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<p>U ovom radu pripremljeni su različiti polimerni i keramički nanostrukturni materijali, u cilju ispitivanja uticaja vrste i udela nanopunila (čađ, fuleren, silicijum(IV)oksid, aluminijum(III)oksid i titanijum(IV)oksid) na strukturu, reolo&scaron;ko i toplotno pona&scaron;anje kompozita, dobijenih na osnovu stirena, metilmetakrilata i akrilamida, primenom različitih metoda sinteze. Ispitivan je uticaj prisustva različitog udela nanočestica (1, 3 i 5 %<em> m/m</em>) na kinetiku polimerizacije stirena, i na oblast prelaska u staklasto stanje polistirenskih hibridnih materijala. Sintetisana je i serija nanokompozita polimerizacijom metilmetakrilata u prisustvu čestica (silicijum(IV)oksid, aluminijum (III)oksid i titanijum(IV)oksid) različitih dimenzija i hidrofilnosti, ali istog zapreminskog udela (1 %<em> v/v</em>). Na osnovu primene izotermne diferencijalno skanirajude metode (DSC), razvijen je kinetički model za opisivanje dve razičite reakcije tokom polimerizacije vinilnih monomera (reakciju prvog reda i samoubrzanje), i izračunata je debljina međufaznog sloja polimera na čestici u cilju određivanja njegovog uticaja na temperaturu prelaska u staklasto stanje hibridnih materijala. Za ispitivanje strukture i morfologije polistiren/silicijum(IV)oksid nanokompozita dobijenih metodom isparavanja rastvarača, kori&scaron;dene su infracrvena spektroskopija sa Furijeovom transformacijom (FT-IR) i skanirajuda elektronska mikroskopija (SEM). Radi utvrđivanja uticaja udela hidrofobnog silicijum(IV)oksida (2, 5, 10, 15 i 30 %<em> m/m</em>) na toplotnu postojanost polistirenskih materijala, primenjene su istovremena termogravimetrijska i diferencijalno skanirajuda analiza (TG-DSC). Takođe, određen je uticaj veličine čestice fulerena C60 i submikronske čestice čađi na reolo&scaron;ka svojstva polistirenskih kompozita sintetisanih taloženjem polimera iz rastvora. Ispitivanjem reolo&scaron;kog pona&scaron;anja hibridnih materijala, proučavan je uticaj veličine čestica, molekulske mase polimera i indeksa polidisperznosti na viskoznost polistirenskih kompozita. Na osnovu<em> in-situ</em> reolo&scaron;kih analiza polimerizacije u toku želiranja suspenzije nanočestica aluminijum(III)oksida u vodenom rastvoru monomera metakrilamida i N,N&rsquo;-metilenbisakrilamida, utvrđena je jaka katalitička aktivnost povr&scaron;ine aluminijum(III)oksida na nastajanje slobodnih radikala. Radi nalaženja veze između željenih svojstava keramičkih proizvoda i načina njihovog dobijanja, proučavan je uticaj uslova vođenja polimerizacije na slaganje čestica u dobijenom odlivku i na gustinu krajnjeg sinterovanog proizvoda.</p> / <p>In this work, polymeric and ceramic nanostructured materials were prepared using different methods, in order to investigate the influence of nanofiller content and its type (carbon black, fullerene, silica, alumina and titania) on the structure, rheological and thermal behavior of composites, based on styrene, methylmethacrylate and acrylamide. The effect of particles content (1, 3 and 5 wt. %) on the kinetics of styrene radical polymerization and on the glass transition temperature of polystyrene/silica composites was investigated. A series of polymethylmethacrylate nanocomposites containing 1 vol. % of silica, alumina or titania particles (differing in dimensions and surface properties) was obtained. On the basis of isothermal differential scanning calorimetry (DSC), the kinetic model for describing two reactions during vinyl monomer polymerization (first order and autoacceleration) was developed, and the thickness of interfacial layer formed on nanoparticle surface was determined, in order to investigate its influence on the glass transition temperature of polymethylmethacrylate hybrid materials. The structure and the morphology of polystyrene/silica nanocomposites prepared by solvent evaporation were investigated using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The influence of&nbsp; hydrophobic silica content (2, 5, 10, 15 and 30 wt. %) on polystyrene thermal stability was studied by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). The effect of fullerene C60 and submicron carbon black particle size on rheological properties of polystyrene composites