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Dissertations / Theses on the topic 'Crystals'

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Published: 4 June 2021
Last updated: 31 July 2024

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1

Shopova, Denitsa. "Crystal chemistry of fullerene co-crystals." [S.l. : s.n.], 2005. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB12103660.

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2

Bridgland, Lydia Naomi. "Crystal engineering of porous steroidal organic crystals." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627972.

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Porous materials are highly valued for a wide variety of scientific and technological applications and organic molecular crystals offer an alternative to established inorganic materials. In this thesis, the porosity of tris-N-phenylureido steroidal crystals IS characterised and the versatility of the steroidal crystal system is demonstrated. Material properties can often be adjusted by mixing components in varying proportions to form alloys, but this phenomenon is rarely demonstrated for organic molecules. In organic crystals, molecules pack into an array which has symmetry and dimensions specific to the compound. Thus, in general, molecules cannot be substituted for molecules of a different compound. The studies presented here demonstrate that organic alloys are possible if the crystal structure possesses voids which are able to accommodate significant p0l1ions of the new molecules. A variety of multi-component steroidal crystals have been created with diverse and complex channel interiors. These have been characterised by optical microscopy, single X-ray crystallography, IH NMR and mass spectrometry. Finally, molecular machines which perform mechanical work on a molecular level are of great interest within the scientific community. The operational range of molecular motion is often too restricted to create macroscopic phenomena, but by confining the molecular machines to small spaces such as nanopores, molecular movement on the nanometre level can be sufficient to dominate the physical and chemical behaviour of guest molecules. In this thesis, the prospect of creating a new type of molecular machine assembly to propel molecules unidirectionally along crystal channels has been investigated. Crystal engineering has been used to design porous steroidal crystals with azobenzene moieties, capable of photoinduced isomerisation, protruding into the crystal channels. The resulting crystals have been analysed by optical microscopy and solid-state UV-vis spectroscopy, and the distribution of guest molecules within the crystals has been investigated by Raman and IR microspectroscopy and fluorescence microscopy.
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3

Bullard, Theresa Vivian. "Luminescence labeling and dynamics of growth active crystal surface structures /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/9680.

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4

Higgenbottom, Morris Scott. "Liquid crystal modulation of retroreflection : a low-power communication/location technology." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/16695.

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5

Ahmed, Sayima J. "Crystal engineering of pharmaceutical salts and co-crystals." Thesis, University of Reading, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515715.

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6

Legge, Coulton Heath. "Structural modifications in liquid crystals and liquid crystal polymers." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306164.

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7

Pyzer-Knapp, Edward Oliver. "Exploring the crystal energy landscapes of porous molecular crystals." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648625.

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8

Oliveira, José E. B. (José Edimar Barbosa). "Generalized anisotropic acoustooptic diffraction in uniaxial crystals." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72766.

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9

Richartz, Melanie. "Klassifikation von selbstdualen Dieudonnégittern in einem dreidimensionale polarisierten supersingulären Isokristall." Bonn : [s.n.], 1998. http://catalog.hathitrust.org/api/volumes/oclc/41464660.html.

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10

Wu, Haixia. "Anchoring Behavior of Chiral Liquid Crystal at Polymer Surface: In Polymer Dispersed Chiral Liquid Crystal Films." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04082004-154054/unrestricted/wu%5Fhaixia%5F200405%5Fmast.pdf.

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Thesis (M.S.)--Textile and Fiber Engineering, Georgia Institute of Technology, 2004.
Griffin, Anselm, Committee Member; Srinivasarao, Mohan, Committee Chair; Park, Jung O., Committee Member. Includes bibliographical references (leaves 101-105).
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11

Griffin, Alexandra. "Crystal synthesis : a study of ionic hydrogen-bonding in crystals." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443673.

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12

Jones, J. R. "CLAT crystals." Thesis, Swansea University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637453.

