Organic-inorganic nanostructured composites are nowadays integrated in the field of material science and technology. They are used as advanced materials directly or as precursors to novel composites with potential applications in optics, mechanics, energy, catalysis and medicine. Many properties of these complex materials depend on conformational rearrangements in their inherently dynamic organic parts. The focus of this thesis is on the study of the molecular mobility in ordered nanostructured composites and lyotropic mesophases and also on the development of relevant solid-state NMR methodologies. In this work, a number of new experimental approaches were proposed for dipolar NMR spectroscopy for characterizing molecular dynamics with atomic-level resolution in complex solids and liquids. A new acquisition scheme for two-dimensional dipolar spectroscopy has been developed in order to expand the spectral window in the indirect dimension while using limited radio-frequency power. Selective decoupling of spin-1 nuclei for sign-sensitive determination of the heteronuclear dipolar coupling has been described. A new dipolar recoupling technique for rotating samples has been developed to achieve high dipolar resolution in a wide range of dipolar coupling strength. The experimental techniques developed herein are capable of delivering detailed model-independent information on molecular motional parameters that can be directly compared in different composites and their bulk analogs. Solid-state NMR has been applied to study the local molecular dynamics of surfactant molecules in nanostructured organic-inorganic composites of different morphologies. On the basis of the experimental profiles of local order parameters, physical motional models for the confined surfactant molecules were put forward. In layered materials, a number of motional modes of surfactant molecules were observed depending on sample composition. These modes ranged from essentially immobilized rigid states to highly flexible and anisotropically tumbling states. In ordered hexagonal silica, highly dynamic conformationally disordered chains with restricted motion of the segments close to the head group have been found. The results presented in this thesis provide a step towards the comprehensive characterization of the molecular states and understanding the great variability of the molecular assemblies in advanced nanostructured organic−inorganic composite materials. / <p>QC 20150225</p>

Thesis (Ph.D.); Submitted to the University of California at Berkeley, Berkeley, CA (US); 1 Sep 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--55023" Li, Liang-shi. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 09/01/2003. Report is also available in paper and microfiche from NTIS.

Submitted by Patricia Rocha de Araújo (patriciarocha39@hotmail.com) on 2018-10-15T01:56:34Z No. of bitstreams: 1 Dissertação Patricia Rocha out 2018.pdf: 3514360 bytes, checksum: 9b0fea77694a33ed0ae69da788c5a4a2 (MD5) / Approved for entry into archive by Maria Irani Coito (irani@fcfar.unesp.br) on 2018-10-16T20:37:01Z (GMT) No. of bitstreams: 1 araujo_pr_me_arafcf.pdf: 3514379 bytes, checksum: dffaf731be630bbca5063c79b406b6ae (MD5) / Made available in DSpace on 2018-10-16T20:37:01Z (GMT). No. of bitstreams: 1 araujo_pr_me_arafcf.pdf: 3514379 bytes, checksum: dffaf731be630bbca5063c79b406b6ae (MD5) Previous issue date: 2018-09-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A candidíase vulvovaginal (CVV) é uma doença causada por espécies do gênero Candida spp. no trato genital inferior feminino que afeta um grande número de mulheres em todo mundo. Porém o uso sistêmico de fármacos causa muitas reações adversas e as formulações tópicas possuem um baixo tempo de retenção na mucosa vaginal devido à diluição dos sistemas na cavidade vaginal. Esse estudo propõe uma terapia antifúngica alternativa empregando sistemas precursores de cristais líquidos mucoadesivos (SPCLM) para a liberação de hipericina (HIP), um potente fotossensibilizador isolado de plantas do gênero Hipericum com e sem o emprego da terapia fotodinâmica (TFD). O sistema visa aumentar o tempo de permanência da formulação, bem como reduzir o número de aplicações e a quantidade de fármaco empregada. O emprego da TFD, por sua vez, se faz como uma forma de diminuir a resistência pelos microrganismos. Observou-se a formação de sistemas isotrópicos no sistema constituído por 30% da fase oleosa constituída por ácido oleico e colesterol na razão de 7:1, 40% de Procetyl AWS como tensoativo e 30% de uma dispersão de poloxamer à 16% empregando as técnicas de microscopia de luz polarizada e espalhamento de raios-X a baixo ângulo. Após a introdução de três diferentes concentrações de fluido vaginal simulado FVS (30, 50 e 100%), as formulações resultantes passaram a apresentar anisotropia e picos característicos de fase lamelar. Análises das propriedades mecânicas, reológicas e mucoadesivas das formulações indicaram que a organização e a mucoadesão dos sistemas aumentaram à medida que a quantidade de FVS aumentou. Os ensaios de validação da metodologia analítica para quantificação de HIP indicaram que o método é aceitável segundo agências regulatórias. Os testes de liberação in vitro demonstraram perfil de liberação sustentada da HIP provavelmente devido à sua alta afinidade pelos componentes da fase oleosa dos sistemas de liberação. Além disso, os SPCLM causaram aumento da retenção e baixa permeação da HIP em mucosa suína. Ensaios microbiológicos indicaram que a HIP é um agente eficaz para inativação das leveduras de Candida albicas com emprego da TFD, porém os SPCLM com HIP não potencializaram a ação antifúngica deste