prepared by the rapid coprecipitation was determined. Following the rheology of hybrid melts, the influence of filler size, molecular weight and polydispersity of polymer matrix on the viscosity of polystyrene composites was studied. On the basis of in-situ rheology analysis of polymerization process during the gelation of alumina nanoparticles suspension in aqueous solution of methacrylamide and N,N&rsquo;- methylene bisacrylamide monomers, the strong catalytic activity of alumina surface on the free radicals formation was determined. In order to find the correlation between desired properties of ceramic products and their preparation procedure route, the influence of polymerization conditions on the green body structure and sintered body density was studied in details.</p>

Ce travail concerne l'élaboration de matériaux hybrides à base de matrices hôtes polymères et de nanocristaux de carbure de silicium (SiC) et l'étude de leurs propriétés électro-optiques. Dans ce contexte, différents échantillons de SiC ont été synthétisés par pyrolyse laser d'un mélange gazeux (silane, acétylène) et deux nanopoudres représentatives ont principalement été exploitées. Les études spectroscopiques ont révélé des états de surface différents, conditionnant les interfaces au sein du composite final. Le dépôt de films minces hybrides a été effectué à partir de suspensions précurseurs homogènes de qualité contrôlée, suivi de traitements thermiques et électriques appropriés. Enfin, au travers de l'étude de différents paramètres (concentration en nanocristallites SiC, état de surface, nature du polymère, etc.), la mesure des coefficients électro-optiques effectifs (Pockels et Kerr), par l'utilisation d'un montage adapté à la géométrie des échantillons, a révélé le rôle prépondérant de l'interface SiC-polymère sur la réponse des composites. Avec des coefficients électro-optiques effectifs de l'ordre de 5 à 7 pm/V, ces composites présentent des performances comparables à celle des cristaux électro-optiques standards et permettent d'envisager une application du système hybride SiC/polymère pour l'optoélectronique intégrée.

Cette thèse porte sur l'étude et la modélisation de l'orientation de fibres de verre dans des thermoplastiques renforcés. Dans une optique de maîtrise et de compréhension du comportement des composites renforcés de fibres longues, nous proposons dans ce travail d'étudier les phénomènes d'orientation et la rhéologie de ces suspensions. Une approche expérimentale a permis de caractériser l'orientation et la structure des fibres dans des pièces injectées. L'analyse de la distribution de longueur des fibres dans une pièce a mis en évidence que la casse des fibres se faisait préférentiellement durant la phase de la plastification de la matière. Les mesures d'orientation, réalisées avec des techniques de mesure 2D et 3D montrent que la concentration en fibres est un paramètre déterminant sur la formation et les caractéristiques de la structure coeur-peau. Une approche numérique de modélisation de l'orientation des fibres dans des pièces injectées, basée sur le calcul direct du mouvement d'orientation d'une population de fibres en écoulement, a permis d'accéder à la physique intrinsèque de la suspension. Ce modèle repose sur une formulation éléments finis multi- domaine développée dans le cadre du logiciel Rem3D. La principale originalité du modèle est qu'il n'est pas nécessaire d'exprimer de manière explicite l'ensemble des forces et interactions hydrodynamiques régissant le système. Lorsqu'on applique un cisaillement simple à un volume élémentaire représentatif, le calcul de simulation directe nous permet d'étudier les phénomènes d'interaction entre particules en fonction de la concentration et du rapport de forme des fibres. Ainsi, nous proposons une méthode d'identification du coefficient d'interaction Ci , paramètre déterminant du modèle statistique de Folgar & Tucker. Les valeurs de Ci sont fonction du rapport de forme et de la concentration des particules. On s'intéresse d'autre part à la validité des approximations de fermeture. On montre que l'approximation hybride est satisfaisante dans le cas d'un écoulement de cisaillement simple. Enfin, ce modèle est appliqué à l'étude rhéologique d'une suspension de fibres.

