Ces travaux concernent l’étude expérimentale des textures se développant dans les ménisques de films smectiques de cristaux liquides thermotropes. Ces fluides complexes nous servent de système modèle pour l’étude des couplages élasto-capillaires qui se manifestent dans certaines conditions par des déformations périodiques de l’interface cristal liquide-air. Dans un premier temps, à partir de l’étude détaillée de la topographie de l’interface par une méthode interférométrique, nous caractérisons les différents types de structures, puis, identifions les principaux paramètres impliqués dans le processus d'apparition des défauts dans le ménisque de films libres suspendus. Ces résultats nous servent de base pour discuter des mécanismes physiques qui génèrent les différents types de défauts observés. Nous regardons en particulier, comment la diminution d’épaisseur de couche associée à une transition de phase va induire une instabilité mécanique responsable de l’apparition des ondulations de l’interface. Dans un deuxième temps, afin d’aller plus loin dans la compréhension des mécanismes, nous avons utilisé des films minces de cristaux liquides déposés sur des substrats solides microstructurés par des plots fabriqués par des techniques photolitographiques. Une telle géométrie permet de générer un ménisque autour de chaque plot et surtout de faire varier un plus grand nombre de paramètres comme par exemple l’ancrage sur le substrat via un traitement chimique de surface. L’ensemble de nos résultats apportent un éclairage nouveau sur la caractérisation et la compréhension des déformations spécifiques aux ménisques de fluides complexes. / The present work is an experimental study of the textures that appear in the meniscus of free standing smectic films with thermotropic liquid crystals. These complex fluids serve as model systems to investigate elasto-capillary phenomena which, under certain conditions, manifest themselves through periodic deformations of the liquid crystalair interface. In the first part of the thesis, we focus our attention on meniscus structures whose interfacial topographies are thoroughly characterized thanks to an in-house optical interferometry technique. Our study allows us to identify the main parameters involved in the development of meniscus structures and to discuss the physical mechanisms that are likely to be responsible for their formation. In particular, we show how a phase transition-induced layer shrinkage triggers a mechanical instability leading to interfacial undulations of the smectic free surface. In the second part of the manuscript, we address the case of thin liquid crystal films deposited on solid patterned solid substrates. The latter consist of regular arrays of microposts fabricated through photolithographic techniques. Such a geometry allows a meniscus to be formed around each micropost and makes it possible to examine the influence of other parameters such as the anchoring conditions on the solid substrate. The results gathered so far are able to shed some light on the characterization and the understanding of the specific deformations and textures that appear in the menisci of complex fluids.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-11-05T22:28:11Z No. of bitstreams: 1 ROSEMARY RIBEIRO RAMOS - DISSERTAÇÃO PPGEQ 1985..pdf: 46832957 bytes, checksum: 99eea8bc7664b29c95a76c9107593a6f (MD5) / Made available in DSpace on 2018-11-05T22:28:11Z (GMT). No. of bitstreams: 1 ROSEMARY RIBEIRO RAMOS - DISSERTAÇÃO PPGEQ 1985..pdf: 46832957 bytes, checksum: 99eea8bc7664b29c95a76c9107593a6f (MD5) Previous issue date: 1985-12-27 / CNPq / Este trabalho de laboratório procurou dar continuidade a uma serie de pesquisas que, com o decorrer do tempo,vem se desenvolvendo com as argilas esmectíticas de cores verde-clara, vermelha e do tipo sortida da localidade de Bravo,Distrito de Boa Vista, Município de Campina Grande, Paraíba, visando o estudo dos efeitos de tratamento de cura* cm algumas propriedades reológicas dessas argilas para uso como fluidos tixotrópicos na perfuração de poços de Petróleo. De início foram feitos os ensaios de caracterização mineralógica. Posteriormente foi feita uma analise das propriedades tecnológjcas verificadas através da determinação das viscosidades aparente e plástica e do volume do filtrado nas argilas em sua forma natural. Em seguida, foram observadas as propriedadesreologicas nas argilas tratadas com carbonato de sódio na proporção de 100meq por 100g de argila seca sem tratamento de cura. Os processos de tratamento de cura foram realizados com o auxílio de uma câmara úmida e autoclave , mantendo-se constante a concentração de carbonato de sódio e umidade relativa, e, variando-se a temperatura e o tempo. Em todas as condições estudadas foi verificado o efeito da diálise e o efeito da diálise com uso de COj. 0 uso da diálise, visa eliminar os compostos solúveis ou parcialmente solúveis de cálcio e magnésio, formados pela reação química de dupla trocapor ocasião de tratamento com o composto de sódio (montmorilonita (Mg ,Ca ,Na ,K ,11) + Na2C03 -> montmori 1 onita (Na) + MgCO^ + CaCO., + CO +llO0 + K? CO ) (|ne se pode dissolver na dispersão aquosa da argila, prejudicando as propriedades coloidais da montmorilonita , principalmente a viscosidade plástica. O uso do CO2 tem a finalidade de observar ate que ponto sua ação prejudica as propriedades reológicas das argilas em estudo. Foram determinados, igualmente, teores de carbonatos e bicarbonatos, existentes na suspensão a 6% de sólidos. Estes valores foram utilizados para explorar possíveis correlações com as viscosidades aparentes, plásticas e volume do filtrado, através da análise de regressões lineares simples e múltipla. Os resultados obtidos dos ensaios tecnológicos mostraram que as argilas de cores verde-clara, vermelha e do tipo sortida após tratamento conveniente, apresentaram excelentes propriedades reológicas, possibilitando, assim, o uso dessas argilas como agentes tixotrópicos em fluidos para a perfuração rotativa de poços de Petróleo. 0 efeito da diálise, por sua vez, tem grande influência na melhoria das propriedades reológicas para o tratamento das argilas sem processo de cura e, após o processo de cura em câmara úmida e autoclavagem ,onde as argilas são tratadas com solução de carbonato de sódio na proporção adequada após a autoclavagem; o uso do CO2 por sua vez, influencia bastante as propriedades reológicas, que por serem solúveis, mostram tendência de flocular o sistema e consequentemente prejudicar as propriedades reológicas. Com relação as correlações obtidas de validade Limitada, tendo em vista o reduzido numero de observações realiza das, foram obtidos coeficientes próximos de 1, mostrando que existe relação linear entre os teores de carbonatos, bicarbonatos e carbonatos mais bicarbonatos com as viscosidades aparentes e plásticas e volume do filtrado em algumas condições de cura. / This work of laboratory aims continue a series of research work, which has been developing, using the smectites clays light green, red and mixed couloured from Bravo, District of Boa Vista,Campina Grande, Paraîra, with purpose to study the effects of treatment of cure in some rheological properties of these clays, keeping in mind its applicability as tixotropic fluids for perfuration of oil well. Inicially, the analysis of the rheological properties was done investing from the determination of the apparent plastic viscosités and filtrate volume in the clays under it natural form. The rheological properties of the clays were observed by the treatment of sodium carbonate at the proportion of lOOmeq per 100g of dry clay without treatment of cure. The processes of cure treatment were done in a humid chamber and autoclave keeping the concentration of sodium carbonate and relative humidity constant and changing the temperature and time. The dialysis effect was investigated with the use of C02 at all conditions studied. The use of dialysis process has the purpose to eliminate either soluble compounds or parcially soluble of calcium and magnesium compounds or parcially soluble of calcium and magnesium compounds formed by double exchange chemical reaction by the • 2 + 2-1- + treatment with sodium compounds (montmorilonite, Mg ,Ca ,Na , K+, H30+)+ Na2C03 - montmorilonite (Na + ) + MgC03 + CC>2 compounds (montmorilonite, Mg ,Ca ,Na , K+, H30+)+ Na2C03 - montmorilonite (Na + ) + MgC03 + CC>2 + H20 + K2C03) that are able to be dissolved into clays aqueous dirpèrsion so this will spoil the colloid properties of the montmorilonite, mainly the plastic viscosité. The use of CC>2 has the objective to observe the maximun point that its action will damage rheological properties of the clays in this study. Carbonates and Bicarbonates existing in the 6% solids suspension were determined. These values were used to find correlation in filtrate volume and apparent and plastic viscosites by simple and multiple linear regression analysis. results obtained from technological tests showed that light green, red and mixed coloured clays, after the treatment, presented rheological properties adequated to be used in the perforation of oil wells. However, the effects,of dialysis has considerable influence in the improvement of the rheological properties to the treatment of the clays without the cure process and after the cure process in chamber and autoclave where the clay are treated with sodium carbonate to adequade to proportion after autoclave process.; The use of CC^,however , has considerable influence on the rheological properties, once it being soluble, presented the tendency to floculate the system and consequently to damage the rheological properties. With relation to correlations obtained showing to be of limited validity, even to the rcdused number of observations taken; so were obtained correlations coeficients approximately one taking that there exists linear relation between amounts of carbonates and carbonates plus bicarbonates with apparent and plastic viscosites and the filtrate volume in some of the cure conditions.