composto, possivelmente devido ao longo período necessário para sua liberação. Os testes de citotoxicidade indicaram que todas as formulações apresentam baixa toxicidade, porém os sistemas com hipericina incorporada apresentaram maior toxicidade para células tumorais L292. Ensaios in vivo do sistema em modelo de CVV são necessários para comprovar a viabilidade do sistema desenvolvido. / Vulvovaginal candidosis (VVC) is a disease induced by Candida strains in the female genital tract that affects a great number of women worldwide. However, systemic drugs cause many adverse reactions. Also, currently employed topical dosage forms present low retention times due to their dilution in vaginal fluids. This study proposes an alternative antifungal therapy through the development of liquid crystalline precursor systems (LCPS) for hypericin release, a potent photosensitizer isolated from Hipericum plants with and without photodynamic inactivation (PDI). The developed system aims to increase the residence time of the formulations, as well as decrease the number of applications and the amount of drug. Photodynamic therapy was used to reduce microorganism resistance. Polarized light microscopy and Small-Angle X-Ray Scattering confirmed the formation of an isotropic system composed of 30% of oil phase containing oleic acid and cholesterol in (ratio of 7:1). After addition of three different concentrations of simulated vaginal fluid -SVF (30, 50 and 100%), the resultant formulations presented anisotropy and characteristic peaks of lamellar phases. Mechanical, rheological and mucoadhesive assays indicated the formation of long-range ordering systems as the amount of SVF increased. Drug validation assays indicated that the method is aceptable for hypericin quantification according to regulatory agencies. In vitro drug release assays exhibited a sustained release profile probably due to the high affinity between HIP and the oily phase components. In addition, the LCPS lead to poor permeability and enhanced retention of HIP in the porcine mucosa. Microbiological assays pointed out that HIP effectively inactivated Candida albicans yeasts with PTD, however the HIP loaded LCPS did not potentiate the antifungal activity of HIP, probably due to the long period for HIP release. Cytotoxic tests indicated that all formulations presented low toxicity, however the HIP loaded presented higher toxicity to L292 tumor cells. In vivo assays should be performed to confirm the viability of the developed system. / 001

La convection de Rayleigh-Bénard est étudiée expérimentalement dans une cellule circulaire. Des fluides à seuil modèles (gels aqueux de Carbopol) sont mis en œuvre. Leurs comportements rhéologiques et leurs perméabilités en relation avec leurs microstructures ont été finement caractérisés. Dans toute la thèse, les expériences ont été menées sans glissement à la paroi. L'influence du seuil d'écoulement et de la distance entre plaques chaudes et froides sur les transferts thermiques a été approfondie. Trois mécanismes sont discutés pour expliquer le déclenchement de la convection: i) les propriétés visco-élastiques au-dessous du seuil, ii) le fluage au-dessous du seuil, iii) une approche d'un milieu poreux pour les gels de Carbopol considérés comme une suspension de micro-gels. On montre que le nombre de seuil Y, représentant le rapport entre la contrainte du seuil et la contrainte de la poussée d'Archimède est un paramètre important gouvernant l'apparition de l'instabilité. Les valeurs critiques de Y^(-1) sont déterminées entre 60 et 90. La visualisation à l'aide des cristaux liquides thermo-chromiques a permis une vue globale de la cinématique. Les structures observées dans les différents états thermiques montrent l'évolution de la convection. Une analyse qualitative du champ de température est également présentée. Enfin, la simulation numérique dans une cellule carré avec un modèle d'Herschel-Bulkley régularisé dans la gamme des nombres sans dimension utilisée dans les expérience a permis de mettre en évidence les paramètres critiques et la morphologie des champs thermiques et cinématique. Les ordres de grandeurs du nombre de seuil critique prédit se comparent raisonnablement avec les valeurs expérimentales. / In this thesis, three main mechanisms proposed in a recent paper (Darbouli et al., Physics of fluids, 25(2) 2013) have been discussed to explain the onset of Rayleigh Bénard Convection in a yield fluid (Carbopol gels): i) the elasto-visco-plasticity behavior of the material below the yield stress, ii) a viscosity at low values of shear rates by creep measurements below the yield stress, iii) a microscopic viewpoint considering the fluid as a porous two phases system. No-slip conditions have been achieved for all the experiments. The results with different Carbopol gels have proved the importance of Y, the yield number which presents the report of the yield stress and the buoyancy effect, as the governing parameter. The critical value of Y^(-1) with no-slip condition has been found between 60 and 90. A visualization measurement with the utilization of thermochromics liquid crystals presents a global view from above. Different structures have been observed in different states of thermal conditions, which describe the evolution of the convection. For several cases the color of the liquid crystals can indicate the temperature field in the whole experiment cell. Numerical simulations with a Herschel-Bulkley model have also been discussed in this thesis. The dimensionless parameters are defined approaching the values obtained in the experiments, so that we can compare the numerical results with some of experimental ones.

