Les matériaux moléculaires vitrifiables présentent généralement des mobilités complexes incluant plusieurs relaxations non-exponentielles (non - Debye) comme le montre la spectroscopie de relaxation diélectrique. Une relaxation de type Debye est cependant observée dans plusieurs alcools primaires et amides et se caractérise par une contribution basse fréquence de très grande amplitude et de forme symétrique. Celle-ci demeure encore très mal comprise car elle correspond à environ 90% de la réponse diélectrique et ne semble pourtant pas couplé à la viscosité η(ω) ou la chaleur spécifique complexe C(ω). Ce type de relaxation Debye très particulière a été récemment identifié dans plusieurs composés pharmaceutiques de la famille des profènes.Au moyen de simulations de dynamique moléculaire, nous avons mené des investigations des propriétés physiques de trois composés moléculaires de la famille des profènes (ibuprofène, flurbiprofène et kétoprofène) dans l’état liquide afin d’analyser leurs organisations, leurs mobilités moléculaires et clarifier l’origine de la relaxation Debye. Nous avons montré que le processus Debye observé expérimentalement provient de mouvements extrêment lents des groupes carboxyliques très polaires dans des environnements moléculaires relaxant rapidement : une conversion interne des groupes O=C-O-H entre deux conformations d’équilibre couplée aux transformations du réseau de liaisons hydrogènes intermoléculaires. L’organisation dominante dans le liquide se trouve être composée de petits agrégats correspondant à des associations en dimères cycliques précurseurs de l’ordre cristallin. L’influence d’une situation de confinement sur les mobilités moléculaires a aussi été explorée en lien avec des études récentes de spectroscopie diélectrique. / Molecular glass-formers usually exhibit complex mobility including multiple non-simple exponential (non-Debye) relaxation processes as observed from dielectric relaxation spectroscopy. However, a Debye relaxation type is observed in several primary alcohols and amides, and is characterized by a low frequency contribution of very large amplitude and symmetrical shape. It is still very poorly understood because it is about 90% of the dielectric response and seems not yet coupled to the viscosity η (ω) or the complex specific heat C (ω). This very peculiar Debye relaxation has been recently identified in several pharmaceutical compounds of the profens family. By means of molecular dynamics simulations, we have conducted an investigation of physical properties of the three molecular compounds of the profens family (ibuprofen, flurbiprofen and ketoprofen) in the liquid state in order to analyze their organizations, their molecular mobilities and to clarify the origin of the Debye relaxation. We have shown that the Debye process observed experimentally originates extremely slow movements of very polar carboxyl groups in the molecular environments with rapidly relaxing: an internal conversion of the O=C-O-H groups between two conformations of equilibrium coupled to changes of the network of intermolecular hydrogen bonding. The dominant organization in the liquid is found to be composed of small hydrogen bonding aggregates corresponding to associations in cyclic dimers precursors of the crystalline order. The influence of a situation of confinement on molecular mobility has also been explored in relation with of the recent studies of dielectric spectroscopy.

