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Tesis sobre el tema "Nematic phases"

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Publicado: 18 de mayo de 2024

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1

Huang, Tsang-Min. "Phase Equilibria of Binary Liquid Crystal Mixtures Involving Induced Ordered Phases". University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1284381816.

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2

Reid, Andrew Charles Edmund. "Nematic phases in fluids of biaxial particles". Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27625.

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The investigation of the possible uniaxial phases of a fluid of biaxial particles undertaken by Bergersen, Palffy-Muhoray and Dunmur forms the starting point for further research into the full range of possible phases of such a fluid. A generalization of their interaction model, free from constraints having to do with interaction details, retaining only the biaxial symmetry, is used in the mean-field approximation to explore the range of possible orientationally-ordered phases for such a system. This model is an equilibrium model which does not include dynamic effects. The basic inter-particle interaction is abstract, having the correct symmetry for biaxial particles, and is the most general biaxial interaction constructable from lowest-order scalar invariants. The self-consistent equations resulting from this formulation are obtained in the mean-field approximation and therefore retain both the symmetry and the generality at the cost of exact numerical correctness. Four order parameters are identified, corresponding (within a numerical factor) to those found by Straley and Freiser, as well as those of Bergersen et al. The phase diagram of a fluid of biaxial particles, then, is mapped out in terms of the behavior of these order parameters, as indicated by the self-consistent equations, as a function of three anisotropy parameters and the temperature. The primary method of analysis is iteration of the self-consistent equations obtained from differentiating the free energy. Numerical results are obtained for the location of the phase boundaries, and the temperature dependence of the order parameters in various phases.
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3

Shamid, Shaikh M. "STATISTICAL PHYSICS OF MODULATED PHASES IN NEMATIC LIQUID CRYSTALS". Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1448892923.

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4

Adhikari, Banani. "Study of physical properties of some liquid crystals having nematic and smectic phases". Thesis, University of North Bengal, 1995. http://hdl.handle.net/123456789/856.

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5

Chakraborty, Anish. "Study of physical properties of bent core mesogens having nematic and smectic phases". Thesis, University of North Bengal, 2017. http://hdl.handle.net/123456789/2647.

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6

Kundt, Matthias [Verfasser]. "Magnetoresponsive liquid crystalline systems based on elongated core-shell particles in nematic phases / Matthias Kundt". München : Verlag Dr. Hut, 2018. http://d-nb.info/1162767863/34.

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7

Prasad, Akhileshwar. "STUDY OF THE INDUCTION OF SMECTIC Ad AND RE-ENTRANT NEMATIC PHASES IN BINARY MIXTURES OF LIQUID CRYSTALS". Thesis, University of North Bengal, 2013. http://hdl.handle.net/123456789/938.

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8

Liu, Harry. "Elastic properties and phases of bent core liquid crystal". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/elastic-properties-and-phases-of-bent-core-liquid-crystal(1428e685-754c-42c0-890b-9ae83f0b5f7c).html.

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The recent interest in bent core liquid crystal has shown many unique physical properties, such the anomalous behaviour of the elastic constants (SplayK1, Twist K2, and BendK3). In bent core liquid crystals it is observed that K3K1). Such behaviour is analogous to calamitic liquid crystals but is in contrast to all other bent-core nematic materials reported to date. Such a result questions some of the current explanations for the elastic behaviour of bent-core materials. Using molecular field theory and atomistic modelling the different elastic behaviour predicted is again in excellent agreement with experimental results. The bend angle is again shown to be an important part in determining the physical properties of bent-core nematic liquid crystals. In a mixture from an oxadiazole dopant and calamitic host liquid crystal, it was found that a filament structure appears in the nematic phase. The filaments appear to interfere with the measurements for elastic constants. In order to understand the filament structure many methods were used including SAXS, dielectric permittivity, and DSC. It was found that the mixture had formed a gel - like phase. The gel is composed of a liquid crystal network and a liquid crystal background, not seen before in any gel system. Due to the liquid crystalline properties both the network and the background can be aligned and manipulated. The new gel phase can possess many new unique properties which warrant further studies understand further into how fundamentally the phase is forming.
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9

Al-Zangana, Shakhawan. "Nano- and micro-particle doped liquid crystal phases". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/nano-and-microparticle-doped-liquid-crystal-phases(31dbb051-7d9c-4780-bda0-d58773846de0).html.