The study of optical, thermal and electronic properties of liquid-crystalline systems has attractedd an enormous interest of the scientific community, due to the potencial applicability of such systems in eletroc-optical devices. In this work, the effects of C60 fullerene addition on the physico-chemical properties of liquid crystals are investigated. By using different experimental techniques, it was possible do determine how the addition of a non-mesogenic and electron donor compound affects important physical parameters, such as the thermal diffusivity and the non-linear refractive index. From time-resolved Z-scan measurements, the thermo-opitical properties of the fullerene-doped and pure liquid crystal samples are investigated.Our results show that the insertion of fullerene reduces the nematics-smectic-A transition temperature, as well as affects the heat diffusion mechanisms in nematic and smectic phases. Concerning the non-linear optical properties, it is observed that the optical Freedericskz transition presents a continuous nature in the nematic phase, with the number of self-modulation rings increasing as the excitationa intensity is enhanced above the Freedericskz threshold. Further, it is observed that the addition of fullerene increases the non-linear optical reponse of the system. Using the two-beam coupling technique and photoconductivity measurements in the steady-state regime, the transport and photorefractive properties of doped sample are also analyzed. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O estudo de propriedades ópticas, térmicas e eletrônicas de sistemas líquido-cristalinos tem atraído enorme interesse da comunidade científica, por conta do grande potencial de aplicação destes sistemas em dispositivos eletro-ópticos. Neste trabalho, são investigados os efeitos da adição de fulereno C60 sobre as propriedades físico-químicas de cristais líquidos. Usando diferentes técnicas experimentais, foi possível determinar como a adição de um agente não-mesogênico e doador de elétrons afeta parâmetros físicos importantes, tais com a difusividade térmica e o índice de refração não-linerar. A partir de medidas de varredura Z resolvida no tempo, as propriedades termo-ópticas das amostras de cristal líquido puro e dopado com fulereno são investigadas. Nossos resultados mostram que a inserção de fulereno reduz a temperatura de transição nemática-esmética-A, bem como afeta os processos de difusão de calor nas fases nemática e esmética-A. No que diz respeito às propriedades ópticas não-lineares, é observado que a transição de Freedericskz óptica apresenta uma natureza contínua na fase nemática, com o número de anéis de auto-modulação de fase aumentado à medida que intensidade da excitação cresce acima do limiar de Freedericskz. Além disso, é observado que a adição de fulereno aumento significativamente a resposta óptica não-linear do sistema. Usando a técnica de acoplamento de dois feixe e medidas de fotocondutividade no regime estacionário, as propriedades de transporte das amostras dopadas também são analisadas.

Le manuscrit est divisé en six chapitres et deux parties indépendantes, la première étant consacrée à l'étude de l'effet de substituants nitro sur des ligands phosphines aromatiques (L). Une série de (N-phényl-benzimidazol-1-yl)diphénylphosphines substituées par 1 à 3 groupes nitro à différentes positions des noyaux N-phényle et benzimidazolyle, a été synthétisée, et comparée au parent non nitré et à l'homologue N-méthyl-benzimidazolium cationique. Dans les complexes trans-L2RhICl(CO) correspondants, des variations faibles mais systématiques de la fréquence d'élongation C=O IR et du déplacement chimique RMN 103Rh fournissent une quantification empirique des effets régio-spécifiques des substituants nitro sur le caractère donneur global du ligand. Les produits secondaires dinucléaires (µ-CO)(LRhCl)2 donnent des cristaux de clathrate uniques à teneur élevée (6,7:1) en solvate de dichlorométhane. La deuxième partie, regroupant cinq chapitres, concerne l'étude de nouveaux types de carbo-mères fortement p-conjugués, principalement conçus pour pallier la faible solubilité limitante du noyau carbo-benzène. La synthèse et la caractérisation des hexaaryl-carbo-benzènes de référence sont revisitées. Une voie de synthèse en 12 étapes améliorée du dérivé hexaphényle connu et de l'homologue p-bis-3,5-di-tert-butylphényle est décrite. Les deux carbo-benzènes ont été entièrement caractérisés, en particulier par analyse par diffraction des rayons X et par électrochimie. Leur utilisation dans les cellules solaires photovoltaïques organiques s'est avérée freinée par leur faible solubilité empêchant la formation de couches minces de haute qualité. Le troisième chapitre porte sur une série de p-dialkyl-tétraphényl-carbo-benzènes à deux chaînes aliphatiques R = CnH2n +1, n = 2, 4, 8, 14, 20. Leur synthèse basée sur l'addition nucléophile de RMgBr sur la [6]péricyclynedione clé conduit à la fois aux dialkyl- et mono-alkyl-carbo-benzènes réduits, le processus de réduction étant supprimé en utilisant un réactif RLi/CeCl3. Une augmentation spectaculaire de la solubilité dans les solvants chlorés a été observée pour n = 8. Un empilement p-p direct des cycles en C18, guidé par les forces de dispersions aliphatiques, a été montré pour la première fois dans la structure cristalline du dérivé bis-tétradécyle, appuyant l'existence de l'allotrope du carbone 3D ?