Consideramos um modelo de interações quadrupolares entre micelas capaz de explicar a ocorrência de fases nemáticas biaxiais. Micelas uniaxiais de formatos variáveis, representando a polidispersividade do sistema, são incluídas. O modelo apresenta uma fase nemática calamítica separada de uma fase discótica por uma fase biaxial, segundo resultados de campo médio e de simulações de Monte Carlo. / We consider a model of quadrupole interactions between micelles which is able to explain the occurrence of biaxial phases. Uniaxial micelles of variable shape, representing system polydispersity, are included. The model displays a calamitic nematic phase separated from a discotic phase by a biaxial phase, according to mean-field and Monte Carlo simulation results.

As propriedades ópticas não-lineares de cristais líquidos liotrópicos dopados com ferrofluido, na escala dos milissegundos, foi estudada mediante a técnica de varredura-z. Estas propriedades foram caracterizadas em diferentes mesofases em função da potência incidente, da quantidade de ferrofluido, da direção do diretor (fase nemática calamítica), da evolução temporal do sinal e da composição relativa das amostras. Propomos que a origem desta resposta óptica não-linear, na escala de tempo de milissegundos, é térmica. Os resultados experimentais foram analisados com base nos modelos de Sheik-Bahae e de Lente Térmica. O modelo de Sheik-Bahae permite obter o índice de refração não-linear n IND.2, e o modelo de Lente Térmica a condutividade térmica k e o coeficiente termoótico dn/dT. É possível estabelecer uma relação entre ambos os modelos, a qual é verificada experimentalmente. Da análise sobre o efeito do ferrofluido na resposta óptica não-linear dos liotrópicos, concluímos que este introduz uma pequena anisotropia na absorção óptica na presença de um campo magnético externo. Um possível mecanismo presente numa amostra ferro-liotrópica iluminada pelo laser é o denominado hipertermia. O estudo da resposta óptica não-linear em amostras liotrópicas com diferentes concentrações relativas, num domínio nemático, à temperatura constante, mostra que é possível associar os comportamentos observados nos parâmetros k, dn/dT e n IND.2, à variação da estrutura microscópica das micelas. / Nonlinear optical properties of ferrofluid-doped lyotropic liquid crystals in the millisecond range were studied using the Z-Scan technique. These properties were characterized in different mesophases as function of the incident power of the laser, ferrofluid concentration, direction of the director (calamitic nematic mesophase), signal\'s temporal evolution and relative concentrations of the samples. We suggest that the lyotropic\'s nonlinear optical properties, in millisecond range, come from a thermal effect. The experimental data were analyzed using the Sheik- Bahae\'s model and the Thermal Lens model. The Sheik-Bahae\'s model allows to get the nonlinear refractive index n2 and the Thermal Lens model gives the thermal conductivity k and the thermo optic coefficient dn/dT. It is possible to set a relationship between Sheik-Bahae\'s model and Thermal Lens model that is experimentally verified. Analyzing the influence of ferrofluid on the lyotropics\'s nonlinear optical response, we conclude that it introduces a small anisotropy in the optical absorption in the presence of an external magnetic field. A possible mechanism that could be present in the ferro-lyotropic sample illuminated by the laser beam is the hyperthermia. The study of the nonlinear optical response of lyotropic samples with different concentrations, in a nematic domain, at constant temperature, shows that it is possible to relate the behaviors observed on k, dn/dT and n2 to a change of microscopic structure of micelles.