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This thesis presents the investigation of the liquid crystal (LC) - particle suspensions. Particles from nano- to micro-size, spherical to two-dimensional shapes, with different functionality are dispersed into nematic and smectic phases. The aim is to create ordered nanoparticle (NP) assemblies and thereby modify the common properties of the liquid crystal, such as dielectric anisotropy and electro-optical, revealing any interaction between particles and LC properties. It is found that for concentrations (>0.5vol%), the ferroelectric NPs have increased the sensitivity of the nematic liquid crystal to the electric field through electro-optical responses, which is seen by an enhancement in the dielectric anisotropy. This could be induced by the coupling of the electrical dipole moments in the spherical NPs with the LC director field. The electro-optical properties of the chiral smectic (SmC*) phase (tilt angle Θ, switching time τ_s and spontaneous polarisation P_s) are found to be independent of the concentration and sizes of the doped NPs. The relaxation frequency f_R of the Goldstone mode is faster in the ferroelectric NPs suspensions of 2.0vol% compared to the paraelectric NPs. In the graphene oxide (GO) - nematic LC (5CB) suspensions, the small GO sizes of mean size 560 nm are more easily dispersible than larger flakes of 2.8 micro metre mean size. As the GO concentration is increased, each of the threshold voltage and splay elastic constant dramatically increases, reaching saturation at ≈1.0wt%. The field driven switching-on time is practically not affected, while the purely elastically driven switching-off time is strongly sped-up. Interestingly, thermotropic and lyotropic LC phases are exhibited in the GO-5CB suspensions when heating the thermotropic liquid crystal into its isotropic phase. The isotropic phase of 5CB acts as a solvent for the GO particles, forming a lyotropic nematic phase with largely reduced birefringence. It is found that the nematic to isotropic phase transition is shifted toward higher temperature for the GO-5CB system compared to the BaTiO3-5CB system. Dispersions of different sizes of GO flakes are prepared in isotropic and nematic fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature range (25-60 ℃) and frequency range (100 Hz-2 MHz). The mixtures containing GO flakes were found to exhibit varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. The relaxation frequencies in the isotropic media were lower compared to the nematic medium. Relaxation frequencies (~10 kHz) are observed in the GO-isotropic media, which are reduced as the size of the GO flakes are decreased, are anticipated to be inherited from GO flakes. However, the fast relaxations (~100 kHz) that are observed in the nematic suspensions could imply strongly slowed down molecular relaxation modes of the nematogenic molecules. Finally, the phase diagram of lyotropic LC as a function of the lateral dimensions of the GO flakes, their concentration, geometrical confinement configuration and solvent polarity was investigated. Polarising optical microscopy was used to determine isotropic-biphasic-nematic phase evolution. The confinement volume and geometry of the sample relative to the GO size are shown to be vital to the observation of the lyotropic phase. GO LCs have the potential for a range of applications from display technologies to conductive fibres. The confinement related LC phase transition is critical toward their applications. It is also found that the stability of the LC phase is higher for the solvent of higher dielectric constant.
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10

Delikatny, Edward James. "NMR studies of carboxylic acids : an investigation of head group behaviour in lyotropic and nematic phases". Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26996.

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The orientational order of the methylene segments adjacent to the head group in the lamellar liquid crystalline phase of potassium palmitate/D₂0 was investigated using multinuclear magnetic resonance. Previous studies had shown that the orientational order near the soap--water interface decreased with decreasing temperature, contrary to intuition. To investigate this phenomenon, three isotopically substituted species of palmitic acid were synthesized: palmitic acid-d₃₁, 1-¹³C-2,2-H₂- palmitic acid-d₂₉, and 2,2,3,3-H₄- palmitic acid-d₂₇. These compounds were treated in two complementary fashions: the acids were dissolved in the liquid crystal 4 - (octyloxy) - benzoic acid (p - OOBA) and the corresponding potassium salts were dispersed in D₂0 at a constant water concentration. Dipolar and quadrupolar couplings were obtained from the ¹H, ¹³C, and ²H nmr spectra of these molecules, in nematic and lamellar liquid crystalline phases, as a function of temperature. In a parallel study, nmr spectra of acetic, propionic, and butyric-2,2 - d₂ acids dissolved in p - OOBA were recorded. In order to observe ¹H - ¹H dipolar couplings, a two dimensional spin echo (π/2 - t₁/2 - π - t₁/2 - echo) was necessary to remove heteronuclear dipolar couplings to the chain deuterons. A refocussing pulse applied simultaneously to the spins allowed observation of the heteronuclear ¹H - ¹³C dipolar couplings in the carbon 13 labelled compound. The complete orientational order matrix of the alpha methylene segment of potassium paImitate/D₂0 and of palmitic acid/p - OOBA was determined from the dipolar and quadrupolar couplings. As the temperature is decreased from 110°C to a temperature just above the gel-liquid crystalline phase transition (45°C), the orientation of the methylene segment of potassium palmitate is rotated by 3° towards a configuration in which the first C - C bond is parallel to the bilayer normal. This is in direct agreement with a previous model, the Abdollal model of lipid - water interaction, in which the decrease in orientational order was postulated to be a strictly geometric effect arising from electrostatic interactions of the lipid with the water. A mean field equilibrium statistical mechanical model, based on the Samulski Inertial Frame Model, was developed to simulate the experimental dipolar and quadrupolar nmr couplings. In potassium palmitate, electrostatic interactions, approximately constant at higher temperatures, increase dramatically as the phase transition is approached. In contrast mean field steric repulsive forces remain constant over the entire temperature range studied. This evidence also supports the Abdollal model of lipid - water interaction. The electrostatic interaction was shown to be of greater importance in the orientational ordering of the solutes in the liquid crystal than in potassium palmitate and this was attributed to intermolecular H - bonding between solute and p - OOBA. The ordering of the head group of carboxylic acids dissolved in p - OOBA was demonstrated to be remarkably similar regardless of the chain length of the solute.
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11

