Rozprawy doktorskie na temat „Soft matter polymer physics”

Recent years have seen remarkable progress in our understanding of physical aging in nondisordered systems with slow, i.e. glassy-like dynamics. In many systems a single dynamical length L(t), that grows as a power-law of time t or, in much more complicated cases, as a logarithmic function of t, governs the dynamics out of equilibrium. In the aging or dynamical scaling regime, these systems are best characterized by two-times quantities, like dynamical correlation and response functions, that transform in a specific way under a dynamical scale transformation. The resulting dynamical scaling functions and the associated non-equilibrium exponents are often found to be universal and to depend only on some global features of the system under investigation. We discuss three different types of systems with simple and complex aging properties, namely reaction diffusion systems with a power growth law, driven diffusive systems with a logarithmic growth law, and a non-equilibrium polymer network that is supposed to capture important properties of the cytoskeleton of living cells. For the reaction diffusion systems, our study focuses on systems with reversible reaction diffusion and we study two-times functions in systems with power law growth. For the driven diffusive systems, we focus on the ABC model and a related domain model and measure two- times quantities in systems undergoing logarithmic growth. For the polymer network model, we explain in some detail its relationship with the cytoskeleton, an organelle that is responsible for the shape and locomotion of cells. Our study of this system sheds new light on the non- equilibrium relaxation properties of the cytoskeleton by investigating through a power law growth of a coarse grained length in our system.
Ph. D.

Nous avons étudié la friction de SBR (Styrene Butadiene Rubber) fondu sur des surfaces de faible rugosité portant des chaines ancrées de SBR, par mesures simultanées de la vitesse locale à la paroi (techniques de vélocimétrie laser par photolyse, mises au point au laboratoire pour des écoulements Couette-plan) et de la contrainte transmise. Le SBR est très enchevêtré par rapport aux études précédentes : ceci entraîne que les taux de cisaillement accessibles dans la fenêtre expérimentale peuvent être supérieurs à l'inverse du temps de reptation des chaines. Afin d'obtenir des surfaces avec des chaines de longueur et de densité contrôlées, nous avons d'abord utilisé des SBR fonctionnalisés monochlorosilane. Cette voie n'a pas abouti en raison d'impuretés résiduelles de synthèse créant des défauts dans les couches. Nous avons alors adsorbé des copolymères diblocs SBR-PDMS dont le bloc PDMS court s'adsorbe plus fortement a la surface que le bloc SBR. Dans toutes les expériences de friction sur des surfaces portant des chaines de SBR, nous avons observé le passage progressif d'un régime de glissement faible vers un régime de glissement fort en fonction du taux de cisaillement. Nous avons observé de manière quasi systématique un blocage de la contrainte sur une large gamme de vitesses de glissement, d'où une friction non linéaire, correspondant à la plage des vitesses de la transition faible -- fort glissement. La comparaison avec les modèles de Brochard-de Gennes ou d'Ajdari et al. reste qualitative compte tenu du nombre restreint de couches contrôlées, mais ces transitions de glissement et le blocage de contrainte correspondent bien an mécanisme d'étirement progressif et d'extraction des chaines ancrées en surface.

Le confinement nanométrique permet d'obtenir la frustration des fluctuations et/ou des transitions de phases spontanées qu'un fluide moléculaire présente en volume (i.e. en " bulk "). Le confinement au sein de matrices poreuses est donc une voie usuelle de stabilisation de phases métastables. Nous détaillons ici les propriétés structurales, dynamiques et thermodynamiques de deux systèmes moléculaires confinés : dans un premier chapitre, nous nous intéressons au cas de l'eau puis, dans un deuxième chapitre, nous traitons le cas spécifique d'un polymère semi-cristallin. Le confinement permet d'abaisser considérablement le point de fusion du fluide confiné. Cette propriété a été récemment mise à profit dans la cadre de nombreux travaux visant à tester l'existence d'un hypothétique point critique à basse température dans l'eau volumique à 228 K and 100 MPa. Dans cette contribution, nous mettons en évidence des propriétés dynamiques surprenantes de l'eau interfaciale à basse température (de 100 à 300 K). Nous proposons un modèle de percolation décrivant les transitions dynamiques et thermodynamiques que nous observons à 150, 220 et 240 K. Nous proposons une description cohérente de cette eau à deux dimensions et de ses propriétés. Nous invoquons le rôle dominant des interactions de surface pour remettre en cause la pertinence de l'utilisation de l'eau confinée pour prouver l'existence d'un point critique à basse température dans l'eau volumique. Cette étude met cependant en évidence l'existence d'une transition liquide-liquide (l'une des conditions pour observer un point critique) impliquant des molécules d'eau. Récemment, un " effet corset " a été proposé : le confinement induirait une réduction d'un ordre de grandeur du diamètre du tube de reptation d'un polymère (quelques nanomètres en volume contre quelques angströms sous confinement). Dans le second chapitre, nous utilisons une approche par diffusion de neutrons pour accéder à une description multi-échelles de la dynamique d'un polymère (en volume puis sous confinement) de l'échelle atomique à temps court (picosecondes) jusqu'à une dizaine de nanomètres, à temps long (600 nanosecondes). Cette étude détaillée de la dépendance spatiale de la relaxation temporelle des chaînes de polymère ne permet pas de mettre en évidence d'"effet corset ". De façon générale, lorsque l'on cherche à tirer profit du confinement nanométrique pour obtenir des "effets de volume", en plus d'"effets de surface" parasites décrits dans le premier chapitre, on est également confronté à une perte significative d'information induite par la moyenne spatiale des observables spectroscopiques. Nous décrivons dans le deuxième chapitre comment utiliser des matrices de confinement orientées macroscopiquement pour s'affranchir de ces effets indésirables et/ou limitants. Dans le troisième et dernier chapitre, nous définissons un système de confinement nanométrique qui permet d'associer i) une orientation macroscopique des pores et ii) une absence totale d'interactions de surface. Un tel système permet d'envisager des effets de volume unidimensionnels très significatifs et ayant une portée sur des distances macroscopiques. Nous discutons pourquoi de tels " tuyaux nanométriques" peuvent potentiellement intéresser à la fois la recherche fondamentale et l'industrie.

The recent development of a framework called non-affine lattice dynamics made it possible to calculate the elastic moduli of disordered systems directly from their microscopic structure and potential energy landscape at zero temperature. In this thesis different types of disordered systems were studied using this framework. By comparing the shear modulus and vibrational properties of nearest neighbour spring networks based on depleted lattices we were able to show that the dominating quantity of the system’s non-affine reorganisation during shear deformation is the affine force field. Furthermore we found that different implementation of disorder lead to the same behaviour at the isostatic point. Later we studied the effect of long range interaction in such depleted lattices with regard to spatial correlation local elasticity. We found that the implementation of long springs with decaying spring constant reproduced the spatial correlation observed in simulations of Lennard-Jones glasses. Finally we looked at simple freely rotating polymer model chains by extending the framework to angular forces and studied the dependence of the shear modulus and the vibrational density of states (VDOS) and length and bending stiffness of the chains. We found that the effect of chain length on the shear modulus and the vibrational density of states diminishes as it depends on the number of backbone bonds in the system. This number increases fast for short chains as many new backbone bonds are introduced but slows down significantly when the chain length reaches 50 monomers per chain. For the dependence on the bending stiffness we found a rich phenomenology that can be understood by looking at specific motions of the monomers relative the the chain geometry. We were able to trace back the different regimes of the VDOS to the simple model of the triatomic molecule. We also explored the limits of non-affine lattice dynamics when describing systems at temperatures T > 0 and gave an approximate solution for the shear modulus in this case.

Le mouillage d'un substrat soluble est une situation couramment rencontrée dans la vie de tous les jours les jours. Par exemple, les motivations pratiques de cette étude concernent la préparation de boissons à partir de poudres déshydratées, constituées de substances solubles dans l'eau telles que les glucides. Les modèles hydrodynamiques décrivant le mouillage sur un substrat non soluble ne peuvent pas expliquer les observations expérimentales dans le cas d'un liquide s'étalant sur un substrat soluble. Tay et al.(1) ont émis l'hypothèse que la fraction d'eau à la ligne de contact contrôle la valeur de l'angle de contact et ils ont montré l'importance du processus d'évaporation/condensation du solvant lors du mouillage. Dans cette étude, nous montrons que d'autres transferts de matière doivent être considérés pour améliorer la compréhension du processus de mouillage d'une couche soluble; ainsi la diffusion dans le polymère de l'eau condensée, ou directement depuis la goutte sont des processus qui contribuent à hydrater le substrat et modifier l'angle de contact de la goutte. Nous avons utilisé l'approche suivante pour réaliser cette étude: (i) pour prendre en compte la diffusion dans le substrat, nous avons réalisé des simulations en éléments finis qui permettent de valider nos arguments théoriques, (ii) des expériences d'étalement de goutte sur des couches minces de maltodextrine ont été réalisées afin d'étudier le mouillage et l'hydratation en avant de la ligne de contact. Ce travail nous permet de mettre en avant l'influence de la diffusion dans la couche qui complexifie les profils d'hydratation en avant de la ligne de contact, avec notamment l'apparition d'une région de diffusion où de l'évaporation est observée. Un diagramme de mouillage épaisseur-vitesse (e − U) avec différents régimes est établi. Nous validons ces régimes expérimentalement et plus particulièrement un régime où l'angle de contact est une fonction du produit eU. Par ailleurs, nous montrons l'influence de la transition vitreuse du polymère sur l'angle de contact et l'hydratation. Enfin, une étude préliminaire est réalisée pour comprendre l'influence de la dissolution du polymère lors du mouillage.