Este trabalho tem por objetivo estudar as interações superfíciais de cristais líquidos em uma interface cristal líquido-polímero, com a utilização de filmes poliméricos contendo cadeias laterais com corante azo. Nesse estudo foi utilizado um fotopolímero, onde pode se promover o ordenamento dos grupos laterais ao longo de uma direção preferencial através de um processo de isomerização trans-cis. Através da irradiação do filme de polímero com luz polarizada é possível promover a formação de uma anisotropia óptica no filme. A intensidade deste efeito pode ser controlada através da energia incidente e da concentração dos grupos laterais corante azo presentes no polímero. Neste trabalho foi realizado um estudo sistemático da orientação induzida ao cristal líquido nemático por um filme contendo corante azo no grupo lateral. Os aspectos investigados são: a estabilidade térmica e temporal do alinhamento induzido ao cristal líquido; a competição entre dois efeitos de orientação induzidos ao cristal líquido, o esfregamento e o fotoalinhamento; a influência da cncentração dos grupos laterais e da energia de irradiação. Para caracterizar as interações entre o cristal líquido e o filme polimérico foram empregadas técnicas ópticas que permitiram a determinação das intensidades de ancoramento azimutal e zenital em função da concentração de grupos laterais e da energia de irradiação. Mostramos ser possível um ancoramento azimutal que pode ter sua intensidade controlada pela concentração dos grupos laterais, pelo tempo de irradiação com luz polarizada, ou ainda pela potência do laser de excitação, e um ancoramento zenital bastante fraco, que praticamente não é afetado pelo processo de foto-isomerização. / The aim of this work is to study the superficial interactions of liquid crystals in an interface liquid Crystal-polymer, with the use of polymer films containing azo-dyes groups as side chain. In this study a photopolymer was used, where the ordering of the side group can be promoted along a preferential direction through a trans-cis isomerization process. Through the irradiation of the polymeric film with polarized light it is possible to promote the formation of an optical anisotropy in the film. The intensity of this effect can be controlled through the incident energy and the concentration of the azo-dye side groups presents in the polymer. In this work a systematic study of the orientation induced to the nematic liquid crystal by a polymeric film containing azo-dye groups in the side group was performed. The investigated aspects are: -The thermal and temporary stability of the alignment induced to the liquid crystal; -The competition among two orientation effects induced to the liquid crystal, the rubbing and the photo alignment; -The influence of the concentration of the side groups and of the irradiation energy. To characterize the interactions between the liquid crystal and the polymeric film we used optical techniques that allowed the determination of the azimuthal and zenithal anchoring strengths as a function of the concentration of side groups and of the irradiation energy. We showed to be possible an azimuthal anchoring that can have its intensity controlled by the concentration of the side groups, and the irradiation time with polarized light, or still for the power of the excitation laser, and a zenithal anchoring quite weak, that practically is not affected by the process of photo isomerization.

Il est actuellement bien connu que les molécules non sphériques peuvent former des mésophases (ou cristaux liquides), c'est-à-dire des phases dont les propriétés sont intermédiaires entre celles des liquides et celles des cristaux. La mésophase la plus connue est la phase nématique. Il s'agit d'une phase caractérisée par une distribution aléatoire des centres de masse des molécules, mais dans laquelle l'orientation des molécules présente une direction préférentielle, désignée par un vecteur unité appelé le directeur du nématique. Une telle phase possède donc la fluidité d'un liquide tout en présentant, tel un cristal, une biréfringence. C'est cette dernière propriété qui est exploitée dans les applications technologiques, principalement dans les dispositifs d'affichage. Dans un tel dispositif, le liquide nématique est contenu dans une cellule (il y a une cellule par pixel), et son directeur est manipulé à l'aide d'un champ extérieur, électrique ou magnétique. Pour une bonne compréhension du fonctionnement de ce dispositif, il est essentiel de connaître le profil du directeur à travers la cellule en l'absence de champ extérieur. Dans le cadre de ce travail, nous avons étudié un nématique torsadé, c'est-à-dire dont le directeur décrit une hélice à travers la cellule. Ce profil est déterminé principalement par les propriétés d'ancrage du liquide nématique sur les parois solides de la cellule. En effet, celles-ci peuvent posséder une direction d'ancrage privilégiée, qui favorise l'alignement du directeur dans une direction particulière. Nous avons considéré ici le cas de directions d'ancrage planaires, c'est-à-dire que le directeur est dans le plan des parois. Alors que l'ajout de parois identiques dans le système induit toujours une non-uniformité spatiale dans la densité du nématique (en comparaison avec un nématique en coeur de phase), l'utilisation de directions d'ancrage différentes induit une non-uniformité orientationnelle dans le directeur du nématique; dans notre cas une torsion. C'est principalement ce profil de directeur torsadé qui nous intéresse ici. L'objectif général de ce travail consiste donc à étudier les propriétés d'ancrage d'une phase nématique confinée et torsadée, d'une part par une théorie microscopique (théorie de la fonctionnelle de la densité), et d'autre part sur le plan de simulations de Monte Carlo, en particulier dans le cas où les molécules ont la forme de disques (discotiques).

