Segmental chain dynamics in polymer blends is a very important topic, not only from a fundamental point of view but also from technological applications. Because of the difficulties in the commercialization of new polymers, industries have turned increasingly towards blending of polymers to optimise their end use (mechanical, rheological) properties. The design of tailor-made materials would be enormously facilitated by the understanding of the blending phenomena at a molecular level. The key question to address is to understand the dynamics of each component of the blend modified by blending? The thesis has systematically studied the effect of multiwalled carbon nanotubes on the chain dynamics, demixing temperature, structural properties and evolution of morphology in a classical miscible polymer blend system (PVDF/PMMA). The thesis comprises of six chapters, Chapter 1 is an introductory chapter that outlines the fundamentals of polymer blends, crystallisation in polymer blends and the basics of dielectric spectroscopy. As one of the rationales of this work is to systematic study whether phase separated in these blends can be used as a tool to develop membrane for water purification. This chapter also gives an overview of the reported studies of ultrafiltration membrane fabrication, factors affecting membrane morphology and flux. In Chapter 2, the materials and methodology used to carry out experiments and the experimental procedures are discussed. Chapter 3 discusses the effect of concentration of PMMA and amine functionalized multiwalled carbon nanotubes (MWNTs) on the crystallisation induced phase separation using FTIR, XRD, POM and shear rheology. Electron microscopy and selective etching confirmed the localisation of MWNTs in the PVDF phase of the blends. Blends with MWNTs facilitated in heterogeneous nucleation manifesting in an increase in crystallisation temperature. The crystallisation induced phase separation in PVDF/PMMA blends was observed to influence the interconnected network of MWNTs in the blends. Chapter 4 discuss the effect of concentration of PMMA and MWNTs on the miscibility and the segmental relaxations was probed in situ by DSC and dielectric relaxation spectroscopy (DRS). The dynamic heterogeneity in the blends as manifested by the presence of an extra relaxation at a higher frequency at or below the crystallisation induced phase separation temperature was also discussed. We found that PVDF/PMMA blend (PVDF ≥ 80 wt%) exhibits three distinct relaxations; αc corresponding to crystalline PVDF, αβ segmental relaxation of PMMA and αm of amorphous miscibility whereas all relaxations overlap and constitute a single broad relaxation in PVDF/PMMA blend (PVDF ≤ 70 wt%). This confirms that there is a certain composition width in this blend wherein three distinct relaxations can be traced. This could due to many reasons like the width of crystal-amorphous interphase in the crystal lamellae, crystal size and morphology is strongly contingent on the concentration of PMMA. Relaxations are not very distinct in presence of MWNTs due to defective spherulites that shift the relaxations towards a higher frequency. Chapter 5 has attempted to tune the microporous morphology of PVDF membranes using crystallisation induced phase separation in PVDF/PMMA blends. As PVDF/PMMA is a melt-miscible blend, the samples were allowed to crystallise and the amorphous PMMA phase, which isolates in the interlamellar or inter-spherulitic regions in the blends, was etched out to generate microporous structures. The pore sizes can be tuned by varying the PMMA concentration in the blends. We observed that 60/40 PVDF/PMMA blends showed larger pores as compared to 90/10 PVDF/PMMA blends. We further modified PVDF membranes by sputtering silver on the surface. The bacterial cell viability was distinctly suppressed (99 %) in silver sputtered membranes. The ICP analysis suggests that slow Ag+ ions release from the sputtered membrane surface assisted in developing antibacterial surface. Our findings open new avenues in designing water filtration membranes and also help in understanding the crystallisation kinetics for tuning pore size in membranes. Chapter 6 summarises the important results of this work. MWNTs act as hetero nucleating agent and specifically interact with PVDF thereby influences the dynamics of PVDF chains. MWNTs can also restrict the amorphous segmental mobility and can influence the intermolecular cooperativity and coupling. The crystallisation induced phase separation in various blends can result in various crystalline morphologies depending on the PVDF concentration. By selectively etching PMMA from the phase-separated blends, microporous morphology can be generated