De nombreuses études théoriques et expérimentales ont été menées au cours des 30 dernières années afin d'établir le lien entre les propriétés d'interaction des protéines, leurs transitions de phase et leur auto-assemblage. Des avancées significatives ont ainsi été permises grâce à l'application de concepts et méthodes de la physique des polymères et des colloïdes. Ces études ont, pour la majeure partie d'entre elles, été limitées à des protéines d'intérêt médical et à des protéines animales. Ce travail de thèse vise à appliquer ce type d'approche aux protéines végétales afin de mieux comprendre leurs propriétés d'interaction à l'origine de leurs propriétés fonctionnelles au sein des grains et dans les matrices alimentaires. Ce travail a été mené sur un isolat de protéines de réserve du blé composé principalement de la fraction monomérique: les gliadines. Nous avons étudié les transitions de phase des gliadines afin de mieux comprendre leurs propriétés d'interaction d'une part et les structures associées d'autre part. Dans un premier temps, une procédure d'extraction a été développée afin de travailler sur un isolat de composition contrôlée dont les masses moléculaires sont comprises entre 20 kDa et 300 kDa. Le comportement de phase de cet isolat a ensuite été étudié en diminuant la qualité du solvant. Nous avons ainsi déterminé le diagramme de phases (T-Φ), où T est la température et Φv la fraction volumique des gliadines. Cette étude a mis en évidence une séparation de phase de type liquide-liquide dans le système par diminution de la température. Une analyse détaillée de la répartition des protéines au sein des deux phases en fonction de leur masse moléculaire a permis d'identifier une masse moléculaire critique séparant des protéines de comportement de type colloïdal et des protéines de comportement de type polymérique. A partir du diagramme de phase, deux études structurales ont été effectuées. La première a étudié les cinétiques de séparation de phase lors de la diminution de la température pour caractériser la dynamique locale de séparation de phase et identifier les mécanismes qui génèrent les systèmes concentrés. Deux grands types de mécanismes de séparation de phase ont été identifiés : nucléation-croissance et décomposition spinodale. La seconde étude structurale a consisté à établir l'équation d'état pression osmotique vs concentration dans des conditions de bon solvant et à caractériser la structure des dispersions de protéines associée. La relation pression osmotique vs fraction volumique a permis de mettre en évidence l'existence de plusieurs régimes de structuration, associés à des changements de structure secondaire et de propriété rhéologique. La discussion générale permet de mettre en relation les propriétés thermodynamiques déduites de cette approche expérimentale et les changements structuraux observés à différentes échelles
A substantial body of theoretical and experimental studies has been conducted over the last 30 years to establish the link between protein interaction properties, phase transitions and self-assembly. Both colloidal and polymer physics provide a new framework for understanding the driving force for proteins phase behaviour. Such studies have been limited to health-related proteins and to a few food proteins, mainly animal proteins such as casein, whey proteins. This thesis aims to apply this approach to plant proteins to better understand their interactions properties, at the basis of their functional properties within grains and food matrices. This work was carried out on a wheat storage protein isolate mainly composed of the monomeric fraction: gliadins.The objective of this PhD thesis is to investigate the phase transitions of wheat proteins to develop our knowledge on their interaction properties and the associated structures. We organized our experimental approach in five steps. First, we developed an extraction procedure to work on a protein isolate of controlled composition with molecular weight ranging from 20 to 300 kg mol-1. Then, we investigated the phase behaviour of the protein isolate by decreasing the solvent quality, here the temperature. We determined the T-Φ phase diagram, where T is the temperature and Φv the protein volume fraction, that maps the phase and structural transitions of the proteins. This study showed the existence of a liquid-liquid phase separation in the system upon a temperature decrease. We evidenced two different behaviours among proteins as a function of their MWs and highlighted a critical protein size above which the molecular weight is the key determinant of the protein properties. From the phase diagram, two structural studies were conducted. The first one studied the kinetics of phase separation upon temperature decrease to characterize the local dynamics of phase separation and to identify the mechanisms that generate concentrated systems. Two main mechanisms of phase separation have been identified: nucleation-growth and spinodal decomposition. The second one studied the effect of protein concentration on the multi-scale structure of wheat gliadins in good solvent. The integration of all these results allowed us to build the phase diagram of wheat gliadins, integrating thermodynamic and structural data

Polymer science is rapidly advancing towards the precise construction of synthetic macromolecules of formidable complexity. The impressive advances in control over polymer composition, topology and uniformity, enabled by the living polymerisation revolution, now permit the introduction of compartmentalisation within macromolecules. Despite the straightforward and versatile synthetic approaches to produce block copolymer, nanostructures built-up from these linear building-blocks rarely reaches dimensions beyond the 5–50 nm range and can be sensitive to their environment. The development of robust controlled polymerisation techniques has enabled the synthesis of covalently-bond polymer architectures that can be used as nano-scale building-blocks. One of these architectures are molecular polymer brushes (also known as bottlebrush polymers or cylindrical polymer brushes). Molecular polymer brushes (MPBs) are unique materials that possess astonishing properties arising from their densely grafted and extended chain structure. The field of MPBs, especially as compartmentalised entities, is rapidly growing. Recent efforts have focussed on achieving MPBs with programmed complexity and the introduction of orthogonal chemical functionality. Compartmentalised brushes can elevate their functionality beyond that of their linear constituent parts, thus offering immense potential in self-assembly and template chemistry. The aim of this thesis is to demonstrate how the compartmentalisation in MPBs can be used for the construction of complex, yet precise, polymer nano- and microstructures with the scope to develop advanced functional materials.

Les défauts créés dans les polymères soumis aux rayonnements ionisants, en atmosphère inerte, suivent pratiquement tous la même évolution en fonction de la dose. Lorsque la dose augmente, leur concentration augmente puis se stabilise. L'hypothèse retenue pour expliquer ce comportement est la mise en place de transferts d'énergie vers les défauts macromoléculaires créés aux faibles doses. Ceux-ci agissent comme des pièges à énergie et conduisent donc à la radio-stabilisation du polymère. Au cours de cette thèse, nous nous sommes attachés à la quantification de l'apport de l'insaturation trans-vinylène dans le comportement sous rayonnements ionisants du polyéthylène. Avec le dihydrogène, ce groupement compte parmi les défauts majoritaires créés dans ce polymère. Du fait de la variété des défauts et de la simultanéité de leur création, nous avons choisi une méthodologie nouvelle consistant à insérer par voie de synthèse, de manière spécifique et à différentes concentrations, des insaturations de type trans-vinylène, dans les chaînes de polyéthylène. Les polymères résultants ont été irradiés, en atmosphère inerte, avec des rayonnements de faibles TEL (gamma, bêta) et de forts TEL (ions lourds). Tant les défauts macromoléculaires que l'émission de dihydrogène ont été quantifiés. Il apparaît, sur la base des résultats expérimentaux, que l'apport des groupements trans-vinylènes est prédominant dans la radio-stabilisation du polyéthylène en atmosphère inerte.

This thesis presents four investigations into mechanical aspects of soft thin structures, focusing on the effects of stochastic and thermal fluctuations and of material inhomogeneities. First, we study the self-organization of arrays of high-aspect ratio elastic micropillars into highly regular patterns via capillary forces. We develop a model of capillary mediated clustering of the micropillars, characterize the model using computer simulations, and quantitatively compare it to experimental realizations of the self-organized patterns. The extent of spatial regularity of the patterns depends on the interplay between cooperative enhancement and history-dependent stochastic disruption of order during the clustering process. Next, we investigate the influence of thermal fluctuations on the mechanics of homogeneous, elastic spherical shells. We show that thermal fluctuations give rise to temperature- and size-dependent corrections to shell theory predictions for the mechanical response of spherical shells. These corrections diverge as the ratio of shell radius to shell thickness becomes large, pointing to a drastic breakdown of classical shell theory due to thermal fluctuations for extremely thin shells. Finally, we present two studies of the mechanical properties of thin spherical shells with structural inhomogeneities in their walls. The first study investigates the effect of a localized reduction in shell thickness—a soft spot—whereas the second studies shells with a smoothly varying thickness. In both cases, the inhomogeneity significantly alters the response of the shell to a uniform external pressure, revealing new ways to control the strength and shape of initially spherical elastic capsules.
Engineering and Applied Sciences

Un polymère thermoplastique fondu glisse sur une surface solide lisse et non-adsorbante : la vitesse est non nulle à l'interface. Le glissement est réduit si l'on greffe des macromolécules à la surface. Dans ce travail théorique, nous modélisons cette réduction du glissement à l'aide de mécanismes moléculaires, donc à l'échelle nanométrique. Le comportement microscopique des molécules et la réponse rhéologique macroscopique de l'interface sont décrits. Les prédictions du modèle présenté et celles d'autres modèles moléculaires sont confrontées aux résultats des expériences menées par une équipe du lavoratoire. Un certain nombre des lois de comportement sont expliquées, mais la gamme explorée des paramètres ne permet pas de départager tous les modèles. Un test différent est proposé, utilisant des polymères en étoile. D'autres problèmes ont été abordés : conformation d'une macromolécule unique dans un fondu chimiquement différent, statique d'une brosse polymère et d'une étoile dans les mêmes conditions, pénétration partielle d'un fondu dans une brosse chimiquement identique très dense, généralisation aux polymères branchés statistiques d'une méthode de séparation de polymères en étoile en solution diluée, détermination du point de gel pour une structure constituée de polymères en anneau (gel "olympique"), dynamique d'étalement d'une goutte d'hélium superfluide analogue à celle d'une goutte de polymère liquide. Présentation (PDF p. 6, English p. 8) Partie I. Statique et dynamique de polymères liquides (PDF p. 10) Chapitre 1. Généralités sur les polymères (PDF p. 11, English p. 12, français p. 16) Chapitre 2. Polymères fondus : propriétés et mise en oeuvre (PDF p. 39, English p. 40, français p. 42) Chapitre 3. Polymères fondus : éléments de théorie (PDF p. 58, English p. 59, français p. 66) Partie II. Statique et dynamique de chaînes greffées (PDF p. 153) Chapitre 4. Statique de chaînes greffées (PDF p. 154, English p. 155, français p. 158) Chapitre 5. Glissement d'un polymère fondu sur une surface greffée (PDF p. 200, English p. 201, français p. 223) Partie III. Autres problèmes (PDF p. 313) Chapitre 6. Caractérisation de polymères branchés par perméation (PDF p. 314, français p. 315, article in English p. 318) Chapitre 7. Gel olympique (PDF p. 332, English p. 333, français p. 338) Chapitre 8. Étalement d'une goutte par effet Josephson (PDF p. 358, français p. 359, article in English p. 361) Conclusion (PDF français p. 370, English p. 372) Bibliographie (PDF p. 374) Table des matières / Table of contents (PDF p. 380)