-graphityne (carbo-mère putatif du graphite). Le quatrième chapitre décrit deux trialkoxyaryléthynyl-tétraphényl-carbo-benzènes et l'étude des propriétés mésogènes de l'un d'entre eux. Une mésophase rectangulaire colonnaire, mise en évidence à 115 °C par des analyses DSC, POM et PXRD, ouvre des perspectives pour une étude systématique des cristaux liquides apparentés. Les constantes du réseau 3D sont cohérentes avec les images STM 2D du carbo-mésogène sur HOPG. Le cinquième chapitre décrit trois carbo-mères de squelette de bis- et ter-phényles, conçus pour leur relation aux fils moléculaires OPP ou OPE. Un carbo-terphényle a montré un très faible potentiel de réduction (-0,39 V/SCE), sans précédent en série carbo-mère. Dans le dernier chapitre, de nouveaux types de carbo-mères sont illustrés: les carbo-barrélènes et les carbo-stilbènes. Leur préparation repose sur l'addition de triyne dinucléophiles sur un ou deux équivalents d'un précurseur [6]péricyclyne (di)one. Dans la série tricyclique, deux carbo-barrélènes non macro-aromatiques et un dérivé bis-butatriénique partiellement réduit, se sont révélés suffisamment stables pour permettre une caractérisation complète, y compris par cristallographie. Le rôle de cage d'un carbo-barrélène vis-à-vis de petites molécules telles que NH4+, même si elle n'a pas encore été clairement établie, a été étudiée théoriquement et expérimentalement. Les carbo-stilbènes ont été obtenus sous forme de mélanges. En l'absence d'analyse cristallographique, ils ont été attribués aux diastéréoisomères cis et trans sur la base de la spectroscopie RMN 1H et des calculs DFT. / The manuscript is divided into six chapters and two independent parts, the first part being dedicated to the investigation of the effect of nitro substituents on aromatic phosphine ligands (L). A series of (N-phenyl-benzimidazol-1-yl) diphenylphosphines substituted with 1 to 3 nitro groups at different positions of the N-phenyl and benzimidazolyl cores, were synthesized, and compared with the non-nitrated parent and cationic N-methyl-benzimidazolium counterpart. In the corresponding trans-L2RhICl(CO) complexes, prepared in two steps and fully characterized, moderate but systematic variations of the C=O IR stretching frequency and 103Rh NMR chemical shift provide an empirical quantification of regio-specific effects of the nitro-substituents on the global donating character of the P-ligand. Dinuclear (µ-CO)(LRhCl)2 side-products were shown to give unique clathrate crystals with a high content (6.7:1) of dichloromethane solvate. The second part, gathering five chapters, concerns the study of new types of highly p-conjugated carbo-mers, primarily devised to palliate the limiting poor solubility of the aromatic C18 carbo-benzene core. The synthesis and characterization of reference hexaaryl-carbo-benzenes are revisited. An improved 12-step synthetic route to the long known hexaphenyl derivative and p-bis-3,5-di-tert-butylphenyl homologue is described. Both carbo-benzenes were fully characterized, in particular by X-ray diffraction analysis and electrochemistry. Their use in organic photovoltaic solar-cells was found to be hampered by their very low solubility preventing the formation of high quality thin films. The third chapter focusses on a series of p-dialkyl-tetraphenyl-carbo-benzenes with two aliphatic chains R = CnH2n+1, n = 2, 4, 8, 14, 20. The synthetic route based on nucleophilic addition of RMgBr to a key [6]pericyclynedione ultimately led to both the dialkyl- and reduced mono-alkyl-carbo-benzenes, the reduction process being found suppressed by using a RLi/CeCl3 reactant. A dramatic enhancement of solubility in chlorinated solvents was observed for n = 8. A direct p-p stacking of C18 rings, driven by aliphatic dispersions forces, could be evidenced for the first time in the X-ray crystal structure of the bis-tetradecyl derivative, giving experimental support to the existence of the a-graphityne 3D carbon allotrope (putative carbo-mer of graphite). The fourth chapter describes two trialkoxyarylethynyl-tetraphenyl-carbo-benzenes and the study of the mesogen properties of one of them. A columnar rectangular mesophase, evidenced at 115 oC by DSC, POM and PXRD analyses, opens prospects for a systematic study of related liquid crystals. The 3D lattice constants are consistent with 2D STM images of the carbo-mesogen deposited on HOPG. The fifth chapter reports on three skeletal carbo-mers of bis- and ter-phenyls, devised for their acquaintance with OPP or OPE molecular wires. A carbo-terphenyl was found to exhibit a very low first reduction potential (-0.39 V/SCE), unprecedented in the carbo-mer series. In the last chapter, new types of carbo-mers are exemplified: carbo-barrelenes and carbo-stilbenes. Their preparation relies on the addition of triyne dinucleophiles to either one or two equivalents of a [6]pericyclyne(di)one precursor. In the tricyclic series, two non-macroaromatic carbo-barrelenes and one partially reduced bis-butatrienic derivative, both containing two sp3-C bridgeheads, were found to be sufficiently stable to allow full characterization, including by crystallography. The cage-ability of a carbo-barrelene toward small molecules such as NH4+, albeit not clearly proven yet, was investigated both theoretically and experimentally. The carbo-stilbene product was evidenced as an unseparated mixture of two isomers. In the absence of crystal of suitable quality for crystallography, they were assigned to the cis and trans diastereoisomers on the basis of 1H NMR spectroscopy and DFT calculations.

