Chromonic liquid crystals are a relatively new class of lyotropic liquid crystals. In an effort to understand this lyotropic phase better, studies on the phase behavior, defects formed in these systems and characterization of the order were performed. We studied three chromonic liquid crystal materials in nematic and biphasic regions: Sunset Yellow FCF (SSY, a food dye), a cationic perylene diimide derivative (PDI, a conducting dye) and cromolyn sodium (DSCG, a drug). For SSY chromonics in the nematic region, order parameters ( and ) were obtained by polarized Raman measurements. Using the order parameters the flow behavior was predicted and was found to be non-flow aligning. A comprehensive viscoelastic property set of SSY chromonics was obtained by studying the statics and dynamics of defects during the formation of planar aligned monodomain. Applications of PDI thin films as vapor sensors were explored; anisotropic electronic properties of oriented PDI films show good conductivity along the columns presumably arising from the overlap between the ? systems. In the biphasic region, growth and fluctuation of SSY tactoids and interesting patterns of biphasic DSCG under capillary geometry were observed; elastic properties and surface tension were estimated based on the shape of DSCG tactoids. Polymer dispersed lyotropic chromonic liquid crystals with different drop shapes and director configurations were also fabricated using various water-soluble polymers.

In biomechano-transducing, cellular generated tension can be measured by soft substrates based on polymers but these techniques are limited either by spatial resolution or ability to detect localised cell traction forces (CTF) due to their non-linear viscous behaviour under shear rates. A newly developed cell traction force transducer system based on cholesteryl ester lyotropic liquid crystals (LCTFT) was developed to sense localised traction forces of human keratinocyte cell lines (HaCaTs), in which the length of the deformation line induced represents the intensity of the CTF exerted. The physical properties of the cholesteryl ester based lyotropic liquid crystals (LLC) were characterised by using polarising microscopy, rheology, atomic force microscopy (AFM) based nano-indentation, spherical indentation, and micro-tensile tests. The interactions of LLC with cells were studied by using cell viability studies, cytochemical treatments, widefield surface plasmon resonance (WSPR) microscopy and various immuno-staining techniques. The results show that LLC is thermally stable (0-50 °C) and linearly viscoelastic below 10% shear strain at shear rates of < 1 s⁻¹. AFM nano and spherical indentations show a good agreement on the Young's modulus of both determined at ~110 kPa which is close to the elastic modulus of the epidermis. The Poisson's ratio of LLC was determined at ~0.58 by using micro tensile tests. The biophysical interaction studies indicated that LLC is biocompatible and allowed cell attachment. Cell relaxation technique by cytochalasin-B treatment suggested that the attachment and contraction of cells on LLC was due to the contractile activity of actin cytoskeletons that are mediated by focal adhesions. The staining experiments showed that cells consistently expressed the same suites of integrins (α2, α3, α5 and β1) and ECM proteins (collagen type IV, laminin and fibronectin) on both glass and LLC coated substrates. Interfacial interaction of cells with LLC observed via the staining of actin and vinculin, and WSPR imaging suggest the association of marginal actin filaments and focal adhesions in attaching HaCaT cells to the LLC. Linear static analysis applied in the Finite Element model of focal adhesion-LC confirmed the compressive force patterns induced by cells. By applying cell relaxation techniques and Hooke's theorem, the force-deformation relationships of the LLC were derived and used for direct quantification of CTF in culture. The sensitivity of the LCTFT was implied by a wide range of CTF (10 - 140 nN) measured at high resolutions (~2 μm). Nonetheless, a custom-built cell traction force measurement and mapping software (CTFM) was developed to map CTF of single cells. Reliability of the LCTFT was evaluated by using a known pharmacological active cytokine, TGF-β1, in inducing contraction of human keratinocytes. This study inferred internal consistency and repeatability of the LCTFT in sensing contraction responses of HaCaT cells in a concentration dependent manner of TGF-β1. The overall LCTFT and CTFM software had shown good potential for use in the study of contraction and migration of keratinocytes.