Putzig, Elias. "An Exploration of the Phases and Structure Formation in Active Nematic Materials Using an Overdamped Continuum Theory". Thesis, Brandeis University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10620560.

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Active nematics are a class of nonequilibrium systems which have received much attention in the form of continuum models in recent years. For the dense, highly ordered case which is of particular interest, these models focus almost exclusively on suspensions of active particles in which the flow of the medium plays a key role in the dynamical equations. Many active nematics, however, reside at an interface or on a surface where friction excludes the effects of long-range flow. In the following pages we shall construct a general model which describes these systems with overdamped dynamical equations. Through numerical and analytical investigation we detail how many of the striking nonequilibrium behaviors of active nematics arise in such systems.

We shall first discuss how the activity in these systems gives rise to an instability in the nematic ordered state. This instability leads to phase-separation in which bands of ordered active nematic are interspersed with bands of the disordered phase. We expose the factors which control the density contrast and the stability of these bands through numerical investigation.

We then turn to the highly ordered phase of active nematic materials, in which striking nonequilibrium behaviors such as the spontaneous formation, self-propulsion, and ordering of charge-half defects occurs. We extend the overdamped model of an active nematic to describe these behaviors by including the advection of the director by the active forces in the dynamical equations. We find a new instability in the ordered state which gives rise to defect formation, as well as an analog of the instability which is seen in models of active nematic suspensions. Through numerical investigations we expose a rich phenomenology in the neighborhood of this new instability. The phenomenology includes a state in which the orientations of motile, transient defects form long-range order. This is the first continuum model to contain such a state, and we compare the behavior seen here with similar states seen in the experiments and simulations of Stephen DeCamp and Gabriel Redner et. al. [1]

Finally, we propose the measurement of defect shape as a mechanism for the comparison between continuum theories of active nematics and the experimental and simulated realiza- tions of these systems. We present a method for making these measurements which allows for averaging and statistical analysis, and use this method to determine how the shapes of defects depend on the parameters of our continuum theory. We then compare these with the shapes of defects which we measure in the experiments and simulations mentioned above in order to place these systems in the parameter space of our model. It is our hope that this mechanism for comparison between models and realizations of active nematics will provide a key to pairing the two more closely.

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12

Potisk, Tilen [Verfasser] y Helmut [Akademischer Betreuer] Brand. "Macroscopic aspects of ferromagnetic nematic phases, tetrahedral order in ferrogels, and magnetorheological fluids / Tilen Potisk ; Betreuer: Helmut Brand". Bayreuth : Universität Bayreuth, 2019. http://d-nb.info/1194059929/34.

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13

Paineau, Erwan-Nicolas. "Transitions de phases dans les argiles : influence de la minéralogie et de la morphologie : comportement sous écoulement et sous champs". Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL005N/document.

