To see the other types of publications on this topic, follow the link: Dielectric relaxation.
Dissertations / Theses on the topic 'Dielectric relaxation'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Dielectric relaxation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Barelli, Eleonora. "Dielectric relaxation in biological materials." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9102/.
Full textAbstract:
The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important in order to explain various phenomena in Solid-State Physics and in Physics of Biological Materials.
Indeed, during the last two centuries, many scientists have tried to explain and model the dielectric relaxation. Starting from the Kohlrausch model and passing through the ideal Debye one, they arrived at more com- plex models that try to explain the experimentally observed distributions of relaxation times, including the classical (Cole-Cole, Davidson-Cole and Havriliak-Negami) and the more recent ones (Hilfer, Jonscher, Weron, etc.).
The purpose of this thesis is to discuss a variety of models carrying out the analysis both in the frequency and in the time domain. Particular attention is devoted to the three classical models, that are studied using a transcendental function known as Mittag-Leffler function. We highlight that one of the most important properties of this function, its complete monotonicity, is an essential property for the physical acceptability and realizability of the models.
Lo studio delle proprietà dielettriche riguarda l’immagazzinamento e la dissipazione di energia elettrica e magnetica nei materiali. I dielettrici sono importanti al fine di spiegare vari fenomeni nell’ambito della Fisica dello Stato Solido e della Fisica dei Materiali Biologici.
Infatti, durante i due secoli passati, molti scienziati hanno tentato di spiegare e modellizzare il rilassamento dielettrico. A partire dal modello di Kohlrausch e passando attraverso quello ideale di Debye, sono giunti a modelli più complessi che tentano di spiegare la distribuzione osservata sperimentalmente di tempi di rilassamento, tra i quali modelli abbiamo quelli classici (Cole-Cole, Davidson-Cole e Havriliak-Negami) e quelli più recenti (Hilfer, Jonscher, Weron, etc.).
L’obiettivo di questa tesi è discutere vari modelli, conducendo l’analisi sia nel dominio delle frequenze sia in quello dei tempi. Particolare attenzione è rivolta ai tre modelli classici, i quali sono studiati utilizzando una funzione trascendente nota come funzione di Mittag-Leffler. Evidenziamo come una delle più importanti proprietà di questa funzione, la sua completa monotonia, è una proprietà essenziale per l’accettabilità fisica e la realizzabilità dei modelli.
2
Chowdhry, Bhawani Shankar. "On-line measurement of dielectric relaxation." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277344.
Full text
3
Faddis, David Brian. "Dielectric Relaxation in Controlled Pore Glass." W&M ScholarWorks, 1993. https://scholarworks.wm.edu/etd/1539625813.
Full text
4
Jouravleva, Svetlana. "Dielectric relaxation time spectroscopy for tissue characterisation." Thesis, Oxford Brookes University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364927.
Full text
5
Park, Taigyoo. "Dielectric relaxation behavior of poly(3-hydroxybutyrate)." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-163615/.
Full text
6
Wang, Henry F. S. (Henry Fu-Sen). "Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 335 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode." Thesis, University of North Texas, 1994. https://digital.library.unt.edu/ark:/67531/metadc279039/.
Full textAbstract:
The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute temperature, it can be seen that each sample shows "transition temperatures". In this work, Slater's perturbation equations for a resonant microwave cavity were used to analyze the experimental results for the microwave data.
7
Yin, Ye. "Dielectric Relaxation and Electrooptical Effects in Nematic Liquid Crystals." Kent State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=kent1190843503.
Full text
8
Sugiyama, Masaki. "Viscoelastic and dielectric relaxation phenomena of chemically treated wood." Kyoto University, 2008. http://hdl.handle.net/2433/136699.
Full textAbstract:
Kyoto University (京都大学)0048
新制・論文博士
博士(農学)
乙第12216号
論農博第2674号
新制||農||959(附属図書館)
学位論文||H20||N4383(農学部図書室)
UT51-2008-C986
京都大学大学院農学研究科林産工学専攻
(主査)教授 矢野 浩之, 教授 中野 隆人, 准教授 師岡 敏朗
学位規則第4条第2項該当
9
Barry, Donald. "Studies of Aggregation Pathways for Amyloidogenic Peptides by Dielectric Relaxation Spectroscopy." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-dissertations/143.
Full textAbstract:
Diseases associated with amyloid aggregation have been a growing focus of medical research in recent years. Altered conformations of amyloidogenic peptides assemble to form soluble aggregates that deposit into the brain and spleen causing disorders such as Alzheimer's disease and Type II diabetes. Emergent theories predict that fibrils may not be the toxic form of amyloidogenic structures and that smaller oligomer and protofibril aggregates may be the primary source of cellular function damage. Studies show that these amyloidogenic aggregates are characterized by an increased number of poorly dehydrated hydrogen backbones and large surface densities of patches of bulk like water which favor protein association. When proteins aggregate to form larger structures, there is a redistribution of water surrounding these proteins. The water dynamics of amyloidogenic aggregation is different than the monomeric form and has a decrease in the number of patches occupied by molecules with bulk-like water behavior. We demonstrate that the redistribution of water during amyloid aggregation is reflected in a change in the dielectric relaxation signal of protein-solvent mixtures. We use dielectric relaxation spectroscopy (DRS) as a tool for studying the dynamics of amyloidogenic peptides--amyloid beta (Ab 1-42) and human islet amyloid polypeptide (hIAPP)--during self-assembly and aggregation. Non-amyloidogenic analogs-- scrambled (Ab 42-1) and rat islet amyloid polypeptide (rIAPP)--were used as controls. We first present studies of amyloidogenic peptides in a deionized water buffer at room temperature as a function of concentration and incubation time. From this we were able to determine differences in amyloidogenic and non-amyloidogenic peptides through the dielectric modulus. We next present the same analytes in a deionized water-glycerol buffer to facilitate the study of the dielectric permittivity at sub-freezing temperatures and model the kinetics of the alpha- and beta- relaxation processes. We conclude our work by studying the peptides in a bovine serum albumin (BSA) and glycerol buffer to demonstrate dielectric spectroscopy as a sensitive tool for measuring amyloidogenic peptides in an in vivo- like condition.
10
Elsby, David J. "Conformational analysis and dielectric relaxation of polycarbosilanes and related materials." Thesis, Aston University, 1994. http://publications.aston.ac.uk/9685/.
Full textAbstract:
The conformational characteristics of poly(dimethylsilmethylene), poly(dimethylsilethene), poly(dimethylsilethane) and a related material, poly(2,2,5,5-tetramethyl-1-oxa-2,5-disilapentane), have been investigated using the method of molecular mechanics. In this method, a quantitative analysis of the factors affecting the nature and magnitude of the bond rotation potentials governing their conformational behaviour has been undertaken. Along with their structural data, the results obtained were employed to calculate a variety of conformationally-dependent properties for these polymers, including the characteristic ratio, the dipole moment ratio and the mean-square radius of gyration. In addition, the dielectric relaxation behaviour of two samples of poly(2,2,5,5-tetramethyl-1-oxa-2,5-disilapentane) with molar masses Mw = 28000 and Mw = 46000 respectively, have been studied as a function of temperature (179K-205K) and frequency (100-105Hz). Activation energies for the -relaxation process and Davidson-Cole empirical distribution factors have been calculated.
11
Wang, Jingsong Johari G. P. "Thermodynamics of polymerization, dielectric properties, and a new orientational glass /." *McMaster only, 2003.
Find full text
12
Zhao, Chun. "Dielectric relaxation and frequency dependence of Hf02 doped by lanthanide elements." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/17673/.
Full textAbstract:
The decreasing sizes in complementary metal oxide semiconductor (CMOS) transistor technology requires the replacement of SiO2 with gate dielectrics that have a high dielectric constant (k). When the SiO2 gate thickness was reduced below 1.4 nm, electron tunneling effects and high leakage currents occurred which presented serious obstacles for the reliability issue in terms of metal-oxide-semiconductor field-effect transistor (MOSFET) devices. In recent years, various alternative gate dielectrics have been researched. Following the introduction of HfO2 into the 45 nm process by Intel in 2007, the screening and selection of high-k gate stacks, understanding their properties, and their integration into CMOS technology has been a very active research area. Frequency dispersion of high-k dielectrics was commonly observed and classified into two parts: extrinsic and intrinsic causes. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was studied. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled using a dual frequency technique. The effect of surface roughness on frequency dispersion is also investigated. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. Some of the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Other relaxation models were also introduced. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which was dependent on the structure of the high-k material. The degree of polarization was attributed to the enhancement of the correlations among polar nano-scale size domain within the materials. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain size due to its higher concentration of grain boundary.
13
Norris, Ann Marie Walstrom. "Dielectric studies of novel polymeric systems." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53656.
Full textAbstract:
This work combines many characterization techniques in an effort to enhance understanding of molecular motions of polymers and. how they are influenced by' structure. The primary characterization method was dielectric spectroscopy which utilizes an AC electric field as the stress field.