Dans ce travail, on s'intéresse à l'étude mathématique des phénomènes de charge des satellites dans les orbites basses (Low Earth Orbit, LEO).Aprės un rappel du contexte physique, nous dérivons un modėle de type bi-fluide pour le plasma entourant le satellite. En effet, en orbite LEO, le plasma peut être considéré fortement collisionnel comparativement au cas par exemple des orbites polaires ( Polar Earth Orbit, PEO). Le modėle utilisé est composé des équations d'Euler pour la conservation de la masse, de la quantité de mouvement et de l'énergie ainsi que de l'équation de Poisson pour le potentiel électrostatique et est obtenu dans le cas tri-dimensionnel.Pour l'étude mathématique du modėle nous nous concentrons sur le cas uni-dimensionnel afin de mettre en évidence les principales difficultés.Nous considérons d'abord les équations d'Euler stationnaires couplées à l'équation de Poisson. La dynamique de charge du satellite est alors contenue dans les conditions limites qui font apparaître la dérivée en temps du potentiel. Nous donnons des résultats d'existence et d'unicité de solution ainsi que des simulations numériques. Ici nous utilisons uniquement des conditions limites de Dirichlet pour les quantités macroscopiques. Elles peuvent être loin de celles qui sont physiquement intéressantes et que nous ne connaissons qu'au niveau microscopique.C'est pourquoi, nous proposons ensuite une solution numérique permettant d'utiliser dans la simulation des équations évolutives d'Euler des conditions limites venant d'une modélisation microscopique au travers d'un régime où le libre parcours moyen est petit. La condition limite vient d'une analyse de couche limite qui s'explique par le fait que le flux cinétique peut être loin de l'équilibre thermodynamique. / In this work we are concerned with a mathematical study of the spacecraft charging phenomena of Low Earth Orbit (LEO).After recalling the physical context, we derive a two-fluid type model for the plasma around the spacecraft. Indeed in LEO, the plasma can be considered highly colisional compared with the case for example of Polar Earth Orbit (PEO). The model used here consist in the Euler equations for the conservation of mass, momentum and energy plus a Poisson equation for the electrostatic potentiel and is derived in the three dimensionnal case.For the mathematical study of the model, we concentrate our attention on the one dimensionnal case to point out the main difficulties.We first consider the stationnary Euler equations coupled to the Poisson equation. The charging dynamics is then embodied into the boundary conditions where the time derivative of the potentiel appears. We present rigourous existence and unicity results together with numerical simulations. Here we only use some Dirichlet boundary conditions for the macroscopic quantities. They can be far from the ones of physical interest wich we only know at a kinetic level.That's why we next propose a numerical solution to incorporate in the simulation of the evolutive Euler equations boundary condition that come from a microscopic modeling in the small mean free path regime. THe boundary condition relies on the analysis of boundary layers formation that accounts from the fact that the incoming kinetic flux might be far from the equilibrium.

Nanosecond pulse electroporation of biological cells is gaining significant interest due to its ability to influence intracellular structures. In nanosecond pulse electroporation of biological cells nanosecond duration pulses with high frequency spectral content are applied to the cell. In this research we show that accurate modeling of the nanosecond pulse electroporation process requires considering the effect of the membrane dielectric relaxation on the electric potential across the membrane. We describe the dielectric relaxation of the membrane as dispersion in the time-domain and incorporate it into the nonlinear asymptotic model of electroporation. Our nonlinear dispersive model of a biological cell is solved using finite element method in 3-D space enabling arbitrary cell structures and internal organelles to be modeled. The simulation results demonstrate two essential differences between dispersive and non-dispersive membrane models: the process of electroporation occurs faster when the membrane dispersion is considered, and the minimum required electric field to electroporate the cell is significantly reduced for the dispersive model.

Nanosecond pulse electroporation of biological cells is gaining significant interest due to its ability to influence intracellular structures. In nanosecond pulse electroporation of biological cells nanosecond duration pulses with high frequency spectral content are applied to the cell. In this research we show that accurate modeling of the nanosecond pulse electroporation process requires considering the effect of the membrane dielectric relaxation on the electric potential across the membrane. We describe the dielectric relaxation of the membrane as dispersion in the time-domain and incorporate it into the nonlinear asymptotic model of electroporation. Our nonlinear dispersive model of a biological cell is solved using finite element method in 3-D space enabling arbitrary cell structures and internal organelles to be modeled. The simulation results demonstrate two essential differences between dispersive and non-dispersive membrane models: the process of electroporation occurs faster when the membrane dispersion is considered, and the minimum required electric field to electroporate the cell is significantly reduced for the dispersive model.