En dépit de leur importance pratique considérable, et bien que de nombreuses expériences établissent une corrélation certaine entre les hétérogénéités d'interaction de surface (rugosité ou inhomogénéités chimiques) et les propriétés de friction des surfaces, le rôle de ces interactions sur la friction n'est encore pas bien décrit par les modèles et les expériences existants. Dans ce travail de thèse, nous nous sommes intéressés à l'identification des mécanismes moléculaires de la friction aux interfaces polymères souples. Dans ce contexte, nous avons réalisé deux études complémentaires. La première partie du travail concerne le mouvement d'une ligne triple solide-liquide-vapeur qui se déplace sur une surface solide sous l'effet de différentes forces (gravité, forces capillaires et tensions interfaciales), et en particulier le lien entre le piégeage et le dépiégeage de la ligne triple et l'hystérèse de l'angle de contact. Cette méthode permet de mesurer des angles de contact d'avancée et de reculée avec une précision sans précédent (0,1°)et s'avère être particulièrement sensible aux mécanismes qui tendent à ancrer la ligne triple. Ceci en fait un outil de choix pour étudier la friction liquide/solide. Dans la seconde partie du travail, nous avons cherché à comprendre comment des chaînes de polymère flexibles, fortement ancrées sur une surface solide, dans le régime des fortes densités de greffage affectent la friction entre une telle surface et un élastomère réticulé constitué du même polymère. Nous avons montré que le comportement en friction de cette couche confinée suit exactement le comportement rhéofluidifiant observé pour des couches de fondu de masses molaires équivalentes mais avec un temps de relaxation beaucoup plus long que celui des chaînes en fondu,la reptation n'étant pas permise pour les chaînes ancrées. Enfin, en comparant les résultats obtenus pour des couches greffées chimiquement à une extrémité et des couches fortement adsorbées, ayant par ailleurs les mêmes caractéristiques moléculaires (masse molaire des chaînes et épaisseur de la couche ancrée), nous avons mis en évidence que la friction est remarquablement sensible à l'organisation moléculaire au sein de la couche ancrée.

Materials where thermal energy is comparable to the interaction energy between molecules are called soft materials. Soft materials are everywhere in our life: food, rubber, polymer diaper, our own body, etc. The thermal fluctuation endows soft materials with fundamentally different behavior comparing to hard materials like metals and ceramics. This dissertation studies three aspects of the mechanics and physics of soft materials, as is reviewed below. First, soft materials are generally swellable and viscous. The combination of diffusion and viscous flow gives rise to a length scale we called poroviscous length. The emergence of a length scale results in size dependent relaxation. We show that the coupling between diffusion and viscous flow explains the Brownian motion in supercooled liquids, where the classical result of Stokes-Einstein relation generally fails. The concurrent diffusion and viscous flow cannot be described by the classical hydrodynamics, where all the material transport is lumped into velocity field. We formulated a continuum theory to modify the classical hydrodynamics. In particular, the new theory predicts a new bulk viscosity that could exist in incompressible material. We generalize this idea of bulk viscosity to binary systems and study the mixing of materials that is limited by local structural rearrangement instead of diffusion. This model develops formulation of non-equilibrium thermodynamics by removing the common assumption of local equilibrium. Second, capillarity has strong influence on the morphology of soft materials. The competition between capillarity and elasticity gives rise to the elastocapillary length, which is defined as surface tension over the shear modulus. We show that elastocapillary effect explains the complex nucleation of crease, a widely observed surface instability in soft elastic materials. We also explore the possible competition between capillarity and osmosis in gels, which defines the osmocapillary length, the surface tension divided by osmotic pressure. We show that at small enough length scale or for a gel that is nearly fully swollen, surface tension can pull liquid solvent out from the gel phase, a phenomenon we termed osmocapillary phase separation. Third, soft materials are nearly incompressible. The incompressibility and softness makes elastomers ideal for the design of seals. Although the failure of seals has been studies for decades, existing studies mainly focus on the damage and degradation of materials. Here we study the leak of a seal due to elastic deformation without any damage. We call such a failure mode the elastic leak. We point out that elastic leak is involved in any leak event no matter whether material is damaged or not. We also show that the reversible nature of the elastic leak enable seal series to achieve higher sealing capability.
Engineering and Applied Sciences - Engineering Sciences

The collective motion of organisms such as flights of birds, swimming of school of fish, migration of bacteria and movement of herds across long distances is a fascinating phenomenon that has intrigued man for centuries. Long and details observations have resulted in numerous abstract hypothesis and theories regarding the collective motion animals and organisms. In recent years the developments in supercomputers and general computational power along with highly refined mathematical theories and equations have enabled the collective motion of particles to be investigated in a logical and systematic manner. Hence, this study is focused mathematical principles are harnessed along with computational programmes in order to obtain a better understanding of collective behaviour of particles. Two types of systems have been considered namely homogeneous and heterogeneous systems, which represent collective motion with and without obstacles respectively. The Vicsek model has been used to investigate the collective behaviour of the particles in 2D and 3D systems. Based on this, a new model was developed: the obstacle avoidance model. This showed the interaction of particles with fixed and moving obstacles. It was established using this model that the collective motion of the particles was very low when higher noise was involved in the system and the collective motion of the particles was higher when lower noise and interaction radius existed. Very little is known about the collective motion of self-propelled particles in heterogeneous mediums, especially when noise is added to the system, and when the interaction radius between particles and obstacles is changed. In the presence of moving obstacles, particles exhibited a greater collective motion than with the fixed obstacles. Collective motion showed non-monotonic behaviour and the existence of optimal noise maximised the collective motion. In the presence of moving obstacles there were fluctuations in the value of the order parameter. Collective systems studies are highly useful in order to produce artificial swarms of autonomous vehicles, to develop effective fishing strategies and to understand human interactions in crowds for devising and implementing efficient and safe crowd control policies. These will help to avoid fatalities in highly crowded situations such as music concerts and sports and entertainment events with large audiences, as well as crowded shopping centres. In this study, a new model termed the obstacle avoidance model is presented which investigates the collective motion of self-propelled particles in the heterogeneous medium. In future work this model can be extended to include a combination of a number of motionless and moving obstacles hence bringing the modelling closer to reality.

Soft magnetic $ rm Ni sb{ it x}Co sb{ it 100-x}$/Cu multilayers in the range x = 20 to 80 have been prepared by DC-magnetron sputtering. NiCo alloys were chosen because of their small magnetoelastic parameters around the range x = 70-80 and very small lattice mismatch between NiCo and Cu. This combination of parameters should lead to good giant magnetoresistance (GMR) with a small saturation field. Structural characterization reveals that high quality layered structures were obtained. Quantitative interpretation of the superlattice structure parameters, such as interface roughness, interfacial mixing profiles and layer-thickness disorders, have been carried out by modelling the X-ray diffraction data.
GMR was found to be largest at x = 80 with well-defined oscillations as a function of the thickness of the Cu layer, mirroring the interlayer magnetic coupling. In particular, GMR with small saturation fields around Cu thickness near the second MR maximum (t$ sb{Cu}$ = 20A) will be technologically important because of the very high magnetic field sensitivity. Correlating the multilayer structure to the GMR allow us to optimize the structural parameters by enhancing the spin-dependent interfacial scattering in a high quality layered structure. Direct observation of the simple antiferromagnetic order has been achieved by the presence of the (0,0,${1 over2})$ wavevector in small angle neutron scattering experiments. A near-perfect antiferromagnetic spin arrangement is found for a Cu thickness t$ sb{Cu}$ = 20 A, that can be readily aligned ferromagnetically in a small external field of less than 200 Oe.
A complementary system, FM/Ag (FM = $ rm Ni sb{81}Fe sb{19}, Ni sb{80}Co sb{20}$ and $ rm Ni sb{66}Co sb{18}Fe sb{16})$ granular multilayer prepared by annealing multilayers, has also been studied. Enhanced magnetoresistance observed in these systems is shown to be controlled by the size, concentration and thermal stability of the magnetic precipitates in a nonmagnetic matrix. For a particular multilayer structure with a magnetic layer of 20 A, annealed at around 325$ sp circ$C, a GMR of $ sim$4% with a characteristic saturation field of 10 Oe was found, leading to a high magnetoresistive sensitivity of $ sim$0.4%/Oe at room temperature.

Ce manuscrit présente les résultats d'expériences illustrant différentes manifestations de la présence de polymères dans un écoulement. Pour chacune d'elles, nous étudions l'interaction entre la structure microscopique et l'écoulement.Lorsqu'une goutte se détache d'un capillaire, la colonne de liquide liant la goutte au capillaire doit se rompre. Pour les liquides simples, l'amincissement suit des lois universelles bien établies. La dynamique de détachement d'une goutte de fluide complexe est très différente. Pour les solutions de polymères, après une phase de décroissance rapide du diamètre de cette colonne, il se forme un long filament cylindrique entre la goutte et le capillaire. Afin de mieux comprendre comment les polymères présents en solution donnent naissance à ce filament, nous avons observé leurs conformations au cours du détachement. Ces observations confirment que l'étirement des polymères est à l'origine du ralentissement du processus de détachement. Cependant, lors de l'amincissement du filament, la distribution des longueurs reste inchangée. Ce résultat inattendu, nous a amené à mettre en place une nouvelle méthode pour estimer la viscosité élongationnelle.D'autres expériences sont présentées, l'une porte sur un effet de déplétion qui apparait lors de l'écoulement confiné d'une solution de polymères, alors que l'autre porte sur l'écoulement instable d'une solution concentrée de polymères dans une conduite rectiligne.