‘Soft condensed matter’ is a newly-emerged sub-discipline of physics concerned with the study of systems that are mechanically soft such as colloids, emulsions, surfactants, polymers, liquid crystals, granular media and various biomaterials including DNA and proteins. These materials display a broad range of interesting microstructures and phase behaviours and have a myriad of applications in the materials, food, paint and cosmetic industries as well as medical technologies. Soft condensed matter physics presents new opportunities and challenges for the development of new ideas and concepts in experimental and theoretical physics alike. Because the field overlaps with many different disciplines, the study of soft matter also offers promising developments to other fields of science including chemistry, chemical engineering, materials science, biology, and environmental science. The behaviour of these systems is dominated by one simple fact: they contain mesoscopic structures in the size range 10 nm to 1 µm that are held together by weak entropic forces. The elastic constants of these materials are 109 times smaller than the conventional atomic materials and hence are easily deformable by external stresses, electric or magnetic fields, or even by thermal fluctuations. We have studied two important classes of soft matter systems in this thesis -colloidal suspensions and surfactant systems. The thesis is divided into two main themes: (a) Effects of electric field on the colloidal suspensions, and (b) Effects of shear on surfactant solutions. Motions of colloidal particles under the influence of applied electric field were observed under a microscope and were studied using image analysis and particle tracking. We have also used tracking of thermal fluctuations of colloidal particles embedded in surfactant gels to study microrheology of surfactant solutions. Linear and non-linear rheology of aqueous solutions of cationic cetyltrimethyl ammonium bromide (CTAB) and anionic sodium-3-hydroxynapthalene-2-carboxylate (SHNC) were studied using bulk rheology in a commercial rheometer. Rheological studies of an anionic surfactant sodium dodecyl sulphate (SDS) in the presence of strongly binding counterion p-toluidine hydrochloride (PTHC) has also been done. Chapter 1 starts with a general introduction to soft condensed matter systems and then we proceed to describe two specific class of soft condensed materials which we have studied in this thesis -colloidal suspensions and surfactant/water systems. After describing different types of colloids, we discuss why colloids are suitable as model systems in condensed matter physics. This is followed by a discussion on the chemical structure, phase behaviour and self assembling properties of surfactant molecules in water. We then discuss the inter-macromolecular forces such as van der Waals interaction, the screened Coulomb repulsion, hydrogen bond, hydrophobic and hydration forces and steric repulsion which are the major players in the interaction in soft condensed matter systems. The systems that have been the subject of our experimental studies, viz. polystyrene colloidal suspensions, CTAB+SHNC, SDS+PTHC and CTAT have also been discussed in detail. Then we have given an overview of effects of electric field on the colloidal suspensions. Two types of geometries have been discussed: one in which the field is parallel to the plates and another when the field is perpendicular to the electrodes. Application of colloidal particles in diagnostic tests (Latex Agglutination Tests) has been discussed after this. Some methods used to enhance the sensitivity of LATs have also been reviewed. This is followed by a theoretical background of linear and non-linear rheology. We have also given an introduction to digital video microscopy, its advantages and discussed few quantities like pair correlation function, structure factor which can be extracted using digital video microscopy and particle tracking. The concluding part of this chapter describes the organization of this thesis. Chapter 2 discusses the experimental apparatus and techniques used in our studies. We describe our setup for applying the electric field to the colloidal particles and imaging and tracking their motion. We also discuss the image processing and analyzing methods for extracting the useful quantities from the digitized images. We have described the various components of the MCR-300 stress-controlled rheometer (Paar Physica, Germany) and the AR-1000N stress-controlled rheometer (T. A. Instruments, U. K.) followed by different experimental geometries that we have used for our experiments. Next we have described the various experiments that can be done using a commercial rheometer. Calculation of surface charge of colloidal particles using a conductivity meter has been demonstrated for our colloidal particle suspensions. We also describe the sample preparation methods employed in different experiments. In Chapter 3, we have discussed our study of clustering of colloidal particles under the influence of an ac electric field as a function of frequency. The field was applied in a direction perpendicular to the confining walls. Two regimes are observed, a low frequency regime where the clusters are isotropic with a local triangular order and a new high-frequency regime where the clusters are highly elongated (anisotropic) with no local order. The crossover from one regime to the other occurs at a critical frequency, fc. The formation of elongated clusters seen at high frequencies is explained in terms of rotation of particles due to a phase lag between the polarization of the electric double layer around a particle and the applied electric field that arises because of inhomogeneities of the conducting surface. We have also observed that the threshold field for the cluster formation, Eth, increases with frequency in both the regimes. We did these studies on two different sizes of particles and found that both Eth and fc were lower for the larger particles. Our model based on particle rotation was able to estimate the value of fc correctly for both the sizes of the particles. Chapter 4 describes a method employing an ac electric field applied perpendicular to the confining walls to increase the sensitivity of recognition of ligands by their corresponding receptors grafted on Brownian latex particles. Application of electric field assists the colloidal micro-particles grafted with receptors to come nearer due to electro-hydrodynamic drag. This increase in the local concentration of the latex particles results in improving the chances of ligand-receptor interaction leading to the aggregation of the latex particles. With this technique we have been able to increase the sensitivity of the ligand-receptor recognition by a factor as large as 50. We have demonstrated the utility of our method using streptavidin as the model receptor and biotinylated