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No description available.

Neste trabalho investigamos os efeitos de superfícies de contorno e de confinamento na ordem orientacional de cristais líquidos, onde utilizamos cristais líquidos termotrópicos e liotrópicos. A importância deste estudo deve-se à aspectos tanto de interesse tecnológico (formas de alinhamento) como de pesquisa básica. Com relação aos cristais líquidos termotrópicos, determinamos que cargas eletrostáticas superficiais induzidas por esfregamento influenciam as propriedades orientacionais do cristal líquido, essas cargas foram medidas com a técnica de microscopia de força eletrostática (EFM). Estudamos novas formas de alinhamento ao tratar a superfície com polímeros fotosensíveis, onde foi possível introduzir uma competição entre dois potenciais superficiais de alinhamento (grades de relevo e fotoalinhamento) e geramos padrões microtexturizados com diferentes direções de alinhamento, o que pode ser aplicado na elaboração de dispositivos biestáveis. Em ambos os casos, uma forma de alinhamento local pode ser obtida com o uso de um microscópio óptico de campo próximo (SNOM). Com o uso de um surfactante (OTE) produzimos um perfil periódico de alinhamento homeotrópico e planar para tentar observar estados orientacionais esperados teoricamente, além de propor novos tratamentos superficiais. As análises topográficas foram feitas com medidas de microscopia de força atômica (AFM) e as análises de textura do cristal líquido com um microscópio óptico de luz polarizada. O efeito do confinamento de uma amostra de cristal líquido liotrópico foi investigado através do comportamento dinâmico induzido por campos magnéticos externos, dando evidências de uma transição de fase induzida apenas pelo confinamento da amostra. A ocorrência desta transição de fase foi confirmada através de medidas diretas com o uso de técnicas ópticas não-lineares, como a geração de segundo harmônico e Varredura-Z. / In this work we investigated the boundary surface and confinement effects on the orientational order of liquid crystals, where we used thermotropic and lyotropic liquid crystals. The importance of these studies refers to technological and fundamental research aspects. Regarding to the thermotropic liquid crystals, we determined that the electrostatic charges induced by rubbing of polymeric surfaces influence the liquid crystal orientational properties, these charges were measured with the electrostatic force microscopy technique (EFM). We studied new liquid crystal aligning forms with photosensitive polymers, where it was possible to impose a competition between two surface aligning potentials (surface relief gratings and photoalingment) and we created microtextured patterns of diferent alignment directions, which favors the use in bistable devices. In both cases, a local treatment can be achieved with a scaning near-field optical microscope (SNOM). With a surfactant (OTE) we produced periodic patterns of homeotropic and planar states to investigate the possibility of new orientational states induced to the liquid crystal, which are expected theoretically. The topographic analysis were done by atomic force microscopy (AFM) measurements and the liquid crystal texture was investigated with a polarized microscope. The confinement effect on a lyotropic liquid cristal was investigated according to theoretical approches of the dynamical behavior induced by external magnetic fields, giving evidences of a phase transition induced only due to the sample confinement. This phase transition was confirmed with direct measurements of the transition by using nonlinear optical techniques, as second harmonic generation and Z-scan.

