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Yasarawan, Nuttawisit. "Dye-doped colloidal liquid crystals." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503864.
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This thesis presents three experimental studies using model suspensions of dye-doped colloidal sepiolite clay rods. In all cases, dye molecules adsorbed onto the outer surfaces of the rods were removed by Soxhlet extraction, yielding dye-doped rods which were then sterically stabilised in toluene. The liquid crystalline phase behaviour of these rods was examined and was similar to that observed previously for undyed particles. The isotropic-nematic phase boundary was as expected for hard spherocylinders of the same aspect ratios; however the transition was broadened due to polydispersity of the rods. Aligning the dyedoped rods in a 9 T magnetic field resulted in a single-domain nematic phase with a marked dichroism. This was due to the restricted orientations of the dye molecules within the zeolitic channels of sepiolite. The order parameter of the dye in the aligned colloidal rods was up to 0.5, similar to typical values for dye in aligned molecular liquid crystals.
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Dammone, Oliver James. "Confinement of colloidal liquid crystals." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:f33c315d-263b-47ad-ace8-1658c532a9c3.
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The behavior of colloidal liquid crystals in confinement is addressed on the single particle level using laser scanning confocal microscopy. We seek to disentangle how equilibrium director fields are controlled by the complex interplay between confinement, elasticity and surface anchoring. First, we study the nematic phase confined to wedge structured channels. Varying the wedge opening angle leads to a splay to bend transition mediated by a defect in the bulk of the wedge. Our results are in quantitative agreement with lattice Boltzmann simulations, and we show that comparison between experiments and simulation yields a new method to obtain the splay-to-bend elasticity ratios of colloidal and biological liquid crystals. Next, we extend our study of the wedge structured channels to the cholesteric phase, and measure a splay to twist transition with increasing wedge angle. We directly visualise the 3D nature of the twisted state, and explain how the transition is intricately determined by the anchoring strength and the splay, bend, and twist elasticities. Next, we investigate the effect of rectangular confinement on the nematic phase. The rectangle aspect ratio is systematically varied and we observe five distinct director fields. Comparison with computations of the Frank-Oseen energies yields the extrapolation length, which we find to be of the order of the rod length. Next, we confine the nematic phase to annular geometries of varying dimensions, and observe the novel director fields that are adopted. We approach a level of confinement which is of the order of the particle size. Interpreting our observations with Monte Carlo simulations, which take into account the finite size of the particles, illuminates the applicability of continuum theories down to microscopic lengthscales. We finish with a study of the isotropic-nematic interface in bulk and confinement. We show that parallel anchoring occurs at the interface, and measure the width of the interface to be of the order of the rod length.
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Stark and 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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Speranza, Alessandro. "Effects of length polydiversity in colloidal liquid crystals." Thesis, King's College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397810.
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Foffano, Giulia. "Colloidal dispersions in active and passive liquid crystalline fluids : a simulation study." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/11756.
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In this thesis we study the physics of colloidal dispersions in active and passive liquid crystals by computer simulations. Liquid crystals are materials that exhibit long-range orientational order, with characteristics intermediate between the ones of simple, isotropic fluids and the ones of crystalline solids. Active fluids are suspensions of particles that continuously stir their ambient fluid. Like liquid crystals, active fluids undergo phase transitions to orientationally ordered phases. The framework that we apply here to describe them extends hydrodynamic equations for liquid crystals to the active case, in which their constituent particles exert local stresses on the simple fluid in which they are embedded. Studying systems of colloids embedded in these materials can be done with multiple aims. Here we use colloids as probe particles to investigate the rheological properties of active nematics. To do so we apply a constant force to a spherical particle embedded therein and define an effective viscosity, which we determine by measuring the velocity in steady state. We find an important dependence of the effective viscosity on the size of the particle, and a regime characterised by a steady state of negative drag. We also consider collective properties for systems of many colloids and analyse how they are affected by activity. We find that spontaneous flow can either hinder or favour colloidal aggregation, depending mainly on whether a fixed orientation of the liquid crystal is imposed close to the colloidal surface. This remains true independently of the initial condition chosen for the liquid crystal, which only affects the transition to spontaneous flow.
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Fischermeier, Ellen [Verfasser], Klaus [Gutachter] Mecke, and Jens [Gutachter] Harting. "Simulations of Colloidal Liquid Crystals / Ellen Fischermeier ; Gutachter: Klaus Mecke, Jens Harting." Erlangen : FAU University Press, 2016. http://d-nb.info/1120120632/34.
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Fischermeier, Ellen [Verfasser], Klaus R. [Gutachter] Mecke, and Jens [Gutachter] Harting. "Simulations of Colloidal Liquid Crystals / Ellen Fischermeier ; Gutachter: Klaus Mecke, Jens Harting." Erlangen : FAU University Press, 2016. http://d-nb.info/1120120632/34.
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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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Tait, James Robert. "Optical trapping of colloidal core-shell particles in organic solvents and in liquid crystals." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445881.
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Mirzaei, Javad. "Optical and Electro-optical Properties of Nematic Liquid Crystals with Nanoparticle Additives." The Royal Society of Chemistry, 2011. http://hdl.handle.net/1993/30280.
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Liquid crystals (LCs) are an interesting class of materials that are attracting significant attention due to their ever-growing applications in a wide variety of fields such as liquid crystal display (LCD) technology, materials science and bioscience. In recent years, along with the developments of materials at the nanoscale, doping LCs with nanoparticles (NPs) has emerged as a very promising approach for improving LC properties. Nanoparticle additives can introduce novel effects on optical and electro-optical properties of nematic liquid crystals (N-LCs), such as altered molecular alignment, faster response time and increased efficiency. This thesis studies the impacts that the inclusion of metallic NPs made of gold or semiconductor CdSe quantum dots (QDs), have on optical and electro-optical properties of N-LCs. Using polarized optical microscopy and detailed capacitance and transmittance measurements of nematic mixtures in electro-optic test cells, characteristics such as optical texture, phase transition temperatures, switching voltages and dielectric anisotropy are investigated in pure as well as doped samples. Surface ligands in NPs and their chemical functionalization play an important role in the LC-NP interactions, largely by determining the dispersibility of NPs and stability of the nanocomposites. One important objective of this thesis is to investigate and prepare a series of gold nanoparticles (Au NPs) with specially formulated robust coatings that maximizes solubility and stability in LC medium. Silanization of NPs is developed as a method to overcome the stability challenge. The functionalization of silanized NPs with aliphatic ligands or liquid crystalline molecules, provides chemically and thermally stable NPs with hydrophobic and structurally compatible surfaces required for dispersion in N-LCs. After complete characterization the synthesized particles are used to make the new nematic nanocomposites.
By analysis of the structure-property relationships governing LC-nanomaterial composites and by comparison of new results and data from previous studies on other types of NPs, this thesis will further reveal the mechanism of the interrelations between host LC molecules and NP, considering the role of variables such as core composition, size and surface chemistry of NPs (e.g. siloxane shell, aliphatic ligand vs. liquid crystalline ligand) in achieving stable LC composites with desired optical and electro-optical properties.
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Pishnyak, Oleg. "New electro-optical applications of liquid crystals from beam steering devices and tunable lenses to negative refraction and field-induced dynamics of colloids /." [Kent, Ohio] : Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1246407095.
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Thesis (Ph.D.)--Kent State University, 2009.Title from PDF t.p. (viewed Feb 25, 2010). Advisor: Oleg Lavrentovich. Keywords: electro-optical applications of liquid crystals, beam steering devices, polarization rotator, negative refraction, electrically tunable lens, colloidal dynamics, bidirectional motion of colloidal particles in liquid crystals controlled by backflow. Includes bibliographical references.
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Frise, Anton. "Nano-segregated soft materials observed by NMR spectroscopy." Doctoral thesis, KTH, Fysikalisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-30337.
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This thesis is about using nuclear magnetic resonance (NMR) spectroscopy for studying soft materials. Soft materials may be encountered everyday by most readers of this thesis, for example when taking a shower or watching TV. The usefulness of these materials originates from them being soft yet, at the same time, having some kind of a structure. The characteristic length scale of those structures is often on the order of nanometers (10-9 m) and the structure can respond to various external stimuli such as temperature, electric and magnetic fields, or the presence of interfaces. NMR spectroscopy excels when studying soft materials because it is a non-invasive technique with a large spectral resolution. Moreover, different NMR methods allow us to study local molecular dynamics or longer-range translational diffusion. Understanding those latter aspects is very important for the development of dynamic and responsive materials. Papers I-III present our work on assessing molecular adsorption on interfaces in colloidal dispersions. Here, carbon nanotubes (CNTs) or silica particles were the colloidal substrates to which proteins, polymers or surfactants adsorbed. Papers IV-VI concern ionic mobility in liquid crystals (LCs). The influence of material structure on, for example, the anisotropy of diffusion or on the association/dissociation of ions was studied in several LC phases.QC 20110225
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Kolacz, Jakub. "Energy Minimization in Nematic Liquid Crystal Systems Driven by Geometric Confinement and Temperature Gradients with Applications in Colloidal Systems." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1448898699.
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Hernández, Navarro Sergi. "Colloidal Dispersions in Fluid Media: Electric, Magnetic and Light Control." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/292362.
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In the present thesis I have worked with particle dispersion in water as well as in liquid crystal.
As the first study of this thesis, I have studied the aggregation of isotropic (spherical) and elongated anisometric (pear-shaped) colloidal particles in aqueous medium, confined in two dimensions when subjected to perpendicular external alternating current (AC) electric fields. For low frequencies (f < 2.5kHz) the electrohydrodynamic flow is predominant, and particles tend to aggregate in clusters. On the contrary, for higher frequencies the repulsive dipolar interaction dominates, and particles disperse.
Although both types of particles feature a similar behavior under AC field, pear-shaped particles present a richer phase diagram, that is, they have more phases than the spherical ones. I have also found that pear-shaped particles tend to form smaller and more elongated aggregates, with faster aggregation kinetics. I have also tested different ways to measure the strength of the colloidal aggregates using magnetic probes.
The following studies of this thesis focus on colloidal dispersions in liquid crystals, which are widely used nowadays to clarify new fundamental concepts and original applications.(1–5) Nematic liquid crystals (NLC) are anisotropic organic fluids whose molecules exhibit the positional disorder of a liquid, but are aligned in a certain direction (called the director of the NLC) (6,7). The director field is usually controlled by certain boundary conditions imposed on the plates of the experimental cell.