RNase A as the model ligand. We have also applied our technique to a commercially available kit for rheumatoid factor (RF) with successful results. The same method was also successfully applied for the detection of typhoid whose antibodies were purified and attached to polystyrene particles by our collaborators from DRDE Gwalior. In Chapter 5, we have studied the statics and dynamics of colloidal particles at different applied electric fields from zero to beyond the threshold field. We have taken a series of time-lapsed images and calculated out the pair-correlation function, mean squared displacement, structure factor, non-Gaussian parameter etc. We have studied both mono-dispersed colloidal system and binary colloidal system (mixture of two different sizes of particles). The aggregates formed in the two cases were analysed with the help of Voronoi polygons to quantify the microscopic structure. In mono-dispersed system, the aggregates formed were two-dimensional hexagonal crystals and we have used this system to study the freezing transition in 2-dimension. The properties of the system in the liquid and the crystalline state satisfy various criteria for the 2-d freezing transition. The first maximum of the structure factor at the voltage at which freezing occurs, is 5.5 as has been suggested for the 2-d freezing. This is reflected in the dynamics of the system also, where the ratio D/D0 falls below 10%, in accordance with the LPS (L¨owen, Palberg, Simon) criterion for freezing in 2-d colloidal systems [Phys. Rev. Lett. 70, 1557 (1993)]. However, in the binary colloidal system the clusters formed were not crystalline but more like 2-d dense liquids. A closer inspection of these clusters reveals that the motion of a smaller subset of particles is cooperative and follows string-like paths. The mean square displacement of such a system shows a plateau in the intermediate times which indicates the “caging” of particles by its neighbours. A peak in non-gaussian parameter indicates the presence of dynamical heterogeneities in the system. In Chapter 6, we have described the use of multiple particle tracking to study the microrheology of semidilute solutions of wormlike micelles and compared the results with those from macrorheology experiments done on the same samples. Two concentrations of CTAT (1.3% and 2%) were used. We observed that, in spite of the mesh size being much smaller than the size of the probe particles, the viscoelastic response function calculated using the one-point microrheology does not match with that measured from macrorheology. This can be attributed to the fact that there is another important length scale in the system, the mean micellar length, and it is comparable to the probe particle size. Two-point microrheology was successful in verifying the macrorheology results for CTAT 1.3% but it fails to do so for CTAT 2%. We attribute this to the fact that in a higher viscosity sample (2%), the hydrodynamic force propagate to a lesser distance, thereby limiting the measurable correlation between the particles and precluding the success of two-point microrheology. Chapter 7 describes a rheological study of aqueous solutions of varying concentration of cationic cetyltrimethyl ammonium bromide (CTAB) and anionic sodium-3-hydroxynapthalene-2-carboxylate (SHNC) kept at a fixed molar concentration ratio [CTAB]/[SHNC] = 2. At this molar ratio, the surfactants self-assemble into wormlike micelles which get entangled above the overlap concentration to form viscoelastic gel. The range of the total surfactant concentration φ varies from 1.17% to 5.16% by weight. We found that, plateau modulus, G0, shows a power law dependence on the surfactant concentration, φ, with an exponent 3, which is higher than the expected value of 2.25 observed for the one-component wormlike micelles. Zero shear viscosity, η0, and relaxation time, τR show a maximum at the surfactant concentration, φmax = 1.9% in contrast to a monotonic increase with φ. We propose that this non-monotonic behaviour is due to the unusual dependence of the average micellar length L ¯on φ, showing a maximum in average micellar length L at φmax. This argument provides a strong support to the model of micellar growth in the presence of electrostatic interactions developed by Mackintosh et. al [Europhys. Lett. 12, 697 (1990)]. The presence of electrostatic interactions also appears in the behaviour of the plateau modulus G0 that exhibits a larger φ dependence than in highly screened micelles. In the non-linear flow experiments, a minimum observed in critical shear rate (the shear rate at which shear thinning starts), ˙γc, at φmax strengthens our arguments. In Chapter 8, we describe the phase behaviour and rheology of SDS+PTHC (sodium dodecyl sulphate + p-toluidine hydrochloride) micellar solutions at different molar ratios α=[PTHC]/[SDS]) of the two components. At low values of α, polarizing microscopy observations reveal a transition from an isotropic to a nematic phase of disk-like micelles, whereas a transition to a lamellar phase occurs at higher α values > 0.5, on increasing the surfactant content. Linear rheology of the isotropic micellar solution reveal a viscous behaviour over a large range of surfactant concentrations. Surprisingly, this also extends to the nematic phase of disk-like micelles observed at α =0.2 and φ =0.35. These systems also exhibit a viscoelastic behaviour over a narrow range of surfactant concentration as reported in earlier studies. The extent of the viscoelastic region of the isotropic micellar solution also decreases with increase in α. Frequency sweep curves in this region, scaled on to a master curve is reminiscent of dilute suspensions of hard spheres or rigid Brownian rods. Consistent with the results from oscillatory shear measurements, the f;ow behaviour examined under steady shear is Newtonian over a large range of surfactant content in the isotropic micellar solution. An interesting result in these studies is the non-monotonic behaviour of the viscosity with increase in surfactant concentration. It is likely that the sharp rise in viscosity arises from a jamming effect of the rigid rods. Dynamic light scattering studies suggest that the drop in viscosity is due to the decrease in the length of the micellar aggregates. This is followed by a change in the morphology of the micelles from rods to disks as indicated by the transition to a nematic phase of disk-like micelles or a lamellar phase. A change in the morphology of micellar aggregates with increase in α is expected in mixed surfactant systems with strongly binding counterions. However, the surprising result is the change in morphology of the micellar aggregates with surfactant content. Such a behaviour is seen in mixed surfactant systems for the first time. The thesis concludes with a summary of our main results and a brief discussion of the scope of future work in Chapter 9.