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We report here the results of investigations into three related but distinct aspects of studies on montmorillonites. The first examines the alumina pillaring of montmorillonite by the introduction of the so-called 'Keggin ion' via cation exchange. The level of pillar precursor ion introduced is controlled by inducing layer charge reduction by controlled calcination. Previously, neither the effective charge on the Keggin ion nor the pillar densities achieved were known with any certainty since the analyses of Al and Si present substantial difficulty. We have introduced a new technique to calculate the number of pillars introduced which we call 'isomorphous metal dilution'. This is based on analysis of Fe3+ and Mg2+, which is achieved with accuracy. The results are self consistent and establish that the Keggin ion charge here is 3+ , not 7+ as assumed previously. The next section explores the possibility of incorporating more Li+ into the layers of Texas montmorillonite during the process of lithiation. It involved successive calcination of Li+ exchanged clay, base regeneration of cation exchange capacities, further Li+ exchange and calcination, etc. This was successfully carried out five times, and enhanced the level of lithiation. However, it was established that this reaches a limit. Suggestions are offered to account for this. These clays also showed high solvent stability as compared to the parent material, a distinct commercial benefit. Finally, the catalytic alkylation of thiophene, has been investigated. C3 to C6 alk-1-enes and alkan-1-ols were employed as alkylating reagents. The broad range of reaction products have been characterised by GC/MS and by a comprehensive gas chromatographic study based on structural dependences of retention volume. Alkanols were shown to represent inefficient reagents. Alkenes on the other hand gave results establishing that, by suitable adjustment of temperature and relative reactant concentrations, highly competitive product yields and selectivity compared to conventional catalysts may be produced.
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13

Liu, Zhijian. "Photo-aligned LC cell with weak anchoring energy and specific profiles : physics & applications /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20LIU.

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14

Paturi, Naveen Kumar. "Analysis of photonic crystal defects for biosensing applications." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4861.

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Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains viii, 70 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 55-57).
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15

Reznikov, Dmytro. "Effect of surface alignment layer on electro-optical properties of ferroelectric liquid crystal displays." [Kent, Ohio] : Kent State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1227562895.

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Thesis (Ph.D.)--Kent State University, 2008.
Title from PDF t.p. (viewed Jan 5, 2010). Advisor: Philip J. Bos. Keywords: liquid crystal, smectic, display, ferroelectric. Includes bibliographical references (p. 190-194).
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16

Cosquer, Guirec Yann. "Liquid crystals with novel terminal chains as ferroelectric liquid crystal hosts." Thesis, University of Hull, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322457.

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17

Shattock, Tanise R. "Crystal engineering of co-crystals and their relevance to pharmaceutical forms." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002101.

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18

Brown, Stephen James. "The Czochrlaski growth and characterisation of single crystals of lead molybdate." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364392.

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19

Merlin, Jessica M. "SURFACE MEDIATED NONLINEAR OPTIC EFFECTS IN LIQUID CRYSTALS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1169755107.

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20

Evans, Herbert Elgin 1962. "Preparation of high-purity aluminum bicrystals." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277076.

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The preparation of bicrystal specimens of high interfacial purity and accurately controlled mismatch of orientation between grains with a specific boundary orientation are critical for fundamental studies of the structure and properties of grain boundaries. A method was developed for routinely producing high-purity aluminum bicrystals of desired mismatch and boundary orientation. A strain annealing technique was used for making large single crystals. The orientation, structural perfection, and chemical purity of the seeds were characterized, then the seeds were joined by using an electron beam welder. The welder was designed and built as a major portion of this work.
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21

Tuffin, Rachel Patricia. "Macrocyclic liquid crystals." Thesis, University of Hull, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337245.

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22

Nanan, Suwat. "Conducting liquid crystals." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505079.