A variety of new, well controlled polymeric systems were studied. The first series included a number of radial starblock copolymers, styrene/isoprene, t-butyl- styrene/isoprene, and t-butyl-styrene/butadiene. These ABA copolymers consisted of hard and soft blocks, with the soft block comprising 75% by weight. The effect of microstructure of the soft block, casting solvent, hydrogenation, and chemical composition of the hard block were some of the variables studied. The amount of phase separation and the molecular motions occurring will be influenced by these parameters. Hydrogenation of the soft block increased the phase separation.
Another system investigated included some stereospecific poly(alkyl methacrylates) which were synthesized anionically. In this series the alkyl group was systematically changed in order to study the effects of the bulkiness of the substituent and the tacticity on the a and ß transitions. The ß transition associated with side chain rotations was only observed in the case of the methyl and ethyl substituents. The Havriliak-Negami data analysis was used to evaluate the breadth and the skewness of the distribution of relaxation times.
Finally, some high temperature thermoplastic polymers were evaluated with dielectric spectroscopy. The effect of the backbone composition, moisture, and fillers on the β transition was looked at. These studies showed that moisture and fillers play an important role on the magnitude and temperature of the observed β transition.Ph. D.
14
Gu, Mingxia. "Effects of Dielectric Relaxation on Director Dynamics in Uniaxial Nematic Liquid Crystals." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1236368118.
Full text
15
Goodwin, Andrew A. "Dielectric relaxation of polysiloxanes and kerr effect of p-phenylene vinylene oligomers." Thesis, Aston University, 1987. http://publications.aston.ac.uk/14500/.
Full textAbstract:
The dielectric relaxation behaviour of a series of cyclic and linear poly(dimethylsiloxanes) with overline nn in the range 28 to 99 has been studied, as a function of temperature (142.0K-157.5K) and frequency (12-105Hz). Activation energies for the -relaxation process, Davidson-Cole empirical distribution factors, , and mean-square dipole moments per repeat unit, < 2> , have been calculated. Differences in values of H_act reflected restricted dipolar rotation for the cyclic structures, compared to the linear structures, over the range of molecular weights studied. The dielectric relaxation behaviour of a series of linear oligomers of methyl phenyl siloxane, with n in the range 4 to 10, a series of linear fractions of poly(methyl phenyl siloxane), with overline n_n in the range 31 to 1370, and a cyclic oligomer of mehyl phenyl siloxane, with n = 10, has been studied as a function of temperature (155.5K-264.0K) and frequency (12-105Hz). Activation energies for the -relaxation process, Davidson-Cole and Cole-Cole empirical distribution factors, and , respectively, and mean-square dipole moments per repeat unit have been calculated. The reduced flexibility of short methyl phenyl siloxane chains, compared to dimethyl siloxane chains, was apparent from a comparison of dipole moment ratios. The dilectric relaxation behaviour of poly(methyl hydrogen siloxane) and poly(n-hexyl methyl siloxane) has been studied as a function of temperature and frequency. A polysiloxane liquid crystal has been synthesised and its dielectric relaxation behaviour has been studied, as a function of temperature and frequency, in the liquid crystalline phase and below T_g. Poly(p-phenylene vinylene) and related oligomers have been synthesised and characterised by a variety of experimental techniques. The Kerr effect of two oligomeric fractions, in solution in PPG 2025, has been measured. The electrical conductivities of the undoped and I_2-doped polymer and oligomers have been measured.
16
Stráník, Rostislav. "Dielektrická relaxační spektroskopie glycerolu." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-233415.
Full textAbstract:
This doctoral thesis deals with the analysis of dielectric spectra of glycerol with dielectric relaxation spectroscopy (DRS). Dielectric spectra of glycerol have been measured in the frequency range 20 Hz to 10 MHz and in the temperature range 10 K to 300 K. The observed dielectric spectra featured a typical relaxation maximum, which could be in the first approximation described by the Arrhenius equation. The activation energy of the relaxation process observed was 90 MJ/kmol. The relaxation strength as well as the shape of the relaxation peak remained in the temperature interval 180 K - 230 K (visibility of peak) almost the same, thus indicating that no change of the relaxation mechanism comes about. Much attention was in the thesis paid to the analysis of the excess component of the relaxation alfa process, in the literature commonly denoted as "excess wing". The thesis puts forward a procedure for the quantification of the magnitude of the excess wing. The excess wing magnitude thus determined turns out to increase monotonously with increasing temperature. The excess wing is here interpreted as a manifestation of a weakly-pronounced beta relaxation.
17
Brás, Ana Rita Elias. "Influence of constraining and confinement in the molecular mobility of low molecular weight materials." Doctoral thesis, FCT - UNL, 2009. http://hdl.handle.net/10362/2670.
Full textAbstract:
Dissertation presented to obtain a Ph.D. Degree in Chemical PhysicsDespite the importance that the glassy state has nowadays, the transition from liquid to the glass, glass transition, still remains a matter of debate which constitutes one of the great condensed matter physics challenges. Since this fact is closely related to the cooperativity dynamics, the study of this phenomenon in glass-forming liquids under confinement in the nanometer scale, has recently emerged as a strategy to clarify factors such as the existence of an inherent length scale of the cooperative dynamics that determines the glass transition temperature. In this context, this thesis represents an additional contribution to the study of molecular dynamics of glass-forming liquids under confinement in nanoporous inorganic materials. As target compounds the liquid crystal E7 and the drug Ibuprofen were selected. Since the first exhibit various transitions makes it more sensitive to perturbations and thus appears as the ideal candidate to evaluate confinement effects. The study of ibuprofen is of particular interest because confinement emerges as a method of stabilizing the amorphous phase that is mostly important in pharmaceutical applications. Dielectric Relaxation Spectroscopy(DRS) is the main technique used to obtain detailed information about the molecular mobility in a wide range of frequencies (10-2-109Hz) (Chapter I and II). The first part of the thesis is devoted to the characterization of the two target compounds in the bulk state. The combination of DRS with the specific heat spectroscopy allowed to determine which of the E7 observed relaxation processes (a process in the isotropic phase and two processes in the nematic phase: δ and tumbling) is responsible for the glass transition temperature Tg (tumbling process). Detailed studies of ibuprofen molecular mobility in the liquid, supercooled liquid and glassy states are also presented in this chapter, where four relaxation processes are detected: two secondary processes (γ and β), the cooperative process related to Tg (α ) and the Debye process (D), probably related to the hydrogen bonding dynamics. This study was preceded by an optimization of the conditions to obtain amorphous Ibuprofen which is a crystal in its natural state (Chapter III). In the next chapter (Chapter IV), the molecular dynamics of E7 confined to untreated and phospholipid lecithin treated rigid inorganic membranes with 20 nm pore diameter was evaluated. It was found that both the liquid crystal alignment, as well as the dynamics is influenced by confinement and treatment of the surface pores. Additionally, E7 was further studied confined to the mesoporous materials MCM-41 and SBA-15 type, 100% silica composition and pore size between the 2.8 and 6.8 nm. A multiplicity of relaxation processes was revealed by DRS, including the modes already observed in the bulk E7. In addition, two
Fundação para a Ciência e Tecnologia (FCT),financial support by means of the PhD grant SFRH/BD/23829/2005
18
Comer, Anthony C. "DYNAMIC RELAXATION PROPERTIES OF AROMATIC POLYIMIDES AND POLYMER NANOCOMPOSITES." UKnowledge, 2011. http://uknowledge.uky.edu/cme_etds/1.
Full textAbstract:
The dynamic relaxation characteristics of Matrimid® (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (ƴ and β transitions), and the glass-rubber (α) transition. For Matrimid, the low-temperature ƴ transition is purely non-cooperative, while the β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the ƴ transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The β relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (α) transition, dynamic mechanical studies reveal a strong shift in Tα to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement.
The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or immobilized at the particle-polymer interface. Dielectric measurements, which were used to probe the time-temperature response across the local sub-glass relaxations, indicate no variation in relaxation characteristics with particle loading.
Nanocomposite studies were also conducted on rubbery poly(ethylene oxide) networks crosslinked in the presence of MgO or SiO2 nanoparticles. The inclusion of nanoparticles led to a systematic increase in rubbery modulus and a modest positive offset in the measured glass transition temperature (Tα) for both systems. The sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in these crosslinked networks.
19
Bačkovský, Pavel. "Simulace absorpčních charakteristik dielektrických materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218363.
Full textAbstract:
This projects deal with dielectric materials. Characterize definition of dielectric and polarization of dielectric. Shows dielectric relaxation. Specified conception dielectric absorption and interpreted them with DC voltage charging condensator. However, this thesis be engaged in simulation of this process. Output is simulation program of dielectric absorption characteristics for two relaxation mechanism.
20
Buckingham, David Tracy Willis. "High-Resolution Thermal Expansion and Dielectric Relaxation Measurements on H2O and D2O Ice Ih." Thesis, Montana State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10607201.
Full textAbstract:
Ice Ih, formed by freezing liquid water below 273∼K at atmospheric pressure, is well-known and highly-studied, but some of its fundamental physical properties have mystified scientists since the early twentieth century. The thermal expansion is one of those properties; the low relative-resolution of past measurements has left questions regarding the structural isotropy and negative thermal expansion (NTE). Furthermore, the existence of relaxation phenomena near 100∼K, related to the residual entropy at 0∼K, may reveal itself through subtle features in the thermal expansion and, thus, warrants further investigation. Here we measure the thermal expansion of ultra-pure single crystal ice from 5–265∼K with 106 times higher relative resolution than has previously been made. The data reveal a distinct crossover to NTE below 62∼K, and a third-order transition along the crystallographic \(c\)-axis near 100∼K, as evident by an unambiguous relaxational decrease in the thermal expansion coefficient on cooling. To further understand the nature of the transition, isotopic substitution and dielectric measurements were performed.