Pure intermetallic compounds Al3Fe, AlmFe, AlxFe, ac-AlFeSi, and Al6(Fe,Mn) have been extracted from Bridgman grown model aluminium alloys by dissolving the aluminium matrix in butanol. The resultant transmission Mdssbauer spectra for each intermetallic compound were interpreted according to their crystal structure. Variable temperature 57Fe Mdssbauer studies have enabled the Debye temperature thetaD of each compound to be determined. The crystal structure of Al3Fe contains five different Fe sites within the unit cell. Four of the iron, Fe(l)-Fe(4), sites are approximately identical and produced a thetaD = 434 +/- 5 K. The remaining Fe site, Fe(5), produced a thetaD = 488 +/- 5 K, and the combined spectral areas a 3D = 452 +/- 5 K. There is only one individual site within the crystal structures of AlmFe, AlxFe, and Al6(Fe,Mn), which produced a thetaD of 358 +/- 5 K, 360 +/- 5 K, and 352 +/- 5 K respectively. The ternary intermetallic compound, ac-AlFeSi, has two different Fe sites within the unit cell. Fe(l) had a thetaD - 291 +/- 5 K, and Fe(2) thetaD = 329 +/- 5 K. The combined spectral areas of these two sites produced a thetaD = 311 +/- 5 K. The variation in the OD values was attributed to changes in the Al-Fe shortest bond within the Fe centred A1 polyhedra. The Fe centred A1 polyhedra are a common feature of all the intermetallic compounds studied. The iron atom in all the intermetallic compounds may have existed in a Fe2+ oxidation state. A Direct Chill-cast ingot was grown and two samples, A and B, were taken from regions within the ingot containing a mixture of two intermetallic compounds. Alloy sample A was found to contain the intermetallic compound combination Al3Fe + Al6Fe. The intermetallic combination Al6Fe + ac- AlFeSi was found to exist in alloy sample B. Transmission Mdssbauer spectroscopy was performed on the extracted phases and the insitu phases to determine the relative proportions of the intermetallic compounds within the two alloy samples. Alloy sample A had 50:50 +/- 5 % Al3Fe + Al6Fe, whereas alloy sample B had 30:70 +/- 5 % Al6Fe + ac-AlFeSi. The surface of alloy sample B was investigated using several surface techniques, CEMS, SAAES, and SAXPS, to determine whether the same relative proportions existed in the surface, and near surface, regions of the sample. A region of very fine amorphous iron super-paramagnetic grains were to dominate the near surface region of the sample, which was present due to selective oxidation of the Al6Fe intermetallic compound. This was then removed when the surface of the alloy sample was KI electro-etched, which had the effect of leaving the intermetallic particles standing proud of the surface. The CEMS technique identified that the Al6Fe + ac-AlFeSi existed in a 80:20 +/- 5 %. This change in phase ratio after the KI electro-etch process was attributed to the preferential etching of the ac-AlFeSi aluminium intermetallic compound.

I have used the Embedded Atom Method (EAM) to investigate the vibrational behaviors of a large number of metallic systems. The systems examined are the bulk bcc metals Li, Na, K, Rb, Cs, Nb, Ta, Mo, W, and Fe, the bulk fcc metals Ni, Cu, and Al, the (100), (110), (111), and (211) surfaces of the Li, Na, K, Rb, and Cs, and the (100), (110), and (111) surfaces of Ni and Cu. I have conducted a more detailed and extensive review of existing EAM models and their ability to characterize bulk vibrational behavior than has ever previously been reported. I show the ability of an EAM model to quantitatively predict the vibrational properties of the bulk alkali metals in excellent agreement with experiment. The present work remedies a lack of computational investigation into bcc metallic surfaces by performing lattice dynamics calculations of the (110), (100), (111), and (211) alkali metal surfaces. Additionally, I present lattice dynamics calculations on the (111), (100), and (110) surfaces of Cu and Ni. An accurate set of surface Debye temperatures for these metal surfaces has been calculated. The extensive number of metals and planar geometries studied has enabled the identification and clarification of general relationships between surface phonons, surface coordination, and atomic density. The changes in vibrational behavior due to the truncation of the bulk near a surface can be understood by the consideration of three things: the vibrational behavior of a 1-D chain of harmonic oscillators, the bulk dispersion relation in the direction perpendicular to a surface, and the atomic coordination of near surface atoms. In general, relaxation causes force constants between atoms to stiffen, resulting in higher vibrational frequencies. The impact of stiffening on the vibrational characteristics depends largely on the surface geometry, as well as the particular properties of the metal. It can cause new surface modes and resonances, or cause surface vibrations to be more strongly coupled to the vibrations of bulk atoms.

No description available.