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In this thesis, the physical properties of disco tic liquid crystals have firstly been studied but the main focus concerns an investigation of photoconduction properties of liquid crystals using the Time-ofFlight (ToF) method. Photoconduction ofHAT6, HAT6-NOz and 8H2Pc have been reinvestigated. These materials show good ToF signals and the transit times can obviously be determined. The mobility of each compound agrees well with that reported in the literature. HAT6 shows temperature independence of hole mobility over the entire mesophase range. In contrast, the hole mobility of HAT6-N02 increases with increasing temperature and this supports the hopping conduction model. Interestingly, 8H2Pc shows very short transit time and provides a high hole mobility value (10-' cm2y-'s'). The hole mobilities of HHTT in the Colh phase determined from various systems are in reasonable agreement with those reported in the literature. Increasing the temperature results in decreasing of the hole mobility. This suggests a band conduction mechanism. The laser power strongly influences both the shape and the transit time of the ToF signals obtained from HHTT. This behaviour is ascribed to a space charge effect and measured signals agree qualitatively well with those simulations previously run by Leon Lever using a Monte Carlo method. HTTT shows an Onsager-type mechanism of photocharge generation. At low light intensities the quantum yield is in the range of 10-4. The ToF photoconduction ofH7T shows good transit shapes and a hole mobility of 2.5xl0's cm2V's' was found. The addition of an extra hexyloxy (C6H130) group into the HAT6 structure results in a decrease of the transition temperature and a lowering of the el~ctronic conduction. The ToF photoconduction of quinone-HAT6 shows good ToF signals having the transit times in the range of hundreds of microsecond. A hole mobility value of 8.1 x 1 0-scm2V-' s-' was obtained. Chare carrier transport of Octa(5-methylhexyl)phthalocyanine has been investigated by the ToF method and it shows good ToF signals. A very high hole mobility value of 0:14 cm2V-'s-' was obtained. This value is slightly higher than that observed in octaoctylphthalocyanine (8H2Pc) (10-' cm2V-'s-'). ToF photoconductions ofHABT8 and chloroquinone-HAT6 were attempted. Unfortunately, the loglog plots of the ToF signals obtained from both materials did not show clear transit times. As a result, detennination of the hole mobility over the meso phase range is hard to achieve. A charge injection study of some triphenylene-based discotic liquid crystals has been made. Unfutunately, neither Schottky model nor Bardeen model can be used to explain the barrier heights at the metallDLC interfaces. This suggests .that the alternative model is needed.
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23

Richtzenhain, Heiko. "Macrocyclic liquid crystals." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243475.

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24

Martin, Francoise. "Magnetic liquid crystals." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324741.

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25

Pidwell, Andrew David. "Macrocyclic liquid crystals." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324027.

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26

Barnes, Peter Jeremy. "Oligomeric liquid crystals." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241159.

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27

Ibanescu, Mihai 1977. "Cylindrical photonic crystals." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32306.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.
Includes bibliographical references (leaves 106-114).
In this thesis, we explore the properties of cylindrical photonic crystal waveguides in which light is confined laterally by the band gap of a cylindrically-layered photonic crystal. We show in particular that axially-uniform photonic band gap waveguides can exhibit novel behavior not encountered in their traditional index-guiding counterparts. Although the effects discussed in each chapter range from hollow-core transmission to zero and negative group velocity propagation and to high-Q cavity confinement, they are all a result of the photonic band gap guiding mechanism. The reflective cladding of the photonic crystal waveguide is unique in that it allows one to confine light in a low index of refraction region, and to work with guided modes whose dispersion relations lie above the light line of air, in a region where the longitudinal wave vector of the guided mode can approach zero. Chapter 2 discusses hollow-core photonic band gap fibers that can transmit light with minimal losses by confining almost all of the electromagnetic energy to a hollow core and preventing it from entering the lossy dielectric cladding. These fibers have many similarities with hollow metallic waveguides, including the fact that they support a non-degenerate low-loss annular-shaped mode. We also account for the main differences between metal waveguides and photonic band gap fibers with a simple model based on a single parameter, the phase shift upon reflection from the photonic crystal cladding. In Chapter 3 we combine the best properties of all-dielectric and metallic waveguides to create an all-dielectric coaxial waveguide that supports a guided mode with properties similar to those of the transverse electromagnetic mode of a coaxial cable.
(cont.) In Chapter 4, we introduce a mode-repulsion mechanism that can lead to anomalous dispersion relations, including extremely flattened dispersion relations, backward waves, and nonzero group velocity at zero longitudinal wave vector. The mechanism can be found in any axially-uniform reflective-cladding waveguide and originates in a mirror symmetry that exists only at zero longitudinal wave vector. In Chapter 5 we combine the anomalous dispersion relations discussed above with tunable waveguides to obtain new approaches for the time reversal (phase conjugation) and the time delay of light pulses. Chapter 6 discusses a new mechanism for small-modal-volume high-Q cavities based on a zero group velocity waveguide mode. In a short piece of a uniform waveguide having a specially designed cross section, light is confined longitudinally by small group velocity propagation and transversely by a reflective cladding. The quality factor Q is greatly enhanced by the small group velocity for a set of cavity lengths that are determined by the dispersion relation of the initial waveguide mode. In Chapter 7, we present a surprising result concerning the strength of band gap confinement in a two-dimensional photonic crystal. We show that a saddle-point van Hove singularity in a band adjacent to a photonic crystal band gap can lead to photonic crystal structures that defy the conventional wisdom according to which the strongest band-gap confinement is found at frequencies near the midgap.
b y Mihai Ibanescu.
Ph.D.
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28