As a novel way to determine the director orientation, I have demonstrated that paramagnetic anisometric inclusions can be used to locally control the in-plane orientation of the director field by means of external weak magnetic fields. To better understand the phenomenon I have also developed a theoretical model based on the free energy density of the NLC. Additionally, I have found that, by rotating the paramagnetic inclusions more than 100º from their initial orientation, a target pattern of dark and light alternated circles appear. This phenomenon is also captured by the model proposed.
In the third phase of this project, I have investigated the controlled motion of micrometer inclusions dispersed in a nematic liquid crystal, propelled by an alternating current (AC) electric field. Recently it has been reported in the literature that micrometric particles can be propelled in NLC by using AC fields, provided that these particles break the symmetry of the NLC director around them. The mechanism explaining this propulsion is called Liquid Crystal-Enabled Electrophoresis (LCEEP) (3).
By taking advantage of this mechanism, I have demonstrated that aqueous microdroplets are also propelled by LCEEP. One can make these droplets transport solid polystyrene microparticles, or perform a chemical reaction by coalescing two microdroplets containing separate reactants. In addition, I have also demonstrated the control of the activation or deactivation of LCEEP by using photosensitive particles, which change the NLC director symmetry around them upon UV-visible irradiation.
In the last part of this thesis I have developed a novel technique to separately control particle driving from steering under LCEEP. Using photo-induced patterns, I assemble and dynamically control ensembles of particles in a NLC medium. These swarms are assembled, transported and dynamically addressed by local irradiation of the photosensitive cell plate with UV light. With this technique I have demonstrated different potential applications: from the formation and reconfiguration of lattices composed of particle swarms, to segregation of particles with different sizes, as well as the storage and subsequent release of a swarm inside physical constraints, or the formation of particle jets. All these phenomena unveil novel possibilities in the field of collective transport of driven inclusions.
References:
(1) Koenig, G. M.; Lin, I.-H.; Abbott, N. L. Chemoresponsive Assemblies of Microparticles at Liquid Crystalline Interfaces. Proc. Natl. Acad. Sci. 2010, 107, 3998–4003.
(2) Lintuvuori, J. S.; Stratford, K.; Cates, M. E.; Marenduzzo, D. Colloids in Cholesterics: Size-Dependent Defects and Non-Stokesian Microrheology. Phys. Rev. Lett. 2010, 105, 178302.
(3) Lavrentovich, O. D.; Lazo, I.; Pishnyak, O. P. Nonlinear Electrophoresis of Dielectric and Metal Spheres in a Nematic Liquid Crystal. Nature 2010, 467, 947–950.
(4) Pishnyak, O. P.; Tang, S.; Kelly, J. R.; Shiyanovskii, S.; Lavrentovich, O. D. Levitation, Lift, and Bidirectional Motion of Colloidal Particles in an Electrically Driven Nematic Liquid Crystal. Phys. Rev. Lett. 2007, 99, 127802.
(5) Tasinkevych, M.; Mondiot, F.; Mondain-Monval, O.; Loudet, J.-C. Dispersions of Ellipsoidal Particles in a Nematic Liquid Crystal. Soft Matter 2014, 10, 2047–2058.
(6) Oswald, P.; Pieranski, P. Nematic and Cholesteric Liquid Crystals: Concepts and Physical Properties Illustrated by Experiments; Taylor& Francis: Boca Raton, 2005.
(7) Kleman, M.; Lavrentovich, O. D. Soft Matter Physics - An Introduction; Springer, 2003.Durant aquesta tesi, he treballat amb dispersions de partícules en l'aigua, així com també amb dispersions en cristall líquid nemàtic (NLC). Com a primer estudi d'aquesta tesi, he investigat la influència de camps elèctrics en dispersions col·loïdals de partícules sòlides en un medi aquós. He estudiat l'agregació de partícules col·loïdals isotròpiques (esfèriques) i anisomètriques allargades (amb forma de pera) en un medi aquós confinat en dues dimensions, quan se sotmet a un camp elèctric de corrent alterna (AC) perpendicular a la superfície de confinament. En un segon estudi he demostrat que es poden utilitzar inclusions anisomètriques paramagnètiques per controlar localment l'orientació d’un NLC, per mitjà de camps magnètics febles. Per entendre millor el fenomen també he desenvolupat un model teòric basat en la densitat d'energia lliure del NLC. A més, he estat capaç de generar patrons complexos, que també s’expliquen amb model proposat. En la tercera fase d'aquest projecte, he investigat el moviment controlat d'inclusions micromètriques disperses en NLC, impulsades per un corrent altern (AC) a traves d’un mecanisme anomenat “electroforesi habilitada per cristall líquid” (LCEEP). He demostrat que microgotes aquoses es poden propulsar per LCEEP. Es pot fer que aquestes microgotes transportin micropartícules sòlides de poliestirè, o dur a terme una reacció química mitjançant la coalescència de dos microgotes que contenen reactius separats. A més, també he demostrat el control de l'activació o desactivació de la LCEEP mitjançant l'ús de partícules fotosensibles, en funció de la irradiació UV-visible. En l'última part d’aquesta tesi he desenvolupat una nova tècnica per a controlar separadament la propulsió i la direcció de moviment de les partícules transportades per LCEEP. Mitjançant l’ús de patrons fotoinduïts, es poden formar i controlar dinàmicament conjunts de partícules en un medi de NLC. Aquests eixams es formen, es transporten i es dirigeixen dinàmicament per irradiació local amb llum UV. Amb aquesta tècnica he pogut demostrat diferents aplicacions potencials: des de la formació i reconfiguració de xarxes cristal·lines compostes d'eixams de partícules, a la segregació de partícules de diferents mides, així com l'emmagatzematge i posterior alliberament d'un eixam dins d’un canal micromètric, o la formació de jets de partícules. Tots aquests fenòmens revelen noves possibilitats en el camp del transport col·lectiu d'inclusions propulsades.
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Repula, Andrii. "Structure and dynamics of rod-like colloids with patchy interaction." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0097.
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Les dispersions de virus filamenteux présentent une succession d'états cristallins liquides comprenant les phases nématique, smectique (ou lamellaire) et colonnaire. L’auto-organisation de ces particules colloïdales en forme de bâtonnet s’est révélée être essentiellement pilotée par l’entropie dont résulte un potentiel d’interaction entre particules purement répulsif. Dans cette thèse, les propriétés structurales et dynamiques de bâtonnets présentant une interaction attractive directionnelle fortement localisée (interaction dite à « patch ») à l'une des extrémités des particules ont été étudiées. L’interaction attractive locale a été obtenue en fonctionnalisant les extrémités des virus filamenteux par greffage régiosélectif de colorants fluorescents hydrophobes qui jouent le rôle de « patch » enthalpique. La force d'attraction peut être modulée en faisant varier le nombre de molécules de colorant liées. Nous avons montré que cette interaction à « patch » stabilise la phase smectique au détriment de la phase nématique, laissant les autres phases cristallines liquides essentiellement inchangées. En outre, la présence de molécules de colorant fluorescent sur les extrémités des virus permet l'observation de structures lamellaires cristal-liquides avec un contraste et une résolution exacerbés. La visualisation in situ de défauts topologiques en phase smectique, telle des dislocations de type coin et vis, a été réalisée à l'échelle de la périodicité du réseau. Le champ de déplacement autour d’une dislocation coin a été établi expérimentalement et comparé au profil prédit par les théories élastiques. Des dislocations de type vis ont également été mises en évidence, pour lesquelles la taille du cœur et l'helicite ont été déterminées.La dynamique des virus « patchy » et de ceux non fonctionnalisés a été étudiée par suivi temporel du déplacement des particules individuelles en microscopie de fluorescence. Dans toutes les phases cristallines liquides, la diffusion de particules « patchy » s'est avérée être entravée. En particulier dans la phase smectique, les bâtonnets « patchy » ont tendance à résider dans les couches diffusant principalement dans la direction perpendiculaire à l'axe principal du virus, tandis que les bâtonnets non fonctionnalisés présentent une diffusion entre couches beaucoup plus prononcée. Ce comportement peut s’explique par la plus grande valeur du potentiel smectique associé et mesuré expérimentalement dans les deux types de dispersion.Nous avons combiné des effets de « patch » entropique et enthalpique en ajoutant des polymères non-absorbants à la dispersion virale fonctionnalisée. Dans ce cas, les bâtonnets s’auto-assemblent latéralement par déplétion en des clusters. La diffusion de rayons X et la microscopie optique ont été utilisées pour comparer les propriétés structurales et dynamiques des dispersions virales fonctionnalisées - ou pas - mélangées à des polymères non absorbants, et pour établir les diagrammes de phases correspondants.En résumé, nous avons démontré un nouveau moyen efficace de contrôler la structure de fluides complexes par la modifications régio-sélective des particules constituantesDispersions of filamentous viruses exhibit a plethora of liquid crystalline states including nematic, smectic (or lamellar), and columnar phases. Self-organization of these rod-shaped colloidal particles has been shown to map the hard-core behavior for which the interaction potential is purely repulsive. In this thesis, the structural and dynamical properties of rods with highly localized directional attractive interaction (or “patchiness”) between one of the ends of the particles have been studied. Local attraction has been achieved by functionalizing the filamentous virus tips via regioselective grafting hydrophobic fluorescent dyes which act as enthalpic patch. The single tip attraction strength can be tuned by varying the number of bound dye molecules. We have shown that increasing attraction interaction stabilizes the smectic phase at the cost of nematic phase leaving all other liquid crystalline transitions unchanged. Furthermore, the fluorescent dye molecules on the viral tips enable the observation of liquid crystalline lamellar structures with improved contrast and resolution. In situ visualization of topological defects in the smectic phase such as edge and screw dislocations has been thus performed at the lattice periodicity level. The displacement field around an edge dislocation has been experimentally established and compared to the profile predicted by elastic theory. Screw dislocations have been also evidenced, for which the core size and handedness have been determined.Dynamics of patchy and pristine viruses has been investigated by tracking individual rod displacements. In all liquid crystalline phases, the self-diffusion of patchy rods has been found to be hindered compared to the self-diffusion of pristine rods. Particularly in the smectic phase, patchy rods tend to reside within the layers mainly diffusing in the direction perpendicular to the main virus axis, contrary to pristine rods whose self-diffusion between layers is far more pronounced. This behavior is explained by the higher unidimensional smectic ordering potential experimentally measured in the dispersions of patchy rods compared to that obtained for pristine rods.We have combined both entropic and enthalpic patchinesses by adding non-adsorbing polymers into tip-functionalized viral dispersions. In this case, rod sides act as entropic patchy sites due to attractive depletion interaction between them. Small angle X-ray scattering and optical microscopy techniques have been used to compare the structural and dynamical properties of pristine and tip-functionalized viral dispersions mixed with hydrophilic polymers acting as depletants agent. We have determined and compared the phase diagrams obtained for the two types of virus-polymer systems.In summary, we have demonstrated a new and efficient way to control the structure of complex fluids by implementing site-specific modifications of building blocks
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Junior, Edgard Goncalves Fernandes. "Estudo do comportamento reológico de sistemas líquido cristalino liotrópicos colestéricos à base de cloreto de decilamônio." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/46/46132/tde-27112018-103800/.