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L’objectif de ce travail est d’étudier les transitions de phases sol-gel et isotrope-nématique dans des suspensions de smectites dioctaédriques en fonction de la morphologie et de la nature minéralogique des argiles. Bien que tous les systèmes étudiés présentent une transition sol-gel à de faibles fraction volumique, la transition cristal-liquide isotrope-nématique n’a pu être identifiée que dans le cas de suspensions de smectites ayant un déficit de charge tétraédrique. L’effet de la localisation de la charge sur le comportement colloïdal a été déterminée à l’aide de la diffusion des rayons X aux petits angles (SAXS) et par des mesures rhéologiques. La nature des interactions électrostatiques dans ces suspensions est purement répulsive et rejette l’idée d’une structure tridimensionnelle de type « château de carte ». Cependant, les smectites ayant un déficit de charge tétraédrique sont plus répulsives et ont des propriétés viscoélastiques plus faibles que celles ayant un déficit octaédrique. Il a également été montré que la dépendance en taille de particules de la position de la transition sol-gel était liée à une statistique de piégeage hydrodynamique des plaquettes d’argile. Finalement, l’application de champs externes (électrique et magnétique) a permis d’obtenir l’alignement de la phase nématique tandis que dans la phase isotrope, le champ électrique induit un ordre antinématique parfait. Afin de préserver l’ordre induit, ces suspensions ont été polymérisées sous champ permettant l’obtention de nanocomposites orientées et structurés
The aim of this work is to study sol-gel and isotropic-nematic phases transitions in suspensions of dioctahedral smectites depending on the morphology and mineralogical nature of clays. Although all the systems studied exhibit a sol-gel at low volume fraction, the liquid-crystalline isotropic-nematic transition could be identified only in the case of smectites with tetrahedral charge deficit. The effect of charge location on the colloidal behavior was determined using small-angle X-ray scattering (SAXS) and rheological measurements. The nature of electrostatic interactions in these suspensions is purely repulsive and rejects the idea of the so-called “house of card” network. However, smectites with a charge deficit located in the tetrahedron are more repulsive and their viscoelastic properties are lower than octahedrally substituted clays. It was also shown that the particle size dependence of the volume fraction corresponding to the sol-gel transition c was related to a simple statistical hydrodynamic trapping of clay platelets. Finally, the application of external fields (electric and magnetic) has resulted in the alignment of the nematic phase while in the isotropic phase, the electric field induces a perfect antinematic order. To preserve the induced alignment, these suspensions were polymerized under the field to obtain perfectly aligned and patterned nanocomposites
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14

Bladon, Peter. "Phase transitions in nematic polymer liquid crystals". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307042.

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Yuan, Xiangqun. "Nematic ordering of wormlike polymers". Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1280.

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In this thesis, based on the Onsager excluded volume interaction model, two nematic ordering problems of wormlike (semiflexible) polymer are studied: one is to investigate the isotropic-nematic interface of polymers for three typical cases—the flexible one, the rigid-rod one and the intermediate one; the other is to investigate a very long polymer confined between two infinite flat hard walls.

Many previous studies of the isotropic-nematic phase coexistence are mainly focused on either rigid rod-like polymers with small flexibility, or flexible polymers with large flexibility. The phase coexistence of polymers with intermediate flexibility is desired to be investigated. For these three typical cases (flexible, rigid-rod and intermediate), the profiles for density, order parameter and tension contribution were shown for different tilt angles. The interface tension was studied. The simulation results are consistent with those reported by other people.

We investigated the confinement of a long polymer between two flat hard walls, which are separated by a distance comparable to the effective Kuhn length of polymer chain by the wormlike chain model with or without the Onsager excluded volume interaction. Without the interaction, the results are compared with those of the Gaussian chain model. Including the interaction, the phase diagram is analyzed.
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16

Mottram, N. J. "Boundary effects in nematic liquid crystal layers". Thesis, University of Bristol, 1996. http://hdl.handle.net/1983/3f718f68-e280-4994-afa2-29a7845c73f7.

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17

Martin, Pamela Jean. "The Search for the Elusive Biaxial Nematic Phase". Thesis, University of York, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485834.

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Liquid crystals are ordered fluids formed ofanisotropic molecules, and there are a number of different mesophases within the liquid crystal state. This thesis is concerned with the search for a specific liquid crystal mesophase, known as the biaxial nematic phase, which has largely eluded experimentalists since it was first hypothesised. The re~earch is based on two, different strategies that use synthesised molecular candidates designed as a result of the interpretation of theory. Deuterium NMR spectroscopy is used to determine the phase symmetry. Chapter 1 commences with an introduction to the liquid-crystalline state, with a general description of the structures and of their constituent molecules. The structure and topology of the nematic phase and biaxial nematic phase are discussed in detail while only some of the more common mesophases are described. The general methods utilised in the characterisation of liquid crystals are discussed and this is followed by a discussion of techniques specific to the identification ofthe biaxial nematic phase. The successful discovery of biaxial nematic phases in some systems is highlighted, after which the theory behind strategies employed in forming a biaxial nematic phase in lowmolar- mass thermotropic systems are considered along with possible applications. Chapter 2 deals with one of the approaches in forming a biaxial nematic phase, namely combining rods and discs. The importance of preventing phase separation is highlighted and strategies discussed. The synthesis of a series of laterally attached rod-disc dimers and their component parts is described and their mesophase behaviour is presented. The amphiphilic nature of covalently linked rod-disc dimers is discussed and a detailed miscibility study of the dimer with its component parts is presented. Intermediary conclusions are drawn as to the nature of the phase behaviour. Chapter 3 presents the synthesis undertaken to produce selectively deuterated analogues of the rod-disc dimer, and its component parts. Deuterium NMR spectroscopic studies on some of the mixtures described in chapter 2 and aspects of the phase behaviour of these mixtures are investigated. Chapter 4 discusses the results from the preceding two chapters and draws conclusions about the phase behaviour of the rod/disc/dimer mixtures. A detailed phase diagram is suggested. Chapter 5 deals with bent-core mesogens as candidates for the biaxial nematic phase and the structures of some mesophases specific to bcnt-core mesogens a~e reviewed. Mesogens with an oxadiazole central core are discussed and the problems associated with the high transition temperatures highlighted. The introduction of flexibility into the mesogen via hydrogen-bonding is proposed to generate materials with much lower transition temperatures. The synthesis of three bent-core oxadiazole systems is described and the effect of both flexibility and core structure are discussed. In addition, the selective deuteration of a fuBy covalent oxadiazole biaxial ncmatic candidate is described and results from deuterium NMR spectroscopy performed on this matcrial are presented.
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18