Cette étude a porté sur l'effet de différents fluidifiants (plus particulièrement le PolyNaphatalène Sulfonate : PNS et PolyCarboxylatePolyéthoxylé : PCP) sur la rhéologie d'une suspension de particules de gypse. Cette rhéologie a été caractérisée essentiellement par la contrainte seuil, par la viscosité dynamique et les modules de cisaillement. Nous avons montré, en utilisant différentes tailles de particules et différentes longueurs pour les molécules de fluidifiant, que la contrainte seuil était inversement proportionnelle au diamètre des particules et au carré de la distance entre les surfaces de particules. Un modèle nous a permis de remonter à l'épaisseur de la couche de polymère adsorbée sur la surface du gypse. Nous avons observé une diminution de l'efficacité du fluidifiant avec l'augmentation de la fraction volumique de particules de gypse qui a été associée à une diminution de l'écart entre les surfaces des particules. La viscosité dynamique d'une suspension de gypse broyé reste importante malgré la présence de fluidifiant et reflète la présence d'agrégats contenant plusieurs dizaines de particules. Les impuretés (ions divalents : Mg2+, trivalents : Al3+ et Fe3+) ainsi que la température (T>45°C) entraînent une dégradation de l'efficacité du PCP soit en réduisant l'interaction entre le polymère et la surface des particules dans le cas des cations, soit en réduisant la solvatation des polymères dans le cas de l'élévation de température.

The equilibrium properties of polymers end-grafted to an impenetrable interface, the "polymer brush", are investigated. Relevant concepts and techniques of statistical polymer physics are discussed; in particular, a simulation technique that is very efficient for studying polymer brushes is introduced. This technique is demonstrated through simulations of a well characterized polymer brush system. The results of original investigations of phase separation in polymer brushes are also presented. An instability in the lateral monomer density of a polymer brush is observed under sufficiently poor solvent conditions. The onset of this instability is found to agree with a previous prediction. A compositional instability is found in the lateral densities of a two-component polymer brush under conditions of sufficient immiscibility between the two components. The effects of varying solvent conditions are considered. Finally, the onset of the compositional instability is determined using the technique of the self consistent mean field, and the results compared to simulation.

The ability to accurately represent polymer melts at various levels of coarse graining is of great interest because of the wide range of time and length scales over which relevant process take place. Schemes for developing effective interaction potentials for coarse-grained representations that incorporate microscopic level system information are generally numerical and thus suffer from issues of transferability because they are state dependent and must be recalculated for different system and thermodynamic parameters. Numerically derived potentials are also known to suffer from representability problems, in that they may preserve structural correlations in the coarse-grained representation but many often fail to preserve thermodynamic averages of the coarse-grained representation. In this dissertation, analytical forms of the structural correlations and effective pair potentials for a family of highly coarse-grained representations of polymer melts are derived. It is shown that these effective potentials, when used in mesoscale simulations of the coarse-grained representation, generate consistent equilibrium structure and thermodynamic averages with low level representations and therefore with physical systems. Furthermore, analysis of the effective pair potential forms shows that a small long range tail feature that scales beyond the physical range of the polymer as the fourth root of the number of monomers making up the coarse-grained unit dominates thermodynamic averages at high levels of coarse graining. Because structural correlations are extremely insensitive to this feature, it can be shown that effective interaction potentials derived from optimization of structural correlations would require unrealistically high precision measurements of structural correlations to obtain thermodynamically consistent potentials, explaining the problems of numerical coarse-graining schemes. This dissertation includes previously published and unpublished co-authored material.

I present applications of imaging and spectroscopy to understand mechanical, chemical, and electrical dynamics in biological materials. The first part describes the development and characterization of a protein-based fluorescent calcium and voltage indicator (CaViar). The far-red fluorescence of CaViar faithfully tracks the cardiac action potential in cardiomyocytes. CaViar's green fluorescence reports the resulting calcium transients. I demonstrated the applicability of CaViar in vivo with transgenic zebrafish designed to express CaViar in their hearts. Spinning disk confocal imaging allowed detailed three-dimensional mapping of simultaneous voltage and calcium dynamics throughout the heart of zebrafish embryos, in vivo, as a function of developmental stage. I tested the effect of channel blockers on voltage and calcium dynamics and discovered a chamber-specific transition from a calcium-dependent to a sodium-dependent action potential. I also describe a new measurement technique using a fluorescent voltage indicator to report absolute voltage via the indicator's temporal response.
Physics

Multifunctional polymer nanocomposites (PNCs) are attractive for the design of tunable RF and microwave components such as flexible electronics, attenuators, and antennas due to cost-effectiveness and durability of polymeric matrices. In this work, three separate PNCs were synthesized. Magnetite (Fe ₃O₄) and cobalt ferrite (CFO) nanoparticles, synthesized by thermal decomposition, were used as PNC fillers. Polymers used in this work were a commercial polymer provided by the Rogers Corporation (RP) and polyvinylidene fluoride (PVDF). PNCs in this thesis consist of Fe₃O ₄ in RP, CFO in RP, and Fe₃O₄ in PVDF. Characterization techniques for determining morphology of the nanoparticles, and their resulting PNCs, include x-ray diffraction, transmission electron microscopy and magnetometry.

All magnetometry measurements were taken using a Quantum Design Physical Property Measurement System with a superconducting magnet. Temperature and external magnetic field magnetization measurements revealed that all samples exhibit superparamagnetic behavior at room temperature. Blocking temperature, coercivity and reduced remnant magnetization do not vary with concentration. Tunable saturation magnetization, based on nanoparticle loading, was observed across all PNCs, regardless of polymer or nanoparticle choice, indicating that this is an inherent property in all similar PNC materials.

Tunability studies of the magneto-dielectric PNCs were carried out by adding the PNC to cavity and microstrip linear resonator devices, and passing frequencies of 1–6 GHz through them in the presence of transverse external magnetic fields of up to 4.5 kOe, provided by an electromagnet. Microwave characteristics were extracted from scattering parameters of the PNCs. In all cases, losses were reduced, quality factor was increased, and tunability of the resonance frequency was demonstrated. Strong magnetic field dependence was observed across all samples measured in this study.

In this thesis, we present a thorough investigation into the rigidity of a polymer melt above and below its glass transition (GT) at a temperature TG = 0.465 (in reduced Lennard-Jones units). We use an isothermal-compression method to enter the glassy phase and NPT ensemble is realized through molecular dynamics simulations. We monitor such quantities as the mean-square displacement, the heat capacity CP, the volume and time-dependent shear modulus G(t). Whenever possible, these quantities are monitored below the GT as well. We also compute the shear modulus mu via external deformations and, in the zero-shear limit, find reasonably good agreement with G(t → infinity). The rigidity transition (RT) in the system is found to occur slightly below the GT at a temperature TR = 0.44. The results are explained in terms of sufficient free volume above TR allowing collective motion and local stress relaxation. This is seen through dynamics which are not only heterogeneous, but also spatially correlated. We appeal to notions such as "jamming" within the system and the presence of floppy modes (which allow for deformations without energy cost) to interpret the RT phenomenon. We also characterize the response to external deformation: small and large deformation regimes can be identified, the latter type causing a non-negligible reconfiguration, an over-stretching of the chains and a move to a more shallow potential energy "well." Furthermore, we analyze the "aging" phenomenon as a series of intermittent collective rearrangements and show that the two types of instantaneous shear deformations both induce "overaging," but in two completely different manners.

In this thesis we asses the phenomena of arising interactions in soft matter in coexistence with soft active matter. As a non-equilibrium bath we introduce ensembles of self-propelled particles, granular shaken beds, and photo active catalytic particles. We start the thesis with a detailed study of the widely used Active Brownian Particle (ABP) model. This model exhibits a non-equilibrium phase transition which has been intensively studied in recent years, we have finally reported that this transition satisfies all features of equilibrium first order phase transitions. Then, we introduce aligning interactions in ABP and characterize the emergent collective phenomena. In parallel, we explore the emergent forces, from mechanical contact forces, in probe particles in suspensions of aligning active particles and horizontally shaken granular beds. We characterize the forces and identify the emergence of long range interactions in both systems, in aligning active particles long range attractive interactions appear as alignment is increased, and in granular shaken media when the pair of particles align in the shaking direction. Finally, we conclude this thesis with the study of emergent interactions in spherically symmetric systems of catalytic active particles. Symmetry does not permit such particles to propell but the symmetry is broken with the addition of neighboring particles. We model the pair interaction in terms of the relative velocity between particles, and proceed to explore the emergent structures in mixtures of catalytic magnetic particles, and passive particles. We have unveiled the formation of clusters of passive particles. The addition of magnetic interactions between active particles leads to the formation of ramified gel-like structures for dense configurations of active particles. In this case, experimentalists have checked the formation of structures with the same morphologies in experiments in the laboratory.
En aquesta tesi abordem el fenomen de les interaccions emergents en matèria tova en coexistència amb matèria tova activa. Com a sistemes de matèria tova activa introduïm col·lectius de partícules autopropulsades, col·loides amb capacitat de catalitzar productes químics i medis granulars agitats. Primer de tot estudiem en detall un model molt estès per a partícules actives, el model de les partícules actives brownianes (ABP). D'aquest model estudiem amb detall una transició de fase de no equilibri i comprovem que la transició satisfà amb les característiques d'una transició en equilibri de primer ordre. Seguidament incorporem interaccions d'alineació en el model de partícules actives i procedim a estudiar les propietats col·lectives de les suspensions de partícules actives amb alineació. Per tal d'abordar l'objectiu de la tesi introduïm partícules de prova en suspensions de partícules actives, i en medis granulars amb forçament periòdic horitzontal, amb diferents paràmetres d'activitat per tal d'estudiar les forces, des d'un punt de vista mecànic, que emergeixen entre les parelles. Hem caracteritzat les forces i hem identificat l'aparició d'interaccions de llarg abast per sistemes de partícules amb alineació i en sistemes granulars en la direcció del forçament. Finalment, tanquem la tesi amb l'estudi i modelització d'interaccions emergents per a partícules catalítiques amb simetria esfèrica. La simetria no permet a les partícules d'autopropulsar-se però la presència de partícules al seu entorn sí que dóna lloc a interaccions, en forma de velocitats induïdes. Amb un model raonable de la interacció a distància hem calibrat la magnitud de la interacció amb sistemes experimentals i procedit a caracteritzar les estructures emergents per a mescles de partícules actives i passives que van des de la formació d'agregats en forma de clústers. L'addició d'interaccions magnètiques entre partícules actives permet la formació d'estructures ramificades de tipus gel. En aquest cas l'equip experimental ha pogut comparar l'aparició d'estructures amb les mateixes característiques al laboratori.