Neste trabalho investigamos os efeitos de superfícies de contorno e de confinamento na ordem orientacional de cristais líquidos, onde utilizamos cristais líquidos termotrópicos e liotrópicos. A importância deste estudo deve-se à aspectos tanto de interesse tecnológico (formas de alinhamento) como de pesquisa básica. Com relação aos cristais líquidos termotrópicos, determinamos que cargas eletrostáticas superficiais induzidas por esfregamento influenciam as propriedades orientacionais do cristal líquido, essas cargas foram medidas com a técnica de microscopia de força eletrostática (EFM). Estudamos novas formas de alinhamento ao tratar a superfície com polímeros fotosensíveis, onde foi possível introduzir uma competição entre dois potenciais superficiais de alinhamento (grades de relevo e fotoalinhamento) e geramos padrões microtexturizados com diferentes direções de alinhamento, o que pode ser aplicado na elaboração de dispositivos biestáveis. Em ambos os casos, uma forma de alinhamento local pode ser obtida com o uso de um microscópio óptico de campo próximo (SNOM). Com o uso de um surfactante (OTE) produzimos um perfil periódico de alinhamento homeotrópico e planar para tentar observar estados orientacionais esperados teoricamente, além de propor novos tratamentos superficiais. As análises topográficas foram feitas com medidas de microscopia de força atômica (AFM) e as análises de textura do cristal líquido com um microscópio óptico de luz polarizada. O efeito do confinamento de uma amostra de cristal líquido liotrópico foi investigado através do comportamento dinâmico induzido por campos magnéticos externos, dando evidências de uma transição de fase induzida apenas pelo confinamento da amostra. A ocorrência desta transição de fase foi confirmada através de medidas diretas com o uso de técnicas ópticas não-lineares, como a geração de segundo harmônico e Varredura-Z. / In this work we investigated the boundary surface and confinement effects on the orientational order of liquid crystals, where we used thermotropic and lyotropic liquid crystals. The importance of these studies refers to technological and fundamental research aspects. Regarding to the thermotropic liquid crystals, we determined that the electrostatic charges induced by rubbing of polymeric surfaces influence the liquid crystal orientational properties, these charges were measured with the electrostatic force microscopy technique (EFM). We studied new liquid crystal aligning forms with photosensitive polymers, where it was possible to impose a competition between two surface aligning potentials (surface relief gratings and photoalingment) and we created microtextured patterns of diferent alignment directions, which favors the use in bistable devices. In both cases, a local treatment can be achieved with a scaning near-field optical microscope (SNOM). With a surfactant (OTE) we produced periodic patterns of homeotropic and planar states to investigate the possibility of new orientational states induced to the liquid crystal, which are expected theoretically. The topographic analysis were done by atomic force microscopy (AFM) measurements and the liquid crystal texture was investigated with a polarized microscope. The confinement effect on a lyotropic liquid cristal was investigated according to theoretical approches of the dynamical behavior induced by external magnetic fields, giving evidences of a phase transition induced only due to the sample confinement. This phase transition was confirmed with direct measurements of the transition by using nonlinear optical techniques, as second harmonic generation and Z-scan.

No description available.

No description available.

No description available.