Powell, Norman James. "The modelling of nematic liquid crystal phase devices". Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5749/.

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The implementation of nematic liquid crystal optical devices, which exploit the voltage dependent, optical path length modification of the electrical Freedrichsz transition, is presented. By combining refractive elements in a diffractive zone structure, efficient and flexible devices with relatively high refractive powers can be constructed. Continuously variable optical properties can be achieved by scaling the optical profile of the refractive elements and applying a phase correction to ensure that the transition between adjacent zones is an integral number of wavelength, hence a continuous optical profile is constructed. Two such devices are postulated; a variable deflection angle prism and a variable focal length lens, though the approach may be extended to other devices. The zones are addressed through combed electrode structures. The required voltage profile is produced by dropping the applied voltages across a shaped conductive strip. A sampling of the profile is transported along the length of the zone via discrete electrodes. In order to produce the required scalability and independent phase correction of the optical profile, it is necessary to restrict the design and operation of the electrodes to the approximately linear region of the response curve. Two-dimensional optical structures can either be achieved through the use of planar earth plates, to mask connections to the centre of the device, or by cascading devices with electrode structures open to connection at the edges. In order to predict the optical profiles of these and other devices, a model was constructed which describes the director orientation through a two-dimensioned electrode structure. The variational finite element method was employed to minimize the electrical Gibbs free energy of a liquid crystal cell, in order to find the equilibrium director orientation. A preliminary version of this model is presented which is restricted to rotation of the liquid crystal to within the plane of the solution.
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19

Zhang, Zichen. "Phase-only nematic liquid crystal on silicon devices". Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610052.

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Nguyen, Hoang-Phuong. "Structure and elasticity of nematic and isotropic liquid crystals". [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=96397677X.

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Braun, Frank Nicholas. "Surface phase transitions in liquid crystals". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242564.

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Stark y Holger. "Physics of Inhomogeneous Nematic Liquid Crystals: Colloidal Dispersions". Thesis, Universitaet Stuttgart, 1999. http://elib.uni-stuttgart.de/opus/volltexte/2001/746/index.html.

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Omnes, Laurent. "Towards the biaxial nematic phase via specific intermolecular interactions". Thesis, University of Exeter, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368368.

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Verwey, Giles Christian. "Soft deformations, instabilities and phase transitions in nematic elastomers". Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627515.

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Steven, David Paul. "Application of nematic liquid crystals as tunable optical filters". Thesis, Edinburgh Napier University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367642.

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Ganji, Tahereh. "THE INFLUENCE OF NANOPARTICLES ON THE KERR EFFECT AT THE NEMATIC-ISOTROPIC PHASE TRANSITION". University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1481025104288989.

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Hunt, Jonathan James. "The biaxial nematic phase : synthesis and characterisation of candidate materials". Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312283.

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Stark, Holger. "Physics of inhomogeneous nematic liquid crystals colloidal dispersions and multiple scattering of light /". [S.l. : s.n.], 1999. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8921083.

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29

Yethiraj, Anand. "The nematic-smectic-A phase transition, a high resolution experimental study". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0024/NQ51939.pdf.

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Chakraborty, Saonti. "SHORT - RANGE ORDER IN THE NEMATIC PHASE OF REDUCED SYMMETRYTHERMOTROPIC MESOGENS". Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1385158954.

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31

Jaffer, Karim M. "The nematic-isotropic phase transition in rigid linear fused hard-sphere chain fluids". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ40422.pdf.

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32

Chien, Chiao-Ying. "Light-driven modulation of liquid-crystalline order in the nematic phase with azobenzene-containing copolymer". Kyoto University, 2020. http://hdl.handle.net/2433/259718.

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33

Zhang, Chiqun. "Theory and Computation of Line Defect Fields in Solids and Liquid Crystals". Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1058.