Pour ce travail de thèse, nous nous sommes intéressés dans une première partie à la conception et à la synthèse de nouveaux matériaux multifonctionnels (LC, photosensible, systèmes moléculaires dendritiques) capables d'être élaborés en films minces anisotropes et doués de propriétés photo-induites. Nous avons réalisé l'étude complète des propriétés mésomorphes de ces nouveaux matériaux et de dérivés structuraux (en fonction de la connectivité dendritique intrinsèque) par la diffraction des rayons X aux petits angles; l’étude de leurs propriétés optiques a également été effectuée. Dans une seconde partie, nous avons fonctionnalisé des nanoparticules d'or avec des ligands dendritiques mésogènes afin d'organiser ces particules dans des structures mésomorphes. Les objectifs principaux de cette partie sont tout d’abord la synthèse d'une "bibliothèque" de nanoparticules mésomorphes dendronisées, et ensuite la caractérisation de réseaux simples formée par l’auto-assemblage des particules précédentes. / The need to expand further the range of mesomorphic organization, develop original materials where different functionalities can be added (i.e. multifunctional), and to design “multitask materials” with tunable properties are particularly interesting and crucial challenges for potential uses in future technologies. On the one hand, we focused on the design and synthesis of multifunctional materials (liquid crystalline, dendritic, photoresponisve) which are suitable for making thin films where photoinduced optical anisotropy and surface relief gratings can be generated. The mesomorphic behaviour of these dendrimers was investigated and also their optical properties. On the other hand, we grafted structurally related protodendritic mesogenic ligands to monodisperse gold nanoparticles to elaborate liquid crystalline hybrids in order to self-organize NPs in periodic arrays. A set of dendronized gold nanohybrids was synthesized to carry out this study.

Self-assembled monolayers and surface-initiated polymer, or polymer brushes, have attracted attention as they form dense layers with much higher structural order than bulk or solution polymers. Another field of research which has emerged over the last two decades is the field of organic and polymer electronics. In this field molecular order and surface modification are of major influence on the device performance, hence that both self-assembled monolayers as polymer brushes have been investigated to find applications in organic electronic devices. After an introduction into the field self-assembled monolayers, polymer brushes and organic electronics, the first part of this thesis focusses on three applications of surface modification techniques for applications in devices. Alignment of the active material is crucial for high mobilities in organic electronics. Chapter 2 discusses the synthesis of a liquid crystalline surface-initiated polymer and its application to induce strong homeotropic alignment. The alignment is homogeneous over large areas and can be patterned by combining the polymerization with soft lithographic techniques. Mobilities of organic electronic materials can also be strongly influenced by dopants in the material. In field-effect transistors the positioning of the dopant is thought to be crucial, as the conductance predominantly takes place in only a small channel near the dielectric interface. In chapter 3 dopant functionalized monolayers and polymer brushes are presented which enable the localized deposition of dopants in the channel of organic transistors. It is shown that the mobility of charges and hence the device performance is affected by the introduction of this dopant layer. Polymer brushes have been suggested for the fabrication of highly ordered semiconducting polymers. In chapter 4 the use of a thiophene functionalized polymer brush is shown, that can be used as a template for the subsequent growth of highly conjugated surface grafted polythiophene layers. Thick polythiophene layers are obtained, that are low in roughness and show photoluminescence and polychromism upon doping. The second part (chapter 5 and 6) of this thesis presents new techniques for surface polymerizations. It is attractive to investigate reduction of reactor volume for polymer brush growth. Chapter 5 discusses a method to achieve volume reduction by back-filling the superfluous volume with beads. It is found that this influences the polymerization kinetics significantly. The combined advantages of less volume and enhanced reaction speeds enable reduction of the total amount of monomer needed by up to 90%. Chapter 6 presents a controlled way to convert initiators for atom transfer radical polymerization into initiators for nitroxide mediated polymerization. In this way mixed polymer brushes and block co-polymer brushes become accessible. This combination makes it an attractive tool to fabricate complex polymer architectures. The technologies used in this thesis show that the synthesis of polymer brushes enable the fabrication of complex architectures without the wastes normally associated with surface-initiated polymers. Combined with several functionalized polymer brushes with properties that enhance order, influence mobility or serve as template for the growth of surface attached conjugated polymers this shows the high potential for the application of surface-initiated polymers in organic electronics.