Advancements in science and technology increasingly involve systems operating at the nanoscale. Interfaces are often present in these systems. Nanoscopic interfaces are ubiquitous in biological systems, nanofluidic devices, and integrated circuits. Properties at the interface may be quite different from the bulk, and in fact a true bulk may not be present in these systems. At the nanoscale the ratio of interface to volume is large, and the interface may have the dominant role in determining system behavior. Interfacial characteristics and their connection to interfacial properties are the focus of my thesis. Using molecular simulations of model interfaces we characterize how properties like chemistry, composition, and topography affect such phenomena such as hydrophobicity, heat transfer, and momentum transport at the nanoscale. An interface is defined simply as where two materials meet and a change in some structure or order parameter is observed. In aqueous systems, the type studied here, these changes are relatively sharp and occur within a distance of nanometers. Water molecules near the interface are expected to display sensitivity to the underlying surface. Indeed, water near a hydrophobic surface is more deformable and has greater fluctuations. The hydrophobicity of chemically heterogeneous surfaces and proteins are characterized using these nanoscopic measures. We find the effect of mixing hydrophobic and hydrophobic head group chemistries is asymmetric, i.e., it is easier to make a hydrophobic surface hydrophilic than the reverse. The role of hydrogen bonding in hydrophobic and ion hydration is also characterized using a short range water model. Hydrophobic and ion hydration are reasonably captured with the short range water model. These studies show the importance of chemical composition and local hydrogen bonding in determining surface hydrophobicity. Interfaces also lead to anomalous behavior in heat and momentum transport. Interfaces disrupt local structure and create boundary resistances that manifest in temperature discontinuities and interfacial slip. We explore the effects of chemical heterogeneity, nanoscale surface roughness, and directionality on thermal conductance across model solid-water interfaces. Interfacial conductance is directly influenced by the coupling strength or wettability of the surface. For chemically mixed surfaces, interfacial conductance does not precisely match with wettability. Surface roughness in general enhances conductance, but the improvement cannot be completely attributed to increased solvent accessible surfaced area. Momentum transport displays similar discontinuities at aqueous interfaces. These effects can be reduced through the use of osmolytes. Collectively this work highlights the influence of interfaces on heat and momentum transport. Insights are provided for modifying interfacial behavior and altering the property of interest.

There has been an increasing appreciation of the role in which elasticity plays in soft matter. The understanding of many shapes and conformations of complex systems during equilibrium or non-equilibrium processes, ranging from the macroscopic to the microscopic, can be explained to a large extend by the theory of elasticity. We are motivated by older studies on how topology and shape couple in different novel systems and in this thesis, we present novel systems and tools for gaining fundamental insights into the wonderful world of geometry and soft matter. We first look at how defects, topology and geometry come together in the physics of thin membranes. Topological constraint plays a fundamental role on the morphology of crumpling membranes of genus zero and suggest how different fundamental shapes, such as platonic solids, can arise through a crumpling process. We present a way of classifying disclinations using a generalized “Casper-Klug” coordination number. We show that there exist symmetry breaking during the crumpling process, which can be described using Landau theory and that thin membranes preserve the memory of their defects. Next we consider the problem of the shapes of Bacillus spores and show how one can understand the folding patterns seen in bacterial coats by looking at the simplified problem of two concentric rings connected via springs. We show that when the two rings loses contact, rucks spontaneous formed leading to the complex folding patterns. We also develop a simple system of an extensible elastic on a spring support to study bifurcation in system that has adhesion. We explain the bifurcation diagram and show how it differs from the classical results. Lastly, we investigate the statistical mechanics of the Sadowsky ribbon in a similar spirit to the famous Kratky-Porod model. We present a detail theoretical and numerical calculations of the Sadowsky ribbon under the effect of external force and torsion. This model may be able to explain new and novel biopolymers ranging from actin, microtubules to rod-like viruses that lies outside the scope of WLC model. This concludes the thesis.
Physics

The motivation for this study was to further characterize a relatively new high-temperature polymer for application as a matrix resin for carbon fiber composites. The two primary questions addressed in this study dealt with the structural and chemical changes occurring in these polymers on exposure to high temperature.;To investigate the structural changes in the heat-treated samples, a positron annihilation lifetime spectrometer was designed, built and optimized. Because the lifetime of a positron in a material reflects the electronic structure of the material in which it annihilates, measurements by positron annihilation lifetime spectroscopy can be used to investigate changes in a material at the Angstrom level. The results of applying this technique indicate that positron annihilation lifetime spectroscopy is able to detect microstructural changes in these heat-treated polymers.;In order to study the chemical changes occurring in these polymers during heat treatment, an array of solid state analytical techniques was applied. These techniques included Differential Scanning Calorimetry, Elemental Analysis, Thermo-gravimetric and Thermo-mechanical analyses, Fourier Transform Infrared, {dollar}\sp{lcub}13{rcub}{dollar}C Cross Polarization Nuclear Magnetic Resonance, Electron Spin Resonance, and Dynamic Nuclear Polarization. The results of applying these techniques provide previously unavailable data into the chemical structures of these polymers before and after heat treatment. Additionally, the presence of stable free radicals in the polymer samples both before and after heat treatment was confirmed and the origin and location of these free radicals is proposed.

The discovery of ferroelectricity at the nanoscale has incited a lot of interest in perovskite ferroelectrics not only for their potential in device application but also for their potential to expand fundamental understanding of complex phenomena at very small size scales. Unfortunately, not much is known about the dynamics of ferroelectrics at this scale. Many of the widely held theories for ferroelectric materials are based on bulk dynamics which break down when applied to smaller scales. In an effort to increase understanding of nanoscale ferroelectric materials we use atomistic resolution computational simulations to investigate the dynamics of polar perovskites. Within the framework of a well validated effective Hamiltonian model we are able to accurately predict many of the properties of ferroelectric materials at the nanoscale including the response of the soft mode to mechanical boundary conditions and the polarization reversal dynamics of ferroelectric nanowires. Given that the focus of our study is the dynamics of ferroelectric perovskites we begin by developing an effective Hamiltonian based model that could simultaneously describe both static and dynamic properties of such materials. Our study reveals that for ferroelectric perovskites that undergo a sequence of phase transitions, such as BaTiO3. for example, the minimal parameter effective Hamiltonian model is unable to reproduce both static and dynamical properties simultaneously. Nevertheless we developed two sets of parameters that accurately describes the static properties and dynamic properties of BaTiO3 independently. By creating a tool that accurately models the dynamical properties of perovskite ferroelectrics we are able to investigate the frequencies of the soft modes in the perovskite crystal. The lowest energy transverse optical soft modes in perovskite ferroelectrics are known to be cause of the ferroelectric phase transition in these materials and affect a number of electrical properties. The performance of a ferroelectric device is therefore directly influenced by the dynamics of the soft mode. Interestingly, however, little study has been done on the effect of mechanical boundary conditions on the soft modes of perovskites. Understanding the effect of mechanical forces on the soft modes is critical to device applications as complicated growth structures often are the cause of pressures, stresses and strains. Using classical molecular dynamics we study the effect of hydrostatic pressure, uniaxial stress, biaxial stress and biaxial strain on the soft modes of the ferroelectric PbTiO3. The results of this study indicate the existence of Curie-Weiss laws for not only hydrostatic pressure, which is well known, but also for uniaxial stress, biaxial stress and biaxial strain. The mode frequencies are also seen to respond very differently to these mechanical forces and lead to a more complete picture of the behavior of nanoscale ferroelectrics. One nanoscale geometry of perovskite ferroelectrics is the pseudo one-dimensional nanowire. These structures have very unique properties that are highly attractive for use as interconnects, nanoscale sensors or more directly in computer memory devices. Perovskite nanowires have only recently been synthesized and the techniques are not well developed. While progress has been made towards consistently fabricating uniform, high quality nanowires experimental investigation of their properties is prohibitively difficult. Of immediate interest is the polarization reversal dynamics of ferroelectric nanowires. The reading and writing of bits of information stored in a wire's polarization state is done by switching the polarization. Again using classical molecular dynamics we study the polarization reversal dynamics in ferroelectric nanowires made of Pb(Ti1-xZrx)O3 disordered alloy. We find that there are two competing mechanisms for polarization reversal and that the interplay of these mechanisms is dependent on electric field strength. The dynamics in nanowires also sheds light on long standing theories about polarization reversal mechanisms in thin film and bulk geometries.