Three properties of the dielectric relaxation in ice were probed at temperatures between 80--250∼K; the thermally stimulated depolarization (TSD) current, static electrical conductivity, and dielectric relaxation time. The dielectric data agree with relaxation-based models and provide for the determination of activation energies which identify the dielectric relaxation in ice as being dominated by Bjerrum defects below 140∼K. An anisotropy was also found in the data which revealed that molecular reorientations, in the form of propagating Bjerrum point defects, are energetically favored along the \(c\)-axis between 80--140∼K. Furthermore, a similar relaxational effect to that observed in the thermal expansion was observed in the TSD along \(c\), providing a strong correlation between dielectric relaxation and inherent thermodynamic relaxation in ice. Finally, isotopic substitution in both measurement sets indicates the transition is related the movements of hydrogen nuclei, not those of the whole molecule, and provides details about the low-temperature phonon modes. These findings paint a picture of ice as a proton-disordered crystal which undergoes a partial ordering on cooling near 100∼K but, before an ordered equilibrium state is realized, the exponentially increasing relaxation time rapidly slows the ordering and ultimately freezes-in the residual entropy, causing a continuous decrease in the thermal expansion coefficient.
21
Ježík, Jan. "Studium dielektrické relaxace v základních materiálech DPS a v izolacích kabelů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219358.
Full textAbstract:
This study investigates relaxation polarization in some dielectric components of tester UNISPOT S40 developed by company UNITES Systems a.s. Relaxation polarization in the PCB substrates and in tester’s cable insulation causes undesirable deceleration of some test steps. Relaxation polarization in selected PCB substrates and various cables are examined by method of dielectric relaxation spectroscopy in the frequency domain and by measurement of polarization or depolarization current.
22
Marashdeh, Wajeeh. "Relaxation Behavior and Electrical Properties of Polyimide/Graphene Nanocomposite." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595850361812632.
Full text
23
Chiu, Ching-Wen. "Effects of Electric Fields on Forces between Dielectric Particles in Air." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/76755.
Full textAbstract:
We developed a quantitative measurement technique using atomic force microscopy (AFM) to study the effects of both DC and AC external electric fields on the forces between two dielectric microspheres. In this work we measured the DC and AC electric field-induced forces and adhesion force between two barium titanate (BaTiO?) glass microspheres in a low humidity environment by this technique. The objective here is to find out the correlation between these measured forces and applied field strength, frequency, and the separation distance between the two spheres was studied. Since the spheres would oscillate under an AC field, the AC field-induced force was divided into dynamic component (i.e., time-varying term) and static component (i.e., time-averaged term) to investigate. The oscillatory response occurs at a frequency that is twice the drive frequency since the field-induced force is theoretically proportional to the square of the applied field. This behavior can be observed in the fast Fourier transformation (FFT) spectra of the time series of the deflection signal. The magnitude of the vibration response increases when the frequency of the drive force is near resonant frequency of the particle-cantilever probe. The amplitude of this vibration increases with proximity of the two particles, and ultimately causes the particles to repeatedly hit each other as in tapping mode AFM.
The effect of the Maxwell-Wagner interfacial relaxation on the DC electric field-induced force was discovered by monitoring the variation of the field-induced force with time. The static component of the AC electric field-induced force does not vary with the applied frequency in the range from 1 to 100 kHz, suggesting that the crossover frequency may equal to or less than 1 kHz and the permittivities of the BaTiO? glass microspheres and medium dominate the field-3 induced force. The AC field-induced force is proportional to the square of the applied electric field strength. This relationship persists even when the separation between the spheres is much smaller than the diameter of the microspheres. The large magnitude of the force at small separations suggests that the local field is distorted by the presence of a second particle, and the continued dependence on the square of the field but the measured force is much larger than the theoretical results, suggesting that the local electric field around the closely spaced spheres is distorted and enhanced but the effects of the local field distortion may have not much to with the applied electric field. Compared with the calculated results from different models, our results demonstrate that the field-induced force is much more long-range than expected in theory. In addition, the DC field-induced adhesion force is larger than the AC field-induced one due to the interfacial charge accumulation, agreeing with the discovery of the Maxwell-Wagner interfacial relaxation effect on the DC field-induced force. No obvious correlation between the field-induced adhesion and the applied frequency is found. However, both the DC and AC field-induced adhesion forces display the linearity with the square of the applied electric field strength as well.Master of Science
24
Kalakkunnath, Sumod. "VISCOELASTIC RELAXATION CHARACTERISTICS OF RUBBERY POLYMER NETWORKS AND ENGINEERING POLYESTERS." UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/486.
Full textAbstract:
The relaxation characteristics of rubbery poly(ethylene oxide) [PEO] networks have been investigated as a function of network composition and architecture via dynamic mechanical analysis and broadband dielectric spectroscopy. A series of model networks were prepared via UV photopolymerization using poly(ethylene glycol) diacrylate [PEGDA] as crosslinker: variations in crosslink density were achieved either by the introduction of water in the prepolymerization reaction mixture, or by the inclusion of mono-functional acrylate such as poly(ethylene glycol) methyl ether acrylate [PEGMEA] or poly(ethylene glycol) acrylate [PEGA]. Copolymerization with mono-functional acrylate led to the insertion of flexible branches along the network backbone, and the corresponding glass-rubber relaxation properties of the copolymers (i.e., Tg, relaxation breadth, fragility) were a sensitive function of network architecture and corresponding fractional free volume. Relatively subtle variations in network structure led to significant differences in relaxation characteristics, and a systematic series of studies was undertaken to examine the influence of branch length, branch end-group, and crosslinker flexibility on viscoelastic response. Dielectric spectroscopy was especially useful for the elucidation of localized, sub-glass relaxations in the polymer networks: the imposition of local constraint in the vicinity of the crosslink junctions led to the detection of a distinctive fast relaxation process in the networks that was similar to a comparable sub-glass relaxation observed in crystalline PEO and in the confined regions of PEO nanocomposites. Gas permeation studies on the model PEGDA networks confirmed their utility as highly-permeable, reverse-selective membrane materials, and strategic control of the network architecture could be used to optimize gas separation performance. Dynamic mechanical and dielectric measurements have also been performed on a semicrystalline polyester, poly(trimethylene terephthalate) [PTT], in order to assess the influence of processing history on the resultant morphology and corresponding viscoelastic relaxation characteristics. Studies on both quenched and annealed PTT revealed the presence of a substantial fraction of rigid amorphous phase (RAP) material in the crystalline samples: dielectric measurements showed a strong increase in relaxation intensity above the glass transition indicating a progressive mobilization of the rigid amorphous phase with increasing temperature prior to crystalline melting.
25
Hunger, Johannes. "Effects of polar compounds on the dynamics and dielectric properties of room-temperature ionic liquids." kostenfrei, 2009. http://epub.uni-regensburg.de/11973/.
Full text
26
Ledru, Romuald. "Mesure par spectroscopie d'admittance de jonctions Métal/Oxyde/Semi-Conducteur Organique : Analyse de la réponse diélectrique du pentacène." Thesis, Reims, 2012. http://www.theses.fr/2012REIMS035/document.
Full textAbstract:
Les transistors organiques sont la base de nombreuses applications de l'électronique organique mais leur rendement électrique ainsi que leur stabilité dans le temps sont encore des verrous technologiques devant être levés. De plus, le phénomène de transport de charges dans ces dispositifs reste une notion encore à l'étude même si différents modèles sont utilisés afin d'expliquer l'effet de champ des transistors organiques. C'est dans ce cadre que s'inscrit cette étude portant sur la caractérisation par spectroscopie d'admittance de jonctions Métal/oxyde/semi conducteur organique/métal. Elle a pour but d'analyser le comportement électrostatique du semi conducteur organique. Les mesures de spectroscopie d'admittance ont été réalisées sur une large bande de fréquence (0.1Hz à 1Mhz) dans laquelle les pertes diélectriques mesurées peuvent être associées à des phénomènes d'orientation (oscillation) de dipôles présents dans la structure. Les réponses en fréquences montrent trois types de comportements dynamiques. A basses fréquences, nous avons observé une diffusion ionique, liée au déplacement d'ions H+ à travers la structure. A hautes fréquences, la réponse est due aux imperfections de l'oxyde. Enfin, aux fréquences intermédiaires, la réponse du semi-conducteur organique est identifiée et attribuée à des dipôles permanents. A partir de ces différentes réponses, un modèle analytique est établi et permet de décrire l'ensemble des réponses dynamiques. Le comportement du semi-conducteur est décrit par la somme d'une fonction de type Debye et de type Cole-Cole. L'analyse des paramètres de ce modèle a permis de mettre en évidence l'influence des dipôles permanents sur la permittivité du film de semi-conducteur organique. Enfin, ce modèle a été validé sur différents échantillons à base de pentacène et a été ensuite appliqué au Poly-3-hexylthiophèneOrganic transistors are vital in many applications of organic electronics but the electrical performance and time stability are technological limitation in order to make this technology reliable. Moreover, in these devices, the charge transport phenomenon has not to be clearly understood even if different models are commonly used to explain the field effect in organic transistors. In this context, this thesis talks about the admittance spectroscopy characterization of metal / oxide / organic semiconductor / metal junctions and analysis the organic semiconductor electrostatic behavior.The admittance spectroscopy measurements were performed on a wide frequency range (0.1Hz to 1MHz) in which the measured dielectric loss may be associated with the orientation phenomenon (as oscillation) of dipoles present in the structure.The frequency responses show three dynamic behaviors. At low frequencies (<10Hz), we observed an ionic diffusion, which is related to the ions movement of H+ through the structure. At high frequencies, (>10kHz) the response is due to defects into the oxide. Finally, at intermediate frequencies, the organic semiconductor response is identified and assigned to the permanent dipoles into the bulk. From these responses, an analytical model is developed and used to describe the dynamic responses. The semi-conductor behavior is described by the sum of a Debye and Cole-Cole function type. The analysis of the model parameters has highlighted the influence of permanent dipoles on the organic semiconductor permittivity. Finally, this model has been agreed on different samples based on pentacene and was applied to the Poly-3-hexylthiophene
27
Jankowska-Sumara, Irena. "Dielectric relaxation, electrostrictive properties and Raman light scattering in PbZrO3 and PbHfO3 single crystals pure and doped with small amount of PbTiO3." Metz, 1997. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1997/Jankowska_Sumara.Irena.SMZ9751.pdf.