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The theory and computation of line defects are discussed in the context of both solids and liquid crystals. This dissertation includes four parts. The Generalized Disclination theory is discussed and applied to numerous interfacial and bulk line defect problems. An augmented Oseen-Frank energy as well as a novel 2D-model is proposed and demonstrated for disclination dynamics in liquid crystal. A model based on kinematics and thermodynamics is devised to predict tactoid dynamics during the process of the isotropic-nematic phase transition in LCLC. In the first part of the thesis, the utility of the notion of generalized disclinations in materials science is discussed within the physical context of modeling interfacial and bulk line defects. The Burgers vector of a disclination dipole in linear elasticity is derived, clearly demonstrating the equivalence of its stress field to that of an edge dislocation. An explicit formula for the displacement jump of a single localized composite defect line in terms of given g.disclination and dislocation strengths is deduced based on the Weingarten theorem for g.disclination theory at finite deformation. The Burgers vector of a g.disclination dipole at finite deformation is also derived. In the second part, a numerical method is developed to solve for the stress and distortion fields of g.disclination systems. Problems of small and finite deformation theory are considered. The fields of various line defects and grain/phase boundary problems are approximated. It is demonstrated that while the far-field topological identity of a dislocation of appropriate strength and a disclinationdipole plus a slip dislocation comprising a disconnection are the same, the latter microstructure is energetically favorable. This underscores the complementary importance of all of topology, geometry, and energetics (plus kinetics) in understanding defect mechanics. It is established that finite element approximations of fields of interfacial and bulk line defects can be achieved in a systematic and routine manner, thus contributing to the study of intricate defect microstructures in the scientific understanding and predictive design of materials. In the third part, nonsingular disclination dynamics in a uniaxial nematic liquid crystal is modeled within a mathematical framework where the kinematics is a direct extension of the classical way of identifying these line defects with singularities of a unit vector field representing the nematic director. We devise a natural augmentation of the Oseen-Frank energy to account for physical situations where infinite director gradients have zero associated energy cost, as would be necessary for modeling half-integer strength disclinations within the framework of the director theory. A novel 2D-model of disclination dynamics in nematics is proposed, which is based on the extended Oseen-Frank energy and takes into account thermodynamics and the kinematics of conservation of defect topological charge. We validate this model through computations of disclination equilibria, annihilation, repulsion, and splitting. In the fourth part, the isotropic-nematic phase transition in chromonic liquid crystals is studied. We simulate such tactoid equilibria and dynamics with a model using degree of order, a variable length director as state descriptors, and an interfacial descriptor. We introduce an augmented Oseen-Frank energy, with non-convexity in both interfacial energy and the dependence of the energy on the degree of order. A strategy is devised based on continuum kinematics and thermodynamics. The model is used to predict tactoid dynamics during the process of phase transition. We reproduce observed behaviors in experiments and perform an experimentally testable parametric study of the effect of bulk elastic and tactoid interfacial energy constants on the interaction of interfacial and bulk fields in the tactoids.
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34

Sigdel, Krishna P. "Phase transition studies of liquid crystal colloids with solvents and nano-solids". Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-dissertations/137.

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Liquid crystals (LCs) are anisotropic fluids that exhibit numerous thermodynamically stable phases in between an isotropic liquid and a three-dimensionally ordered solid. In their simplest ordered phase, the nematic, LCs show orientational order due to molecular self assembly and at the same time maintaining fluid flow properties. In the smectic phase, they show both orientational and partial translational order characterized by a 1-d density wave. Liquid crystalline substances have been extensively studied due to their applications and as important physical models of self-assembly. The effect of the disorder and impurities on LC systems is an important and challenging problem to the fundamental understanding of phases ordering or self-assembly and continually attracts the attention of researchers. The disordered systems often display complex and rich phenomena, being the generalization of the pure (ideal) systems. Disorder can dramatically alter the physical properties of multi-component, composite systems. In particular, the effect of disorder on phase transitions is important as the disorder typically couples to the order parameter, which can be usefully described as a random local field that is conjugate to the order parameter. This is usually realized in systems with random inclusions in a phase ordering media, e.g., a colloidal dispersion of solids in a complex fluid. Another form of disorder is presented by dilution effects, which imposes instead the random breaking or weakening of intermolecular bonds or interactions responsible for the phase ordering. Exploring a good physical system representing random dilution effects in a controlled manner offers a physical probe to unresolved problems in the understanding of mesophasic order. This Dissertation presents a series of studies of dilution and different form of disorder effect on liquid crystal phase transitions. We have used high-resolution AC-calorimetry, dielectric spectroscopy as well as polarizing microscopy to characterize the effects of solvent such as hexane, acetone, decane, and nanomaterials such as multiwall carbon nanotubes and ferroelectric nanoparticles on the phase transitions of several liquid crystals. The liquid crystals of interest are: pentylcyanobiphenyl (5CB), octylcyanobiphenyl (8CB), and decylcyanobiphenyl (10CB). Studies have been carried out as a function of solvent, nanotube, and nanoparticles concentration and temperature spanning the isotropic to nematic (I-N), nematic to smectic-A (N-SmA), and isotropic to smectic-A (I-SmA) phase transitions.
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35

Hubbard, S. D. "The influence of dye solutes on the static and dynamic electro-optic properties of nematic mesophases". Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377752.