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Esta dissertação apresenta os resultados obtidos na caracterização reológica, utilizando ensaios rotacionais e oscilatórios, de sistemas de cristais líquidos liotrópicos nemáticos e colestéricos à base de cloreto de decilamônio (CDA). Os sistemas colestéricos foram obtidos pela adição às matrizes nemáticas de indutores quirais hidrofóbico (Colesterol) ou hidrofilico (D-(+)Manose) que conferem à estrutura liquidocristalina um arranjo helicoidal. Procuramos analisar os efeitos da concentração do indutor no comportamento reológico, bem como da sua natureza e da quantidade de solvente presentes nestes sistemas mesomórficos. Os ensaios rotacionais foram realizados utilizando-se taxas de cisalhamento constante e variadas. Os resultados obtidos mostraram que ocorre uma mudança no comportamento reológico dependente da natureza do indutor quiral. Fases com indutor hidrofóbico têm sua viscosidade diminuída com a adição de colesterol, enquanto as fases com D-(+)-Manose têm sua viscosidade aumentada. Também foram observadas mudanças no comportamento reológico segundo a quantidade de solvente presente na mesofase. Para sistemas com colesterol e com maior quantidade de água em sua composição, a viscosidade aumenta ao longo do tempo até atingir um valor máximo, seguido de uma diminuição. Este comportamento deve indicar que nestes sistemas, as fases devem primeiro sofrer uma deformação atingindo um máximo de tensão, a partir da qual começa a ocorrer uma melhor acomodação da sua estrutura, provocando a diminuição da viscosidade. Nos sistemas com indutor hidrofóbico e com menor. quantidade de solvente, a viscosidade diminui até atingir um valor mínimo. Pode-se observar que quanto maior for a concentração de indutor, maior é o tempo necessário para se atingir este mínimo. A partir deste ponto há um aumento da viscosidade até um valor constante. Isto sugere a ocorrência de uma quebra da estrutura do sistema, seguida por sua reorientação por fluxo. Em sistemas em que o indutor é D-(+)-Manose, o comportamento reológico observado é semelhante tanto em fases com maior ou menor quantidade de solvente, ou seja, aumento da viscosidade até um valor máximo, seguido pela sua diminuição. A diferença observada é que em sistemas com maior quantidade de solvente, o máximo é atingido mais cedo. O aumento da viscosidade deve caracterizar uma deformação da estn1tura que após atingir uma tensão máxima, começa a se orientar em uma direção preferencial, causando a diminuição da viscosidade sem quebra do edifício colestérico. A determinação da entalpia livre de ativação de fluxo (ΔH≠) mostra que para os sistemas em que o colesterol foi usado como indutor, a energia diminui com o aumento da concentração de indutor, quando D-(+)-Manose é utilizado, a energia aumenta. No caso do indutor hidrofóbico, a força quiral auxiliaria na orientação por fluxo das micelas, pois ao se movimentar uma micela, as outras seriam arrastadas pelas forças elásticas, diminuindo a entalpia de ativação de fluxo. Quando o indutor utilizado é hidrofílico, a entalpia de ativação aumenta, possivelmente devido à natureza do indutor, que possui uma interação maior com o solvente, agindo como uma barreira para a movimentação e orientação das micelas por fluxo. Os ensaios oscilatórios, por sua vez, mostram que a capacidade de armazenamento e devolução de energia, determinada pelo valor do módulo de armazenamento (G\') é maior que capacidade de dissipação desta por calor ou difusão das partículas, obtida pelo módulo de perda (G\"). Ambos os módulos apresentam uma dependência em relação quantidade de indutor, natureza de indutor e quantidade de água disponível, porém não foi possível se determinar nenhuma relação direta entre esses fatores. Esse sistema liotrópico pode ser descrito pelo modelo de Burger, contanto que seja levado em consideração que a componente elástica do elemento de Maxwell possua uma dependência temporal. Esse efeito provavelmente é devido à própria inércia do sistema.This dissertation shows the results obtained on the rheological characterization, using rotation and oscillatory essays, for nematics and cholesterics lyotropic liquid crystals based on decylammonium chloride (CDA). The cholesteric systems were obtained adding chiral inductors, hydrophobic (Cholesterol) or hydrophilic (D-(+)-Mannose) to nematic matrixes, inducing a helical arrangement on the liquid crystalline stn1cture. The effect of the inductor concentration besides of its nature and the amount of solvent in these mesomorphic systems were correlated to the rheological properties obtained. The rotation essays were done using constant and varied shear rates. The obtained results showed a change in the rheological behavior dependent of the chiral inductor nature. Phases with hydrophobic inductor presented viscosity decreased with the increase of cholesterol concentration, while the increase of D-(+)-Mannose concentration leads to the viscosity increase. Changes in the rheological behavior were also observed according to the amount of solvent present on the phase. For systems with cholesterol and larger amount of water, the viscosity increases along the time until reaching a maximum value, followed by a decrease. This behavior should indicate that in these systems, the phases should suffer some kind of deformation until reaching a maximum of tension. After that, an accommodation process of the structure causes the viscosity decrease. For the systems with hydrophobic inductor and with smaller amount of solvent, the viscosity decreases until reach a minimum value, that is reached later as larger it is the inductor concentration. After that, there is an increase of the viscosity until a constant value be obtained. It suggests the occurrence of a breakdown of the stn1cture, proceeded by its reorientation by flow. For the systems with D-(+)-Mannose, the rheological behavior observed is quite similar for phases with larger or smaller amount of solvent, i.e., increase of the viscosity to a maximum value, followed proceeded by its decrease. The difference is that in systems with larger amount of solvent, the maximum is reached earlier. The increase of the viscosity should characterize a deformation of the stn1cture that after reaching a maximum tension, it will be orientated in a preferential direction, causing the decrease of the viscosity without break of the cholesteric building. The flow activation free enthalpy (ΔH≠) determination shows a decrease of energy value for increase of inductor concentration in lyotropic cholesteric liquid crystal that used cholesterol as inductor. When D-(+)-Mannose was used, the flow activation free enthalpy value increases. In the systems that hydrophobic inductor is used, the chiral forces should help in micelles flow orientation process, seemingly, after the movement of a micelle, the others would be dragged by the elastic forces, decreasing the flow activation enthalpy. When it is used a hydrophilic inductor, flow activation enthalpy increases with increases of inductor concentration, probably because the inductor nature that has a greater interaction with the solvent, acting as a barrier against the micelles flow orientation. The oscillatory essays show that the storage energy capacity, determined by the value of the storage modulus (G\') is larger than heat or diffusion dissipation capacity of the particles, obtained by the loss modulus (G\"). Both modulus (G\' and G\") decrease for the phases with smaller amount of available water and stay constant for the systems with larger amount of water. The lyotropic mesophase studied can be described by a Burger model modified by taken into account a temporary dependence to the elastic Maxwell component. This effect should be probably due to the inertia of the system.
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Sharma, Vivek. "Colloidal gold nanorods, iridescent beetles and breath figure templated assembly of ordered array of pores in polymer films." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/37168.
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Water drops that nucleate and grow over an evaporating polymer solution exposed to a current of moist air remain noncoalescent and self-assemble into close packed arrays. The hexagonally close packed, nearly monodisperse drops, eventually evaporate away, leaving a polymer film, with ordered array of pores. Meanwhile, typical breath figures or dew that form when moist air contacts cold surfaces involve coalescence-assisted growth of highly polydisperse, disordered array of water drops.
This dissertation provides the first quantitative attempt aimed at the elucidation of the mechanism of the breath figure templated assembly of the ordered arrays of pores in polymer films. The creation and evolution of a population of close packed drops occur in response to the heat and mass fluxes involved in water droplet condensation and solvent evaporation. The dynamics of drop nucleation, growth, noncoalescence and self-assembly are modeled by accounting for various transport and thermodynamic processes. The theoretical results for the rate and extent of evaporative cooling and growth are compared with experiments. Further, the dissertation describes a rich array of experimental observations about water droplet growth, noncoalescence, assembly and drying that have not been reported in the published literature so far. The theoretical framework developed in this study allows one to rationalize and predict the structure and size of pores formed in different polymer-solvent systems under given air flow conditions.
While the ordered arrays of water drops present an example of dynamics, growth and assembly of spherical particles, the study on colloidal gold nanorods focuses on the behavior of rodlike particles. A comprehensive set of theoretical arguments based on the shape dependent hydrodynamics of rods were developed and used for centrifugation-assisted separation of rodlike particles from nanospheres that are typical byproducts of seed mediated growth of nanorods. Since the efficiency of shape separation is assessed using UV-Vis-NIR spectroscopy and transmission electron microscopy (TEM), the present dissertation elucidates the shape dependent parameters that affect the optical response and phase behavior of colloidal gold nanorods. The drying of a drop of colloidal gold nanorods on glass slides creates coffee ring like deposits near the contact line, which is preceded by the formation of a liquid crystalline phase. The assemblies of rods on TEM grids are shown to be the result of equilibrium and non-equilibrium processes, and the ordered phases are compared with two dimensional liquid crystals.
The methodology of pattern characterization developed in this dissertation is then used to analyze the structure of the exocuticle of iridescent beetle Chrysina gloriosa. The patterns were characterized using Voronoi analysis and the effect of curvature on the fractions on hexagonal order of tiles was determined. Further, these patterns were found to be analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal.
In summary, the dissertation provides the crucial understanding required for the widespread use of breath figure templated assembly as a method for manufacturing porous films, that requires only a drop of polymer solution (dilute) and a whiff of breath! Further, the dissertation establishes the physical basis and methodology for separating and characterizing colloidal gold nanorods. The dissertation also suggests the basis for the formation and structure of tiles that decorate the exoskeleton of an iridescent beetle Chrysina gloriosa.
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Ruhwandl, Roland Wilfried. "Colloid particles in liquid crystals." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627338.
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Pawsey, Anne Claire. "Colloids at liquid crystal interfaces." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8969.