Theoretical calculations have predicted the importance of two-photon absorptions in the third order optical nonlinearities of polydiacetylenes. We have used electro-absorption techniques to make these two-photon transitions slightly one-photon allowed and therefore observable in the one-photon absorption spectrum. Our findings, although unable to ascertain the existence of below-gap two-photon states, nevertheless provide an unexpected view of the conduction band in conjugated chain polymers. The observation of a field induced oscillatory change in the absorption around the vicinity of the band edge and comparison of this signal with theoretical calculations leads to the conclusion that the conduction band is composed of both one-photon and two-photon states. This oscillatory signal cannot be solely explained by one-photon or two-photon states but must include both types for this high energy signal to be reproduced in the theoretical calculations.

This thesis contains details of a series of experiments performed to investigate the acoustic and elastic properties of ultra-thin polymer structures. Three main investigations were conducted. The first involved studying quantised vibrations in ultra-thin (∼100 nm) polystyrene films on silicon substrates. These films were vibrated via the picosecond acoustic technique, an optical pump-probe method. Quantised, harmonic vibrations were observed in the films with frequencies of the order of 10 GHz. The polymer films were then loaded by evaporating small thicknesses (2.5 - 30 nm) of gold. The frequencies of loaded areas were observed relative to the unloaded films. This frequency shift is described via a theory that considers the elastic wave equation in the structure with appropriate boundary conditions. Excellent agreement between experiment and theory is achieved, suggesting the potential for using these films as ultra-sensitive mass sensors. The second experimental chapter deals with experiments performed on polymer Bragg reflectors. These multilayer structures were again investigated via the picosecond technique. The reflected intensity of the probe laser beam was observed to be modulated by the strain pulse as it travelled through the structure. These results were compared to theoretically generated signals and this comparison suggests that, in the polymer structures considered here, the modulation can be described almost exclusively by the photo-elastic effect. Although the modulation is small it opens up the possibility of using similar structures in combinations with micro-cavities to act as high frequency optical components. The final experimental chapter details attempts to develop a new metrology for elastic properties in ultra-thin polymer films floated on a water surface. The films were cut into annuli and placed on a Langmuir-Blodgett trough before surfactant was placed around the outside. By moving the barriers of the trough, a surface pressure difference between the inside and outside of the annulus could be controlled and a wrinkling pattern induced around the annulus. A system for imaging and counting the wrinkles as a function of the surface pressure difference was developed and a theory that attempts to describe this is detailed. While the experimental technique is successful in producing highly controlled, reproducible wrinkles, the theoretical analysis currently overestimates the Young's modulus of the films. The reasons for this as well as avenues for further work are considered. The results of these three investigations all demonstrate the rich physics accessible in ultra-thin polymer films. Furthermore, it points to their potential to b e a key material as devices are more commonly manufactured at the nano-scale.

A theoretical formalism to reconstruct structural and dynamical properties of polymer liquids from their coarse-grained description is developed. This formalism relies on established earlier analytical coarse-graining of polymers derived from the first principles of liquid theory. The polymer chain is represented at a mesoscale level as a soft particle. Coarse-grained computer simulations provide input data to the reconstruction formalism and allow one to achieve the most gain in computational efficiency. The structure of polymer systems is reconstructed by combining global information from mesoscale simulations and local information from small united-atom simulations. The obtained monomer total correlation function is tested for a number of systems including polyethylene melts of different degrees of polymerization as well as melts with different local chemical structure. The agreement with full united-atom simulations is quantitative, and the procedure remains advantageous in computational time. The dynamics in mesoscale simulations is artificially accelerated due to the coarse-graining procedure and needs to be rescaled. The proposed formalism addresses two rescalings of the dynamics. First, the internal degrees of freedom averaged out during coarse-graining procedure are reintroduced in "a posteriori" manner, rescaling the simulation time. The second rescaling takes into account the change in friction when switching from a monomer level description to mesoscopic. Both friction coefficients for monomer and soft particle are calculated analytically and their ratio provides the rescaling factor for the diffusion coefficient. The formalism is extensively tested against the united-atom molecular dynamic simulations and experimental data. The reconstructed diffusive dynamics of the center-of-mass for polyethylene and polybutadiene melts of increasing degrees of polymerization show a quantitative agreement, supporting the foundation of the approach. Finally, from the center-of-mass diffusion the monomer friction coefficient is obtained and used as an input into Cooperative Dynamics theory. The dynamics of polymer chains at any length scale of interest is described through a Langevin equation. In summary, the proposed formalism reconstructs the structure and dynamics of polymer melts enhancing computational efficiency of molecular dynamic simulations. This dissertation includes previously published and unpublished co-authored material.

Traditionally, the experimental model of choice for studying the structure and dynamics of glasses or crystals are hard-sphere colloids. An analogy with molecular or atomic materials is often drawn, in which each colloidal particle represents an atom or a molecule. Making the individual particles deformable allows an even wider range of phenomena to be observed. In this thesis, I report the three-dimensional confocal microscopic study of the structure and dynamics of aqueous suspensions of fluorescently labeled poly(N-Isopropylacrylamide)-co-(Acrylic Acid), or p(NIPAm-co-AAc), microgel particles of hydrodynamic diameter 1.0 - 1.5 μm. Image analysis techniques and particle tracking algorithms are used to quantify the particle dynamics and the suspension structure. The phase behavior of the suspensions is dependent on a number of factors including pH, temperature, and concentration. By adjusting the pH, the interactions between the microgel particles can be tuned from purely repulsive near neutral pH, to weakly attractive at low pH. At low pH and low concentration, dynamic arrest results mainly from crystallization driven by the attraction between particles; crystal nucleation occurs homogeneously throughout the sample. The dynamics is nucleation limited where fast crystallization follows a delay time. At low pH and high concentration, relaxation of the suspension is constrained and it evolves only slightly to form disordered solid. At neutral pH, the dynamics are a function of the particle number concentration only; a high concentration leads to the formation of a disordered soft glassy solid. Additionally, the three-dimensional image stacks are studied to determine crystal structure by calculating pair correlation functions, g(r), bond order parameters, and structure factors, s(q). The results show that crystal structure is independent of concentration, charge, size, and stiffness of particles remaining FCC under all conditions. At low concentrations and low pH, the structures formed are polycrystalline solids. Moreover, the ability of the particles to compress enables the suspensions to maintain their crystal structure when subjected to external stress. The results help us better understand the relationship between dynamics and structure in soft colloidal suspensions, enhance our ability to use the colloids to model materials, and improve applications of the colloids in industrial products.
Physics

A new method, probability distribution of diffusivities (time scaled square displacements between succeeding video frames), was developed to analyze single molecule tracking (SMT) experiments. This method was then applied to SMT experiments on ultrathin liquid tetrakis(2-ethylhexoxy)silane (TEHOS) films on Si wafer with 100 nm thermally grown oxide, and on thin semectic liquid crystal films. Spatial maps of diffusivities from SMT experiments on 220 nm thick semectic liquid crystal films reveal structure related dynamics. The SMT experiments on ultrathin TEHOS films were complemented by fluorescence correlation spectroscopy (FCS). The observed strongly heterogeneous single molecule dynamics within those films can be explained by a three-layer model consisting of (i) dye molecules adsorbed to the substrate, (ii) slowly diffusing molecules in the laterally heterogeneous near-surface region of 1 - 2 molecular diameters, and (iii) freely diffusing dye molecules in the upper region of the film. FCS and SMT experiments reveal a strong influence of substrate heterogeneity on SM dynamics. Thereby chemisorption to substrate surface silanols plays an important role. Vertical mean first passage times (mfpt) in those films are below 1 µs. This appears as fast component in FCS autocorrelation curves, which further contain a contribution from lateral diffusion and from adsorption events. Therefore, the FCS curves are approximated by a tri-component function, which contains an exponential term related to the mfpt, the correlation function for translational diffusion and a stretched exponential term for the broad distribution of adsorption events. Lateral diffusion coefficients obtained by FCS on 10 nm thick TEHOS films, thereby, are effective diffusion coefficients from dye transients in the focal area. They strongly depend on the substrate heterogeneity. Variation of the frame times for the acquisition of SMT experiments in steps of 20 ms from 20 ms to 200 ms revealed a strong dependence of the corresponding probability distributions of diffusivities on time, in particular in the range between 20 ms and 100 ms. This points to average dwell times of the dye molecules in at least one type of the heterogeneous regions (e.g. on and above silanol clusters) in the range of few tens of milliseconds. Furthermore, time series of SM spectra from Nile Red in 25 nm thick poly-n-alkyl-methacrylate (PnAMA) films were studied. In analogy to translational diffusion, spectral diffusion (shifts in energetic positions of SM spectra) can be studied by probability distributions of spectral diffusivities, i.e. time scaled square energetic displacements. Simulations were run and analyzed to study contributions from noise and fitting uncertainty to spectral diffusion. Furthermore the effect of spectral jumps during acquisition of a SM spectrum was investigated. Probability distributions of spectral diffusivites of Nile Red probing vitreous PnAMA films reveal a two-level system. In contrast, such probability distributions obtained from Nile Red within a 25 nm thick poly-n-butylmethacrylate film around glass transition and in the melt state, display larger spectral jumps. Moreover, for longer alkyl side chains a solvent shift to higher energies is observed, which supports the idea of nanophase separation within those polymers.