Full textAbstract:
Le travail de recherche est une étude de la relaxation diélectrique, des propriétés électrostrictives et de la diffusion de lumière Raman dans deux systèmes pérovskites à base de plomb dopés au titane : _ le système PbZrO3 pur ou faiblement dopé par des ions de Ti _ le système PbHfO3 pur ou faiblement dopé par des ions de Ti qui ont comme caractéristique commune de présenter une (pour PbZrO3) voire deux (pour PbHfO3) transitions de phase structurales vers des phases anti-ferroélectriques (AFE). Le but des travaux de la thèse est d'étudier expérimentalement et théoriquement les transitions de phase structurales exhibées par les deux systèmes, et notamment celles menant à des phases AFE, ainsi que d'en comprendre les mécanismes. Pour arriver à ces objectifs, il a été mis en œuvre des mesures de relaxation diélectrique, des propriétés électrostrictives et de diffusion de lumière Raman, cela dans des intervalles de températures allant 10 k à 700 k et dans des gammes de fréquences de 10 hz à 10 mhz pour les mesures diélectriques et électrostrictives. Les différentes mesures ont été réalisées sur des monocristaux purs de PbZrO3 et de PbHfO3 et sur des monocristaux présentant de faible dopage (de l'ordre de 1%) en ions Ti. Le développement de la thèse comporte quatre parties détaillant les différentes phases du travail. Le premier chapitre, consacré à un rappel des propriétés diélectriques et structurales des deux systèmes étudiés, pose l'objet scientifique de l'étude envisagée en la situant dans le champ des connaissances déjà acquises et en posant les problèmes non résolus et abordes. Le second chapitre du mémoire est consacré aux propriétés diélectriques des cristaux étudiés. A partir des éléments théoriques essentiels concernant les fonctions de susceptibilités diélectriques de matériaux isolants et du rappel des conditions et dispositifs expérimentaux mis en œuvre, ce chapitre donne un aperçu systématique des résultats expérimentaux obtenus. Une forte relaxation a été mise en évidence à la basse fréquence et est attribuée à des processus de type électrochimique. Les échantillons étudiés présentent également la propriété commune d'une dispersion diélectrique significative dans le domaine du khz attribuée aux impuretés et à des désordres dans le sous-réseau des ions oxygène. Le troisième chapitre du mémoire décrit les études électromécaniques entrepris sur les systèmes cristallins analyses et montre l'apparition, simultanément aux relaxations dipolaires, de dispersions de la déformation électrostrictive. Le quatrième chapitre de la thèse, concernant une étude expérimentale systématique de la diffusion de lumière Raman met en évidence l'existence d'amas dipolaires dynamiques dans la phase paraélectrique ainsi que l'occurrence d'un mode ferroélectrique mou. Par ailleurs, les contributions respectives des dynamiques phononiques et relaxationnelles sont analysées lors de la transition de phase PE - AFE2 - AFE1The research concerns a study of the dielectric relaxation, the electrostrictive properties and the Raman light scattering of two lead based and titanium doped perovskites : the PbZrO3 system, pure and weakly Ti doped ; the PbHfO3 system, pure and weakly Ti doped. These systems have the common characteristics to exhibit one (for PbZrO3) structural phase transitions towards antiferroelectric phases (AFE). The aim of the thesis is to study experimentally and theoretically the phase transitions exhibited by these two systems, and especially those leading to the AFE phases, and to understand their mechanisms. In order to reach these objectives, dielectric relaxation, electrostrictive and light scattering measurements have been performed in a temperature range from 10 K to 700 K and for frequencies from 10Hz to 10 MHz for the dielectric and electrostricitve investigations. The measurements have been performed on monocristals of PbZrO3 and PbHfO3 pure or lightly (about 1%) Ti doped. The thesis is constitued by four parts, each of it detailing the various phases of the study. The first part, devoted to a recall of the dielectric and structural properties, states the scientific purpose of the investigation. The second chapter is concerned with the dielectric behaviour of the systems. Starting from theoretical elements necessary to understand the susceptibility functions of insulating materials and based on the experimental disposal used in the investigations, this part details the main experimental data obtained. A strong relaxation has been evidenced at low-frequency and is attributed to electro-chemical processes. The samples also present a significant dielectric dispersion in the kHz range interpreted to be due to impurities and disorder in the oxygen sublattice. The third chapter of the thesis describes the electromechanical studies and shows appearance, simultaneously with dipolar relaxation, of dispersions due to electrostrictive deformations. The last part, concerned with a systematic Raman light scattering study, shows the existence of dynamical dipolar cluster in the paraelectric phase as well as indications of a ferroelectric soft mode occurence. The respective contributions of the vibrational and relaxational dynamics are analysed at the PE-AFE2-AFE1 phase transitions
28
Mydlář, Marek. "Analýza složené soustavy s různým podílem plniva." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-217945.
Full textAbstract:
This master’s thesis applies dielectric relaxation spectroscopy to analyse impact of climatic changes on dielectric properties of composite material samples (TSA 220S varnish combined with 60.030 mica). Experiments aim to analyse effect of mica composite mass ratio (0, 4, 8 and 16 % of mica), relative humidity (0, 33, 55, 65, 75 and 95 %) and temperature (23, 30, 40 and 50 C) on complex permitivity as a function of frequency.
29
Monreal, Jorge. "Polymer Characteristics of Polyelectrolyte Polypeptides." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6326.
Full textAbstract:
Polypeptides are polymerized chains of amino acids linked covalently through peptide bonds. Polyelectrolyte polypeptides are polypeptides with electrolyte repeating groups. Several amino acids contain ionizable side chains which result in charge distributions when dissolved in aqueous solutions. This dissertation is motivated by a desire to gain knowledge of polyelectrolyte polypeptides as recent advances in chemical synthesis of polypeptides have made possible the fabrication of designed polypeptides that do not naturally occur in nature. Potential applications of newly designed polypeptides span the range from medical to clothing and energy even to robotics.
In this dissertation we compare the characteristic behavior of two polypeptide polyanions: Poly-(L-Glutamic Acid) [PLE] and Poly-(L-Glutamic Acid4, Tyrosine1) [PLEY(4:1)]. Comparative characteristic behaviors of each is conducted through relaxation phenomena in the context of mechanical elasticity measurements of hydrogels and dielectric relaxation of aqueous solutions in a radio frequency range of 1 MHz to 1000 MHz. Hydrogels are fabricated by crosslinking each polyanion with Poly-(L-Lysine) [PLK], a polycation, via the crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Elasticity and viscoelasticity measurements are conducted in a fixture designed by our lab. Dielectric relaxation behavior is studied on aqueous solution of both PLEY and PLE using a capacitive fixture, also designed in our lab. RF signals provided by an impedance analyzer are converted to permittivity and dielectric loss measurements. Peaks in dielectric loss provide evidence of relaxation mechanisms. A comparison of experimental results to theoretical expectations reveal both expected and some surprising behavior. Relaxation times for crosslinked hydro-gels scale according to theoretical expectations according to so-called reptation dynamics. However, relaxation times of aqueous solutions did not scale as entangled polyelectrolytes. First, both PLEY and PLE scaled as neutral polymers rather than polyelectrolytes. This was expected because of the high concentrations studied. However, due to the high concentrations, it was expected that polypeptides were entangled in solutions. Data compared to theory did not support this expectation.
We, additionally, conducted a self-crosslinking experiment of a polyampholyte: RADA16. RADA16 is known to self-assemble into nano-fibers formed by -sheet stacking. The self-crosslinking was also mediated by EDC. Results of crosslinking showed formation of polypeptide spherules as well as nano-crystals nominally orthorhombic in shape. It was not possible to ascertain composition of the nano-crystals due to both the limited amount of raw material available and the capabilities of measurement equipment as of this writing. It is hypothesized that nano-crystals are composed of some type of urea by-product from the crosslinking reaction. The spherules, on the other hand, seem to be described by the theory of hydrophobic polyelectrolytes.