Les sources d'énergie renouvelable connaissent un essor grandissant. Parmi celles-ci se trouvent les cellules photovoltaïques. Elles ont pour objet la transformation de la lumière en électricité. Les dispositifs actuels, basés sur le silicium, nécessitent des matériaux de très grande pureté et de hautes températures de mise en œuvre, les empêchant de concurrencer les principales sources d’énergie actuelles (fossile, nucléaire).<p>Une alternative pourrait provenir des matériaux semi-conducteurs organiques. En effet, l’utilisation de méthodes de mise en œuvre à partir de solutions pourrait permettre la fabrication de dispositifs flexibles et bon marché. Des résultats encourageants ont été obtenus avec des polymères conjugués et de petites molécules organiques. Les cristaux liquides discotiques CLDs forment une catégorie particulièrement intéressante de matériaux. Ils ont en effet la capacité de s’organiser spontanément en colonnes de molécules, formant des semi-conducteurs à une dimension. Leurs propriétés intéressantes en tant que semi-conducteurs, combinées à une mise en œuvre facile, en font de bons candidats pour de futures applications.<p>Dans ce travail, deux familles complémentaires de matériaux discotiques ont été développées, formant une paire de semi-conducteurs de type n et p. Leurs structures chimiques ont été étudiées en vue d'obtenir des matériaux possédant un ensemble de propriétés choisies afin d’optimiser les paramètres clefs du processus de photo-génération de charges. Ces propriétés sont les suivantes: forte absorption de la lumière dans le visible, fort caractère semi-conducteur de type n ou p, pas de phase cristalline à température ambiante, présence d'une phase cristal liquide colonne, phase isotrope en dessous de 200°C. De plus, les matériaux doivent être accessibles en un nombre minimum d’étapes d’une synthèse efficace, et ce avec un haut niveau de pureté. Ils doivent également être fortement solubles dans les solvants organiques usuels.<p>Cette étude comporte, pour chacune des deux familles de matériaux, le design de leur structure chimique, leur synthèse et la caractérisation de leurs propriétés physiques (thermotropes, optoélectroniques, électrochimiques). Comme possible semi-conducteur de type p, cinq dérivés tétrasubstitués de la phthalocyanine non-métallée ont été synthétisés, donnant un matériau possédant l’ensemble des propriétés recherchées. Comme possible semi-conducteur de type n, six dérivés hexasubstitués de l’hexaazatrinaphthylène ont été étudiés. L’un d’eux possède les propriétés requises.<p>Finalement, les propriétés optoélectroniques et photovoltaïques de mélanges des deux matériaux les plus prometteurs, ensemble ou avec d’autres matériaux, ont été étudiées. Des cellules solaires de rendement maximum de 1 % ont été obtenues pour deux dispositifs de compositions différentes.<p>Ces rendements, bien qu’inférieurs à ceux obtenus précédemment par d’autres groupes (jusqu’à 34 % à ce jour), sont néanmoins révélateurs des potentialités des matériaux organiques, et plus particulièrement des cristaux liquides discotiques, pour de futures applications dans le domaine des dispositifs électroniques.<p> / Doctorat en sciences, Spécialisation chimie / info:eu-repo/semantics/nonPublished

The objective of this research is to explore the possibilities of developing transmit/receive (T/R) modules using silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) BiCMOS technology to integrate with organic liquid crystal polymer (LCP) packages for the next-generation phased-array radar system. The T/R module requirements are low power, compact, lightweight, low cost, high performance, and high reliability. All these requirements have provided a very strong motivation for developing fully monolithic T/R modules. SiGe HBT BiCMOS technology is an excellent candidate to integrate all the RF circuit blocks on the T/R module into a single die and thus, reducing the overall cost and size of the phase-array radar system. In addition, this research also investigates the effects and the modeling issues of LCP package on the SiGe circuits at X-band.