These days, organic photovoltaic devices (OPV) have received a large interest from both academic and industrial researchers as alternative energy source to replace petroleum and nuclear fission. New organic semi-conductors (OSC) are actively researched since these materials can be purified and processed by solution techniques that are cheaper than those required for silicon. The current record efficiency is 8.3%. Further improvement of the OPV performances is desired in order to decrease both the pay-back time of the device and the price of the energy produced. On that purpose, academic research is focused on two main axes: (i) develop new organic materials characterized by high charge mobilities for both p-type (holes) and n-type (electrons) semi-conduction and (ii) increase as much as possible the contact surface between both p-type and n-type OSC (p-n junction), where the electric charges are created. In the frame of this PhD thesis, we proposed to investigate this second aspect by building the interface at a nanoscopic scale, creating a molecular heterojunction. Liquid crystalline (LC) materials composed of donor-acceptor dyads were chosen as OSC since they can lead to complex supramolecular structures made of two interpenetrated networks: the first one is related to the donor and provides holes transport, while the second one is related to the acceptor and affords electrons conduction. In this context, we decided to synthesize new donor-acceptor molecules composed of a phthalocyanine (donor) covalently connected to a fullerene (acceptor) through a non-conjugated bridge and to investigate their supramolecular assembly in solution and solid state. This specific molecular structure was inspired from a mesogenic phthalocyanine developed earlier in our laboratory and the very popular fullerene derivative referred to as PCBM. Four dyads with different bridge lengths were prepared via multi-step synthesis. Two key steps are: (i) the formation of low-symmetry A3B phthalocyanines bearing three mesogenic substituents and one hydroxyl-terminated chain and (ii) the esterification of these phthalocyanines with the carboxylic acid homologue of PCBM. In solution, no electron transfer from the phthalocyanine to the fullerene is evidenced in the ground state. On the contrary fluorescence quenching indicates that a photo-induced charge transfer takes place. Also, cyclic voltammetry measurements confirmed that both phthalocyanine and fullerene moieties act as independent -systems in the ground state. Strong self-aggregation in solution was demonstrated as well by combined use of 1H NMR and UV-Visible absorption spectroscopies. Impact of concentration and temperature on the level of aggregation was studied. Finally, supramolecular organization in the solid state was investigated for pure dyads and in blends. All four dyads produced amorphous phases, mainly due to the important steric hindrance created by the bulky fullerenes in the columnar mesophase of phthalocyanines. On the contrary, mesomorphism was observed in binary blends with two different mesogenic phthalocyanines. We showed that three parameters can be used to tune the supramolecular organization of dyads: (i) the chemical structure of the phthalocyanine used for the blend, (ii) the composition of the blend and (iii) the eventual application of a thermal annealing to the material. Supramolecular organization of the fullerenes in a regular lattice could not be demonstrated./Actuellement, les panneaux solaires à base de matériaux organiques sont pressentis pour devenir dans un futur proche une source d’énergie alternative au pétrole et à la fission nucléaire et constituent dès lors un pole de recherche important dans les domaines académiques et industriels. Une part importante de la recherche se concentre sur le développement de nouveau matériaux semi-conducteurs organiques. Ces derniers présentent l’avantage de pouvoir être purifiés et mis en œuvre plus aisément au départ d’une solution, contrairement au silicium. Le record d’efficacité actuel pour les cellules solaires organiques est de 8.3%. Toutefois, afin de diminuer le prix de l’électricité ainsi produite de même que le coût de revient du dispositif photovoltaïque, il est souhaitable d’en améliorer encore l’efficacité. Dans cette optique, la recherche académique se concentre principalement sur deux axes : (i) développer de nouveaux semi-conducteurs organiques caractérisés par une mobilité de charges élevée tant pour le transport de trous que celui des électrons et (ii) augmenter au maximum la surface de contact entre les deux matériaux semi-conducteurs (jonction p-n), lieu où sont produites les charges électriques. Dans le cadre de travail, nous nous sommes proposés d’étudier ce second aspect en essayant de construire cette interface à une échelle nanoscopique : la jonction moléculaire. Le système choisi consiste en des diades donneur-accepteur pour lesquelles la formation de phases cristal-liquide est souhaitée. En effet, ce type de phases peut mener à des structures supramoléculaires complexes correspondant à deux réseaux imbriqués distincts imbriqués : le premier formé par les unités donneuses assure le transport de trous, tandis que le second, formé par les unités accepteuses, permet le transport d’électrons. Dans ce contexte, nous avons décidé de synthétiser de nouvelles diades incluant une phtalocyanine (donneur) connectée à un fullerène (accepteur) par un pont covalent non-conjugué. La deuxième partie du travail concerne l’étude de leurs propriétés tant en solution qu’à l’état solide. Cette structure moléculaire particulière se compose d’une moitié PCBM, un dérivé bien connu du fullerène, et d’une phtalocyanine précédemment étudiée au sein de notre laboratoire et formant des phases cristal liquide d’autre part. Quatre diades comportant des ponts covalents de longueur différente ont été synthétisées par le biais d’une synthèse multi-étapes. Deux étapes-clés de la synthèse sont : (i) la formation de phthalocyanines de type A3B substituées par trois groupes mésogènes et un quatrième portant une fonction alcool libre et (ii) l’estérification de ces phthalocyanines à l’aide de l’homologue acide carboxylique du PCBM. En solution, aucun transfert de charge spontané à l’état fondamental n’a pu être mis en évidence. Au contraire, le quenching de fluorescence observé pour la phthalocyanine indique qu’un transfert d’électron photo-induit de la phthalocyanine vers le fullerène a lieu. D’autre part, les études de voltammétrie cyclique on confirmé que les deux systèmes électroniques de la phthalocyanine et du fullerène sont indépendants à l’état fondamental. L’utilisation combinée des spectroscopies d’absorption UV-Visible et de RMN 1H ont permis de mettre en évidence la forte tendance des diades à s’agréger en solution. L’impact de la température et de la concentration ont dès lors été étudiés. Finalement, l’organisation supramoléculaire des diades à l’état solide a été étudiée à la fois en tant que matériaux purs mais également au sein de mélanges. Les quatre diades produisent des phases amorphes, principalement dû à l’encombrement stérique important généré par les fullerènes au sein de la phase colonne des phthalocyanines. Au contraire, la formation de mésophases colonne a été observée dans le cas de mélanges avec deux phthalocyanines mésogènes. Aucun arrangement régulier des fullerènes sur un réseau défini. Nous avons donc pu illustrer l’impact de trois paramètres sur les propriétés thermotropes des mélanges : (i) la structure chimique de la phthalocyanine utilisée pour réaliser le mélange, (ii) la composition du mélange et (iii) l’application ou non d’un recuit thermique sur l’échantillon.