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36

Tuchband, Michael R. "Revealing the Nanoscale Structure and Behavior of the Twist-Bend Nematic Liquid Crystal Phase". Thesis, University of Colorado at Boulder, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10752109.

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The nematic phases of liquid crystals have been the most thoroughly investigated since the founding of the liquid crystal field in the early 1900’s. The resulting technologies, most notably the liquid crystal display, have changed our world and spawned an entire industry. Consequently, the recent identification of a new type of nematic – the twist-bend nematic – was met with as much surprise as excitement, as it melds the fluid properties and environmental responsiveness of conventional nematics with the intrinsic polarization and complex ordering of bent-core liquid crystals. I summarize the history of the twist-bend nematic phase, charting the development of our understanding from its first identification to the present day. Furthermore, I enumerate and highlight my own efforts in the field to characterize the behavior and nanoscale organization of the twist-bend phase.

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37

Gu, Mingxia. "Effects of Dielectric Relaxation on Director Dynamics in Uniaxial Nematic Liquid Crystals". Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1236368118.

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38

Hällstig, Emil. "Nematic Liquid Crystal Spatial Light Modulators for Laser Beam Steering". Doctoral thesis, Uppsala University, Quantum Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4693.

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Laser beam control is important in many applications. Phase modulating spatial light modulators (SLMs) can be used to electronically alter the phase distribution of an optical wave-front and thus change the direction and shape of a laser beam. Physical constraints set limitations to the SLM and an ideal phase distribution can usually not be realised. In order to understand how such components can be used for non-mechanical beam control three nematic liquid crystal (NLC) SLMs have been thoroughly characterised and modelled.

The pixel structure and phase quantisation give a discrepancy between ideal and realised phase distributions. The impact on beam steering capability was examined by measurements and simulations of the intensity distribution in the far-field.

In two of the studied SLMs the pixel period was shorter than the thickness of the LC layer giving the optical phase shift. This results in a so-called “fringing field”, which was shown to degrade the phase modulation and couple light between polarisation modes. The deformation of the LC was simulated and a finite-difference time-domain (FDTD) algorithm was used to calculate how polarised light propagates through the optically anisotropic SLM.

Non-mechanical beam steering and tracking in an optical free-space communication link were demonstrated. Continual optimisation of the steering angle was achieved by feedback from a video camera.

The optical properties of the SLM in the time period right after a voltage update were studied. It was shown how light is redistributed between orders during the switching from one blazed grating to another. By appropriate choice of the blazed gratings the effects on the diffraction efficiency can be minimised.

The detailed knowledge of the SLM structure and its response to electronic control makes it possible to predict and optimise the device performance in future systems.

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39

Yao, Xuxia. "Studies on lyotropic chromonic liquid crystals in nematic and biphasic regions". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50131.

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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.
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40

Babakhanova, Greta. "Elastic effects in flexible dimeric and elastomer nematics". Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent155145733547706.

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41

Frese, Thomas. "Holographische Speicherung thermischer Gain-Effekt bei nematisch-kolumnaren und teilkristallinen Materialien /". [S.l.] : [s.n.], 2003. http://archiv.ub.uni-marburg.de/diss/z2003/0080.

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42

Severing, Kirsten. "A biaxial nematic phase in a thermotropic liquid crystalline side-chain polymer a deuterium NMR study /". [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976850222.

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43

Parsouzi, Azad Sharabiani Zeinab. "DYNAMIC LIGHT SCATTERING STUDY OF FLEXIBLE LIQUID CRYSTALLINE N-MERS THAT FORM THE TWIST-BEND NEMATIC PHASE". Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1563246206806784.

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44

Boyd, Nicola Jane. "Investigations of the nematic phase structure and biaxiality of selected oxadiazole mesogens employing an optimized force field". Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12127/.