This thesis describes direct measurements of equilibrium adsorption of ions in thin (< 100 nm) aqueous films. Adsorption in thin films is important because it is through adsorption that the stability of colloidal suspensions is frequently tuned. The vast majority of measurements of adsorption to date have been to a single interfaces, whereas the subject of this thesis is adsorption in a thin film between two interfaces. There are two isolated interfaces when particles in a suspension are far apart, but during the collision, a thin film forms between the particles, and the properties of the thin film determines the stability of the colloid. Thus, adsorption in the thin film determines the stability of the colloidal dispersion. There is a distinct gap in the scientific literature concerning adsorption in thin films mainly because there is no technique for measuring such adsorption. To fill this gap in knowledge, I first developed of a technique to directly measure adsorption in thin films, and then applied this technique to explore the behavior of co-ions near charged interfaces as a function of bulk solution composition and the thickness of the film. The adsorption behavior of fluorescein, a di-anion, to negatively charged silica interfaces was studied in dilute electrolytes. The focus was on the effect of the electrostatic screening length, or Debye-length. The separation was measured using interference microscopy and the adsorption of fluorescein was measured using fluorescence microscopy. The Debye-length was altered by variation of the background salt (NaCl) concentration in dilute (<1 M) solution. The surface excess of adsorption for fluorescein was shown to depend on both the Debye-length and the separation distance between two interfaces. Increasing the Debye-length from 4 nm to 21 nm increased the plateau surface excess at large separations, and decreasing the separation lead to a monotonically decreasing surface excess. The surface excess varied over a range that scaled with the Debye-length. The results were compared to solution of the Poisson-Boltzmann model and good agreement was found between the model and the experiment. The effect of background salt concentration on fluorescein adsorption was also studied in concentrated electrolytes (2.5 – 10 M) for various monovalent salts (LiCl, NaCl and CsCl). The results showed that the fitted electrostatic screening length showed an opposite trend to predictions from Poisson-Boltzmann, with the screening-length increasing with increasing salt concentration. That is, the Debye-length prediction was quantitatively incorrect and predicts the incorrect trend. For example, in 10 M LiCl where the Debye-length is 0.1 nm, and therefore colloidal chemists would traditionally predict that double-layer forces are negligible, my results show that the actual decay length is about 10 nm, which is about the same as in 10-3 M LiCl solution. The rate of increase of screening-length as a function of concentration was also an ion specific effect. In addition, the results show that there is an inversion of the surface charge in concentrated salt solution. The original device on which all the above measurements were made had two limitations: (1) the maximum film thickness was 50 nm and (2) the film was asymmetric, which hampered calculation of the surface excess and increased the number of degrees of freedom in modeling of the adsorption. In the last part of my thesis, I describe development of a symmetric sample which (1) enables measurement of films up to 1 µm, (2) simplifies modeling of the optics by eliminating optical interference of the fluorescence excitation, and reduces the number of parameters when comparing to models. / Doctor of Philosophy / This thesis aims to understand the behavior of electrically charged molecules and atoms in thin nanometer scale (< 100 nm) liquid films subject to confinement between two charged interfaces. This situation frequently arises in colloidal suspensions, which consist of tiny sub-microscopic particles (colloid), droplets and large molecules dispersed in a second continuous medium. The stability of these suspensions, i.e. whether the colloidal materials agglomerate and sediment out of the suspension or remain stably suspended, depends on the surface forces between their interfaces during collision events, which frequently arise due to Brownian motion. As the fluid between particles thins as they approach each other during these collision events, the behavior of the dissolved molecules can be significantly different than when they are far apart due to the presence two interacting interfaces. Typically the dissolved molecules are used to tune the surface forces and understanding their behavior in confinement is relevant to a colloid scientist whose aim is to tune the behavior of the suspension. In the first part of this work, a technique is developed that serves as the static analogue to colloidal objects colliding with each other. The equilibrium behavior of a negatively charged fluorescent ion is measured as a function of film thickness and background salt concentration between two negatively charged interfaces. The Poisson-Boltzmann model predicts that with decreased salt concentration, there is a greater magnitude of depletion of the fluorescent ion at large separations and the characteristic length over which there is a change in the magnitude of depletion increases. Good agreement is found between the model and the experiment validating the technique developed and providing the first direct observation of molecular behavior subject to confinement as a function of solution composition. This effect of background salt type and concentration was tested for concentrated electrolytes as well. The experimental results showed an opposite trend to predictions from the Poisson-Boltzmann model. The fluorescent ion was now adsorbed to negatively charged interfaces indicating that the negatively charged interfaces were now positively charged. The magnitude of adsorption at large separations and characteristic length over which the magnitude of adsorption changes was a function of the salt concentration and the ion type. Finally, improvements were made to the original device to overcome limitations with the original device. The limitations were that (1) the maximum film thickness was 50 nm and (2) the interfaces were asymmetric which complicated theoretical calculations of the equilibrium behavior of the ions. In the last part of my thesis, I develop a sample which (1) enables measurements of films up to 1 µm and (2) simplifies the optical modeling necessary in the first two sections of this thesis.