Carbon allotropes have taken central stage of nanotechnology in the last two decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential building blocks for nanotechnology. Their superlative electrical, thermal and mechanical properties make them desirable for a number of technological applications ranging from lightweight strong materials to electrical wires and support for catalysts. However, transferring the exceptional single molecule properties into macroscopic objects has presented major challenges. This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids and these solution can processed into macroscopic objects. Chapter 2 reviews neat CNT fiber literature. Specifically, the two main processing methods —solid– state and solution spinning — are discussed. CNT aspect ratio and fibers structure are identified as the main variables affecting fiber properties. Chapter 3 shows that graphite can be exfoliated into single-layer graphene by spontaneous dissolution in chlorosulfonic acid. The dissolution is general and can be applied to various forms of graphite, including graphene nanoribbons. Dilute solutions of graphene can be used to form transparent conductive films. At high concentration, graphene and graphene nanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directly into continuous fibers. Chapter 4 describes a solution–based method to form a thin CNT network. This network is an ideal specimen support for electron microscopy. Imaging nanoparticles with atomic resolution and sample preparation from reactive fluids demonstrate the unique feature of solution–based CNT support compared to state–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase. Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despite nanotube liquid crystals having been reported in various CNT systems, a number of anomalies such as low order parameter and spaghetti–like, nematic droplets are reported. However, CNTs in chlorosulfonic acid show elongated, bipolar droplets typical of other rod–like molecules. Moreover, their large aspect ratio allows capturing the transition from homogeneous to bipolar transition expected from scaling arguments.The equilibrium shape and merging dynamics demonstrate the liquid nature of CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiber spinning. The influence of starting material, spinning dope concentration, spin draw ratio and coagulation on fiber properties is discussed. The linear scaling of fiber strength with CNT aspect ratio is demonstrated experimentally, once the best properties from different batches are compared. Moreover, Successful multi–hole spinning demonstrates the intrinsic scalability of wet spinning to meet the typical production output of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers to other CNTs fibers as well as existing engineered materials. Acid–spun CNT fibers combine the typical specific strength of high–strength carbon fibers to the thermal and electrical conductivity of metals. These properties are obtained because of a highly aligned, dense structure. The combined strength and electrical conductivity allow acid-spun fibers to be used as structural as well as conducting wire while the combined electrical and thermal properties allow for exceptional field emission properties. In conclusion, we demonstrate that multifunctional properties of carbon nanotubes that have fuelled much of the research in the past 20 years, can be attained on a macroscopic level via rational design of fluid–phase processing.