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A unique class of bent-core nematics, based on the bis-phenyl-oxadiazole motif, have attracted considerable attention due to their unusual properties, including the possibility of forming the elusive biaxial nematic phase, a phase with significant potential for technological applications. A summary of current research into biaxial nematics is given, including experimental evidence,controversies,and the different computational models used to study this phase. Fully atomistic molecular dynamic simulations were employed to study the differences and relationships in the mesophase molecular organization of four closely related oxadiazole bent-core molecules. As an accurate force field is essential to model liquid crystal systems, it was first found necessary to partially re-parametrize the General Amber Force Field, (GAFF), to accurately reproduce phase transitions of liquid crystal mesogens. Dramatic improvements of phase transition temperature predictions for a number of liquid crystals were achieved with the new force field, compared to the original GAFF predictions. Using the improved force field, GAFF-LCFF, the uniaxial and biaxial orientational order parameters were deduced for the four oxadiazole derivatives. These were found to be in good agreement with experimental data, where available. Small differences in the magnitude of the biaxial order parameters were found between the four oxadiazole systems in their respective nematic phases, with the bent-core mesogen, C5-Ph-ODBP-Ph-OC12 displaying the largest values. The simulations confirm that the nematic phase biaxiality is predominantly local and not macroscopic, and do not support the presence of large cybotactic clusters with inherent biaxial order. The atomistic simulations enabled the distinct differences in structure and molecular organization in the nematic phase of the four systems to be identified and analyzed, and the simulations were found to accurately represent a range of experimental observables, including the manifestation of enhanced local biaxial correlations for a trimethlylated oxadiazole based mesogen. The study also provides the novel result of the first simulation insight into the local structure of the dark conglomerate (DC) phase, and shows evidence of pretran- sitional fluctuations relating to the onset of the DC phase in the bent-core mesogen C5-Ph-ODBP-Ph-OC12. A number of explanations linking key molecular chemical and structural features to mesophase behaviour have also been proposed.
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45

Walker, Rebecca. "Synthesis and characterisation of novel liquid crystalline materials : structure-property relationships, chirality, and the twist-bend nematic phase". Thesis, University of Aberdeen, 2019. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=240697.

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The principal aim of this Thesis is the synthesis and characterisation of a range of novel liquid crystals designed to exhibit the twist-bend nematic phase (NTB), in order to enhance our understanding of the relationships between molecular structure and the observation of NTB behaviour. Moreover, the inclusion of chiral fragments allowed the effects of molecular chirality on the structure of the NTB phase, specifically the chiral twist-bend nematic phase, N*TB, to be studied. In Chapter 3, a series of non-symmetric odd-membered liquid crystal dimers are prepared and the terminal chain length m is varied. A change in the local molecular structure from intercalated to bilayer is seen on increasing m, but this has no apparent effect on the stability of both the nematic and twist-bend nematic phases, which show a regular dependence on m. A novel twist-bend smectic phase is reported. Chapter 4 investigates the effects of branching this terminal chain on phase behaviour. It is evident that in dimers with a shorter spacer, branching destabilises the N and NTB phases while stabilising smectic behaviour, but in longer homologues smectic behaviour is also destabilised. Chapter 5 explores the effect of molecular bulk on phase behaviour, specifically the stability of the NTB phase, by the incorporation of a pyrene moiety. This group supresses crystallisation such that stable, low temperature NTB phases are formed despite the bulky group. Chapters 6 and 7 study the inclusion of chiral moieties in bent-shaped, odd-membered dimers: specifically, 2-methylbutyl, 1-methylheptyl (6) and lactic esters (7). New examples of the rarely observed chiral twist-bend nematic phase are seen. Phase behaviour is investigated and compared to achiral and racemic analogues. Chapter 8 describes the mesogenic behaviour of molecular complexes assembled by hydrogen bonding between both achiral and chiral stilbazole-based and benzoic acid-based fragments. A selection of the complexes exhibit the N(*)TB phase despite only one or neither component being mesogenic.
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46

challa, Pavan Kumar. "OPTICAL STUDIES OF BLUE PHASE III, TWIST-BEND AND BENT-CORE NEMATIC LIQUID CRYSTALS IN HIGH MAGNETIC FIELDS". Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1397825912.

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Stojadinovic, Strahinja. "Light Scattering Studies of Dynamics of Bent-Core Liquid Crystals". Kent State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=kent1105330884.

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48

Khanal, Kiran. "Liquid-Crystalline Ordering in Semiflexible Polymer Melts and Blends: A Monte Carlo Simulation Study". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1373901748.

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49

Wu, Chonggang. "Transesterification, Phase Transition, Rheology, and Mechanical Properties of Blends of Thermoplastic Polyester and Thermotropic Polyester". University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1143780405.

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50

Talbaoui, Ahmed. "Etude en microscopie électronique par cryofracture des systèmes chlorures et bromure de dodécylamine-eau". Rouen, 1989. http://www.theses.fr/1989ROUES006.

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Après une importante bibliographie concernant les phases lyotropes et les techniques cryogéniques en microscopie électronique, l'auteur expose les résultats de ses observations en cryofracture sur les systèmes du titre. Description de la transition lamellaire-nématique et comparaison aux modèles présentés par d'autres auteurs. Discussion de la validité de la technique de cryofracture pour ce type de systèmes
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