Synthesis and Studies of Dendritic Poly(Ether Imine) Boronates and Cholesteryl-Functionalized Mesogens SYNOPSIS Dendrimers are hyperbranched synthetic macromolecules having branches-upon-branches structures, high molecular weights, globular shapes and monodispersities. Dendrimers possess a large number of modifiable functional groups at their peripheries. Initial efforts were largely concerned with the synthesis, design and development of new dendrimers. Exploring the chemical, biological and material applicability of these macromolecules are relevant to current interests, as a result of the unique structural features of dendrimers. Incorporation of transition metals and organic moieties at the peripheries of the dendrimers was studied to determine their efficacies in catalysis. Evolution of dendritic effects was observed in few instances, that were non-linear in nature. On the other hand, dendritic peripheries were also utilized to study mesogenic properties in liquid crystals. Chapter 1 of the Thesis gives an overview of the types of dendrimers, its structural features and their application in catalysis and as liquid crystalline materials. Chapter 2 describes the synthesis of a new type of poly(ethyl ether imine) dendrimer, having nitrogen as a branching unit, ethylene moiety as the spacer and an oxygen as the connecting linker. Synthesis, characterization, and studies of the photophysical properties of these dendrimers are described in this chapter. The molecular structure of second generation dendrimer is shown in Figure 1. Synthesis of this dendrimer was initiated using 2,2'-oxy-bis(ethan-1¬amine) as the core. The reaction sequence of two alternate nucleophilic substitutions and two alternate reductions, involving ethyl bromoacetate and bromoacetonitrile as monomers was employed in the synthesis of the dendrimer. The formation of dendrimers having ether linkage and tertiary amines as branching unit was established by spectroscopies and mass spectrometry. A number of functional groups, such as, acid, alcohol, amine, ester and nitrile are present at the peripheries of each generation the dendrimers that open up the possibilities for further studies. Carboxylic acid terminated poly(ethyl ether imine) dendrimers are substituted iminodiacetic acids, belonging to the class of polyaminocarboxylic acid. Methyl iminodiacetic acid boronates with NB coordination have emerged as an excellent substitute for unstable boronic acids. Upon increasing the steric bulk on the nitrogen moiety, the hydrolytic stability of the boronates to a base-catalyzed hydrolysis is increased. Combining the structure of carboxylic acid terminated dendrimer and the stability of the dendritic boronates, such dendritic iminodiacetic acids were reacted with arylboronic acids to prepare bis-and tetrakis-boronates (Figure 2). Kinetic hydrolytic studies of boronates were conducted to assess the stabilities of the newly synthesized dendritic boronates. From the studies it was observed that the tetrakis-boronate was ~20 times more stable in comparison with dimeric and monomeric boronates (Figure 3). Subsequent to synthesis and hydrolytic stability studies, C-C bond-forming Suzuki-Miyaura cross-coupling reactions were conducted. A comparison of the reactivities among monomeric, dimeric and tetrameric arylboronates in C-C bond-forming reactions showed a higher reactivity of monomeric and dimeric boronates, than the tetrameric aryl boronate to construct ter-and tetra-aryl in one-pot iterative manner (Figure 4). Chapter 3 of this Thesis describes the synthesis and characterization of dendritic boronates and studies of their hydrolytic stability in Suzuki-Miyaura cross¬coupling reactions to construct ter-and tetraaryls. Figure 4. Synthesis of (a) ter-(6) and (b) tetra-aryls (7) by following one-pot iterative cross-coupling reactions. Step-wise iterative synthesis of dendrimer allows a uniform branching throughout the structure. The first and second generation poly(ether imine) dendrimer series, having hydroxyl groups at their peripheries were chosen for further modification. A versatile mesogenic group, namely, cholesterol was covalently attached at the peripheries of the dendrimers with succinic moiety as linker, so as to install 4 and 8 cholesteryl moieties at the peripheries of the dendrimers (Figure 5), that were characterized by H, C NMR spectroscopies and elemental analysis, so as to confirm their structural homogeneities. Figure 5. Molecular structures of the first and second generation dendritic mesogens. Subsequent to synthesis and characterization, liquid crystalline properties of all the dendritic mesogens was assessed through differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) studies. In POM study, broken fan or leaf like texture revealed the lamellar arrangement, whereas homeotropic appearance of texture on surfactant (cetyltrimethylammonium bromide) coated substrate indicated the lamellar nature of G1-Et-(OCS)4, G1-Pr-(OCS)4 and G2-Pr-(OCS)8 (Figure 6). From DSC studies, the change in enthalpy was found to increase with increase in generation and change in enthalpy per mesogenic unit was found to be ~ -1 1-2 kJ mol, which indicated the mesophase arrangement to be lamellar. Decrease in the length of spacer dendritic backbone and increase in the generation increased the isotropization temperature of the dendritic liquid crystals. Variable temperature XRD studies were undertaken to characterize the mesophase property. Two sharp peaks in small