Azo-Dye Doped Liquid Crystal (DDLC) is a developed material which can be used to fabricate optical shutter, displays, etc. In this thesis, we presents of the transient grating on a planar aligned DDLC. The effect of various polarizations of writing and probing beams, and of temperature on the transient grating are examined. Then, we propose a model to explain the result. Through this study, we understand the factors that determine the light-induced aligning Dye effect on nematic liquid crystals.

The study of the first-order diffraction efficiency and the mechanism of formation have been investigated on dye-doped liquid crystals (DDLC) and liquid crystals with azo-dye-doped polymer film. The thesis mainly contains three experimental parts by changing the temperature of sample and the polarizations of writing and probing beams. The first part includes the study of temporal profiles of diffraction efficiency for transient gratings and their temperature and polarization dependence in azo-dye-doped liquid crystals. The dynamics of molecular reorientation of transient gratings can be understood by analyzing the build-up time of the peak efficiency and the relaxation decay of the first-order diffraction. The study of the polarization and temperature dependence allows us to understand the underlying mechanism of laser-induced transient gratings. The second part is concentrated in the diffusion process of photoexcited dye in a planar liquid crystal host. The experiment result reveals that the diffusion coefficient is larger for the molecular director along the grating vector than the perpendicular case and the diffusion will be faster as temperature increases. The third part is focused on the mechanism of formation and the temperature dependence of holographic grating for the liquid crystals with azo-dye-doped polymer film. The temporal profile of the first-order diffraction intensity shows a dip at the temperatures of nematic phase. The dip of the first-order diffraction intensity is temperature dependent and can be explained to be the light scattering due to the photothermal effect. The transient behavior in the dip of transmitted probe beam is also temperature dependent. The surface modulation has been measured by using atomic force microscope (AFM). The depth of surface relief grating of liquid crystals with azo-dye-doped polymer film is deeper than that of azo-dye-doped polymer film and the first-order diffraction efficiency is also larger for the liquid crystals with polymer film.

The crown ether derivative application have been widely reported,but is very difficult to see by the liquid crystal primarily report. We have used dibezn-18-crown-6 as the starting material to synthesis and study their properties of liquid crystal.

Chemical vapor deposition is an important thin film process for the fabrication of TFT-LCD(Thin-Film-Transistor Liquid Crystal Display), the heat transfer coefficient on the substrate is the important influence parameter in the manufacturing process. For this reason, the main object of this thesis is to set up a temperature measurement system of transient thermochromatic liquid crystals. Furthermore, an experimental is carried out in the present study to investigate the characteristics of heat transfer resulting from a low speed air jet impinging onto a rectangular substrate confined in a vertical rectangular chamber. Finally, empirical equations are proposed to correlate the effect of Reynolds number¡BSeparation distances and Ratio of outlet.