Gegenstand dieser Arbeit war das Stabilitätsverhalten von binären kolloidalen Suspensionen mit hohen Feststoffkonzentrationen (z. B. keramische Suspensionen). Dabei wurde die Stabilität mit Hilfe des Sedimentationsverhaltens bewertet und mit dem Grenzflächenzustand korreliert, der als effektives Zetapotenzial erfasst wurde. Die Untersuchungen erfolgten an drei Oxiden mit unterschiedlichen physiko-chemischen Eigenschaften, wobei die Suspensionszusammensetzung und der pH-Wert über weite Bereiche variiert wurden. Ein wesentliches Ergebnis dieser Arbeit besteht im Nachweis, dass die Löslichkeit der einzelnen partikulären Komponenten in den binären Suspensionen zu einer gegenseitigen Beeinflussung der Grenzflächeneigenschaften führt und dadurch das Stabilitätsverhalten des gesamten Systems maßgeblich bestimmt. Von Relevanz ist zudem das Mischungsverhältnis, von dem zum einen das Löse- und Adsorptionsverhalten und zum anderen die Morphologie von Heteroaggregaten abhängt und das auf diese Weise auch für das makroskopische Verhalten entscheidend ist. Die Arbeit zeigt deutlich, dass das Reich der Kolloide neben universellen Mechanismen von stoffspezifischen Phänomenen beherrscht wird. Daraus folgt, dass eine allumfassende Behandlung der Stabilität nicht möglich ist. Vielmehr kann nur an Beispielen demonstriert werden, welche Art von Phänomenen auftreten und wie sie genutzt oder vermieden werden können.

Made available in DSpace on 2016-12-12T20:27:39Z (GMT). No. of bitstreams: 1 Heric Denis Farias.pdf: 2196819 bytes, checksum: ebe776ba26727b6ab81d9c4b1fb49e5d (MD5) Previous issue date: 2016-09-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The application of high electric fields on biological cells causes the formationof pores in the cell membrane, thereby causing an increase in their permeability. This phenomenon, called electropermeabilization have attracted increasing attention due to its wide application in biotechnology. Even being known for decades, the pore opening process in biological cell membranes is still not fully understood, nor was it even properly modeled. In this paper, two types of modeling are presented, which allow characterizing the electropermeabilization in biological cell suspensions. One of the methods is based on the analysis of the electrical impedance spectra of suspensions using genetic algorithm to determine parameters of a generic model dielectric dispersion. The other method uses instantaneous voltage and current values applied to a cell suspension during the electroporation experiment to determine the variation of the medium conductivity and thus, through the analytical model proposed by Ramos and colleagues (RAMOS et al., 2012), determine the cell conductivities. By modeling the impedance spectrum, it was observed the change in the dielectric dispersion of the sample due to the electropermeabilization process, in addition to obtaining the electrical conductivity and permittivity of the involved media. Using the electroporated cell model proposed by Ramos and colleagues (RAMOS et al., 2012), it was possible to determine the change of membrane conductance during the electropermeabilization. The validity of this model is assessed using finite element simulations, which showed good agreement with the analytical model used. Genetic algorithms are used in obtaining the parameters of the various models presented, showing great robustness in obtaining parameters based on the git between experimental and theoreticalcurves. / A aplicação de campos elétricos intensos em células biológicas provoca a formação de poros na membrana celular, causando assim o aumento de sua permeabilidade. Este fenômeno, denominado de eletropermeabiliza ção têm atraído cada vez mais atenção devido a sua ampla aplicação em biotecnologia. Mesmo sendo conhecido há várias décadas, o processo de abertura de poros em membranas de células biológicas ainda não é plenamente entendido e nem foi ainda corretamente modelado. Neste trabalho, apresenta-se dois tipos de modelagem que permitem a caracterização da eletropermeabilização em suspensões de células biológicas. Um dos métodos baseia-se na análise do espectro de impedância elétrica de suspensões com o uso de algoritmo genético para determinar parâmetros de um modelo genérico de dispersão dielétrica. O outro método utiliza valores instantâneos de tensão e corrente aplicados em uma suspensão de células durante um experimento de eletropermeabiliza ção para determinar a variação da condutividade do meio e com isso, através do modelo analítico proposto por Ramos e colaboradores (RAMOS et al., 2012), determinar a condutividade das células. Através da modelagem do espectro de impedância, foi possível verificar a alteração da dispersão dielétrica da amostra devido ao processo de eletropermeabiliza ção, além da obtenção das condutividades e permissividades elétricas dos meios envolvidos. Utilizando o modelo de célula eletropermeabilizada proposto por Ramos e colegas (RAMOS et al., 2012), foi possível obter a variação da condutância de membrana durante a eletropermeabilização. A validade deste modelo é avaliada utilizando simulações em elementos infinitos, as quais apresentaram grande concordância com o modelo analítico utilizado. Algoritmos genéticos são utilizados na obtenção dos parâmetros dos diversos modelos apresentados, mostrando grande robustez na obtenção de parâmetros baseada no ajuste entre curvas experimentais e teóricas.