O presente estudo versa sobre a proposição ou extensão de modelos simples para descrever os seguintes fenômenos envolvendo agregados anfifílicos: i-) Influência de sal na concentração micelar crítica (CMC) e número médio de agregação () de micelas zwitteriônicas. ii-) Influência da interação eletrostática (neste caso, repulsiva) e tamanho de \"domínios\" nas isotermas de monocamadas iônicas insolúveis. iii-) Influência do tamanho e polaridade do \"pool\" aquoso de micelas reversas de AOT na reprotonação de sondas fotoácidas aniônicas. Em i-), foi assumido o formalismo termo-molecular para a energia livre de micelização, necessária nas estimativas da CMC e . A energia livre de micelização foi descrita como aditiva, com termos descrevendo a interação interfacial do agregado com o solvente (no caso, água), a repulsão estérica entre as \"cabeças\" do detergente, empacotamento das \"caudas\" e interação dipolar entre os \"zwitterions\". Embora nos formalismos termo-moleculares convencionais, micelas zwitteriônicas não sejam afetadas por eletrólitos, dados experimentais de supressão de fluorescência, salto de pH com sondas fotoácidas, espalhamento de luz dinâmico e estático e condutividade indicam que micelas zwitteriônicas \"ligam\" íons e \"ligam\" seletivamente. A ligação iônica pode ser tratada como um processo de absorção ou adsorção e muda a interação eletrostática das \"cabeças\". Assim, o formalismo termo-molecular foi estendido para incluir as propriedades elétricas de um capacitor com a casca externa permeável aos íons como modelo de micela zwitteriônica. Em ii-), uma nova expansão para potenciais repulsivos (chamada de expansão y) foi aplicada ao problema da interação entre detergentes iônicos em monocamadas insolúveis e comparada com a expansão virial. A interfase foi modelada como uma mistura de pseudo-fluidos bidimensionais, no nível de descrição de McMillan-Mayer (onde o solvente não aparece explicitamente, ou seja, a pressão calculada é uma pressão osmótica). A interação intermolecular na interfase foi considerada como a soma de um potencial de curto alcance (disco rígido) e um termo de longo alcance (potencial de campo médio). Na transição entre as fases líquido-condensada e líquido-expandida, a pressão do sistema é descrita por uma interpolação entre dois subsistemas na mesma densidade superficial. Finalmente em iii-), um modelo para reprotonação de uma sonda fotoácida residindo no pool aquoso de micelas reversas de AOT foi desenvolvido. A sonda (8-hidroxi-1,3,6-pirenotrisulfonato) foi tratada como uma partícula esférica posicionada no centro de um poro esférico (\"pool\" da micela reversa). A constante de reprotonação no poro foi calculada via equação de Debye-Smoluchowski junto com o potencial de força média calculado segundo a equação de Poisson-Boltzmann. O efeito da constante dielétrica aparente na reprotonação foi explorado. / The present work focus on the proposition or extension of simple models to describe the following phenomena involving amphiphile self-association aggregates: i-) Salt influence on the critical micelle concentration (CMC) and on the averaged association number () of zwitterionic micelles. ii-) Influence of the electrostatic interaction (repulsive, in this case) and of the domain size in the isotherms for ionic insoluble monolayers. iii-) Effect of size and polarity of the aqueous pool of AOT reverse micelles in the reprotonation of anionic photoacid probes. For i-), the thermo-molecular formalism for the micellization free energy, necessary for the estimate of the CMC and was assumed. The micellization free energy was described by the addition of the following terms: the interfacial interaction of the aggregate with the solvent (water, in this situation), the steric repulsion among the surfactant headgroups, the packing of the hydrocarbon tails, and the dipolar interaction