabrication of a phase-shifter and a frequency tunable patch antenna are made and a low voltage piezoelectric actuation (+/- 30 V) is chosen. The phase-shifter figure of merit reaches up to 312 °/dB which is beyond the state of the art in terms of analogic phase-shifting. Regarding the antenna, the frequency tuning potentially reaches up to 35 \% of a central frequency of 55 GHz. Unlike the classic solidstate or RF-MEMS based solutions, this reconfiguration mechanism does not impact the radiation performance of the antenna whose radiation efficiency is 94 \%. In a second approach, a micro-fluidic solution is studied. Frequency tuning capability is created in different antennas by the flow of successive liquids with different permittivities in integrated micro-channels. A large frequency tuning of 51 \% for a central frequency of 22 GHz is achieved. This study goes along with the search and characterization of several fluids with the objective of increasing both the frequency shift and the radiation performance of those antennas

This master‘s thesis deals with measurement of liquid dielectric materials (insulators). Above all, it is the different kinds of clean and drinking water, but also transformer oils. There was done theoretical information retrieval about the given topic in this project and on the basis of theory there were realized the relevant measurements of selected properties of liquid dielectric, such as permittivity, capacitance, loss number, conductivity, but also temperature dependence of these parameters. The measurements were realized with the help of product manufactured at the faculty FEKT VUT and with the help of measuring system AGILENT 16452A. The measured results were evaluated, graphically processed and compared.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.
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Includes bibliographical references.
by Steven Marc Gasworth.
Ph.D.

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

Дисертація присвячена вирішенню науково-технічної задачі створення нового методу і пристрою контролю в’язкості діелектричних рідин на основі мостових електорфлюїдних перетворювачів. Розроблений метод контролю ґрунтується на закономірностях течії рідини через мостовий дросельний перетворювач з подальшим його зрівноваженням електрофлюїдними перетворювачами. Синтезовано схеми зрівноважених мостових електрофлюідних перетворювачів (МЕФП), визначено статичні характеристики перетворення та наведена методика розрахунку чутливих елементів МЕФП. Розроблено структурні та принципові схеми автоматичного пристрою контролю в’язкості діелектричних рідин на основі МЕФП зі слідкуючим та розгортальним зрівноваженням. Наведено результати досліджень статичних і динамічних характеристик мікропроцесорного пристрою контролю в’язкості, алгоритм і програмне забезпечення процесу вимірювання в’язкості діелектричних рідин.
Dissertation is devoted to decision of scientific and technical task of creation of new method and device on the basis of bridge electrofluid transfonners for control of viscosity of dielectric liquids. The developed control method is based on conformities to the law of flow of liquid through bridge choke transformer with subsequent his balancing by electrofluid transformers. The charts of the balanced bridge of electrofluid transformers (BEFT) are synthesized, static descriptions of transformation are certain and tire method of calculation of pickoffs of BEFT is resulted. The structure and principle diagrams of automatic control device of viscosity of oil products are developed on the basis of BEFT with the tracker and developing balancing. The results of researches of static and dynamic descriptions of microprocessor device of control of viscosity, algorithm and software of process of control of viscosity of oil products software, are resulted.

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.

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.

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

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.

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.

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

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

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

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

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.

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.