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This thesis presents a study of colloidal particles dispersed in thermotropic liquid crystals. It has a specific focus on colloids in the presence of an interface between the liquid crystal and an isotropic fluid. Three systems are studied: colloids trapped at a planar interface between a cholesteric liquid crystal (CLC) and an isotropic oil, nematic emulsions with interfacial colloids and the influence of colloids on the phase transition kinetics of the cholesteric blue phase. Experiments are carried out using polarising optical and confocal microscopy. By combining these techniques, the director field of the liquid crystals could be imaged in combination with precise observation of the colloid locations. Custom image analysis algorithms are developed to extract the information. In the first system, we create an interface between a cholesteric liquid crystal and an isotropic liquid. Homeotropic anchoring leads to a well aligned cholesteric layer and the formation of the fingerprint texture. Fluorescent colloidal particles with planar surface anchoring are dispersed in the CLC. A majority of these particles decorate the interface. The final distribution of particles perpendicular to the interface has a clear dependence on the particle size. In the plane of the interface, surface defects form a template for the colloids. The second system is a particle dispersion within a short pitch CLC which exhibits a blue phase. The colloidal particles and associated defects act as nucleation sites for the blue phase in the cholesteric to blue phase transition. Colloidal particles cause localised melting from the blue phase to the isotropic phase and lead to a larger temperature range for coexistence between isotropic and blue phases. Furthermore, the isotropic regions can be faceted, their shape and size is controlled by the blue phase elasticity. In the final system, a nematic emulsion is created. Droplets of nematic LC are dispersed in water. Colloidal particles initially mixed into the liquid crystal decorate the interface between the two fluids. The addition of a surfactant switches the liquid crystal alignment at the fluid-fluid interface from planar to homeotropic. This forces a change in defect structure, from two boojums at the poles to a hedgehog defect in the droplet centre. The presence of colloids affects the switching dynamics and alters the final liquid crystal alignment preventing the droplets from forming a central radial defect. There is a symbiotic relationship between the particle properties - size and anchoring at the surface - and the elastic properties of the liquid crystal in the bulk and in the presence of an interface with an isotropic fluid. How the systems respond when the balance of these factors is altered is explored throughout the thesis.
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Peters, Jeffrey. "Formation of Vesicles in Lipid-Liquid Crystal Colloidal Mixtures." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-theses/622.
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The formation, phase ordering, and evolution has been studied in lipid and liquid crystal (LC) colloidal aqueous mixtures as a function of LC concentration and thermal history. The lipid used was 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC) while the liquid crystal was pentylcyanobiphenyl (5CB). POPC is a naturally occurring lipid in eukaryotic cell membranes and mimics many of the properties of human cell walls. 5CB is a polar liquid crystal that exhibits a thermodynamically stable orientationally ordered (nematic) state at room temperature. Colloidal dispersions were made at various 5CB and POPC concentrations in water and studied via optical microscopy (phase contrast, confocal, florescence, and cross-polarizing) to probe phase order and evolution as well as by calorimetry to study phase transformations. Very large vesicles (larger than 100 micrometers) were observed to form that appear to use the phase separated 5CB droplets as scaffolds. Also, there appears a unique promotion of dye (used to image the lipid bilayers) crystallization within liquid crystal domains well above room temperature.
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Pagès, Casas Josep M. "Transport and assembly of colloids in liquid crystals." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667256.
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Particles dispersed in nematic liquid crystals (NLCs), also called nematic colloids, are nowadays typical experimental systems studied in the field of Soft Matter. In this scenario, the interactions and forces between colloidal particles are in equilibrium, and thus, elasticity governs inter-particle interactions. Furthermore, the application of an AC electric external field leads to a totally different scenario where the system is out-of-equilibrium, and thus, new physical phenomena can emerge. Nematic colloidal particles can be propelled under the application of an electric field, which allows for driven particles scenarios. Briefly, motion of colloids arises from the appearance of electroosmotic flows surrounding the particles. The symmetry breaking of these flows at particles apexes induces net propulsion to the particles.
In this dissertation, we show that the transport modes of a single particle propelled in a NLC are different for the motion parallel and perpendicular to the averaged molecular orientation of the material, the director field. Here, the observed trends do not depend on the driving mechanism neither the propulsion speed. While motion is ballistic in the driving direction (parallel to the nematic director), our experiments show that transversal fluctuations can become superdiffusive depending on the configuration of the NLC surrounding the particle. For the superdiffusive behaviour, which is related to dipolar configurations of the nematic director, we have proposed a mechanism based on the geometry of the liquid crystal backflow to justify the persistence of thermal fluctuations affecting on the orientation of the dipolar configuration, and thus, the observed superdiffusive modes.
Going further, and by using hundreds of anisometric particles, we have induced colloidal clusters assembled above a topological defect. By tuning the elastic properties of the NLC material by in situ modification of the anchoring conditions, two different configurations can be induced, aster or rotating mills. This process is achieved thanks to a photosensitive surface which allows to switch from the trans (homeotropic) to the cis (planar) isomer (NLC) under UV-light irradiation. In the case of asters, we observe the formation of stationary clusters that display radially extended density gradients with three different states of aggregation, an innermost “jammed” part, followed by a liquid-like corona and ending in a diluted, gas-like, phase. Moreover, we can describe our system with a non-equilibrium equation of state and directly determine the effective pressure and temperature in the system. In contrast, for the rotating mills we obtained a dynamic assembly that has been analysed in terms of velocities and order parameters. To understand either the different assemblies obtained or the phases observed, we developed a theoretical model that combines different interactions resulting from phoretic propulsion, dipolar forces and hydrodynamics allowing to capture the basic physics of the process.
The last part of this thesis is based on steering and guiding the collective colloidal transport by means of both photo-patterning and confining devices. The first set of experiments of experiments is based on understanding the dynamics of an ensemble of flocking particles dispersed in a NLC. Furthermore, we show the implementation of obstacles for the flock to pass.
To conclude, this work not only increases our fundamental knowledge of micron-sized particles dispersed in anisotropic materials, such as nematic liquid crystals, but it serves as a starting platform to explore the motion of driven colloids inside them. Special emphasis will be put on the implementation of new techniques for guiding and steering the colloidal trajectories by means of both photo-patterning and microfluidic devices, as it has been demonstrated to be key towards the control of colloidal trajectories.Les partícules dispersades en un cristall líquid nemàtic (CLN), també anomenats col·loides nemàtics, són avui dia sistemes experimentals estudiats en el camp de la “Soft Matter”. En aquest escenari, les interaccions i forces entre partícules col·loïdals es troben en equilibri, així, l’elasticitat governa les interaccions entre partícules. Més enllà, l’aplicació d’un camp elèctric altern dóna lloc a un escenari totalment diferent, on el sistema es troba fora d’equilibri, i així, nous conceptes físics poden sorgir. Els col·loides nemàtics es poden propulsar sota l’acció d’un camp elèctric, el qual permet escenaris on els col·loides són dirigits. Breument, el moviment de les partícules és degut a l’aparició de fluxos electroosmòtics al voltant de les partícules. El trencament de la simetria dels fluxos a banda i banda de la partícula indueix una propulsió neta. En aquest manuscrit es mostra des de l’estudi del transport d’una partícula individual en termes de modes de transport fins a l’estudi de moviments col·loïdals col·lectius. L’estudi d’una partícula individual s’ha dut a terme sota l’acció de dos mecanismes diferents de propulsió, el de sedimentació-difusió i la “Liquid Crystal-Enabled Electrokinetics”. Per altra banda, prenent avantatge de la última hem pogut auto-assemblar centenars de partícules formant clústers amb una distribució radial inhomogènia de la densitat de partícules. Per entendre aquest tipus de clústers hem desenvolupat un model teòric i el Dr. Arthur Straube ha realitzat simulacions que concorden tant qualitativa, com quantitativament amb les tendències experimentals. Finalment, hem estudiat el fet de traslladar un eixam de partícules, però també el fet de posar-li obstacles per on hagi de passar. Per concloure, aquest treball no només augmenta el coneixement general de partícules micro- mètriques dispersades en CLNs, però serveix com a eina per iniciar-se i explorar el moviment dirigit de col·loides dispersat en aquests.
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Zhang, Ke. "Microparticles as a new analytical method to study liquid crystal colloids." [Kent, Ohio] : Kent State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1145051154.
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Thesis (Ph.D.)--Kent State University, 2006.Title from PDF t.p. (viewed Sept. 19, 2006). Advisor: John L. West. Keywords: nematic isotropic interface, liquid crystal colloids, dielectrophoresis, microparticle, drag effect, Raman mapping, IR imaging. Includes bibliographical references (p. 152-164).
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Lavery, Roan. "Dynamics and structure of liquid crystal colloids." Thesis, University of Edinburgh, 2001. http://hdl.handle.net/1842/11037.
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This thesis sets out to investigate the dynamic and structural properties of liquid crystal colloids. In themselves the fields of colloidal and liquid crystal science have been well studied, but the combination of these produces a wealth of new physics which has provoked much interest over the past few years. The research began by investigating the dynamics of dilute suspensions of colloidal particles in the isotropic phase of liquid crystal near the nematic transition. It was found that the particles exhibit an anomalously low diffusion which was explained in terms of the formation of an ordered layer of liquid crystal molecules surrounding the particles even when the bulk phase was disordered. It was also discovered around this time that due to the preparation procedure the particle could become coated with a thin layer of another type of solvent which dramatically affected the particle diffusion and this lead to an offshoot study in this area. It was found that the diffusion of these coated particles was much faster than expected because of a change to the boundary conditions at the particle surface as a solvent coating caused partial slip boundary conditions which altered the diffusion. Latterly the nature of this coating was investigated more and a hydrodynamic model employed to compare experimental results with the predictions given by the theory. It was found that these were in good agreement. The focus of investigation then changed, focusing on more concentrated systems of colloidal particles in liquid crystal solvents as these exhibited unusual structural phenomena. It was seen that a concentrated suspension of particles in liquid crystal shows a huge increase in the rigidity of the material in its nematic phase, compared with the pure liquid crystal. This is due to the creation of a honeycomb-like aggregate particle network, which increases the elastic strength of the material. The network formation was observed using microscopy and the elastic modulus was measured rheologically to be many orders of magnitude higher than the pure liquid crystal alone. The role of cooling rate from the isotropic to nematic phase was also investigated thoroughly as this has a large impact on the final structure of the material.
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Sengupta, Anupam. "Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://hdl.handle.net/11858/00-1735-0000-000E-00FA-B.
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Nakamatsu, Sandra. "Dispersão de nanopartículas de látex em um cristal líquido liotrópico." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-27112008-125412/.