La spectroscopie RMN alliée à l’utilisation de solvants cristal-liquide fortement et faiblement orientants est une stratégie efficace pour élucider les structures et distributions conformationnelles de petites molécules organiques rigides et flexibles en solution, et déterminer les ordres orientationnel et positionnel des solutés comme des solvants orientés. Dans une première partie, afin d’explorer les différentes contributions aux couplages dipolaires d’un soluté donné, la très faible amplitude de l’ordre orientationnel d’une molécule quasi-sphérique, le tetramethylallène, dissoute dans un nématique thermotrope est exploitée. Dans cette situation limite, le caractère prédominant des mécanismes de réorientation et de vibration moléculaire est mis en évidence, et estimé. Dans une seconde partie, les données RMN obtenues à partir de solutés de petites tailles dissous dans des solvants smectiques sont combinées aux résultats de calculs reposant sur des concepts de thermodynamique statistique et de la théorie de la fonctionnelle de densité. L’efficacité de cette méthode dans la détermination des paramètres d’ordres positionnel du solvant et orientationnel des molécules-sondes est démontrée aussi bien dans le cas de phases conventionnelles smectiques A que celui plus délicat de smectiques interdigitées Ad. La stratégie d’analyse proposée est ensuite étendue à l’investigation des structures tridimensionnelles et équilibres conformationnels de molécules flexibles bioactives ou biomimétiques. Dans une perspective méthodologique, à l’aide d’études expérimentale et théorique portant sur le biphényle, molécule symétrique constituée d’un unique rotor, il est tout d’abord démontré l’intérêt des méthodes de simulations par dynamique moléculaire pour évaluer l’ensemble des couplages dipolaires d’un soluté donné dans une phase thermotrope, ultérieurement utilisés comme paramètres initiaux dans une analyse spectrale itérative, et in fine déterminées précisément. L’analyse spectrale chronophage et dont l’aboutissement est incertain si les paramètres initiaux sont difficiles à estimer, en est ainsi facilitée. Puis, les distributions conformationnelles d’anti-inflammatoires non stéroïdiens de dérivés salicylés et profènes, fluorés ou non, constitués d’un ou deux rotors indépendants sont présentées. Via l’utilisation inédite du modèle AP-DPD dans les solvants nématiques (chiraux) lyotropes faiblement orientants, et à partir des couplages dipolaires homo- et hétéronucléaires notamment obtenus grâce à l’expérience RMN GET-SERF, créée à propos pour permettre l’extraction simple et rapide des couplages 1H-19F, les surfaces d’énergie potentielle de ces biomolécules sont décrites de façon satisfaisante. Enfin, les équilibres conformationnels de deux stilbénoïdes constitués de deux rotors coopératifs sont déterminés dans deux solvants cristal-liquide, l’un fortement, l’autre faiblement orientant. Ces études comparatives permettent de discuter la fiabilité, la précision et l’accessibilité des observables RMN extraites dans les phases, et d’établir la complémentarité des analyses RMN réalisées dans ces solvants. / NMR spectroscopy in weakly and highly orienting media is used as a route for dealing with orientational, positional, structural and conformational problems of a variety of small rigid and flexible organic molecules in solution. First, the very weak orientational order of a quasi-spherical molecule dissolved in a nematic phase is exploited for exploring the role of the different contributions to the observed dipolar coupling. In such a limit condition, a predominant effect of the non-rigid reorientation-vibration coupling term emerges. Then, NMR data obtained from small rigid probes dissolved in smectic solvents are combined with a statistical thermodynamic density functional theory, in order to measure the positional order parameters of both solutes and solvent. The methodology gives good results when applied to a conventional smectic A liquid crystal and to the more delicate case of an interdigitated smectic Ad phase. The strategy is subsequently extended to the investigation of structure, order and conformational equilibrium of flexible bioactive or biomimetic molecules dissolved in various partially ordered NMR solvents. A first experimental and theoretical study is presented on the symmetric single-rotor molecule of biphenyl dissolved in a thermotropic liquid crystal. This test-case indicates molecular dynamics simulations are a promising tool for estimating a set of dipolar couplings of a solute in a thermotropic solvent, to be used as starting set of parameters in a standard operator-mediated NMR spectral analysis. Then, we report the conformational study of some single- and two-rotor nonsteroidal anti-inflammatory drugs, belonging to the families of salicylates and profens, dissolved in weakly orienting chiral nematic PBLG phases. A new pulse sequence, the Gradient Encoded heTeronuclear 1H-19F SElective ReFocusing NMR experiment (GET-SERF), is proposed here for the trivial edition of all 1H-19F couplings in one single NMR experiment, for a given fluorine atom. Starting from homo- and heteronuclear dipolar couplings, difficult to extract in thermotropic solvents because of a too complex spectral analysis, the torsional distributions of such molecules can be satisfactory described by the Additive Potential model combined with the Direct Probability Description of the torsional distribution in terms of Gaussian functions (AP-DPD approach). Finally, the conformational and orientational study of two stilbenoids displaying cooperative torsions is discussed in both a highly and weakly ordering liquid crystal phase. This comparative study allows to draw some conclusions on reliability, accuracy and accessibility of desired data in the two phases. Overall, this work proves NMR in liquid crystals is a flexible and meaningful tool for studying order, structure and conformation and it can greatly benefit from the availability of several aligning media inducing a different degree of order.