The work presented in this doctoral thesis employs colloidal suspensions to explore key open problems in condensed matter physics. Colloidal suspensions, along with gels, polymers, emulsions and liquid crystals belong to a family of materials that are collectively labelled as soft matter. Compositionally, colloidal suspensions consist of particles whose size ranges from a few nanometers to a few microns, dispersed in a solvent. A hallmark feature of these systems is that they exhibit Brownian motion, which makes them suitable for investigating statistical mechanical phenomena. Over the last fifteen years or so, colloids have been used extensively as model systems to shed light on a wide array of such phenomena typically observed in atomic systems. The chief reason why colloids are good mimics of atomic systems is their large size and slow dynamics. Unlike atomic systems, the dynamics of colloids can be probed in real time with single-particle resolution, which allows one to establish the link between macroscopic behavior and the microscopic processes that give rise to it. Yet another important feature is that colloidal systems exhibit various phases of matter such as crystals, liquids and glasses, which makes them versatile model systems that can probe a broad class of condensed matter physics problems. The work described in this thesis takes advantage of these lucrative features of colloidal suspensions to gain deeper insights into the physics of glass formation as well as shear-induced anisotropic grain growth in polycrystalline materials. The thesis is organized into two preliminary chapters, four work chapters and a concluding chapter, as follows. Chapter 1 provides an introduction to colloidal suspensions and reviews the chief theo-retical concepts regarding glass formation and grain boundary dynamics that form an integral part of subsequent chapters. Chapter 2 describes the experimental methods used for performing the work presented in the thesis and consists of two parts. The first part describes the protocols followed for synthesizing the size-tunable poly (N-isoprolypacrylamide) (PNIPAm) particles used in our study of shear-induced grain growth. The second part describes the instrumentation and techniques, such as holographic optical tweezers, confocal microscopy, rheology and Bragg diffraction microscopy, used to perform the measurements described in the thesis. Chapter 3 deals with our work on the dynamical facilitation (DF) theory of glass forma-tion. Despite decades of research, it remains to be established whether the transformation of a liquid into a glass is fundamentally thermodynamic or dynamic in origin. While obser-vations of growing length scales are consistent with thermodynamic perspectives, the purely dynamic approach of the DF theory has thus far lacked experimental support. Further, for glass transitions induced by randomly freezing a subset of particles in the liquid phase, theory and simulations support the existence of an underlying thermodynamic phase transi-tion, whereas the DF theory remains unexplored. In Chapter 3, using video microscopy and holographic optical tweezers, we show that dynamical facilitation in a colloidal glass-forming liquid grows with density as well as the fraction of pinned particles. In addition, we observe that heterogeneous dynamics in the form of string-like cooperative motion, which is consid-ered to be consistent with thermodynamic theories, can also emerge naturally within the framework of facilitation. These findings suggest that a deeper understanding of the glass transition necessitates an amalgamation of existing theoretical approaches. In Chapter 4, we further explore the question of whether glass formation is an intrinsi-cally thermodynamic or dynamic phenomenon. A major obstacle in answering this question lies in determining whether relaxation close to the glass transition is dominated by activated hopping, as espoused by various thermodynamic theories, or by the correlated motion of localized excitations, as proposed in the Dynamical Facilitation (DF) approach. In Chapter 4, we surmount this central challenge by developing a scheme based on real space micro-scopic analysis of particle dynamics and applying it to ascertain the relative importance of hopping and facilitation in a colloidal glass-former. By analysing the spatial organization of excitations within cooperatively rearranging regions (CRRs) and examining their parti-tioning into shell-like and core-like regions, we establish the existence of a crossover from a facilitation-dominated regime at low area fractions to a hopping-dominated one close to the glass transition. Remarkably, this crossover coincides with the change in morphology of CRRs predicted by the Random First-Order Transition theory (RFOT), a prominent ther-modynamic framework. Further, we analyse the variation of the concentration of excitations with distance from an amorphous wall and find that the evolution of these concentration profiles with area fraction is consistent with the presence of a crossover in the relaxation mechanism. By identifying regimes dominated by distinct dynamical processes, our study offers microscopic insights into the nature of structural relaxation close to the glass transi-tion. In Chapter 5, we extend our investigation of the glass transition to systems composed of anisotropic particles. The primary motivation for this is to bridge a long-standing di-vide between theories and simulations on one hand, and experiments on molecular liquids on the other. In particular, theories and simulations predominantly focus on simple glass-formers composed of spherical particles interacting via isotropic