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Neste trabalho, estudamos a dinâmica de formação e dispersão de agregados de látex quando inseridos num cristal líquido liotrópico. Esse cristal líquido é um sistema ternário composto de laurato de potássio, cloreto de decilamônia e água; e apresenta fases nemáticas uniaxiais calamítica e discótica (NC e ND, respectivamente) e biaxial (NB). As partículas de látex possuem diâmetro de 100nm e partículas com diferentes tipos de recobrimentos foram testadas. Observamos que nas fases NC e NB há formação de aglomerados de partículas, porém na transição para a fase ND as partículas se dispersam no meio. Verificamos que esse processo de aglomeração e dissociação das partículas está relacionado com a transição de fase NB - ND e foi observado em dois sistemas hospedeiros por resfriamento e por aquecimento. No intervalo de temperatura que corresponde à fase nemática biaxial para o cristal líquido puro, observa-se que há um aumento na dimensão dos aglomerados, que se tornam anemométrico e orientados na direção de orientação do meio. Dois diagramas de fases foram construídos, variando-se a concentração de partículas dispersas no meio, e a composição relativa de surfactantes do sistema hospedeiro. Experimentos de espalhamento de raios X indicam que a distância média entre as micelas que formam o meio hospedeiro não é alterado pela inserção de partículas no cristal líquido e permanece a mesma em todas as fases nemáticas. Foram também realizados estudos de reologia que mostram que a viscosidade do sistema é alterada pela presença das partículas de látex. Os fenômenos observados são interpretados levando-se em conta as flutuações de orientação das micelas nas diferentes fases nemáticas.In this work, we studied the dynamics of agglomeration and dissociation of latex particles when inserted into a lyotropic liquid crystal. This liquid crystal is a ternary system formed by potassium laurate, decilamonium chloride and water, presenting uniaxial calamitic and discotic nematic phases (NC e ND, respectively) and a biaxial nematic phase NB. The latex particles have diameter of 100 nm and particles with different surface treatments were tested. It was observed that in the NC e NB phases the latex particles form agglomerates, however in the transition to the ND phase, the particles disperse in the medium. In the temperature domain of the biaxial nematic phase the agglomerates increase in size, become anisometric and oriented along parallel to the orientation of the medium. Two phase diagrams were built by varying the particle concentration dispersed in the liquid crystal and by varying the relative composition of surfactants of the liquid crystal. X rays diffusion experiments have shown that the average distance between the micelles in the host medium are not affected by the presence of the latex particles and remain the same in all nematic phases. Rheology studies were also performed and it was found that the viscosity of the system is affected by the presence of the particles. The observed phenomenon are interpreted taking into account the orientational fluctuations of miceles in the different nematic phases.
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Li, Jinjiang 1962. "The colloidal and liquid crystal properties of surface modified chitin crystallites." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35403.
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Chitin crystallites were prepared from crab chitin using HCl hydrolysis. On avenge, the surface charge density of the chitin crystallites was calculated to be 0.5 e/nm2 based on conductimetric titration data. The formation of a chiral nematic phase in aqueous suspensions of chitin crystallites and the in situ texture of the crystallite suspensions were investigated using polarised optical microscopy and freeze-fracture transmission electron microscopy. The effect of the interparticle electrostatic interaction on phase separation has been explored through phase diagrams and the interaction energy was calculated based on experimental zeta potentials. The flow properties of the liquid crystalline phases of chitin crystallites have been studied rheologically. Shear thinning behaviour and a two-regime flow curve were observed for isotropic suspensions and biphasic suspensions respectively. A typical three-regime flow curve for liquid crystalline polymers was found for the anisotropic suspension of chitin crystallites. The maximum in the viscosity-concentration curve was found at the phase transition concentration: isotropic to biphasic. Chitin crystallites were systematically deacetylated using NaOH hydrolysis. It was found dud the reaction was pseudo first order. These modified crystallites are highly charged. Their phase behaviour contradicts the theoretical prediction by Stroobants et al. in addition, crystallites with a different extent of N-sulfonation were obtained in an aqueous medium using triethylamine/sulfur trioxide (TEA/SO3) by controlling the TEA/SO3 concentration used in the reaction. The colloidal behaviour of the suspension of the N-sulfonated crystallites was studied by plotting the zeta potential of the suspension as a function of the pH. Once the extent of N-sulfonation reached a certain level (80% or above), the chiral nematic; phase formed while below this level only the nematic phase was observed. TEM studies showed that the crystallites were wel
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Li, Jinjiang. "The colloidal and liquid crystal properties of surface modified chitin crystallites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ44657.pdf.
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Pendery, Joel S. "Nanoscale Patterning and Imaging of Liquid Crystals and Colloids at Surfaces." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396623443.
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Hwang, Hyerim. "Crystal-Liquid Transitions Studied With Colloids in an Electric Bottle." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493595.
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In this thesis, we have presented the experimental investigations on the crystal-liquid transitions in a colloidal system. Colloids behave as big atoms, thus they are good model systems to study the dynamics of condensed matter. Their phases are determined by the particle concentration which can be controlled by external forces. We studied the transitions such as crystallization and melting in a controlled way. With a confocal microscopy, we were able to obsserve the transitions at single particle level in three-dimension.
In Chapters 2-3, we introduced the electric bottle setup which played a significant role to induce the transitions in this thesis. The electric bottle was designed to generate inhomogeneous electric fields, and we were able to employ dielectrophoresis to manipulate the particle concentration using this setup. The colloidal suspension we used here is composed of PMMA particles (Ɛp=2.3), the mixture of cis-decalin and tetrachloroethylene (Ɛm = 2.6$), and surfactant AOT molecules to give repulsive interaction between the particles. We also introduced analysis methods to obtain particle location information from the raw confocal images and to distinguish between the crystal and liquid phases by using their different structures.
In Chapters 4-6, we investigated the crystal-liquid transitions and a crystal-crystal transition. We studied the growth kinetics in crystallization and melting in a system which is covalent to the collision-limited growth of pure metals. We measured the attachment and detachment rates, which can be denoted as jump rates. It was found that the process is governed by the Brownian motion of the particles which is dealing with the random walk. The free energy difference between the two phases gives bias to the random walk, thus we insist that the growth process is a biased random walk. We also studied the equilibrated interfaces in a BCC crystal-liquid system. We measured the equilibrium fluctuations of the interface, which gives an interfacial stiffness of the interface. Although the orientation of the interface plane doesn't have high-rotational symmetry, the stiffness was observed to be isotropic in a long wavelength limit. The last transition we observed is the one between crystals, BCC and FCC crystals.
We explored the crystal-liquid transitions at single particle level using the combination of the electric bottle and colloids. Instead having multiple samples to study the phase behaviors as a function of volume fraction, we were able to obtain a concentration-dependent phase diagram in a single electric bottle sample. The design of the sample cell can be further developed to induce the various kinds of density gradient. Also, many other phase behaviors resulted from different type of interactions can be studied.Engineering and Applied Sciences - Engineering Sciences
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Cleaver, Julie. "Network formation in mixtures of nematic liquid crystal and colloids." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/14543.
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Mixtures of thermotropic liquid crystal (5CB) and colloid (polymethylmethacrylate) particles have been studied. When these composites are cooled through the isotropic-nematic (IN) phase transition an optically switchable material is formed with an unusually high storage modulus. Previous studies have shown that the particles form into an interconnected network. In this thesis the mechanism of network formation, and the morphological and mechanical properties of the network are explored. Time-resolved laser scanning confocal microscopy (LSCM) is used to achieve near-single-particle resolution and observe the kinetics of the network formation upon cooling from the initial isotropic dispersion. As the mixture is cooled below the IN transition temperature (TIN), the particles are expelled by growing droplets of nematic liquid crystal to form the walls of a three dimensional network. This process takes the order of 30 seconds (dependent upon cooling rate), but the IN transition of the pure liquid crystal is much quicker. The presence of impurities adsorbed onto the particles before they are dispersed in liquid crystal could be responsible for this. These impurities open up a biphasic region in the phase diagram and slow down interface movement. Calorimetric data are consistent with this interpretation. Microscopy observations show that upon heating above TIN single particles become free and exhibit Brownian motion. As the sample is heated deep into the isotropic phase the network is broken up but clusters of particles remain. Sedimentation of these clusters causes a density gradient of particles to form across the sample with varying height and upon cooling a new network of particles or ‘clusters of particles’ is formed.
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Podoliak, Nina. "Magneto-optic effects in colloids of ferromagnetic nanoparticles in nematic liquid crystals." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/338023/.
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This thesis describes theoretical and experimental investigation of the optical and magnetic effects in nematic liquid crystals and in ferronematics, namely suspensions of ferromagnetic nanoparticles in nematic liquid crystals. In the experimental part, the effect of the nanoparticles shape and functionality on the suspension stability and magneto-optic properties were studied. Suspensions with magnetic nanospheres showed a linear response to low magnetic fields (< 100 Oersted) and a decrease in the effective Frederiks threshold. Ferronematics with magnetic nanorods coated by 4-n-Octyloxybiphenyl-4-carboxylic acid were more stable and showed a larger decrease in the Frederiks threshold than the spherical magnetic nanoparticles coated by Oleic acid. No ferronematic effects were detected in the weakly magnetic hematite nanorod suspensions. The aim of the theoretical part was to develop a realistic numerical model that could simulate the experimental results of the magnetic-field-induced Frederiks transition in nematic and ferronematic cells. The modelling was carried out in two steps. The first step involved modelling the Frederiks transition of an undoped liquid crystal cell in the presence of an easy axis pretilt and a bias, in-plane, magnetic field. The nematic model predicted that applying a bias field would lead to a shift of the threshold response, which would be sensitive to the bias field direction. This prediction was confirmed as an excellent agreement between the model and experimental data was achieved. In the second stage, a new approach to modelling of ferronematics was proposed, which involved extending previous ferronematic theories to include both the ferromagnetic effect of the particles and the intrinsic magnetic properties of the nematics. There were two variable parameters in the model, which characterise the effective ferroparticle-field interaction, and the ferroparticle-nematic director interaction. These parameters for experimental suspensions were obtained by comparing the model with experimental data. The fitting parameters were used to estimate an effective coupling energy between a nematic host and doped nanoparticles. Up to one order of magnitude higher coupling energy was obtained in the magnetite nanorod suspension as compared to the spherical magnetic nanoparticles. The research presented in this thesis demonstrates a route to prepare highly sensitive and stable ferronematic suspensions, contributes to better understanding of the magneto-optic effects in these suspensions, and highlights their potential for applications as tailor-made optical materials in magnetically driven devices.
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Rogers, Richard B. "The Measurement of Solid-Liquid Interfacial Energy in Colloidal Suspensions Using Grain Boundary Grooves." Cleveland, Ohio : Case Western Reserve University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1138381541.