The importance of soft matter research, as a major class of materials including liquid crystals, polymers, colloids, emulsions, and forms, is attributed to the behavior resemblances in each branch of soft matter responding to the external perturbations. Hence, one of the most required inquiries in soft matter physics is understanding how the structures with characteristic length scales evolve in response to external perturbations, and concomitant phase transitions. We have focused on adopting polarized Raman spectroscopy to probe phase transitions in soft materials consisting of anisometric components and the evolution of molecular orientational ordering as a complementary tool to other methodologies, but distinct in some respects. The primary task is quantifying the degree of molecular orientation, i.e., obtaining orientational order parameters, in liquid crystal (LCs) system. Thermal evolution of orientation degree in a hitherto elusive biaxial nematic (Nb) phase as well as a commonly known uniaxial nematic (Nu) phase were interrogated from the measurements of anisotropy in polarized Raman intensities. We demonstrated reliable and applicable method to quantify the orientation degree for systems possessing anisotropic ordering. We also addressed a strong potential of Raman spectroscopy that the changes of vibrational energy reflect the variations of intermolecular interactions and structural changes on the molecular level induced by phase transitions. As a subfield of soft matter, we characterized phase transitions and anisotropic ordering observed in an evaporating conjugated polymer solution and elucidated the mechanism of the entities undergoing phase transitions using mainly polarized Raman spectroscopy. In addition, we have shown that tracking Raman spectral changes can provide valuable information for understanding structure-property relations when the measurements of the evolution in physical properties are carried out simultaneously.

L'organisation orientationnelle bio-moléculaire des lipides et des protéines dans la membrane plasmique constitue un facteur important dans les processus biologiques au cours desquelles les fonctions peuvent être reliées aux mécanismes d'orientation et d'organisation. Le concept de séparation transitoire des phases à l'échelle nanométrique dans les domaines ordonnés et désordonnés, aussi appelé « radeau lipidique », est maintenant largement accepté. De plus, les domaines ordonnés contiennent des protéines de signalisation, ce qui souligne l'importance des séparations de phase au cours des processus de signalisation. Dans cette thèse de doctorat, nous avons étudié l'ordre orientationnel moléculaire de la protéine de signalisation MHC Class I et de reporters lipidiques tels que di-8-ANEPPQ et DiI(C18). Nous avons étudié l'ordre orientationnel moléculaire de la protéine de signalisation MHC Class I et des reporters lipidiques par imagerie d'anisotropie de fluorescence résolue en polarisation. Nous avons observé l'influence du cytosquelette d'actine sur l'ordre orientationnel moléculaire de la protéine MHC et des reporters lipidiques dans la membrane plasmique. De plus, nous avons trouvé que l'ordre orientationnel moléculaire des reporters dépend de la morphologie cellulaire. Nous avons examiné les plis membranaires en modifiant la forme des cellules de façon mécanique ou pharmacologique. / Biomolecular orientational organization of lipids and proteins in the plasma membrane is a crucial factor in biological processes where functions can be closely related to orientation and ordering mechanisms. The concept of transient nanosized phase separations in ordered and disordered domains, called "lipid rafts" is now widely accepted. Furthermore, the ordered domains are enriched in signaling proteins, which highlights the crucial impact of phase separation during the signaling processes. While this field has been so far largely addressed by studying the translational diffusion behavior of membrane proteins and lipid reporters by Single Molecule Tracking (SMT) or Fluorescence Correlation Spectroscopy (FCS), only little is known about the orientational behavior of signaling proteins and lipid reporters in the plasma membrane. In this PhD thesis we investigated the molecular orientational order of the signaling molecule MHC Class I protein using fluorescence anisotropy imaging as well as of lipid reporter di-8-ANEPPQ using polarization-resolved fluorescence imaging. Fluorescence anisotropy imaging requires a fluorescent label rigidly attached to the system under study, able to report its orientational order behavior. Thus, MHC Class I protein has been successfully labeled in a rigid way. We analyzed the orientational order of MHC Class I protein quantitatively in the endomembrane and plasma membrane and we found that the orientational order of MHC Class I protein in both membranes depends primarily on the maturation state of the protein and its interaction with the cytoskeleton.