In this thesis we studied theoretically and numerically dynamics, order and fluctuations in two dimensional active matter with specific reference to the nematic phase in collections of self-driven particles.The aim is to study the ways in which a nonequilibrium steady state with nematic order differs from a thermal equilibrium system of the same spatial symmetry. The models we study are closely related to “flocking”[1], as well as to equations written down to describe the interaction of molecular motors and filaments in a living cell[2,3] and granular nematics [4]. We look at (i) orientational and density fluctuations in the ordered phase, (ii) the way in which density fluctuations evolve in a nematic background, and finally (iii) the coarsening of nematic order and the density field starting from a statistically homogeneous and isotropic initial state. Our work establishes several striking differences between active nematics and their thermal equilibrium counterparts. We studied two-dimensional nonequilibrium active nematics. Two-dimensional nonequilibrium nematic steady states, as found in agitated granular-rod monolayers or films of orientable amoeboid cells, were predicted [5] to have giant number fluctuations, with the standard deviation proportional to the mean. We studied this problem more closely, asking in particular whether the active nematic steady state is intrinsically phase-separated. Our work has close analogy to the work of Das and Barma[6] on particles sliding downhill on fluctuating surfaces, so we looked at a model in which particles were advected passively by the broken-symmetry modes of a nematic, via a rule proposed in [5]. We found that an initially homogeneous distribution of particles on a well-ordered nematic background clumped spontaneously, with domains growing as t1/2, and an apparently finite phase-separation order parameter in the limit of large system size. The density correlation function shows a cusp, indicating that Porod’s Law does not hold here and that the phase-separation is fluctuation-dominated[7]. Dynamics of active particles can be implemented either through microscopic rules as in[8,9]or in a long-wavelength phenomenological approach as in[5]It is important to understand how the two methods are related. The purely phenomenological approach introduces the simplest possible (and generally additive)noise consistent with conservation laws and symmetries. Deriving the long-wavelength equation by explicit coarse-graining of the microscopic rule will in general give additive and multiplicative noise terms, as seen in e.g., in [10]. We carry out such a derivation and obtain coupled fluctuating hydrodynamic equations for the orientational order parameter (polar as well as apolar) and density fields. The nonequilibrium “curvature-induced” current term postulated on symmetry grounds in[5]emerges naturally from this approach. In addition, we find a multiplicative contribution to the noise whose presence should be of importance during coarsening[11]. We studied nonequilibrium phenomena in detail by solving stochastic partial differential equations for apolar objects as obtained from microscopic rules in[8]. As a result of “curvature-induced” currents, the growth of nematic order from an initially isotropic, homogeneous state is shown to be accompanied by a remarkable clumping of the number density around topological defects. The consequent coarsening of both density and nematic order are characterised by cusps in the short-distance behaviour of the correlation functions, a breakdown of Porod’s Law. We identify the origins of this breakdown; in particular, the nature of the noise terms in the equations of motion is shown to play a key role[12]. Lastly we studied an active nematic steady-state, in two space dimensions, keeping track of only the orientational order parameter, and not the density. We apply the Dynamic Renormalization Group to the equations of motion of the order parameter. Our aim is to check whether certain characteristic nonlinearities entering these equations lead to singular renormalizations of the director stiffness coefficients, which would stabilize true long-range order in a two-dimensional active nematic, unlike in its thermal equilibrium counterpart. The nonlinearities are related to those in[13]but free of a constraint that applies at thermal equilibrium. We explore, in particular, the intriguing but ultimately deceptive similarity between a limiting case of our model and the fluctuating Burgers/KPZequation. By contrast with that case, we find that the nonlinearities are marginally irrelevant. This implies in particular that 2-dactive nematics too have only quasi-long-range order[14].

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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. <p>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. <p>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.<p>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 & / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

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