In this thesis different routes to the formation of extended two-dimensional polymers via on-surface coupling reactions are presented. Polyphenylene networks formed by the molecules tri-(bromo-phenyl)-benzene via on-surface Ullmann coupling reactions are investigated with scanning tunnelling microscopy. The polyphenylene networks with near complete surface coverage exhibit a vitreous structure. The network is composed of linked molecules forming polygons with four to eight edges. A different set of covalently bound molecular nanostructures can be formed on a surface upon thermal activation of porphyrin building blocks. Porphyrin molecules are covalently linked to form one dimensional chains or extended networks using either Ullmann-type coupling reactions to link brominated phenyl sidegroups, or Glaser-Hay-type coupling to form butadiene links via reaction of two phenyl-ethylene sidegroups. The resulting polymers are investigated with scanning tunnelling microscopy and Raman spectroscopy. In a complementary strand of research it is shown that thin films of C60 can promote adhesion between a gold thin film deposited on mica and a solution-deposited layer of the elastomer polymethyldisolaxane (PDMS). This molecular adhesion facilitates the removal of the gold film from the mica support by peeling and provides a new approach to template stripping which avoids the use of conventional adhesive layers. The fullerene adhesion layers may also be used to remove organic monolayers and thin films as well as two-dimensional polymers such as the porphyrin networks discussed previously. Following the removal from the mica support the monolayers may be isolated and transferred to a dielectric surface by etching of the gold thin film, mechanical transfer and removal of the fullerene layer by annealing/dissolution. The use of this molecular adhesive layer provides a new route to transfer polymeric films from metal substrates to other surfaces. A different set of experiments investigated porphyrin nanorings and their interaction with C60 on a gold surface. Solvent-induced aggregates of nanoring cyclic polymers may be transferred by electrospray deposition to a surface where they adsorb as three dimensional columnar stacks. The observed stack height varies from single rings to three stacked rings. Those stacked layers of cyclic porphyrin nanorings constitute nanoscale receptacles with variable height and diameter which preferentially adsorb sublimed C60 molecules. Using scanning tunnelling microscopy the filling capacity of these nanoring traps is determined, as is the dependence of adsorbate capture on stack height and diameter.

This thesis considers two areas of research in non-equilibrium soft matter at the mesoscale. In the first part we introduce active colloids in the context of active matter and focus on the particular case of phoretic colloids. The general theory of phoresis is presented along with an expression for the phoretic velocity of a colloid and its rotational diffusion in two and three dimensions. We introduce a model for thermally active colloids that absorb light and emit heat and propel through thermophoresis. Using this model we develop the equations of motion for their collective dynamics and consider excluded volume through a lattice gas formalism. Solutions to the thermoattractive collective dynamics are studied in one dimension analytically and numerically. A few numerical results are presented for the collective dynamics in two dimensions. We simulate an unconfined system of thermally active colloids under directed illumination with simple projection based geometric optics. This system self-organises into a comet-like swarm and exhibits a wide range of non- equilibrium phenomena. In the second part we review the background of polymer translocation, including key experiments, theoretical progress and simulation studies. We present, discuss and use a common model to investigate the potential of patterned nanopores for stochastic sensing and identification of polynucleotides and other heteropolymers. Three pore patterns are characterised in terms of the response of a homopolymer with varying attractive affinity. This is extended to simple periodic block co-polymer heterostructures and a model device is proposed and demonstrated with two stochastic sensing algorithms. We find that mul- tiple sequential measurements of the translocation time is sufficient for identification with high accuracy. Motivated by fluctuating biological channels and the prospect of frequency based selectivity we investigate the response of a homopolymer through a pore that has a time dependent geometry. We show that a time dependent mobility can capture many features of the frequency response.

Multifunctional polymer nanocomposites (PNCs) are attractive for the design of tunable RF and microwave components such as flexible electronics, attenuators, and antennas due to cost-effectiveness and durability of polymeric matrices. In this work, three separate PNCs were synthesized. Magnetite (Fe3O4) and cobalt ferrite (CFO) nanoparticles, synthesized by thermal decomposition, were used as PNC fillers. Polymers used in this work were a commercial polymer provided by the Rogers Corporation (RP) and polyvinylidene fluoride (PVDF). PNCs in this thesis consist of Fe3O4 in RP, CFO in RP, and Fe3O4 in PVDF. Characterization techniques for determining morphology of the nanoparticles, and their resulting PNCs, include x-ray diffraction, transmission electron microscopy and magnetometry. All magnetometry measurements were taken using a Quantum Design Physical Property Measurement System with a superconducting magnet. Temperature and external magnetic field magnetization measurements revealed that all samples exhibit superparamagnetic behavior at room temperature. Blocking temperature, coercivity and reduced remnant magnetization do not vary with concentration. Tunable saturation magnetization, based on nanoparticle loading, was observed across all PNCs, regardless of polymer or nanoparticle choice, indicating that this is an inherent property in all similar PNC materials. Tunability studies of the magneto-dielectric PNCs were carried out by adding the PNC to cavity and microstrip linear resonator devices, and passing frequencies of 1-6 GHz through them in the presence of transverse external magnetic fields of up to 4.5 kOe, provided by an electromagnet. Microwave characteristics were extracted from scattering parameters of the PNCs. In all cases, losses were reduced, quality factor was increased, and tunability of the resonance frequency was demonstrated. Strong magnetic field dependence was observed across all samples measured in this study.

Depuis son invention en 1986, les microscopes à force atomique (AFM) ont été des puissants outils pour la caractérisation des matériaux et des propriétés des matériaux à l'échelle nanométrique. Cette thèse est entièrement dédiée à la mesure de l'interaction entre une sonde AFM et une surface avec une nouvelle technique AFM appelée Force Feedback Microscopy (FFM). La technique a été développée et utilisée pour l'étude d'échantillons biologiques. Le principe central de la technologie FFM est que la force totale moyenne appliquée à la pointe est égal à zéro. En conséquence, en présence d'une interaction pointe-échantillon, une force égale et contraire doit être appliquée à la pointe par une boucle de rétroaction. La force de réaction est ici appliquée à la pointe à travers le déplacement d'un petit élément piézoélectrique positionné à la base du levier AFM. La boucle de rétroaction permet d'éviter instabilités mécaniques tels que le saut au contact, permettant la mesure complète de la courbe d'interaction. En plus, il donne la possibilité de mesurer simultanément les parties élastique et inélastique de l'interaction. La technique a été appliquée à l'étude des interactions à l'interface solide/gaz, avec un intérêt particulier pour l'observation de la formation et de la rupture des ponts capillaires entre pointe et échantillon. Ensuite, on a focalisé notre attention aux interfaces solide/liquide. Dans ce contexte, courbes complètes de type DLVO sont caractérisées d'un point de vue élastique et dissipatif. Nous avons développé des nouveaux modes d'imagerie AFM pour l'étude des biomolécules. Images de phospholipides et de l'ADN à force constante ont été réalisées et certaines propriétés mécaniques comme le module de Young des échantillons ont été évaluées. En plus, nous avons réalisé une étude spectroscopique de l'élasticité et du coeffcient d'amortissement de l'interaction entre des cellules vivantes de type PC12 et une pointe AFM en nitrure de silicium. L'étude montre que le FFM est un instrument capable de mesurer l'interaction à des fréquences qui ne sont pas nécessairement liées aux résonances caractéristiques du levier. L'étude spectroscopique pourrait avoir dans le futur des applications importantes pour l'étude des biomolécules et des polymères.

The properties of conventional materials are inextricably linked with their molecular composition; to make water flow like wine would require changing its molecular identity. To circumvent this restriction, I have contstructed and characterized a two-dimensional metafluid, so-called because its constitutive dynamics are derived not from atoms and molecules but from macroscopic, chaotic surface waves excited on a vertically agitated fluid. Unlike in conventional fluids, the viscosity and temperature of this metafluid are independantly tunable. Despite this unconventional property, our system is surprisingly consistent with equilibrium thermodynamics, despite being constructed from macroscopic, non-equilibrium elements. As a programmable material, our metafluid represents a new platform on which to study complex phenomena such as self-assembly and pattern formation. We demonstrate one such application in our study of short-chain polymer analogs embedded in our system.

Research on alternative energies has become an area of increased interest due to economic and environmental concerns. Green energy sources, such as ocean, wind, and solar power, are subject to predictable and unpredictable generation intermittencies which cause instability in the electrical grid. This problem could be solved through the use of short term energy storage devices.

Capacitors made from composite polymer:nanoparticle thin films have been shown to be an economically viable option. Through thermal vapor deposition, we fabricated dielectric thin films composed of the polymer polyvinylidine fluoride (PVDF) and the ceramic nanoparticle titanium dioxide (TiO₂). Fully understanding the deposition process required an investigation of electrode and dielectric film deposition. Film composition can be controlled by the mass ratio of PVDF:TiO₂ prior to deposition. An analysis of the relationship between the ratio of PVDF:TiO₂ before and after deposition will improve our understanding of this novel deposition method.

X-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy were used to analyze film atomic concentrations. The results indicate a broad distribution of deposited TiO₂ concentrations with the highest deposited amount at an initial mass concentration of 17% TiO₂.

The nanoparticle dispersion throughout the film is analyzed through atomic force microscopy and energy dispersive x-ray spectroscopy. Images from these two techniques confirm uniform TiO₂ dispersion with cluster size less than 300 nm. These results, combined with spectroscopic analysis, verify control over the deposition process.

Capacitors were fabricated using gold parallel plates with PVDF:TiO ₂ dielectrics. These capacitors were analyzed using the atomic force microscope and a capacohmeter. Atomic force microscope images confirm that our gold films are acceptably smooth. Preliminary capacohmeter measurements indicate capacitance values of 6 nF and break down voltages of 2.4 V.

Our research on the deposition process will contribute to the understanding of PVDF/TiO₂ composite thin films. These results will lead to further investigation of PVDF/TiO₂ high density energy storage capacitors. These capacitors can potentially increase the efficiency of alternative energy sources already in use.