Additional research conducted with regards to electromagnetic hydrodynamic flows during the time frame of this dissertation is also included. The research uses hydrodynamic conservation equations as a starting point to derive one electromagnetic flow momentum equation analogous to the Cauchy momentum equation of hydrodynamics. It also introduces a mass- energy conservation equation for electromagnetic flow that has no hydrodynamic analogue.
We begin this dissertation by introducing in Chapter 1 some of the theoretical background necessary to understand results from experiments. Chapter 2 introduces experimental results from elasticity and viscoelasticity measurements and Chapter 3 explains the dielectric relaxation experiment. We then follow with Chapter 4 which presents conclusions from mechanical and dielectric relaxation experiments in a concise format. Results from the self- crosslinking of RADA16 are presented in Chapter 5. Finally, the additional research on electromagnetic flow is presented in Chapter 6.
30
Motwani, Tanuj Anantheswaran Ramaswamy C. "State of water in starch-water systems in the gelatinization temperature range as investigated using dielectric relaxation spectroscopy." [University Park, Pa.] : Pennsylvania State University, 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4597/index.html.
Full text
31
Murray, Christopher Ian. "The study of side chain organisation in liquid crystalline polymers using dielectric relaxation spectroscopy and X-ray diffraction." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286908.
Full text
32
Rekik, Houda. "Mobilité moléculaire aux interfaces de nanostructures polymères renforcées par des nanocharges fonctionnelles." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10046.
Full textAbstract:
Deux séries d'échantillon à base de PVDF ont été élaborées avec différentes fractions de dioxyde de titane TiO2 en utilisant deux modes d'élaboration : dispersion des nanoparticules de TiO2 par voie fondue habituelle et génération des charges de TiO2 basée sur des réactions d'hydrolyse-condensations d'un alkoxyde de titane (le n-tétrabutoxyde de titane). Dans cette étude, quatre techniques ont été utilisées pour étudier les processus de relaxation dans les polymères semi-cristallins. Le microscope électronique à balayage (MEB) pour étudier la dispersion des nanoparticules de TiO2 dans la matrice PVDF. La calorimétrie différentielle à balayage (DSC) a été utilisée dans cette étude pour caractériser thermiquement les échantillons polymériques semi-cristallins. L'analyse thermo-gravimétrique (ATG) a été utilisée pour voir l'effet de nanoparticules sur les propriétés thermiques du PVDF. De plus, la technique de spectroscopie diélectrique a été utilisée dans la thèse pour étudier l'influence du processus d'élaboration sur la mobilité moléculaire trouvée dans ces systèmes. On a montré que le comportement de ces nanocomposites est proche de celui de PVDF pur. Les changements principaux observés sont le ralentissement de la dynamique de la relaxation alpha (associée à la température de transition vitreuse) et la relaxation alpha c (associée à la phase cristalline) en fonction de l'augmentation de fraction volumique TiO2. L'existence des charges piégées aux interfaces qui met en cause la présence de la polarisation interfaciale (IP) dans les différents nanocomposites a aussi été analysée. Les additions de TiO2 diminuent la mobilité des chaînes polymériques ce qui rend difficile l'orientation des dipôles électriques et augmente l'énergie d'activation de la relaxation de polarisation interfacialePolyvinylidene fluoride (PVDF) films have been filled with different volume fraction of titanate dioxide TiO2 using two ways : dispersion in the melt or in-situ generation based on the hydrolysis-condensation reactions of titanium alkoxide inorganic precursor premixed with PVDF under molten conditions. In this study, four techniques were used to study the relaxation processes in the semi-crystalline polymers. The scanning electron microscope (SEM) was introduced in the field of polymer science to study the dispersion of TiO2 nanoparticules in the PVDF matrix. The differential scanning calorimetry (DSC) was used in this study to thermally characterize the semi-crystalline polymer samples. Thermal gravimetric analysis (TGA) was used to see the effect of nanoparticles on the thermal properties of PVDF. In addition, the dielectric spectroscopy technique was used in the thesis to study the influence of the process on the molecular mobility found in these systems. It was shown that the behavior of PVDF as a matrix in these nanocomposite is close to that of pure PVDF. The main changes observed is the slowing down of the dynamics of the alpha a (associated to the glass transition temperature) and the alpha c (associated to the crystalline phase) relaxations as a function of the TiO2 volume fraction increase. The existence of charge carriers trapping at the interfaces related to the interfacial polarization (IP) in the different nanocomposites has also been analyzed. The additions of TiO2 decrease the mobility of the polymer chains which makes difficult the orientation of electric dipole moment ending in an increase of the energy of activation of IP relaxation
33
Sousa, Washington da Silva. "Estudo da relaxação dielétrica de filmes ultrafinos de poliestireno sulfonado." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-15072009-142644/.
Full textAbstract:
Ionômeros são polímeros carregados que possuem uma variedade de propriedades elétricas e que recentemente vêm sendo aplicados como camadas de transporte em dispositivos poliméricos. Em particular, camadas ultrafinas de ionômeros são depositadas entre o eletrodo e o polímero eletrônico em OLEDs para aumentar a eficiência da injeção de cargas. Entretanto o sucesso desta aplicação envolve fenômenos de armazenamento e mecanismos de transportes de cargas dentro do ionômero que ainda não são claramente entendidos. Neste trabalho foi utilizada a técnica da corrente despolarização termoestimulada (TSDC) com o propósito de esclarecer alguns efeitos relacionados a esse fenômeno. Nós utilizamos o poliestireno sulfonado (X-SPS) com lítio (X = Li) ou potássio (X = K) como contraíon. Foram obtidos filmes ultrafinos com 50 nm de espessura por spincoating obtendo a estrutura metal-polímero-metal para estudo, tendo como metal o alumínio. A técnica de TSDC consiste no aquecimento de uma amostra previamente polarizada a um taxa de aquecimento constante e a corrente de despolarização é medida em função da temperatura da amostra. Os resultados experimentais mostraram que cada termograma apresenta dois picos, sendo que um dos deles mostrou-se fortemente dependente das condições de polarização, ou seja, dependendo da temperatura de polarização e da intensidade do campo de polarização. Os picos foram estudados através da cinética de primeira ordem para a dinâmica de armazenamento e transporte, e dos ajustes teórico-experimental foram obtidos importantes parâmetros, tal como, a energia de ativação e concentração de espécies ativas.Ionomers are charged polymers that exhibit a great variety of electrical properties and more recently they have been applied as transport layers at polymer devices. In particular, thin films of ionomer have been deposited between the electrodes and the electronic polymers in OLEDs to improve the efficiency of the charge injection. Despite the success of such application, the involved phenomena related to the charge storage and transport mechanisms inside the ionomer thin layer are not clear yet. In this work we used thermal stimulated depolarization current technique (TSDC) with the purpose to elucidate such phenomena. We used for this a sulfonated polystyrene (X-SPS) having lithium (X = Li) or potassium (X = K) as cation counter-ions, and we make structure of metal-polymer-metal in which the polymer is a thin film of SPS, at about 50 nm thick and deposited by spincoating, having aluminum as metal. TSDC technique consists of warm up a previously polarized sample at a constant rate of heating and measure the depolarization current in function of the temperature. The experimental results showed that each thermogram presents two peaks, one of them very dependent on the polarization conditions, i. e., it depends on the polarization temperature and the intensity of the polarization bias. The peaks were studied by considering first order trapping-detrapping (or dipole relaxation) kinetics, from which important parameters, as the activation energy, were obtained.
34
Brož, Přemysl. "Analýza složené soustavy s různým podílem plniva." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217181.
Full text
35
Fauché, Pierre. "Plasmonic superradiance in metallo-dielectric nanohybrids." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0281/document.