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Zarubin, Grigorii [Verfasser], and Siegfried [Akademischer Betreuer] Dietrich. "Ferromagnetic colloids in liquid crystal solvents / Grigorii Zarubin ; Betreuer: Siegfried Dietrich." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/118548759X/34.
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ZHANG, KE. "Microparticles as a new analytical method to study liquid crystal colloids." Kent State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=kent1145051154.
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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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Laurens, Gaétan. "Laser generation of nanoparticles in liquids : new insights on crystal structure control and colloidal stability." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1161/document.
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L’engouement pour l’originalité des propriétés physiques des nanoparticules s’est accompagné d’un développement de nombreuses méthodes de synthèse depuis un demi siècle. Parmi elles, l’ablation laser en liquide permet de produire des nanoparticules avec des surfaces libres de tout contaminant et ce pour une multitude de combinaisons de matériaux et de solvants. Cependant, la simplicité apparente de cette technique dissimule la complexité des mécanismes physico-chimiques, ce qui entraîne actuellement un manque de contrôle des objets synthétisés. Tout d’abord, nous nous sommes intéressés à la cinétique des bulles pour laquelle les conditionsextrêmes d’ablation laser en liquide présentent des cas originaux de cinétique dans le domaine de la mécanique des fluides. Puis, ce travail de thèse vise à donner de plus amples perspectives quant à une meilleure maîtrise de la structure cristalline des nanoparticules et de la stabilité colloïdale. Une manière plus directe de contrôler la taille, la phase cristalline et la stabilité colloïdale des solutions contenant des nanoparticules est d’ajouter des ligands. Nous avons donc étudié les mécanismes de stabilisation de ces solutions en utilisant des ions qui se complexent aux nanoparticules d’or. Nous avons aussi réussi à synthétiser des nanoparticules de rubis (alumine dopée chrome). La stabilisation de ces nanoparticules dans une phase métastable en utilisant des ligands organiques a été expliquée par une étude théoriqueLaser generation of nanoparticles in liquids : new insights on crystal structure control and colloidal stability The great interest of nanoparticles for their original physical and an chemical properties has been supported by the development of numerous methods of synthesis. In the nineties, laser generation of nanoparticles in liquids appeared, including Pulsed Laser Ablation in Liquids (PLAL). The PLAL technique enables to produce surface free particles for plenty of material and solvent combinations. However, the apparent simplicity of its implementation hides complex physico-chemical mechanisms resulting in a lack of control of the final products. We firstly investigated the dynamics of the laser-generated bubbles for which the PLAL extreme conditions present new studied cases of bubbles dynamics not encountered in the field of fluid mechanics. Then, we aim to bring new insights into better control of the nanoparticles morphology and their colloidal stability. A straight way to tune sizes, crystal structures and the colloidal stability consists in the addition of stabilizing agents. Hence, we investigated the mechanisms of stabilization of colloidal gold using complexing ions. We also succeed to synthesis nano-rubies, i.e. chromium doped corundum alumina nanoparticles, unexpected at nanoscale. The stabilization of the metastable crystal structure using ligands is explained thanks to a comprehensive theoretical approach
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Álvarez, Francés Laura. "Single particle dynamics in liquid crystalline phases formed by filamentous viruses." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0429/document.
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Cette thèse porte sur la dynamique des différentes mésophases liquides cristallines et des transitions de phase d'un modèle colloïdal de particules en forme de bâtonnent: les virus fd. L'étude de l'auto-organisation des cristaux liquides colloïdaux traite des phénomènes les plus simples de formation de systèmes structurés. Dans un système où les particules anisotropes ont des interactions de noyau rigide, l'auto-organisation est purement entropique en raison de la maximisation du volume libre du système. Ainsi, il y a une modification de la dynamique qui peut être mesurée, et fournisse des informations sur le volume libre disponible et la structure de la mésophase.La dynamique des bâtonnets fd peut être mesurée avec précision à l'aide de techniques de microscopie à fluorescence. Nous quantifions la dynamique autour des transitions de phase et l'effet de la flexibilité et de la longueur en tant que mécanisme pour relâcher la contrainte de leurs voisins. En outre, dans une structure lamellaire guest-host, nous avons prouvé la pérmeation favorisée des bâtonnets longs guest à travers les couches de la matrice Smectique hast formée de plus petites particules. Dans ces conditions, la super-diffusion de la particule invitée est également observée lorsqu'elle se diffuse dans une limite de grain. Il s'agit d'un pas en avant pour comprendre la dynamique des systèmes structurés colloïdaux et aussi dans le développement des nouveaux matériaux basés sur des diffuseurs rapides avec des applications potentielles dans la biologie médicale. Les résultats expérimentaux sont très prometteurs et stimulantesThis thesis treats the dynamics of the different liquid crystalline mesophases and phase transitions of a model colloïdal of rod-like particles: the fd viruses. The study of the self-organization of colloïdal liquid crystals treats the simplest phenomena of forming structured systems. In a system where anisotropie particles have hard core interactions, the self-organization is purely entropy driven due to the maximization of the free volume of the system. Thus, there is a change on the dynamics at single particle level that can be measured, providing information on the available free volume and the structure of the mesophase.The fd rods are a versatile colloïdal system and their self-dynamics can be accurately measured using fluorescence microscopy techniques. We quantify the relaxation of the dynamics around the phase transitions and the effect of flexibility and length as a mechanism to release the constraint of their neighbors. Moreover, in a guest-host lamellar structure we demonstrate that a big guest particle is faster than the small host, if the guest particle is not commensurate in the host energy landscape. In these conditions, also the super-diffusion of the guest particle is observed when it diffuses into a grain boundary. This is a step forward to understand the dynamics of colloïdal structured systems and also in the development the new materials based on fast diffusers with potential applications in drug delivery. The extensive experimental results are completed by a whole analysis and interpretation, being very promising and challenging
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Balin, Andrew. "Statistical mechanics of colloids and active matter in and out of equilibrium." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:2941a082-82ca-400b-ae6b-7c22e75cc90c.
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Thermal and viscous forces compete for dominance at the microscopic length-scales which govern the behaviour of many soft or biological systems. We study three systems of increasing complexity with the central goal of understanding the statistical or hydrodynamic nature of their mechanics. First we study experiments that have been conducted on ferromagnetic colloidal rods. At equilibrium, the magnetically pinned rod is observed to randomly flip between two orientational states, which our theoretical analysis shows is due to a competition between entropic and Hamiltonian forces. We show analytically how entropic forces can arise by considering the coupling between observed and unobserved variables of a system. Experiments in which a rod is driven out of equilibrium by a rotating field display three phases of steady-state behaviour as a function of driving frequency. Using Brownian dynamics simulations we match the lower critical frequency to the experimentally obtained values, showing that thermal fluctuations play an important role in this regime and propose a simple argument to demonstrate that hydrodynamic interactions between the substrate and rod affect the upper critical frequency. We then turn to the biophysical topic of cell locomotion in viscoelastic media. In order to study how bacterial flagella interact with similarly-sized polymers in their environment, we construct a Stokesian dynamics model of a helical filament and bead--spring polymer. Simulating their interaction first for a pinned--rotating helix, then for a swimming helix, we demonstrate that large polymers become hydrodynamically entrained by the flagellum and coil around it, causing both pinned and swimming flagella to expend more work. For the swimming helix, this results in a reduction of swimming speed on average. Finally, we consider an active nematic fluid confined to a channel and show that the inclusion of a passive colloid induces a global state of coherent flow maintained by the intrinsic activity of the system. This flow is persistent, and transports the colloid with it along the channel. By this mechanism, a passive colloid is able to spontaneously induce its own transport through an otherwise quiescent fluid.
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Buyuktanir, Ebru Aylin. "Electro-optical Characterization of Bistable Smectic A Liquid Crystal Displays." Kent State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=kent1207869606.
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Ghanem, Mohamed Ali M. A. "Electrochemical synthesis of nanostructured porous materials using liquid crystal and colloidal templates and their magnetic and optical properties." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392824.
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Bera, Tanmay. "Developing surface engineered liquid crystal droplets for sensing applications." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5125.
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Diagnosis plays a very crucial role in medicine and health care, which makes biosensors extremely important in modern technological context. Till date, various types of biosensors have been developed that are capable of detecting a wide range of biologically important species with great sensitivity and selectivity. However, most of these sensing units require highly sophisticated instrumentation and often lack the desired portability. Liquid crystal (LC) droplets, on the other hand, are a new type of functional material that are finding increasing research attention as a new sensing unit due to their tunable optical property, high surface area, portability and cost-effectiveness. In this dissertation, functionalized LC droplets for biosensing at aqueous-LC interface are highlighted. Chemically functionalized LC droplets dispersed in aqueous solution were prepared by the self-assembly of amphiphilic molecules at the aqueous/LC interface. These functionalized LC droplets showed a well-defined director of configuration and a specific optical pattern when observed with a polarizing light microscope. It was discovered that the interaction of chemically functionalized LC droplets with an analyte triggers transition of the director of configuration of the LC within the droplets, providing a simple and unique optical sign for the detection of the analyte. Moreover, the director of configuration transition happened in a concentration dependent manner, allowing both qualitative and quantitative detection of the analyte. The sensitivity of chemically functionalized LC droplets depends not only on the nature of amphiphilic molecules but also the size and number of the droplets. The dissertation essentially deals with the application of these chemically functionalized LC droplets in detecting several biologically important species. It was observed that the adsorption of charged macromolecules (dendrimers, proteins, and viruses) on polyelectrolyte functionalized LC droplets triggered a bipolar-to-radial configuration transition based on the polar verses non-polar interaction. By using a simple optical microscope, microgram per milliliter concentrations of bovine serum albumin, cowpea mosaic virus, and tobacco mosaic virus could be detected in aqueous solution. The detection limit of Mastoparan X polypeptide decorated LC droplets in detecting E. coli could reach to approximately 10 bacteria per milliliter. In this case, the high affinity of the polypeptide towards the bacterial causes the former to detach from the LC droplets, triggering the director of configuration transition of the LC inside the droplets. Finally, surfactant decorated LC droplets were used to detect lithocholic acid (LCA), a toxic bile acid used as a specific biomarker for colon cancers. In this case, the director of configuration transition of the LC inside the droplets is a result of the replacement of the surfactant from the aqueous/LC interface by LCA. The microgram per milliliter concentration of LCA, a clinically significant concentration, could be easily detected by changing the length of surfactants. These studies highlight the novel use of surface functionalized LC droplets to detect biologically important species. Due to their tunable optical property, coupled with high surface area and portability, surface functionalized LC droplets have great potentials in the design of next generation biosensors.ID: 031001378; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: .; Title from PDF title page (viewed May 21, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 119-134).