Les matériaux poreux silicatés ont été mis à profit pour encapsuler différents types de molécules, clusters ou nano-objets fonctionnels, donnant lieu à des nanocomposites hybrides organiques-inorganiques à propriétés physiques, chimiques ou biologiques remarquables. Élucider l'organisation structurale à l'échelle moléculaire de tels nanocomposites est indispensable pour l'analyse et la compréhension des propriétés macroscopiques qui en découlent. Ainsi, les techniques de diffusion totale associées à la fois à l'analyse Debye et la Fonction de Distribution de Paires (PDF) sont des méthodes de choix pour la caractérisation des propriétés structurales de matériaux hybrides nano-structurés. Le principal objectif de ce travail consiste à l'utilisation des approches basées sur la diffusion totale de rayons X pour l'analyse structurale complète de molécules photoactives confinées dans des matrices silicatées amorphes avec différentes tailles de pores, afin d'étudier l'influence de l'organisation structurale sur les propriétés optiques et d'explorer également les limites de ces approches d'analyse. Nous avons étudié deux systèmes photoactifs. L'analyse structurale du premier complexe confiné, Na2[Fe(CN)5NO].2H2O (SNP), a été entreprise par une approche multi-échelle combinant la RMN du solide et l'analyse PDF. Cette approche a permis l'identification de la nature des espèces incorporées, l'arrangement des cations et des anions ainsi que la distinction des différentes phases existantes : molécules isolées et nanoparticules. Les analyses Debye et PDF sur le deuxième composé étudié, [NdCl2(H2O)6]Cl, montrent que l'organisation structurale du complexe confiné est différente de celle du matériau massif cristallin. De plus, les cations Nd3+ changent de coordination de 8 à 9 durant le processus d'imprégnation et adoptent ainsi un arrangement structural très similaire à celui en solution aqueuse. Cette modification structurale est en accord avec le changement des propriétés luminescentes de ce complexe / Silica xerogels are versatile host materials for the inclusion of molecules, clusters, or nano-objects yielding host-guest compounds with unique physical, chemical or biological properties. The knowledge of the structural organization of the guest within the host is crucial for the understanding of its properties. Total scattering methods, based on Debye function analysis (DFA) and Pair Distribution Function (PDF), have become powerful tools for structural characterization of nanostructured hybrid materials. The aim of this work is to use the X-ray total scattering method to obtain structural information on photoactive molecules embedded into amorphous silica hosts with different pore sizes, to correlate their structure with the optical properties, and to explore the limitations of the chosen method. Two different photoactive complexes have been investigated. In the first example, the combined PDF and NMR study on Na2[Fe(CN)5NO].2H2O (SNP) embedded into silica matrices allows to extract the nature of the inserted species: quasi-free isolated molecules can be distinguished from nanoparticles and in the former case a model for the arrangement of cation-anion can be proposed from the PDF analysis. In the second example, a luminescent Nd3+ complex, the PDF and DFA analysis reveal that the structural organization of the embedded Nd3+ complexes is different from that of the crystalline material. Furthermore, the Nd3+ cations change the coordination from 8 to 9 during the wet-impregnation doping and adopt very similar structural arrangement as in aqueous solution, which is in agreement with the observed change in the luminescence properties

Motion of ions under the influence of electric field has been a subject of scientific interest for many decades. Capillary electrophoresis in particular benefited greatly from this research and mathematical models of electromigration applicable to capillary electrophoresis have been developed. As the sophistication of the models grew, so did the computational demands to evaluate them. In order to fully exploit the possibilities of advanced mathematical models a computer implementation capable of solving non-trivial problems at sufficient speed is necessary. This dissertation thesis explores applications of computer implementations of mathematical models re- lated to electromigration in two different areas. The main focus of this thesis is on the topic of linear theory of electromigration. We discuss the extension of the linear theory of electromigration beyond of just acid-base equilibria and computer implementation of this extented theory which is specialized to include complex-forming equilibria in order to be able to deal with affinity capillary electrophoresis prob- lems. Some technical aspects of the computer implementation are also discussed. This is followed upon by investigating certain selected affinity capillary electrophoresis systems. The purpose of this investi- gation is to re-derive...

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 α. / In 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.