Full textAbstract:
Hybridization of quantum emitters and plasmonic nanostructures has attracted much attention over the last years, due to their potential use as plasmon-based nanolasersor to achieve long-range quantum bit entanglement. Recent theoretical studies suggest that the plasmonic field can induce efficient cross-talking between emitters and lead to the formation of collective superradiant states. In this thesis, we developed a theoretical modelable to analyse collective effects in large ensemble of dipoles coupled by an electromagnetic nanoresonator. We experimentally investigated the plasmon-mediated superradiance of organic emitters grafted at a well-controlled distance from a metal nanosphere at room temperature. We report on the measured decay rates of these hybrid structures at the ensemble and single object levels. We find that the decay rate increases i) with the number ofemitters and ii) as the spacing between the emitters and the metal core decreases, a direct and clear evidence of plasmonic superradiance. This trend was observed for two types of hybrid structures, differing both by the size of the metal core and the type of organic dye used as emitter. The observation of plasmonic superradiance at room temperature opens questions about the robustness of these collective states against decoherence mechanisms.This robustness is of major interest for potential applications of quantum systems at room temperaturePlacer des nanostructures plasmoniques à proximité d’émetteurs quantiques est une approche prometteuse pour concevoir des nanolasers plasmoniques ou réaliser l’intrication de bits quantiques à longue distance. Des études théoriques récentes suggèrent que le champ plasmonique peut induire un couplage efficace entre émetteurs et mener à la formationd’états collectifs superradiants. Dans ce travail de thèse, nous avons développé un modèle théorique afin d’analyser les effets collectifs pour un ensemble de dipoles couplés à un nanorésonateur électromagnétique. Nous avons étudié expérimentalement la superradiance plasmonique d’émetteurs organiques greffés à une distance contrôlée d’une nanosphère metallique,à température ambiante. Nous avons mesuré le taux de relaxation de ces structures hybrides, en ensemble et à l’échelle de l’objet unique. Nous observons que le taux de relaxation augmente i) avec le nombre d’émetteurs et ii) lorsque la distance entre les émetteurs et le coeur métallique diminue, une preuve directe et claire de la superradiance plasmonique.Cette tendance a été observée pour deux types de structure hybride, différentes par la taille du coeur métallique et par le type de molécule utilisée comme émetteur. L’observation de la superradiance plasmonique à température ambiante ouvre des questions sur la robustesse d’un état superradiant contre des mécanismes de décohérence. Cette robustesse présente un intérêt majeur pour des applications potentielles de systèmes quantiques à température ambiante
36
Hegde, Vikas. "Etudes diélectriques des matériaux biodégradables et/ou bio-sourcés." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAT031/document.
Full textAbstract:
L'utilisation extensive des combustibles fossiles, l'émission de gaz à effet de serre dans l'atmosphère et les difficultés de recyclage des résidus de consommation incitent au recours accru aux polymères biodégradables. Dans le domaine du génie électrique, de nombreux polymères trouvent des applications dans les systèmes d'isolation des matériels électriques. Ces polymères sont issus du pétrole, peu respectueux de l'environnement et la plupart d'entre eux ne sont pas biodégradables. Dans le but de les remplacer, des polymères biodégradables ont été explorés.Une revue des travaux de recherche sur les polymères biodégradables dans le domaine du génie électrique a été réalisée. Les propriétés thermiques et électriques de polymères biodégradables et conventionnels sont rapportées et comparées.Les polymères biodégradables et / ou biosourcés sélectionnés et mis en œuvre sont le Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), le polycaprolactone (PCL) et l’acide polylactique PLA. Un matériau nanocomposite basé sur PLA a également été préparé. Les propriétés diélectriques pour une large gamme de température et de fréquence ont été mesurées par spectroscopie diélectrique et analysées en s’appuyant sur les propriétés thermiques obtenues par DSC et DMA. La résistivité volumique et la tenue diélectrique ont pu également être mesurées. Ces polyesters biodégradables sont comparés aux polymères conventionnelsThe declining resources of fossil fuels, increase in wide-spread pollution, emission of green-house gases and difficulties in recycling waste materials are pushing biodegradable polymers into prominence. In the domain of electrical engineering, many polymers find applications in various electrical insulation systems. These polymers are petro-based, not eco-friendly and most of them are not biodegradable. With an objective to replace conventional products, biodegradable polymers are explored for their dielectric properties.In this work, a detailed study on the present status in the research work on biodegradable polymers in the electrical engineering domain is presented. Thermal and electrical properties of both biodegradable and classical polymers are compiled and compared.The polymers processed and studied were Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), Polycaprolactone (PCL), Poly(lactic acid) (PLA) and PLA based nanocomposite. Dielectric properties for a wide range of temperature and frequency were measured by dielectric spectroscopy and analyzed with the help of DSC and DMA experiments. Volume resistivity and electrical breakdown were measured on few polymers. These biodegradable polyesters were compared with conventional polymers
37
Chen, Yan-Fang. "Investigation of interfacial and bulk physical properties of hybrid perovskite-based devices." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0268/document.
Full textAbstract:
Les Pérovskites hybrides organique-inorganique (PHOIs) ont suscité d’intenses recherches au coursdes dernières années. Dans cette thèse, nous avons dans un premier temps mis au point les différentsprocessus de préparation des échantillons et réalisé une caractérisation complète des films parmicroscopie à force atomique, spectroscopie photo-électronique par rayons X, mesure du potentiel desurface par sonde de Kelvin et mesure de la mobilité des charges par temps de vol. La distribution despièges à l'interface PHOI/Au a été étudiée via des mesure J-V-L en fonction de la températurecombinées avec des simulations numériques. Les relaxations diélectriques dans les PHOIs, tels que lamigration des ions et l’orientation du dipôle du cation organique, ont été étudiés par spectroscopied’impédance en fonction de la température. Dans la dernière partie de cette thèse, nous présentons uneétude originale qui démontre un mouvement des protons du groupement ammonium des cationsorganiques à l’interface avec le PEDOT : PSSHybrid-organic-inorganic perovskites (HOIPs) have provoked intense research over the recent years.In this thesis, we contribute to this investigation by first examining the results of different solutionpreparation processes, followed by characterizing the films using atomic force microscopy, X-raydiffraction, ultra-violet photoelectron spectroscopy, X-ray photoelectron spectroscopy, Kelvin probesurface potential measurement, and time-of-flight mobility measurement. The state distribution of theHOIP/Au interface was then studied by low temperature J–V–L measurement combined withnumerical simulation. In the process of these characterizations, it became clear that the dielectricrelaxations in HOIPs, such as ion migration and organic cation dipole orientation, play an importantrole in the material, and the next part of the thesis presents an analysis of these mechanisms with thehelp of temperature dependent impedance spectroscopy measurement. These studies built thefoundations for the final part of the thesis, where we investigated a so far elusive subject in HOIPs, themigration of protons
38
Kchaou, Marwa. "Influence de la méthode de préparation sur la dynamique de relaxation des polymères en films minces." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1017.
Full textAbstract:
L'objectif principal de cette thèse est de mettre en évidence l'effet de la méthode de préparation sur la dynamique de relaxation des polymères en films minces. Nous nous sommes focalisés en particulier sur l'importance de la maîtrise du taux d'évaporation du solvant lors de la préparation des films, en termes de contrôle de la magnitude des contraintes résiduelles et les conséquences engendrées sur les propriétés physiques. Dans un premier temps, nous exposons la problématique de déviation des propriétés de polymères en films minces et le lien avec la technique de préparation. Nous décrivons un moyen simple permettant de contrôler le taux d'évaporation du solvant en ajustant la concentration de la solution et la vitesse de rotation de la tournette. Les expériences de démouillage nous ont permis de suivre l'effet du taux d'évaporation du solvant sur les propriétés viscoélastiques des polymères près de la Tg. Les résultats obtenus sur des films minces de polystyrène mettent en évidence le rôle de la méthode de préparation sur la probabilité de rupture des films, les temps caractéristiques de relaxation, la dynamique de démouillage et la magnitude des contraintes résiduelles. Dans une seconde partie, nous présentons également une expérience basée sur la propagation des fissures dans les films minces vitreux. Une simple observation microscopique, ainsi que des imageries en AFM permettent de prouver le rôle du taux d'évaporation du solvant lors de la préparation. Enfin, nous explorons une nouvelle approche expérimentale portant sur la possibilité d'investigations en temps réel et lors de démouillage la relaxation moléculaire des chaînes dans les films minces par des mesures diélectriques directes. Nous avons réussi à prouver non seulement un rôle de la méthode de préparation des films mais également que la restauration du comportement du polymère en volume « bulk » est possible en fonction du temps quelques soient les paramètres du film. Nous confirmons ainsi que les propriétés anormales observées dans les films minces spin-coatés sont dictées par l'état métastable provoqué par la méthode de préparationThe aim of this work is to highlight the influence of the sample preparation on the relaxation dynamics of supported polymer thin films. We focus in particular on the importance of tuning the solvent evaporation rate during films preparation, in terms of controlling the magnitude of residual stresses, and the impact on the physical properties. Firstly, we expose the deviation of the polymer behavior in thin polymer films related to the preparation technique. Then, we describe how the solvent evaporation rate can be precisely tuned by varying the concentration of the solution and the rotation rate of the spin coater. Dewetting experiments allowed us to investigate the effect of the solvent evaporation rate on the viscoelastic behavior of the polymers near the Tg. The probability of films rupture, the characteristic time, dewetting dynamics and the magnitude of residual stresses are deduced to prove the impact of sample preparation. In the second part, we present cracks propagation experiments in glassy thin films. A simple microscopic observation, as well as AFM imaging are used to emphasize the role of the solvent evaporation rate during the preparation. Finally, we present a new experimental approach to investigate in real time and during dewetting the dynamics of polymers in thin films by direct dielectric measurements. We have successfully proved not only the impact of sample preparation but also the restoration of the bulk behavior of polymers is possible during the time whatever the film parameters. We therefore confirm that the anomalous properties observed in spin-coated films are governed by the metastable state induced by the sample preparation
39
Abuetwirat, Inas Faisel. "Dielektrické vlastnosti tenkých vrstev oxidů niobu a tantalu." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-233619.