Ph.D.
Doctorate
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Ferreira, Guilherme Augusto 1991. "Estruturas de cristais líquidos lamelares obtidos pela associação de brometos de dialquildimetilamônio em solução." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249590.
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Orientador: Watson LohDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química
Made available in DSpace on 2018-08-27T11:59:07Z (GMT). No. of bitstreams: 1 Ferreira_GuilhermeAugusto_M.pdf: 3614152 bytes, checksum: 568d89fdf3adc43ec1f13c46bc935cad (MD5) Previous issue date: 2015
Resumo: Surfactantes são moléculas anfifílicas que, em solução, se organizam dando origem a uma série de estruturas de associação, dentre as quais destacam-se os cristais líquidos. Especialmente os brometos de dialquildimetilamônio se associam formando principalmente estruturas líquido-cristalinas lamelares. Nesse trabalho, foram estudadas as propriedades estruturais de fases lamelares formadas pela auto-organização, em solução aquosa, de dois surfactantes dessa classe: o DDAB (brometo de didodecildimetilamônio) e o DODAB (brometo de dioctadecildimetilamônio). Através das técnicas de caracterização utilizadas, foi verificado que, nas condições de concentração e temperatura estudadas, ambos os surfactantes, DDAB e DODAB, se associam em duas fases lamelares, La e Lß, fases essas que diferem pela organização das cadeias carbônicas nas bicamadas e intumescimento. Além de formarem diferentes fases lamelares, essas também apresentaram distintas propriedades estruturais, dependendo do surfactante utilizado. Estudos de calorimetria diferencial de varredura também permitiram acompanhar as transições entre as fases lamelares obtidas causadas por variação da temperatura. As bicamadas formadas pela auto-associação do surfactante DDAB apresentaram um intumescimento menor do que as formadas pelo análogo DODAB, porém, com esse último, houve a formação de bicamadas menos espessas. Misturas preparadas com ambos os surfactantes em diferentes proporções também indicaram a variação das propriedades investigadas, intumescimento e espessura das bicamadas, aumentando o teor de DODAB. A hipótese levantada é que as propriedades estruturais investigadas são fortemente influenciadas pelas forças eletrostáticas atuantes no sistema. A caracterização de amostras formuladas com os tensoativos acima da temperatura de transição para fase fluída e na presença de sal confirmou esta ideia. O maior intumescimento e a pequena espessura das bicamadas formadas pelo DODAB se devem, provavelmente, à interdigitação das cadeias carbônicas e ao efeito de correlação iônica, respectivamente, descritos em mais detalhes nessa dissertação
Abstract: Surfactants are amphiphilic molecules that self-assemble, in solution, giving rise to a number of association structures, among which the liquid crystals stand out. Particularly the dialkyldimethylammonium bromides associate to form mosty lamellar liquid crystalline structures. In this work, we studied the structural properties of lamellar phases formed by self-organization, in aqueous solution, of two surfactants from this class: DDAB (didodecyldimethylammonium bromide) and DODAB (dioctadecyldimethylammonium bromide). Through the used characterization techniques, we found that under the conditions of concentration and temperature studied, both surfactants, DDAB and DODAB are associated in two lamellar phases, La and Lß, phases that differ by the organization of the carbonic chains in bilayers and swelling degree. In addition to forming different lamellar phases, these also showed distinct structural properties, depending on the surfactant used. Studies with differential scanning calorimetry also allowed us to follow the transitions between the lamellar phases caused by temperature variation. The bilayers formed by self-association of DDAB showed a lower swelling degree than those formed by DODAB, however, with the later, there was the formation of thinner bilayers. Mixtures prepared with both surfactants in different proportions also indicated the variation of the investigated properties, swelling degree and bilayer thickness, upon increasing the DODAB content. We propose that the structural properties investigated are strongly influenced by electrostatic forces acting on the system. The characterization of samples formulated with surfactants above the transition temperature to the fluid phase and in the presence of salt confirmed this hypothesis
Mestrado
Físico-Química
Mestre em Química
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Agha, Hakam. "Interaction de grains colloïdale avec une ligne de disclinaison dans un cristal liquide nématique et d'auto-assemblage d'un nanofil conducteur en 3D." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAE002.
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Dans cette thèse, l'interaction entre les grains colloïdaux avec une ligne de disclinaison dans un cristal liquide nématique est explorée. Deux types de colloïdes ont été utilisés; sphérique (billes de silice) et allongé (nanotubes de carbone). En plus, différents types d'ancrage sur leur surface sont obtenus; planaire, homéotrope, et Janus (moitié planaire - moitié homéotrope). Ces paramètres ont été modifiés dans le but d'examiner et d'évaluer la force nématique agissant entre les grains colloïdaux et la ligne de disclinaison, qui est le résultat de l'interaction élastique entre les deux. Cette force est de l'ordre du pico-Newton et capable d'attirer et de fixer les colloïdes dispersés dans le cristal liquide nématique sur la ligne de disclinaison. Une fois que les colloïdes sont fixés sur la ligne de disclinaison, ils peuvent être collés ensemble par électropolymérisation de pyrrole. Ce qui donne lieu à un nanofil conducteur en 3 dimensions, qui est auto-assemblé et auto-connecté à des électrodes prédéfinies à l'intérieur du cristal liquide nématiqueThroughout this thesis, the interaction between the colloidal grains with a disclination line in a nematic liquid crystal is explored. Two types of colloids were used; spherical (silica beads) and elongated (carbon nanotubes). In addition different types of anchoring conditions on their surface is obtained; planar, homeotropic, and Janus (half planar – half homeotropic). These parameters were varied in the aim to examine and evaluate the nematic force acting between the colloidal grains and the disclination line, which is a result of the elastic interaction between the two respectively. This force is in the order of pico-newton, and capable of attracting and fixing the dispersed colloids, in the nematic liquid crystal, on the disclination line. Once the colloids are fixed on the disclination line, they can be glued together by means of electropolymerization of pyrrole. This gives rise to a 3 dimensional conductive nanowires, which are auto-assembled, and auto-connected to predesigned electrodes inside the nematic liquid crystal
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Sengupta, Anupam Verfasser], Christian [Akademischer Betreuer] Bahr, Jörg [Akademischer Betreuer] Enderlein, Stephan [Akademischer Betreuer] [Herminghaus, and Pawel [Akademischer Betreuer] Pieranski. "Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment / Anupam Sengupta. Gutachter: Jörg Enderlein ; Stephan Herminghaus ; Pawel Pieranski. Betreuer: Christian Bahr." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/1044172940/34.
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Guidetti, Giulia. "Cellulose photonics : designing functionality and optical appearance of natural materials." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277918.
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Cellulose is the most abundant biopolymer on Earth as it is found in every plant cell wall; therefore, it represents one of the most promising natural resources for the fabrication of sustainable materials. In plants, cellulose is mainly used for structural integrity, however, some species organise cellulose in helicoidal nano-architectures generating strong iridescent colours. Recent research has shown that cellulose nanocrystals, CNCs, isolated from natural fibres, can spontaneously self-assemble into architectures that resemble the one producing colouration in plants. Therefore, CNCs are an ideal candidate for the development of new photonic materials that can find use to substitute conventional pigments, which are often harmful to humans and to the environment. However, various obstacles still prevent a widespread use of cellulose-based photonic structures. For instance, while the CNC films can display a wide range of colours, a precise control of the optical appearance is still difficult to achieve. The intrinsic low thermal stability and brittleness of cellulose-based films strongly limit their use as photonic pigments at the industrial scale. Moreover, it is challenging to integrate them into composites to obtain further functionality while preserving their optical response. In this thesis, I present a series of research contributions that make progress towards addressing these challenges. First, I use an external magnetic field to tune the CNC films scattering response. Then, I demonstrate how it is possible to tailor the optical appearance and the mechanical properties of the films as well as to enhance their functionality, by combining CNCs with other polymers. Finally, I study the thermal properties of CNC films to improve the retention of the helicoidal arrangement at high temperatures and to explore the potential use of this material in industrial fabrication processes, such as hot-melt extrusion.
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La, Cotte Alexis de. "(Bio-)fonctionnalisation de bâtonnets colloïdaux modèles et étude de leurs auto-assemblages." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0192/document.
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Cette thèse porte sur les différentes voies de fonctionnalisation et d'auto-organisation d'un système modèle dans le domaine de la matière condensée : le virus fd et ses mutants. Alors que son diagramme de phase cristal-liquide a été établi et sa correspondance qualitative avec les prédictions théoriques montrée, une des perspectives majeure consiste en son utilisation comme brique élémentaire dans la construction de nouveaux auto-assemblages. De telles avancées passent nécessairement par l'ajout de fonctions de manière régio-sélective sur le corps de la particule. Nous proposons dans ces travaux l'étude de plusieurs voies de fonctionnalisation menant à l'ajout d'espèces moléculaires ou macromoléculaires soit sur l'ensemble du virus ou bien uniquement à son extrémité.En réalisant le greffage de polymères thermosensibles, il est alors possible d'explorer les possibilités d'induire une transition de phase par variation du diamètre effectif du bâtonnet. En utilisant des diblocs d'élastine, ce principe est montré sur la transition entre le liquide isotrope et la phase nématique. L'utilisation de mutants particuliers, conçus par phage display, permet de s'intéresser alors uniquement à la fonctionnalisation de la protéine p3 située à une des extrémités du phage. L'ajout de chromophores permet alors une visualisation unique de la phase smectique et de ses défauts et crée également un effet patchy perturbant le diagramme de phase cristal-liquide. La biotine quant à elle permet la création d'auto-assemblages du fait de son interaction spécifique avec les dérivés d'avidine et un tel système est alors comparé avec un mutant dont l'ADN modifié permet l'expression directe d'une étiquette biologique complémentaire de la streptavidine. Les résultats prometteurs obtenus sont également complétés par une étude encourageante pour l'utilisation des systèmes cristal-liquides colloïdaux dans le domaine de l'électro-optiqueThis thesis deals with the different paths of functionalization and self-organization of a model system of colloidal rod-like particles: the fd virus and its mutants. While its liquid-crystalline phase diagram is well established and proven to be in qualitative agreement with theory and numerical simulations, one of the most trending perspectives is its use as building-block in new self-assemblies. For such purposes, it is mandatory to add functions regio-specifically on the particle. We show in this work the study of several ways of functionalization leading to the grafting of molecular or macromolecular compounds onto the whole virus or only onto its tip.When grafting thermoresponsive polymers, we can then explore the possibilities to induce phase transitions by a variation of the effective diameter of the rod. Using diblocs of elastin-like peptides, this principle is shown to work on the isotropic-to-nematic phase transition. The use of particular mutants, engineered by phage display, allows us to functionalize only the tip of the virus. The addition of dyes provides unique features on the smectic phase and its defects and creates a patchy effect which is modifying the liquid-crystalline phase diagram. The functionalization with biotin leads towards the creation of new self-assemblies thanks to its specific interaction with avidine and such a system is then compared with a mutant displaying a biological tag interacting with streptavidin. The results obtained are promising and are completed by a whole study of the use of colloidal liquid-crystalline system in electro-optics
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Guillamat, Bassedas Pau. "Control of active flows through soft interfaces." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/404355.