angle region and a diffused halo in wide angle region in XRD pattern of the material suggested the smectic A (SmA) liquid crystalline arrangement of G1-Et-(OCS)4, G1-Pr-(OCS)4 and G2-Pr-(OCS)8 (Figure 7). Figure 6. POM textures of (a) G1-Et-(OCS)4 at 136 oC; (b) G2-Et-(OCS)8 at 129 oC; (c) G1-Pr-(OCS)4 at 92 oC; (d) G2-Pr-(OCS)8 at 118 oC and (e) transition temperatures for dendromesogens (DSC second heating cycle, heating-cooling rate = 10 oC min-1). Figure 7. Small angle XRD profiles of: (a) G1-Pr-(OCS)4 and (b) G2-Et-(OCS)8 at 60 o C (black), 150 oC (red) and 180 oC (green), (Insets: Lorentzean fit of wide angle peak). The second generation ethyl-linker dendrimer G2-Et-(OCS)8 exhibited a layered structure with a superimposed in-plane modulation (SmÃ), the length of which corresponded to a rectangular column width. Chapter 4 describes the synthesis, characterization and studies of mesophase property and fluorescence property of cholesterol functionalized homologous pairs of the PETIM dendritic liquid crystals. Peripheral functionalization of the dendrimers provides an easy access to dendritic liquid crystalline materials. The covalent functionalization was extended further with the dendrimers for both the series, so as to have 2, 4, 8 and 16 cholesteryl groups at the peripheries of 0, 1, 2 and 3 generation dendrimers, respectively, having succinic amide and phthalic ester functionalities for 1, 2 and 3 generation dendrimers with 4, 8 and 16 cholesteryl groups. Molecular structures of third generation dendrimers are shown in Figure 8. Figure 8. Molecular structures of third generation G3-Pr-(NHCS)16 and G3-Pr-(OCP)16. Subsequent to synthesis and characterization, mesophase property was studied through POM, DSC and XRD techniques. In POM study, a birefringent texture was observed in heating and cooling cycles. Leaflet, broken fan or bâtonnet like texture suggested the layered arrangement of the molecules (Figure 9). In DSC studiues, it was observed that the amide-linked dendrimers showed higher glass transition and isotropization temperatures than that of ester-linked dendrimers within the same generation irrespective of the back-bone of the dendrimer. Succinic moiety linked dendrimers showed lower glass transition temperature than that of phthalic moiety linked dendrimers and consequently, larger mesophase range. The change in enthalpy for isotropization was found to increase with increase in generation, whereas change in -1 enthalpy per mesogenic unit was 1-2 kJ mol, indicative of a layered arrangement in the mesophase. Figure 9. POM textures (20x) of (a) G3-Pr-(NHCS)16 at 90 oC; (b) G3-Pr-(OCS)16 at 90 ooo C; (c) PG1-(NHCS)4 at 134 C; (d) G3-Pr-(OCP)16 at 98 C and (e) transition temperatures for dendromesogens (second cycle, heating-cooling rate = 10 oC min-1). Appearance of two sharp peaks in small angle region and a wide halo in wide angle region in XRD pattern supported lamellar mesophase property of the material (Figure 10). On decreasing the temperature, increase in the layer thickness also suggested the smectic A arrangement of the molecules except third generation phthalate derivative G3-Pr-(OCP)16, which showed rectangular columnar mesophase. For all the dendromesogens, the layer thickness increased with the increase in generation. Upon protonation, the first generation dendrimer showed a change in mesophase from simple smectic A to modulated smectic A with decrease in layer thickness. The change in liquid crystal property of the dendromesogens from lamellar to columnar mesophase by changing the linker of the mesogen is unknown so far in the dendrimer liquid crystals. Chapter 5 gives details of synthesis, characterization and mesophase property study of ester-and amide-linked dendritic liquid crystals. Overall, the Thesis establishes a synthetic methodology for the synthesis of a new homologous series of poly(ether imine) dendrimers with ethyl spacer; synthesis of dendritic boronates and their studies in cross-coupling reactions through in-situ slow release of boronic acid; hydrolytic stability study showed higher stability of dendritic boronates which was used in one-pot iterative cross-coupling reactions to construct ter-and tetra-aryls. decrease in linker length in dendrimer backbone modified the thermal, as well as, mesophase behavior of the dendritic liquid crystals; change in the linker functionality from ester to amide changed the thermal behavior of dendritic liquid crystals; a switching of mesophase property from lamellar to columnar was observed by changing the rigidity of the linker from succinate to phthalate without changing the linker length. The results of the above chapters are in different stages of publications: 1 Dendritic iminodiacetic acids and their boronates in Suzuki-Miyaura cross¬coupling reactions. Sharma, A.; Kumar, P.; Pal, R.; Jayaraman, N. Revised Manuscript submitted. 2 In-plane modulated smectic à vs smectic A lamellar structures in homologous pairs of dendritic liquid crystals. Kumar, P.; Rao, D. S. S.; Prasad, S. K.; Jayaraman, N. Revised Manuscript submitted. 3 Effect of protonation on dendritic liquid crystals of poly(ether imine) dendrimers: structure property relationship studies. Kumar, P.; Rao, D. S. S.; Prasad, S. K.; Jayaraman, N. Manuscript submitted. 4 Smectic to rectangular columnar switch from succinic to phthalic linker alteration in poly(ether imine) dendritic liquid crystals. Kumar, P.; Rao, D. S. S.; Prasad, S. K.; Jayaraman, N. Manuscript in preparation.