Made available in DSpace on 2015-05-14T12:14:08Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1022891 bytes, checksum: c086e09a9f99e06278f85a5575162e2b (MD5) Previous issue date: 2009-11-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Geometry, topology and elasticity are found in various branchs of physics and they play important roles in the understanding of many physical phenomena. In this work, we present three diferent systems where we can see such importance. First, a quantum neutral particle, constrained to move on a conical surface, is used as a toy model to explore bound states due to both a inverse squared distance potential and a delta-function potential, which appear naturally in the model due the geometry and topology of the cone. In the second one, we propose a method for probing the effects of curved 3-space by using materials with large coefficients of thermal expansion. Studying their fluctuations can be naturally cast in terms of a nonflat background geometry. In the last one, we determine the elastic-mediated interaction between colloidal nanoparticles adsorbed on the surface of free-standing smectic films. In contrast with the short-range character of the elastic- mediated force between particles adsorbed on smectic films supported by a solid substrate, the effective force acquires a long-range character in free-standing films, thus playing an important role in the formation of self-assembly structures in these systems. / A geometria, topologia e elasticidade estão presentes em vários ramos da física, e desempemham papel fundamental no entendimento de vários fenômenos físicos. Nesse trabalho, apresentamos três sistemas distintos onde podemos ver esse papéis. No primeiro, uma partícula quântica neutra confinada a mover-se em uma superfície cônica é usada como modelo para explorar estados ligados devido a um potencial proporcional ao inverso do quadrado da distância e devido a um potencial tipo delta. Ambos potenciais aparecem naturalmente devido a geometria e topologia do cone. No segundo, propomos um método de sondar os efeitos de um espaço curvo tridimensional usando materiais de grande coeficiente de expansão térmica. Neste caso, os três ingredientes citados acima são importantes para o entendimento do problema. Por fim, determinamos a interação entre nanocolóides adsorvidos na superfície de um filme esmético livremente suspenso. Essa interação é mediada por deformações elásticas no filme esmético; ela é de longo alcance, o que é importante para a formação de estruturas coloidais auto organizadas na superfície de tal filme.

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We have developed a new modulation calorimetry technique using RF-Field heating. This technique eliminates temperature gradients across the sample leading to a higher precision in evaluating the heat capacity compared to the previous techniques. A frequency scan was carried out on a 8CB+aerosil sample showing a wide plateau indicating the region of frequency independent heat capacity. A temperature scan was then performed through the first-order nematic to isotropic and second order smectic-A to nematic transitions and was shown to be consistent with the previous work. The amplitude of the RF heating power applied to the sample depends on the permittivity and the loss factor of the sample. Since the permittivity of a dielectric material has a strong temperature dependence in liquid crystals, new information is obtained. The heat capacity measurements have a relative resolution of better than 0.06%, and the phase shift a resolution of 0.03%, were shown to be significant improvements over traditional heating methods. We then applied this new RF calorimetry on bulk and aerosil 8CB dispersions. For the bulk 8CB, the step-like character of smectic-A to nematic transition, and first order nematic to isotropic transitions indicated the strong dominance of the permittivity and the loss factor of the material. For the 8CB+aerosil samples at different silica density, our data were consistent with the previous work and provides clear evidence for the coupling between the smectic-A and nematic phases. We have undertaken a combined T-dependent optical and calorimetric investigation of CCN47+aerosil samples through the I-N transition over a range of silica densities displaying the double I-N transition peak. This work offers compelling evidence that the I-N transition with weak quenched random disorder proceeds via a two-step process in which random-dilution is followed by random-field interactions on cooling from the isotropic phase, a previously unrecognized phenomena.

Gegenstand der vorliegenden Arbeit ist die Herstellung und Charakterisierung neuer sternförmiger Mesogene. Bei den aufgeführten Sternverbindungen, handelt es sich um Oligobenzoate, bestehend aus aromatischen Hydroxy- oder Aminocarbonsäuren, die durch Kupplungsreaktionen mit Dicylohexycarbodiimid, in einer konvergenten Synthesestrategie verknüpft wurden. Das besondere Augenmerk der Arbeit richtete sich auf die Charakterisierung der von den neuen Substanzen gebildeten Mesophasen, die mit Hilfe von Polarisationsmikrokopie, dynamischer Differenzialkalorimetrie und Röntgenstreuung erfolgte. Zur Aufklärung spezieller dreidimensionaler Strukturen wurden als zusätzliche Methoden die Rasterkraftmikroskopie angewandt und der Zirkulardichroismus untersucht.

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.