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Groups of animals, bacterial colonies, cellular tissues and assemblies of subcellular extracts are some examples of experimental systems studied in the field of Active Soft Matter. All of them are composed of autonomous self-propelled units that consume and transform energy to generate mechanical work. The interaction between these motile units lead to the emergence of cooperative spatiotemporal patterns, not observed in complex fluids in equilibrium. Despite the morphology and dynamics of these systems are being studied in detail, there is still absence of true control capabilities, which could bring new possibilities in the use or application of active flows. To this end, this thesis aims at the development of strategies to condition active flows by means of non-invasive bounds, namely rheological patterning and confinement, as a tool towards the control of the intrinsic unpredictable chaotic behaviour of active matter systems.
The experimental system used here is an active gel based on a mixture of cytoskeletal proteins, created in the laboratory of Z. Dogic from Brandeis University (MA, USA) in 2012. In brief, ATP-fuelled kinesin motor clusters crosslink and drive bundled microtubules, giving rise to an active network of biofilaments that develops far from thermodynamic equilibrium. The active gel can also self-organize at soft interfaces, where it forms a quasi-2d active nematic liquid crystal, which features spontaneous turbulent-like flows. In this thesis, first, we report experimental evidence of the existence of strong hydrodynamic coupling at the oil/water interface, where the active nematic resides, and the influence of the rheological properties of the oil phase. By changing the viscosity of the contacting oily fluid, we alter the morphology and dynamics of the active nematic, which we have characterized. In addition, in collaboration with M. C. Marchetti and S. Shankar from Syracuse University (NY, USA), we have fitted specific data to a hydrodynamical model in order to extract an estimate value for the viscosity of the active material. Second, based on these observations, and with the objective of steering the active flows, we impose viscosity patterns at the interface. For this purpose, we use a thermotropic liquid crystal, which self-assemble in well-known structures with marked anisotropic viscosity, externally- and in situ-tuneable by means of temperature and/or external fields. Under such rheological constraints, the active nematic flows are commanded at will, rapidly organizing either in localized rotating swirls or parallel stripes of aligned microtubule bundles. Through this process, we have also had the opportunity to study the interaction between active and passive nematic liquid crystals, which in this case, serve as reporters of the active flows. Finally, we prepare active emulsions by dispersing droplets of active gel in different fluids. Inside droplets, the active gel condenses at the inner surfaces to create an active nematic spherical shell, which develops in geometrically and topologically constrained conditions. Due to the confinement restrictions, the active nematic develops strikingly periodic dynamics that transmit coherent flows into the confining phase. Here, with experiments and simulations performed by M. Ravnik and Ž. Kos from the University of Ljubljana (Slovenia), we study emulsions of droplets with an active nematic shell dispersed in thermotropic nematic liquid crystals. In particular, we focus on the interaction between active flows and the usually static topological defects induced around inclusions in liquid crystals.
To conclude, this work not only increases our fundamental knowledge of both thermotropic (passive) and active nematic liquid crystals but it serves as a starting platform to explore the interaction between these two fluid ordered analogues at the interface. Special emphasis will be put on the implementation of anisotropic patterns at interfaces as it has demonstrated to be key towards controlling active flows.Sistemes compostos per grups d’animals, colònies de bacteris, teixits de cèl·lules o assemblatges d’extractes cel·lulars, mostren comportaments dinàmics complexos significativament similars tot i que, evidentment, es desenvolupen a escales espai-temps molt diverses. Aquests sistemes, anomenats sistemes actius, estan generalment formats per unitats individuals auto-propulsades que consumeixen energia de l’ambient, a partir de la qual generen forces i treball mecànic. La interacció entre els constituents d’aquests sistemes propicia moviments col·lectius i cooperatius, així com patrons de flux que no s’observen en sistemes similars en equilibri termodinàmic. Tot i que les característiques morfològiques i dinàmiques d’aquests sistemes s’estan estudiant amb detall, manquen encara estratègies per controlar els fluxos actius que se’n deriven. L’habilitat de controlar sistemes actius, no només en facilita la seva caracterització sinó que possibilita l’aplicació dels fluxos que se’n deriven, per exemple, en dispositius. Amb aquest objectiu, aquesta tesi se centra en el desenvolupament d’estratègies per al condicionament i control de fluxos actius mitjançant constriccions que procuren ser no invasives per als materials implicats. El material estudiat consisteix en un gel actiu aquós format per agregats de microtúbuls, reticulats per complexos de motors moleculars. En presència d’Adenosina trifosfat (ATP), els complexos motors exerceixen forces de cisalla locals entre els microtúbuls que, globalment, provoquen contínuament l’extensió, flexió i trencament dels agregats filamentosos. La interacció entre els constituents actius genera fluxos turbulents a escales molt més grans que les pròpies de les unitats constitutives del material. D’altra banda, en presència d’una interfície aigua/oli correctament funcionalitzada, el gel es pot densificar, desenvolupant els seus fluxos en contacte amb la fase oliosa. D’aquesta manera, s’obté un material actiu quasi-bidimensional molt dens, en el qual els filaments interaccionen entre si i s’organitzen en el pla donant lloc a un gel actiu amb ordre orientational. En particular, en aquesta tesi, s’estudiarà l’efecte de l’acoblament hidrodinàmic d’aquest material amb fluids viscosos isotròpics, amb patrons reològics imposats per cristalls líquids i en confinament, com a eines per al control dels fluxos, fins ara, aparentment caòtics i impredictibles d’aquests sistemes actius.
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Mondiot, Frédéric. "Comportement de particules colloïdales dans des solvants nématiques : influence de la forme et de la taille." Phd thesis, Bordeaux 1, 2011. http://tel.archives-ouvertes.fr/tel-00657747.
Full textAbstract:
Ces travaux de thèse ont pour but d'étudier l'état de dispersion de particules colloïdales dans des cristaux liquides nématiques lyotropes. Ces solvants organisés sont constitués de micelles nanométriques anisotropes. Dans un premier temps, nous montrons qu'il est possible de réaliser des suspensions cinétiquement stables en jouant notamment sur la forme des inclusions micrométriques. Un modèle, développé dans le cadre de cette étude, permet de rendre compte de nos observations. Dans un second temps, nous nous intéressons à l'influence de la diminution de taille de particules sur l'état de dispersion du système. A l'échelle nanométrique, le mouvement brownien, anisotrope dans ce type de milieu, semble gouverner les phénomènes observés.
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Gharbi, Mohamed Amine. "Comportement de colloïdes piégés aux interfaces de nématiques." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2011. http://tel.archives-ouvertes.fr/tel-00650346.
Full textAbstract:
Ce travail expérimental porte sur l'étude du comportement colloïdale aux interfaces de nématiques. Dans un premier temps, nous détaillons la séquence de phase observée par des billes de silice à ancrage homéotrope fort piégées à l'interface air-nématique. En fonction de leur densité ainsi que l'épaisseur du film, les colloïdes forment différentes structures spontanément. A l'aide des pinces optiques, nous mesurons le potentiel de paire et nous discutons les rôles respectifs des forces capillaires et élastiques. Dans un second temps, nous étudions le comportement des colloïdes sur des interfaces nématiques plus complexes. En contrôlant la géométrie des interfaces et la densité des particules piégées, à l'aide de la technique de microfluidique, nous étudions le comportement colloïdale à la surface des coques nématiques fines. La compétition entre les conditions d'ancrage aux interfaces, l'élasticité du CL, les défauts et les densités des fluides est à l'origine de la formation de nouvelles configurations topologiques. Dans cette partie nous discutons le rôle des colloïdes dans la formation de ces structures.
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Vallvé, Antón Maria dels Àngels. "Sistemes nanoestructurats mitjançant monocapes de Langmuir." Doctoral thesis, Universitat de Barcelona, 2010. http://hdl.handle.net/10803/48668.
Full textAbstract:
Els treballs presentats en aquesta tesi fan referència a sistemes amb estructures d’escales nanomètriques. L’estructura d'aquests sistemes s’obté mitjançant la formació de monocapes de Langmuir, dipositant dissolucions de molècules amfifíliques o suspensions de partícules col•loïdals sobre la superfície de l'aigua.
Per una banda, s’han preparat monocapes de Langmuir de la molècula fotosensible 8Az3COOH. Mitjançant la tècnica de Langmuir-Blodgett, aquestes monocapes han estat transferides sobre substrats sòlids que, posteriorment, s’han utilitzat per a formar cel•les de cristall líquid. Aquestes permeten visualitzar les estructures transferides, similars a les observades en la monocapa de Langmuir, però no presenten fotosensibilitat. Les monocapes de Langmuir de 8Az3COOH també s’han utilitzat per a estudiar la dinàmica de les estructures i els defectes observats mitjançant microscòpia d’angle Brewster en la monocapa de Langmuir.
Per altra banda, també s’han preparat monocapes de Langmuir-Blodgett de partícules col•loïdals de diòxid de silici per obtenir cristalls col•loïdals bidimensionals amb propietats fotòniques.The works of this thesis are related to systems with structures in the nanoscale. The structure of these systems is obtained by preparing Langmuir monolayers, spreading solutions of amphiphilic molecules or suspensions of colloidal particles on the water surface. On the one hand, Langmuir monolayers of the photosensitive molecule 8Az3COOH have been prepared. These monolayers have been transferred on solid substrates by the Langmuir-Blodgett technique. Later, these substrates have been used to build liquid crystal cells. These cells allow us to visualize the transferred structures, which are similar to those observed in the Langmuir monolayer, but they do not show photosensitivity. The Langmuir monolayers of 8Az3COOH have also been used to study the dynamics of the structures and the defects observed by Brewster angle microscopy in the Langmuir monolayers. On the other hand, Langmuir-Blodgett monolayers of silica particles have been prepared in order to obtain two-dimensional colloidal crystals with photonic properties.