interactions. Indeed, even the prominent theory of Dynamical Facilitation has not even been formulated to account for anisotropic shapes or interactions. On the other hand, an overwhelming majority of liquids possess considerable anisotropy, both in particle shape as well as interactions. In Chapter 5, we mitigate this situation by developing the DF theory further and applying it to systems with orientational degrees of freedom as well as anisotropic attractive interactions. By analyzing data from experiments on colloidal ellipsoids, we show that facilitation plays a pivotal role in translational as well as orientational relaxation. Further, we demonstrate that the introduction of attractive interactions leads to spatial decoupling of translational and rotational facilitation, which subsequently results in the decoupling of dynamical het-erogeneities. Most strikingly, the DF theory can predict the existence of reentrant glass transitions based on the statistics of localized dynamical events, called excitations, whose duration is substantially smaller than the structural relaxation time. Our findings pave the way for systematically testing the DF approach in complex glass-formers and also establish the significance of facilitation in governing structural relaxation in supercooled liquids. In Chapter 6, we turn our attention away from the glass transition and address the problem of grain growth in sheared polycrystalline materials. The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. While computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the disparate length and time scales involved. In Chapter 6, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the anisotropy in mobility emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. Finally, in Chapter 7, we present our conclusions and discuss possible future directions.

Made available in DSpace on 2016-12-12T17:38:36Z (GMT). No. of bitstreams: 1 Carlos Toshiyuki Matsumi.pdf: 2530177 bytes, checksum: d45251b727305a9062002cf939cb57eb (MD5) Previous issue date: 2009-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Electropermeabilization is the process of transient increase in the permeability of biological membranes of cells subjected to intense electric fields. This technique is currently still in development and has important clinical and technological applications such as electrochemotherapy and gene transfer. Electroporator is the equipment used in the generation and application of such intense fields. This dissertation presents the design, construction and testing of an electroporator for use in biomedical research. The proposed equipment presents versatility and performance appropriate to allow for different types of experiments with biological tissues or cell suspensions. It consists of a voltage generator with programmable wave form, a high voltage amplifier with high output current capability and a system for transduction of voltage and current in the sample. Both the generation of signal as the measured values in the load are monitored by a program built in LabVIEW® environment that triggers a data acquisition card with 16 bits of resolution. The performance of the electronic system developed fully meets the requirements of project. The amplifier can deliver up to 500V and 5A to the load during a time interval enough for the testing of electropermeabilization. The bandwidth, slightly higher than 100kHz and the step response time of the order of 1&#956;s are suitable for performing experiments with different waveforms and different sizes of cells. An important application of the equipment built is demonstrated with an experiment of electropermeabilization in suspension of red cells of rats. This result demonstrated the occurrence of increased conductivity of the sample during stimulation with high-intensity electric field. / Eletropermeabilização é o processo de aumento transitório da permeabilidade das membranas de células biológicas submetidas a campos elétricos intensos. Esta é uma técnica atualmente ainda em desenvolvimento e que possui importantes aplicações clínicas e tecnológicas tais como a eletro quimioterapia e a transferência genética. Os eletropermeabilizadores são equipamentos usados na geração e aplicação desses campos intensos. Esta dissertação apresenta o projeto, construção e teste de um eletropermeabilizador para uso em pesquisa biomédica. O equipamento proposto apresenta versatilidade e desempenho adequados para permitir a realização de diferentes tipos de ensaios com tecidos biológicos ou suspensões de células. É constituído de um gerador de tensão com forma de onda programável, um amplificador de alta tensão e alta corrente de saída e um sistema de transdução de tensão e corrente na amostra analisada. Tanto a geração de sinal quanto os valores medidos na carga são monitorados por um programa construído em ambiente LabVIEW® que aciona uma placa de aquisição de dados com 16 bits de resolução. O desempenho do sistema eletrônico desenvolvido atende completamente os requisitos de projeto. O amplificador pode fornecer até 500V de amplitude de tensão com 5A de corrente de carga durante intervalos de tempo suficientes para os ensaios de eletropermeabilização. A banda passante pouco maior que 100KHz e os tempos de resposta ao degrau da ordem de 1&#956;s são adequados para a realização de experimentos com diferentes formas de onda e diferentes tamanhos de células. Uma importante aplicação do equipamento construído é exemplificada com um experimento de eletropermeabilização em suspensão de hemácias de rato, sendo demonstrada a ocorrência de aumento da condutividade da amostra durante a estimulação com campo elétrico de alta intensidade.