Lipid bilayers are key components of biomembranes; they are self-assembled two-dimensional structures, primarily serving as barriers to the leakage of cell's contents. Lipid bilayers are typically charged in aqueous solution and may electrostatically interact with each other and with their environment. In this work, we investigate electrostatics of charged lipid bilayers with the main focus on the binding and bending of the bilayers. We first present a theoretical approach to charge-correlation attractions between like-charged lipid bilayers with neutralizing counterions assumed to be localized to the bilayer surface. In particular, we study the effect of nonzero ionic sizes on the attraction by treating the bilayer charges (both backbone charges and localized counterions) as forming a two-dimensional ionic fluid of hard spheres of the same diameter <i>D</i>. Using a two-dimensional Debye-H??ckel approach to this system, we examine how ion sizes influence the attraction. We find that the attraction gets stronger as surface charge densities or counterion valency increase, consistent with long-standing observations. Our results also indicate non-trivial dependence of the attraction on separations <i>h</i>: The attraction is enhanced by ion sizes for <i>h</i> ranges of physical interest, while it crosses over to the known <i>D</i>-independent universal behavior as <i>h</i> &rarr; &infin;; it remains finite as <i>h</i> &rarr; 0, as expected for a system of finite-sized ions. We also study the preferred curvature of an asymmetrically charged bilayer, in which the inner leaflet is negatively charged, while the outer one is neutral. In particular, we calculate the relaxed area difference &Delta; <i>A</i>₀ and the spontaneous curvature <i>C</i>₀ of the bilayer. We find &Delta; <i>A</i>₀ and <i>C</i>₀ are determined by the balance of a few distinct contributions: net charge repulsions, charge correlations, and the entropy associated with counterion release from the bilayer. The entropic effect is dominant for weakly charged surfaces in the presence of monovalent counterions only and tends to expand the inner leaflet, leading to negative &Delta; <i>A</i>₀ and <i>C</i>₀. In the presence of even a small concentration of divalent counterions, however, charge correlations counterbalance the entropic effect and shrink the inner leaflet, leading to positive &Delta; <i>A</i>₀ and <i>C</i>₀. We outline biological implications of our results.

L'utilisation de systemes électromécaniques microstructures pour analyser et manipuler des solutions biologiques ou des cellules vivantes (bio-MEMS) à pris un essor considérable ces dernières années. Dans ce genre de dispositifs, I'utilisation de champs électriques est frequente que ce soit pour percer les membranes des cellules et effectuer une transfection de gènes par exemple (électroporation), pour les déplacer ((di )électrophorèse) ou agir sur Ie milieu dans lequel elles baignent (électro-hydrodynamique). La modélisation des phénomènes induits par ces champs électriques dans les solutions aqueuses est un probleme multi-physique et multi-échelle. Au deplacement des électrons s'ajoute en effet la migration des ions présents dans la solution. Ceux-ci se concentrent en particulier aux abords des électrodes formant des couche minces dont les paramètres évoluent de façon encore mal connue en fonction notamment des conditions d'alimentation. La thèse se concentre sur les applications électro-hydrodynamiques dans lesquelles une solution saline est mise en mouvement par des forces électriques agissant sur ses ions, concentrés dans des couches de charges minces, au voisinage des électrodes. Sont d'abord presentés les resultats experimentaux et des modèles simples du problème électromécanique dans Ie cas de structures 2D à électrodes coplanaires. Devant I'importance des écarts entre les résultats théoriques et expérimentaux, des modèles plus complets sont alors proposés et évalués. Malgré les ameliorations fournies par ces modèles, des écarts importants subsistent entre théorie et expérimentation, et une étude totalement découplée des aspects électriques et mécaniques est alors réalisée sur une structure 1D. Cette étude permet de mieux cerner Ies dependances de certains paramètres physiques vis-a-vis des conditions d'alimentation avec une comparaison systématique des résultats expérimentaux et des résultats de modèles circuits Iinéaires et non linéaires, au travers d'une approche fréquentielle par diagrammes de Bode et d'une approche temporelle par figures de Lissajous. II a ainsi pu être mis en évidence I'importance pratique potentielle de certains phénomènes rarement pris en compte dans des modèles globaux : saturation des couches minces, permittivité non constante, effets de bords, ... Des applications pratiques ont pu etre dégagées et testées experimentalement, dans Ie domaine des micro-mélangeurs. Outre ces développements, une brève étude est décrite, portant sur la modélisation des cellules et de leurs membranes extrêmement fines en regard des autres dimensions caractéristiques du systeme, dans la perspective par exemple d'applications en électroporation. Une autre étude est faite portant sur I'utilisation potentielle de méthodes numériques dites " sans maillage " pour ce type d'applications, I'accent étant mis sur Ia résolution du problème de Poisson dans des systèmes 2D.