This thesis, which contains fourteen chapters in two parts, presents theoretical and computer simulation studies of dynamics in supercooled liquids and thermotropic liquid crystals. These two apparently diverse physical systems are unified by a startling similarity in their complex slow dynamics. Part I consists of six chapters on supercooled liquids while Part II comprises seven chapters on thermotropic liquid crystals. The fourteenth chapter provides a concluding note. Part I starts with an introduction to supercooled liquids given in chapter 1. This chapter discusses basic features of supercooled liquids and the glass transition and portrays some of the theoretical frameworks and formalisms that are widely recognized to have contributed to our present understanding. Chapter 2 introduces a new model of binary mixture in order to study dynamics across the supercooled regime. The system consists of an equimolar mixture of the Lennard-Jones spheres and the Gay-Berne ellipsoids of revolution, and thus one of its components has orientational degrees of freedom (ODOF). A decoupling between trans-lational diffusion and rotational diffusion is found to occur below a temperature where the second rank orientational correlation time starts showing a steady deviation from the Arrhenius temperature behavior. At low temperatures, the optical Kerr effect (OKE) signal derived from the system shows a short-to-intermediate time power law decay with a very weak dependence on temperature, if at all, of the power law exponent as has been observed experimentally. At the lowest temperature investigated, jump motion is found to occur in both the translational and orientational degrees of freedom. Chapter 3 studies how the binary mixture, introduced in the previous chapter, explores its underlying potential energy landscape. The study reveals correlations between the decoupling phenomena, observed almost universally in supercooled molecular liquids, and the manner of exploration of the energy landscape of the system. A significant deviation from the Debye model of rotational diffusion in the dynamics of ODOF is found to begin at a temperature at which the average inherent structure energy of the system starts falling as the temperature decreases. Further, the coupling between rotational diffusion and translational diffusion breaks down at a still lower temperature, where a change occurs in the temperature dependence of the average inherent structure energy. Chapters 4-6 describe analytical and numerical approaches to solve kinetic models of glassy dynamics for various observables. The β process is modeled as a thermally activated event in a two-level system and the a process is described as a β relaxation mediated cooperative transition in a double-well. The model resembles a landscape picture, conceived by Stillinger [Science 267, 1935 (1995)], where the a process is assumed to involve a concerted series of the β processes, the latter being identified as elementary relaxations involving transitions between contiguous basins. For suitable choice of parameter values, the model could reproduce many of the experimentally observed features of anomalous heat capacity behavior during a temperature cycle through the glass transition as described in chapter 4. The overshoot of the heat capacity during the heating scan that marks the glass transition is found to be caused by a delayed energy relaxation. Chapter 5 shows that the model can also predict a frequency dependent heat capacity that reflects the two-step relaxation behavior. The high-frequency peak in the heat capacity spectra appears with considerably larger amplitude than the low-frequency peak, the latter being due to the a relaxation. The model, when simplified with a modified description of the a process that involves an irreversible escape from a metabasin, can be solved analytically for the relaxation time. This version of the model captures salient features of the structural relaxation in glassy systems as described in chapter 6. In Part II, thermotropic liquid crystals are studied in molecular dynamics simulations using primarily the family of the Gay-Berne model systems. To start with, chapter 7 provides a brief introduction to thermotropic liquid crystals, especially from the perspective of the issues discussed in the following chapters. This chapter ends up with a detail description of the family of the Gay-Berne models. Chapter 8 demonstrates that a model system for calamitic liquid crystal (comprising rod-like molecules) could capture the short-to-intermediate time power law decay in the OKE signal near the isotropic-nematic (I-N) phase transition as observed experimentally. The single-particle second rank orientational time correlation function (OTCF) for the model liquid crystalline system is also found to sustain a power law decay regime in the isotropic phase near the I-N transition. On transit across the I-N phase boundary, two power law decay regimes, separated by a plateau, emerge giving rise to a step-like feature in the single-particle second rank OTCF. When the time evolution of the rotational non-Gaussian parameter is monitored as a diagnostic of spatially heterogeneous dynamics, a dominant peak is found to appear following a shoulder at short times, signaling the growth of pseudonematic domains. These observations are compared with those relevant ones obtained for the supercooled binary mixture, as discussed in chapter 2, in the spirit of the analogy suggested recently by Fayer and coworkers [J. Chem. Phys. 118, 9303 (2003)]. In chapter 9, orientational dynamics across the I-N transition are investigated in a variety of model systems of thermotropic liquid crystals. A model discotic system that consists of disc-like molecules as well as a lattice system have been considered in the quest of a universal short-to-intermediate time power law decay in orientational relaxation, if any. A surprisingly general power law decay at short to intermediate times in orientational relaxation is observed in all these systems. While the power law decay of the OKE signal has been recently observed experimentally in calamitic systems near the I-N phase boundary and in the nematic phase by Fayer and coworkers [J. Chem. Phys. 116, 6339 (2002), J. Phys. Chem. B 109, 6514 (2005)], the prediction for the discotic system can be tested in experiments. Chapter 10 presents the energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals by determining the inherent structures of a family of one-component Gay-Berne model systems. This study throws light on the interplay between the orientational order and the translational order in the mesophases the systems exhibit. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures. The inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the I-N transition and this breakdown is found to occur at a temperature below which the system explores increasingly deeper potential energy minima. There exists a remarkable similarity in the manner of exploration of the potential energy landscape between the Gay-Berne systems studied here and the well known Kob-Andersen binary mixture reported previously [Nature, 393, 554 (1998)]. In search of a dynamical signature of the coupling between orientational order and translational order, anisotropic translational diffusion in the nematic phase has been investigated in the Gay-Berne model systems as described in chapter 11. The translational diffusion coefficient parallel to the director D// is found to first increase and then decrease as the temperature drops through the nematic phase. This reversal occurs where the smectic order parameter of the underlying inherent structures becomes significant for the first time. The non-monotonic temperature behavior of D// can thus be viewed from an energy landscape analysis as a dynamical signature of the coupling between orientational and translational order at the microscopic level. Such a view is likely to form the foundation of a theoretical framework to explain the anisotropic translation diffusion. Chapter 12 investigates the validity of the Debye model of rotational diffusion near the I-N phase boundary with a molecular dynamics simulation study of a Gay-Berne model system for calamitic liquid crystals. The Debye model is found to break down near the I-N phase transition. The breakdown, unlike the one observed in supercooled molecular liquids where a jump diffusion model is often invoked, is attributed to the growth of orientational pair correlation. A mode-coupling theory analysis is provided in support of the explanation. Chapter 13 presents a molecular dynamics study of a binary mixture of prolate ellipsoids of revolution with different aspect ratios interacting with each other through a generalized Gay-Berne potential. Such a study allows to investigate directly the aspect ratio dependence of the dynamical behavior. In the concluding note, chapter 14 starts with a brief summary of the outcome of the thesis and ends up with suggestion of a few relevant problems that may prove worthwhile to be addressed in future.

In this dissertation we use digital holographic quantitative phase microscopy to observe and measure phase-only structures due to induced photothermal interactions and nanoscopic structures produced by photomechanical interactions. Our use of the angular spectrum method combined with off-axis digital holography allows for the successful hologram acquisition and processing necessary to view these phenomena with nanometric and, in many cases, subnanometric precision. We show through applications that this has significance in metrology of bulk fluid and interfacial properties. Our accurate quantitative phase mapping of the optically induced thermal lens in media leads to improved measurement of the absorption coefficient over existing methods. By combining a mathematical model describing the thermal lens with that describing the surface deformation effect of optical radiation pressure, we simulate the ability to temporally decouple the two phenomena. We then demonstrate this ability experimentally as well as the ability of digital holography to clearly distinguish the phase signatures of the two effects. Finally, we devise a pulsed excitation method to completely isolate the optical pressure effect from the thermal lensing effect. We then develop a noncontact purely optical approach to measuring the localized surface properties of an interface within a system using a single optical pressure pulse and a time-resolved digital holographic quantitative phase imaging technique to track a propagating nanometric capillary disturbance. We demonstrate the method's ability to accurately measure the surface energy of pure media and chemical monolayers formed by surfactants with good agreement to published values. We discuss the possible adaptation of this technique to applications for living biological cell membranes.

xix, 190 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
The electrical properties of conducting polymer-based devices are investigated in order to better understand charge transport through conducting polymers and charge transfer at conducting polymer interfaces with metals and inorganic semiconductors. Experiments on two specific systems are reported: (1) an anionically functionalized conducting polymer between metal electrodes and (2) nanostructured doped conducting polymer-semiconductor interfaces. Temperature dependent impedance measurements are reported on an anionically functionalized polyacetylene sandwiched between two gold electrodes (Au|P A |Au). These measurements provide key quantities regarding the ionic carriers in this system, such as the characteristic frequency for electrode polarization, ionic DC conductivity, activation energy, effective ion concentration, and hopping frequency. Impedance measurements are also reported on samples where excess electronic carriers had been introduced with a DC bias and at temperatures sufficiently low so as to freeze out the ionic carriers. In addition to providing information about the dielectric relaxation of electronic carriers such as the characteristic frequency for electrode polarization and activation energy, these low-temperature impedance measurements also support the ionic dielectric relaxation assignments. Temperature-dependent potential step experiments, in combination with the dielectric measurements probing ionic carriers, demonstrate the direct connection between the redistribution of ions and an enhancement in carrier injection in the Au|P A |Au system. Further potential step experiments followed by relaxation through either a short- or open-circuit configuration demonstrate that the electric field distribution is closely related to the amount of injected electronic carriers. The electric field distribution changes from being mostly determined by ionic carriers to being jointly determined by both ionic and injected electronic carriers when the density of injected electronic carriers is higher than that of the effective ionic carriers. To investigate charge depletion and transport at length scales less than the depletion width of a semiconductor interface, nanoscale metal-InP contacts with low barrier height were embedded within conducting polymer-InP contacts with high barrier height. Electrical measurements on these hybrid interfaces indicate that charge transport across the nanoscale metal contacts is affected by the neighboring high barrier region when the size of the metal contacts is less than the depletion width of the conducting polymer-InP background.
Adviser: Mark Lonergan