A numerical study of dilute suspensions based on a non-Newtonian matrix fluid and rigid spheroidal particles is performed. A Carreau fluid describes the non-Newtonian matrix. The special case of rigid spherical particles is considered. Here, a uniaxial elongational flow around a sphere is simulated and numerical homogenization is used to obtain the bulk viscosity of the dilute suspension for different applied rates of deformation and different thinning exponents. In the Newtonian regime the well-known Einstein result for the viscosity of a dilute suspension of rigid spherical particles is obtained. In the power-law regime it is found that the intrinsic viscosity depends only on the thinning exponent. Utilizing the simulation results a modification of the Carreau model for dilute suspensions with a non-Newtonian matrix fluid is proposed. To investigate the influence of the particle shape another numerical study is performed. In particular, different flows around spheroidal particles with different orientations are simulated and numerical homogenization is used to obtain the intrinsic viscosity of the suspension as function of applied rate of deformation, thinning exponent and aspect ratio. From the results it is possible to extract the rheological coefficients of the Lipscomb model. In the Newtonian regime the simulation results coincide with Lipscomb’s predictions. In the power-law regime the rheological coefficients depend strongly on the thinning exponent. Furthermore, simulation results indicate that the rheological coefficients additionally depend on the particle orientation in the non-linear regime. / Une étude numérique sur des suspensions diluées à base d’un fluide non newtonien et de particules sphéroïdales rigides est réalisée. Le comportement de la matrice est décrit par un fluide de type Carreau. De particules sphériques et rigides est considéré en premier. Un écoulement en élongation uniaxiale autour d’une sphère est simulée. Ensuite, l’homogénéisation numérique est utilisée pour déterminer la viscosité apparente de la suspension pour différents taux de déformation et d’indices pseudoplastiques. Dans le domaine newtonien, le résultat d’Einstein donnant la viscosité d’une suspension diluée de particules sphériques et rigides est obtenu. Dans le régime en loi de puissance on constate que la viscosité intrinsèque dépend uniquement de l’indice pseudoplastique. Une autre étude numérique est effectuée pour investiguer l’influence de la forme des particules. Plusieurs écoulements autour d’une particule sphéroïdale sont simulés pour différentes orientations. Une homogénéisation numérique est ensuite utilisée pour obtenir la viscosité intrinsèque de la suspension en fonction du taux de déformation appliqué, de l’indice d’écoulement et du rapport de forme de la particule. A partir de ces résultats, il est possible d’exprimer les coefficients rhéologiques du modèle de Lipscomb. Dans le régime newtonien, les résultats coïncident avec les prédictions de Lipscomb. Dans le domaine en loi de puissance, les coefficients rhéologiques deviennent fortement dépendent de l’indice pseudoplastique. En outre, les résultats des simulations montrent que ces coefficients rhéologiques dépendent également de l’orientation des particules dans le régime non linéaire. / Numerische Untersuchung zu verdünnten Suspensionen basierend auf einer nicht Newtonschen Matrixflüssigkeit und harten spheroidalen Partikeln wurde durchgeführt. Ein Carreau Fluid beschreibt die nicht Newtonsche Matrix. Zuerst wird der Spezialfall harter Kugeln betrachtet. Hierzu wird eine uniaxiale Dehnströmung um eine Kugel simuliert und numerische Homogenisierung wird verwendet um die effektive Viskosität der Suspension für verschieden aufgebrachte Deformationsgeschwindigkeiten und Verdünnungsexponenten zu bestimmen. Im Newtonschen Bereich wird die bekannte Lösung Einsteins für die Viskosität einer verdünnten Suspension harter Kugeln erhalten. Im power-law Bereich ist die intrinsische Viskosität einzig eine Funktion des Verdünnungsexponenten. Unter Nutzung der Simulationsergebnisse wird eine Modifikation des Carreau Modells vorgeschlagen. Um den Einfluss der Partikelform auf die nichtlinearen Eigenschaften zu untersuchen wird eine weitere numerische Simulationen durchgeführt. Dabei werden verschiedene Strömungen um spheroidale Partikel mit unterschiedlicher Orientierung simuliert und numerische Homogenisierung wird verwendet um die intrinsische Viskosität als Funktion der aufgebrachten Deformationsgeschwindigkeit, des Verdünnungsexponenten und des Partikelaspektverhältnisses zu bestimmen. Es ist möglich die rheologischen Parameter des Lipscomb Modells aus den Simulationsergebnissen zu bestimmen. Im Newtonschen Bereich stimmen die numerisch bestimmten Werte mit der Vorhersage Lipscomb‘s überein. Im power-law Bereich hängen die rheologischen Parameter stark vom Verdünnungsexponenten ab. Weiter kann man aus den Ergebnissen auf eine zusätzliche Abhängigkeit der rheologischen Parameter von der Partikelorientierung schließen.