Lipid bilayers are key components of biomembranes; they are self-assembled two-dimensional structures, primarily serving as barriers to the leakage of cell's contents. Lipid bilayers are typically charged in aqueous solution and may electrostatically interact with each other and with their environment. In this work, we investigate electrostatics of charged lipid bilayers with the main focus on the binding and bending of the bilayers. We first present a theoretical approach to charge-correlation attractions between like-charged lipid bilayers with neutralizing counterions assumed to be localized to the bilayer surface. In particular, we study the effect of nonzero ionic sizes on the attraction by treating the bilayer charges (both backbone charges and localized counterions) as forming a two-dimensional ionic fluid of hard spheres of the same diameter <i>D</i>. Using a two-dimensional Debye-Hückel approach to this system, we examine how ion sizes influence the attraction. We find that the attraction gets stronger as surface charge densities or counterion valency increase, consistent with long-standing observations. Our results also indicate non-trivial dependence of the attraction on separations <i>h</i>: The attraction is enhanced by ion sizes for <i>h</i> ranges of physical interest, while it crosses over to the known <i>D</i>-independent universal behavior as <i>h</i> &rarr; &infin;; it remains finite as <i>h</i> &rarr; 0, as expected for a system of finite-sized ions. We also study the preferred curvature of an asymmetrically charged bilayer, in which the inner leaflet is negatively charged, while the outer one is neutral. In particular, we calculate the relaxed area difference &Delta; <i>A</i>₀ and the spontaneous curvature <i>C</i>₀ of the bilayer. We find &Delta; <i>A</i>₀ and <i>C</i>₀ are determined by the balance of a few distinct contributions: net charge repulsions, charge correlations, and the entropy associated with counterion release from the bilayer. The entropic effect is dominant for weakly charged surfaces in the presence of monovalent counterions only and tends to expand the inner leaflet, leading to negative &Delta; <i>A</i>₀ and <i>C</i>₀. In the presence of even a small concentration of divalent counterions, however, charge correlations counterbalance the entropic effect and shrink the inner leaflet, leading to positive &Delta; <i>A</i>₀ and <i>C</i>₀. We outline biological implications of our results.

Heme-based gas sensor proteins have the ability to sense diatomic molecules such as O2 (FixL, EcDos or HemAT), CO (CooA, a CO-sensing protein of Rhodospirillum rubrum) and NO (guanylate cyclase) molecules and subsequently regulate numerous important biological processes in prokaryotic and eukaryotic organisms. The sensing function of these proteins is initiated by the binding of an effector (i.e., O2, CO, etc5) to the heme iron which then leads to a cascade of conformational events which gives rise to changes in kinase activity, DNA-binding activity, etc... In order to better understand the mechanism heme-based signaling, time resolved photothermal methods as well as transient optical techniques were utilized to obtain thermodynamic profiles for ligand binding/release in heme based signaling proteins including HemAT from Bacillus subtilis (aerotactic transducer), FixL from Sinorhizobium meliloti (regulation of the nitrogen fixation) and CooA from Rhodospirillum rubrum (transcriptional activator). In addition, a number of model systems were examined to understand the underlying thermodynamic processes involved in heme ligation. The variation of volume and enthalpy changes associated with spin state change of the iron from high-spin to low-spin where examined using the spin crossover Fe(III)(salten)(mepepy) complex. In addition, the experimental determination of the volume change due to electrostriction events were using Ru(II)(L)3 and the Debye-Hückel equation. Finally, different model heme proteins were studied to understand how a signal is conformationaly transmitted within a heme protein matrix. Sandbar shark hemoglobin was examined as an example of a non-signaling an allosteric protein. Two different peroxidases (horseradish and soybean) which have a direct channel between the heme pocket and the solvent involving no barrier energetic for the photodissociated ligand leaving the heme pocket were examined as example of non-signaling, non-allosteric proteins. The results show that each protein has a unique thermodynamic profile to conformationaly transmit signals subsequent to photodissociation of CO, even within the same class of protein (i.e. PAS domains, globins, etc...).

Neste trabalho apresentamos os resultados experimentais da medida do calor específico dos compostos Heusler da série Ni2TA1, onde T =Ti, Zr,Hf,V,Nb, Ta. Estas medidas foram feitas utilizando-se um calorímetro adiabático que atua na faixa de 1,84 K a 10,3 K e visaram o estudo da estrutura elêtrônica dos compostos em termos da densidade de estados eletrônicos à nível de Fermi, bem como da dinâmica da rede cristalina, com o uso dos modelos de Debye e de Einstein para o calor específico. Apresentamos, também, uma descrição do calorímetro, seu funcionamento e as alterações ocorridas em função deste trabalho.

Neste trabalho apresentamos os resultados experimentais da medida do calor específico dos compostos Heusler da série Ni2TA1, onde T =Ti, Zr,Hf,V,Nb, Ta. Estas medidas foram feitas utilizando-se um calorímetro adiabático que atua na faixa de 1,84 K a 10,3 K e visaram o estudo da estrutura elêtrônica dos compostos em termos da densidade de estados eletrônicos à nível de Fermi, bem como da dinâmica da rede cristalina, com o uso dos modelos de Debye e de Einstein para o calor específico. Apresentamos, também, uma descrição do calorímetro, seu funcionamento e as alterações ocorridas em função deste trabalho.