Made available in DSpace on 2015-05-14T12:14:03Z (GMT). No. of bitstreams: 1 parte1.pdf: 6372308 bytes, checksum: db3e915edd1663a97d16d8935fc5becf (MD5) Previous issue date: 2012-03-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work we study numerically the generation and dynamics of topological defects in nematic liquid crystals. Our study is based on a Ginzburg-Landau model describing the evolution of the orientational order of a liquid crystal in terms of a symmetric, traceless, second-rank tensor. This phenomenological model allows studies of nematic phases at scales ranging from few nanometers to few micrometers (mesoscopic scale). Within this framework we developed a software named LICRA (Liquid CRystal Algorithm) that combines standard finite difference algorithm for the spatial derivatives with a Runge-Kutta temporal integration to solve the relaxational equations of nematodynamics without thermal fluctuations and hydrodynamic flow. Using this software we investigate the coarsening dynamics of defects of two- and three-dimensional uniaxial nematic liquid crystals. The time dependences of the structure factor and characteristic length scale were computed. The characteristic length scale is expected to grow as a power law in time, L ∝ tα. From dimensional analysis α = 1/2 and we found α = 0, 45±0, 01 in two-dimensions and α = 0, 350±0, 003 in three-dimensions. Furthermore, in all cases Porod s law is satisfied for large values of wave number k. We also investigate, using LICRA, the coarsening dynamics of liquid crystal textures in a two-dimensional nematic under applied electric fields. We consider both positive and negative dielectric anisotropies and two different possibilities for the orientation of the electric field parallel and perpendicular to the two-dimensional lattice. We determine the effect of an applied electric field pulse on the evolution of the characteristic length scale and other properties of the liquid crystal texture network. In particular, we show that different types of defects are produced after the electric field is switched on, depending on the orientation of the electric field and the sign of the dielectric anisotropy. Finally, we present the effect of the rotation of an external electric field on the dynamics of half-integer disclination networks in two and three dimensional nematic liquid crystals with a negative dielectric anisotropy. We show that a rotation of π of the electric field around an axis of the liquid crystal plane continuously transforms all half-integer disclinations of the network into disclinations of opposite sign via twist disclinations. We also determine the evolution of the characteristic length scale, thus quantifying the impact of the external electric field on the coarsening of the defect network. / Neste trabalho estudamos numericamente a formação e dinâmica de defeitos topológicos em cristais líquidos nemáticos. Nosso estudo é baseado no modelo de Ginzburg- Landau, o qual descreve a evolução da ordem orientacional de um cristal líquido em termos de um tensor de segunda ordem simétrico e com traço nulo. Este modelo fenomenológico permite estudar a fase nemática em escalas que vão de poucos nanômetros até poucos micrômetros (escala mesoscópica). Para tal estudo numérico, desenvolvemos um programa de computador que denominamos de LICRA (Liquid CRystal Algotithm). Este programa combina o algoritmo de diferença finita para calcular derivadas espaciais com a integração temporal de Runge-Kutta para resolver a equação de relaxação da nematodinâmica, sem a presença de flutuações térmicas e fluxos hidrodinâmicos. Usando este programa de computador investigamos a dinâmica de coalescência em duas e três dimensões em um cristal líquido nemático uniaxial. Tanto o fator de estrutura quando a escala de comprimento característico foram calculadas no tempo. Espera-se que esta escala cresça como uma lei de potências do tempo, L ∝ tα, onde, a partir de uma análise dimensional, α = 1/2. Encontramos os valores de α = 0, 45 ± 0, 01 em duas dimensões e α = 0, 350 ± 0, 003 em três dimensões. Além disso, em todos os casos verificamos que a lei de Porod é satisfeita para número de ondas k de grandes valores. Utilizando LICRA, investigamos também a dinâmica de coalescência de cristais líquidos nemáticos em duas dimensões submetidos a um campo elétrico externo. Consideramos a anisotropia dielétrica positiva e negativa e duas diferentes possibilidades de orientação do campo elétrico: paralelo e perpendicular ao plano da rede bidimensional. Determinamos os efeitos de um pulso de campo elétrico na evolução da escala do comprimento característico e as alterações nas texturas dos cristais líquidos. Em particular, mostramos que os diferentes tipos de defeitos que são produzidos após o campo elétrico ser aplicado dependem da orientação do campo elétrico e do sinal da anisotropia dielétrica. Finalmente, apresentamos os efeitos da rotação de um campo elétrico externo na dinâmica de uma rede de defeitos semi-inteiros em cristais líquidos nemáticos em duas e três dimensões com anisotropia dielétrica negativa. Mostramos que, girando o campo elétrico por um ângulo π ao redor de um eixo pertencente a plano da rede, ocorre uma transformação contínua de todas as desclinações semi-inteiras da rede em desclinações com sinal oposto. Esta transformação é intermediada por desclinações do tipo torção. Além disso, determinamos a evolução da escala de comprimento característico quantificando o impacto do campo elétrico externo na dinâmica de coalescimento da rede.