Full textAbstract:
Dielektrická relaxační spektroskopie je jednou z užitečných metod pro studium molekulární dynamiky materiálů. Díky nedávnému pokroku v přístrojové a měřicí technice je dnes možné získat dielektrické spektrum v širokém frekvenčním intervalu a pro velice rozdílné materiály. Cílem mé práce bylo studium dielektrických relaxačních spekter a vodivosti oxidů titanu, niobu, tantalu, lanthanu a hafnia pro katody pracující na principu studené emise. Cílem výzkumu bylo analyzovat frekvenční a teplotní chování těchto oxidů, včetně jejich vodivosti, v širokém frekvenčním a teplotním rozsahu, a pokusit se stanovit původ relaxačního mechanismu. Vzhledem k tomu, že původně zadaný rozsah oxidů byl dosti široký, soustředila se pozornost pouze na oxidy tantalu a niobu, rovněž s ohledem na jejich aplikace v elektrolytických kondenzátorech. Elektrické, tepelné a mechanické (při zpracování) vlastnosti oxidů tantalu a niobu jsou dnes již dobře prozkoumány. K dispozici je však jen málo poznatků o jejich dielektrických relaxačních mechanismech. Výsledky získané pro Ta2O5 ukazují existence relaxačního maxima, nacházejícího se v experimentálně dostupném teplotním a frekvenčním intervalu 187 K – 385 K a 1 Hz – 10 MHz. Frekvence ztrátového maxima se řídí Arrheniovým zákonem s aktivační energií 0.048 eV. Ve vodivostních spektrech vykazují tenké vrstvy Ta2O5 na nízkých frekvencích ustálenou hodnotu a při vysokých frekvencích monotónní nárůst, který závisí na teplotě. Pozorovanou vodivost lze popsat mocninnou funkcí s exponentem nepatrně větším než jedna (tzv. superlineární závislost). Výsledky získané pro Nb2O5 v podobné teplotní a frekvenční oblasti, 218 K – 373 K, 1 Hz – 1 MHz rovněž ukazují jedno relaxační maximum. Frekvence ztrátového maxima se opět řídí Arrheniovým zákonem s poněkud vyšší aktivační energií 0.055 eV. Niobové kondenzátory vykazují vodivostní mechanismus shodný s kondenzátory tantalovými.
40
Zhao, Yiqiang. "Thermodynamic and Dynamic Behaviors of Self-Organizing Polymeric Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1094190642.
Full text
41
Klampár, Marián. "Štúdium nanokompozitov pre elektrické izolácie." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-234443.
Full textAbstract:
The dissertation thesis submitted deals with the study of dielectric properties of epoxy nanocomposites containing nanoparticles of inorganic oxides. These nanocomposites may have a promising technologic application for electric insulations in view of their higher resistance against partial discharges; yet information about their behavior in the course of ageing is not available. If at least a partial mass replacement of the currently used epoxy insulation with nanocomposite-based insulations is due to occur, the knowledge of the changes of their dielectric properties in the course of their operation will become indispensable. Within the framework of this dissertation, ensembles of samples of epoxy resins without fillers and with Al2O3, WO3, TiO2 and SiO2 fillers in the form of nanopowders, in concentrations up to 12 wt %, have been prepared. These ensembles have been measured prior to ageing and exposed to long-time (up to 5000 hours) ageing at increased temperatures 200, 250 and 300 °C and in a few cases also at 330 and 360 °C. Samples were measured in the course of ageing roughly in a logarithmic time series after 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000 and 5000 hours. The measured quantities included complex permittivity , internal resistivity i and loss factor tan at temperatures ranging from -153 °C to +167 °C and in the frequency range 10-2 – 106 Hz. Changes in nanocomposites have been investigated using not just dielectric spectroscopy measurements, but other methods, too, namely Fourier-transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The experiments have proved that materials with different fillers respond to the same concentrations of various fillers in different ways. The addition of nanoparticles, without the addition of microparticles, at a relatively low concentration (max 12 wt %), was not sufficient for reaching fundamental changes in dielectric spectrum; only smaller changes of dielectric strength and shifts of relaxations and in relaxation maps have occurred. Out of more pronounced changes, increase of concentration of the SiO2 filler in the epoxy matrix brings about a decrease of electrical conductivity in the resulting nanocomposite. The TiO2 filler had a different impact. Different TiO2 concentrations make their marked appearance in the region between the relaxation and relaxation. The TiO2-filled nanocomposites do not exhibit the unambiguous dependence of electrical conductivity on nanofiller concentration. It can be concluded that the mere addition of nanoparticles, without the addition of established microparticles, does not change the dielectric spectrum substantially. Generally, a serious problem was the production of the nanocomposite with a uniform distribution of nanoparticles. The preparation of such a nanocomposite was not trivial and, in industrial applications, this issue will require a specific focus, so as to avoid the formation of undesirable aggregates. Within the framework of this research, a methodology for the production of an epoxy nanocomposite has been developed with as high as possible uniformity of nanoparticle distribution.
42
Haddad, Azeddine. "Thermodynamique de la relaxation appliquée à la modélisation du comportement des polymères sous chargements complexes : viscoélasticité en régime dynamique fluage thermostimulé/courants thermostimulés et relaxation diélectrique." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL125N.
Full textAbstract:
Une approche des lois de comportements fondée sur la thermodynamique de la relaxation des milieux continus hors équilibre, est développée au laboratoire pour rendre compte de manière cohérente de la réponse des polymères soumis à des chargements complexes. L’objectif de ce travail est d'utiliser cet outil général pour modéliser la viscoélasticité en régime dynamique, le fluage thermostimulé, les courants thermostimulés et les relaxations diélectriques. Dans chaque application, l'analyse du modèle et les simulations qualitatives conduites confirment sa capacité prédictive et sa cohérence avec les principaux faits expérimentaux observés dans les polymères. La dépendance en fréquence ou en température des modules dynamiques, l'introduction de relaxations secondaires sans avoir recours à de multiples spectres de relaxation, les premières pistes élaborées pour l'identification des paramètres sont les grands axes étudiés dans la partie viscoélasticité dynamique. La température de compensation définie pour les expériences FTS trouve ici une interprétation en terme de thermodynamique de la relaxation
43
au, A. Tromans@chem murdoch edu, and Andrew John Tromans. "Solution Chemistry of some Dicarboxylate Salts of Relevance to the Bayer Process." Murdoch University, 2001. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040730.140604.
Full textAbstract:
This thesis deals with certain aspects of the solution chemistry of the simple dicarboxylate anions: oxalate, malonate and succinate, up to high concentrations. These ions are either significant impurities in the concentrated alkaline aluminate solutions used in the Bayer process for the purification of alumina, or are useful models for degraded organic matter in industrial Bayer liquors. Such impurities are known to have important effects on the operation of the Bayer process.
To develop a better understanding of the speciation of oxalate (the major organic impurity in Bayer liquors) in concentrated electrolyte solutions, the formation constant (Log£]) of the extremely weak ion pair formed between sodium (Na+) and oxalate (Ox2{) ions was determined at 25 oC as a function if ionic strength in TMACl media by titration using a Na+ ion selective electrode. Attempts to measure this constant in CsCl media were unsuccessful probably because of competition for Ox2{ by Cs+.
Aqueous solutions of sodium malonate (Na2Mal) and sodium succinate (Na2Suc) were studied up to high (saturation) concentrations at 25 oC by dielectric relaxation spectroscopy (DRS) over the approximate frequency range 0.1 T £h/GHz T 89. To complement a previous study of Na2Ox, formation constants of the Na+-dicarboxylate ion pairs were determined and they were shown to be of the solvent-shared type. Both the Mal2{ and Suc2{ ions, in contrast to Ox2{, were also shown to possess large secondary hydration shells
Apparent molal volumes (Vf) and heat capacities at constant pressure (Cpf) of aqueous solutions of Na2Ox, Na2Suc, Na2Mal and K2Ox were determined at 25 oC up to their saturation limits using vibrating tube densitometry and flow calorimetry. These data were fitted using a Pitzer model. The adherence of Vf and Cpf of various Na+ and K+ salts to Young¡¦s rule was examined up to high concentrations using the present and literature data. Young¡¦s rule was then used to estimate hypothetical values of Cpf and Vf for the sparingly soluble Na2Ox at high ionic strengths, which are required for the thermodynamic modelling of Bayer liquors.
The solubility of Na2Ox in various concentrated electrolytes was measured, at temperatures from 25 oC to 70 oC in media both with (NaCl, NaClO4, NaOH) and without a common ion (KCl, CsCl, TMACl). The common ion effect was found to dominate the solubility of Na2Ox. The solubility of calcium oxalate monohydrate (CaOxªH2O) was also determined. The solubilities of both Na2Ox and CaOxªH2O in media without a common ion increased with increasing electrolyte concentration, except in TMACl media, where they decreased.
The solubility of Na2Ox was modelled using a Pitzer model assuming the Pitzer parameters for Na2SO4 and minimising the free energy of the system. The data were modelled successfully over the full concentration and temperature range of all the electrolytes, including ternary (mixed electrolyte) solutions.
44
Carvalho, Tânia Isabel da Silva. "Development of ion jelly thin films for electrochemical devices." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/10874.
Full textAbstract:
Dissertação para obtenção do Grau de Doutor em Química SustentávelIonic 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.
45
Paščinský, Jiří. "Vliv parametrů vytvrzování na vlastnosti elektroizolačních laků." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219047.