among the headgroup dipoles. Although in the conventional thermo-molecular formalism zwitterionic micelles are not affected by electrolytes, experimental data including fluorescence quenching, próton jump of photoacid probes, static and dynamic light scattering, and conductivity demonstrate that these aggregates bind ions and bind selectively. The ionic binding can be treated as an absorption or adsorption process and change the electrostatic interaction among the headgroup. Thus, the thermo-molecular formalism was extended to include the electrical properties of a capacitor having the external shell permeable to ions as model of zwitterionic micelles. For ii-), a new expansion for the repulsive potentials (called y expansion) was applied to the problem of the interaction between surfactants in an insoluble monolayer and compared with the virial expression. The interface was modeled as a mixture of two-dimensional pseudo-fluids in McMillan-Mayer description level where the solvent does not appears explicitly, that is the calculated pressure is an osmotic pressure. The interfacial intermolecular interaction was considered as the sum of a short-range potential (hard disc) and a long-range term (mean field potential). In the condensed liquid and expanded liquid transition, the surface pressure can be described by an interpolation between two subsystems at the same surface density. Finally in iii-), a recombination model for a photoacid probe residing in the aqueous core of AOT reverse micelles was developed. The probe (8-hidroxi-1,3,6-pyrenetrisulfonate) treated as a spherical particle was positioned in the center of a spherical pore (micelle aqueous pool). The reprotonation was calculated by the Debye-Smoluchowski equation added to the potential of mean force derived from the Poisson-Boltzmann equation. The effect of the apparent dielectric constant in the reprotonation was explored.

<p>Izmereni su Stark-ovi pomeraji maksimuma 8 spektralnih linija neutralnog helijuma u gustoj niskotemperaturnoj plazmi impulsnog luka. Osobine izvora plazme, sem postizanja visoke elektronske koncentracije, obezbeđuju relativno jednostavan način određivanja Stark-ovog pomeraja. Izvr&scaron;ena je dijagnostika plazme, pri čemu je određena elektronska koncentracija u intervalu od (6.2 &minus; 70) &middot; 10²² m^&minus;3 i elektronska temperatura u intervalu (16400 &minus; 21400) K. Eksperimenatlne vrednosti Stark-ovih pomeraja upoređene su sa do sada objavljenim eksperimentalnim rezultatima kao i sa rezultatima teorijskih pristupa. Proveren je uticaj Debye-evog ekraniranja na pomeraj ovih linija. Dobijeni rezultati ukazuju na popravku Stark-ovog pomeraja uračunavanjem<br />uticaja Debye-evog ekraniranja, kao i potrebu korigovanja semiklasičnih teorijskih vrednosti elektronske sudarne polu-polu&scaron;irine i pomeraja.</p> / <p>The results of an experimental study of the Stark shifts AB of 8 neutral helium lines are presented. The plasma sour-ce was a linear pulsed arc with plasma electron&nbsp; density in the range (6.2 &minus; 70) &middot; 10 ²² m^&minus;3 and plasma temperature in the range (16400 &minus; 21400) K. Details of the experimental setup that enables a relatively quick&nbsp; Stark shift determination technique is presented. The results of these measurements are presented together with the corresponding plasma parameters and compared to other experimental and theoretical data. The influence of Debye shielding is carefully examined from the semiclassical point of view. The comparison of experimental&nbsp; results obtained in this work with the semiclassical results suggests that Debye shielding has an important role on higher electron densities. Also, based on all the available experimental data, appropriate correction factors are suggested for the semiclassical Stark shift calculations for the examined lines.</p>