Full textAbstract:
The bachelor thesis submitted deals with properties of electro-insulating lacquer hardenable by ultraviolent radiation and temperature. Within the theoretical part a summary of electro-insulating lacquers used in electrotechnics has been elaborated. Chemical changes that take place in this material group have been described during hardening process. A method of dielectric relaxation spectroscopy specifically focused on mathematic and physical description of polarisation and conductive mechanisms taking place in the structure of the given material has been closely studied. In the experimental part a workplace for hardening and long-term exposition of lacquered samples during simultaneous effect of various climatic elements has been designed and built. The selected electric and mechanical properties have been monitored on three sets of experimental samples prepared by means of different methodical procedures. The results gained have been mathematically evaluated and physically interpreted in term of methodical procedure of hardening and different temperature of measurement.
46
Bao, Congyu. "Cellulose acetate / plasticizer systems : structure, morphology and dynamics." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10049/document.
Full textAbstract:
Les polysaccharides sont l'une des principales options à retenir pour progresser dans l'utilisation ou la conception de polymères renouvelables. Depuis les années cinquante, le développement industriel de ce type de polymères s'était considérablement réduit du fait de l'avènement des polymères synthétiques. Cependant, cet intérêt a cru considérablement ces dernières années en raison de la sensibilisation du public sur la limite des ressources fossiles. Ces biopolymères sont donc devenus un sujet d'importance, tant sur le plan industriel que sur celui de la recherche fondamentale. Toutefois, les systèmes à base de polysaccharides sont le plus souvent transformés via l'utilisation d'importantes quantités de solvants (y compris l'eau), ce qui globalement pénalise le procédé associé en l'affligeant d'une charge environnementale supplémentaire. Par la voie ‘fondue', le développement de polymères thermoplastiques à base de dérivés de la cellulose est un véritable défi, qui concerne autant le mode de transformation de ces systèmes que le niveau des propriétés du matériau final. Pour exemple, la température de dégradation de l'acétate de cellulose (CA) (dont le degré de substitution 2,5 est développé par le Groupe Solvay) est si proche de sa température de fusion que son procédé de mise en oeuvre ne peut être envisagé qu'avec l'ajout d'une quantité importante de plastifiants externes (entre 20 et 30 en poids selon le type d'additif). Le comportement d'un mélange CA-plastifiant est principalement régi par un «réseau» de très fortes interactions polaires, dont la force et la densité dépendent de 3 paramètres spécifiques: le degré de substitution de CA, la typologie de plastifiant et la quantité de plastifiant. Pour expliquer les différents mécanismes de plastification, il est donc important pour nous d'étudier et de comprendre les propriétés dynamiques (en ce qui concerne les phénomènes de relaxation) de ce type de systèmes et comment les trois leviers que nous avons identifiés peuvent influencer ou moduler les différentes interactions échangées dans les mélangesPolysaccharides are one of the main options to the on-going move towards the use of renewable polymers. The industrial interest in this type of polymers drastically shrunk by the advent of synthetic polymers in the fifties, but is currently reviving due to the public awareness on the limit of fossil resources. These biopolymers are nowadays offering a challenging and industrially profitable playground for researchers. However, current polysaccharides based materials are mostly processed with extensive use of solvents (including water) making the total process an environmental burden despite the advantage of the starting material. Development of thermoplastic cellulose-based materials is very challenging regarding both final material properties and polymer processing. The degradation temperature of Cellulose Acetate (CA) (degree of substitution 2.5) is so close to its melting temperature that it can only be processed with a significant amount of external plasticizers (between 20 et 30 wt.% depending on the type of the additive). Behavior of a CA-plasticizer blend is mainly governed by a ‘network’ of high polar interactions, the strength and the density of which clearly depend of 3 specific parameters: the CA’s degree of substitution, the typology of the plasticizer, the amount of plasticizer. In an attempt to explain the different plasticization mechanisms, it is thus of utmost importance for us to study and understand the dynamic properties (regarding the relaxation phenomena) of this kind of systems and how the three levers that we identified can influence or modulate the different interactions exchanged within the blends
47
Badot, Jean-Claude. "Relaxations dielectriques (1 khz-10 ghz) dans les conducteurs protoniques et les materiaux hydrates." Paris 6, 1988. http://www.theses.fr/1988PA066035.
Full textAbstract:
Les premiers resultats experimentaux concernant les proprietes dielectriques, dans une large bande de frequences (10**(3)-10**(10)hz), des conducteurs protoniques sont presentes entre 190 k et 420 k. Des relaxations dielectriques ont ete observees et attribuees aux processus de reorientation des especes protonees et aux sauts d'ions. Les relations entre relaxation dipolaire, transitions de phases et conductivite protonique sont discutees
48
Atawa, Bienvenu. "Mobilité moléculaire et vieillissement physique des composés amorphes chiraux." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMR125/document.
Full textAbstract:
Dans le cadre de cette thèse, nous avons réalisé l’étude de systèmes amorphes moléculaires chiraux en évaluant leur vieillissement, leur mobilité ainsi que leur capacité à recristalliser en fonction de la composition énantiomérique du matériau. Pour limiter les facteurs additionnels à la chiralité, ce travail s’est concentré sur des systèmes modèles formant des conglomérats stables : N-acetyl-α-methylbenzylamine (Nac-MBA) et 5-ethyl-5-methylhydantoin (12H). De ces travaux il ressort que l’impact le plus spectaculaire de la chiralité est exprimé dans la propension à la cristallisation ou l’habilité à former un verre (qui augmente de façon inversement proportionnelle de l’excès enantiomérique (ee)). Les cinétiques de vieillissement sont implicitement impactées par l’ee : Celles-ci sont plus lentes pour les ee importants. Enfin, il semble que les processus de relaxation ainsi que les temps associés soient identiques quelle que soit l’ee, bien que le comportement à la cristallisation soit lui significativement impacté. A noter que la signature la plus manifeste de la chiralité dans l’état amorphe du Nac-MBA s’exprime dans l’intensité diélectrique des processus D et αIn the framework of this thesis, we carried out the study of amorphous chiral molecular systems by evaluating their molecular mobility, the evolution of physical properties during aging and the recrystallization behavior as function of the initial enantiomeric excess (ee). In order to avoid factors additional to chirality itself, we focused on enantiomeric systems forming stable conglomerates (full chiral discrimination in the solid state) by choosing two model compounds: 5-ethy-5-methylhydantoin (12H) and N-acetyl-α-methylbenzylamine (Nac-MBA). From this thesis it was shown that the most spectacular effects of chirality in the amorphous state is expressed in the GFA or the crystallization propensity. The GFA increases as the ee decreases. The kinetics of physical aging is implicitly impacted by chirality. Glassy pure enantiomer requires more time to reach equilibrium than that of an intermediate composition. This situation is hypothetically due to constraints effects mostly resulting from a strong nucleation behavior in the glass state at high ee. Furthermore, the time scale of all the processes (D, α, βJG, γ) and the evolution of their temperature dependency are approximatively identical even though the crystallization behavior is highly impacted by ee. it seems that molecular mobility would not be a key parameter in the crystallization behavior of Nac-MBA. The main expression of chirality in amorphous Nac-MBA is evidenced in the signature of the dielectric strength of both D and α processes
49
Castrovilli, Matteo. "Characterization of the dipole processes of insulating materials used in aeronautical cables." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Find full textAbstract:
The studies of this thesis are focused on aeronautic Polymers materials and their dielectric properties, in order to analyze the relaxation times for the materials of interest under an applied electric field, and in order to increase the work operations of the Novocontrol dielectric spectroscopy measurement machine available in the LAPLACE laboratory. In this context, the research team DSF in collaboration with MDCE, from LAPLACE laboratory, has developed in 2019 a numerical model taking into account the polar mechanisms of the polymer insulators used in the aeronautic industry. However, this theoretical model, is not yet validated. Therefore the aim of this thesis, is to make it possible to validate this theoretical model, then by a series of measurements with dielectric spectroscopy(D.S.) for different materials of interest, different frequencies and temperatures; the measurements consist on the measuration of the phase difference between current and voltage applied to the samples, in order to calculate the permittivity values under different working conditions. The permittivity trend is therefore analyzed to find the polar relaxation under thermoelectrical stresses, and the model will then have to calculate the current density (and from the current density is directly calculated the dissipated energy) of the measured data with dielectry spectroscopy, and the validation will be done if the future measurement values of the current density correspond to the calculated one by the model. For this reasons, the main part of the work for this thesis consist in measurements trought the dielectric spectroscopy (using the following polar materials: Polyimide(PI) and PTFE ) under different working conditions and analyze the results in order to evidence polarization phenomena, because the purpose of this part of the validation process is to have the better polar relaxation data for the future work.
50
Kamenická, Zuzana. "Nejistoty měření v diagnostice izolačních materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-217948.
Full textAbstract:
This work deals with measurement capacity and dissipation factor of capacitor with real dielectric in frequency range 20 Hz to 30 MHz. Liquid and solid dielectrics are measured by LCR instruments and by test fixtures, both from company Agilent. Relative permittivity and loss number are calculated for different instruments settings. The general aim is to specify the influence of parameters as frequency, voltage, integration time and thickness of material on the uncertainties of primary and secondary quantities for measurement.