Fink, Yoel 1966. "Polymeric photonic crystals." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9291.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000.
"February 2000."
Includes bibliographical references (p. 126-129).
Two novel and practical methods for controlling the propagation of light are presented: First. a design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies is derived and used in fabricating an all dielectric omnidirectional reflector consisting of multilayer films. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices. A comprehensive framework2 for creating one, two and three dimensional photonic crystals out of self-assembling block copolymers has been formulated. In order to form useful band gaps in the visible regime, periodic dielectric structures made of typical block copolymers need to be modified to obtain appropriate characteristic distances and dielectric constants. Moreover, the absorption and defect concentration must also be ~ontrolled. This affords the opportunity to tap into the large structural repertoire, the flexibility and intrinsic tunability that these self-assembled block copolymer systems offer. A block copolymer was used to achieve a self assembled photonic band gap in the visible regime. By swelling the diblock copolymer with lower molecular weight constituents control over the location of the stop band across the visible regime is achieved, One and three-dimensional crystals have been formed by changing the volume fraction of the swelling media. Methods for incorporating defects of prescribed dimensions into the self-assembled structures have been explored leading to the construction of a self assembled microcavity light-emitting device.
by Yoel Fink.
Ph.D.
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29

Gorishnyy, Taras. "Hypersonic phononic crystals." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42133.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.
Includes bibliographical references (p. 133-140).
Manipulation of the distribution of phonons inM a solid is important for both basic science and applications ranging from heat management to reduction of noise in electronic circuits and creating materials with superior acoustic and acousto-optical properties. This thesis explores hypersonic phononic crystals as means to achieve control over high frequency acoustic phonons. An integrated approach to fabrication, measurement and analysis of hypersonic phononic crystals with band gaps in the GHz range is presented. First, the phonon dispersion relation for one dimensional polymeric phononic crystals fabricated by coextrusion of a large number of poly(methylmethacrylate)/poly(carbonate) and poly(methylmethacrylate)/poly(ethylene terephthalate) bilayer pairs is investigated as a function of a lattice constant and composition using Brillouin light scattering and numerical simulations. This set of relatively simple multilayer structures represents an excellent platform to gain a basic understanding of phononic band gap phenomena. In addition, their in-plane phonon dispersion is used to extract information about the elastic constants and glass transition temperatures of individual nanolayers in a periodic multilayer arrangement. Next, two dimensional epoxy/air phononic crystals fabricated in a photoresist using interference lithography are studied. These structures are 2D single crystalline, enabling direction-resolved measurements of their phonon dispersion relation. As a result, the complete experimental phononic band diagram is obtained and correlated with numerical simulations. Finally, phononic properties of three dimensional elastomeric poly(dimethylsiloxane) crystals are investigated and the mechanical tunability of their dispersion relation is demonstrated.
(cont.) This set of structures forms the basis for understanding how to design and fabricate acoustic and acousto-optical devices with performance characteristics that can be adjusted dynamically during operation. The investigations described in this thesis demonstrate both theoretically and experimentally that 1D, 2D and 3D periodic submicron structures have complex phonon dispersion relations at GHz frequencies. As a result, these crystals can be used to manipulate the flow of random thermal phonons as well as externally generated acoustic waves resulting in novel acoustic and thermal properties.
by Taras Gorishnyy.
Ph.D.
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30

Glomsås, Guttorm. "Demons and crystals." Thesis, Kungl. Konsthögskolan, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kkh:diva-462.

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At Nordnes in Bergen there are a stone foundation supporting a plateau with buildings and an old fort. In the stone foundation, almost like a cave, there are a public urinal. As rain pours down, the mortar holding together the stones in the structures slowly dissolves into a flow of water. When the water flow passes the room of the urinal it gets exposed to heat from the air and sun which causes the water to evaporate and the minerals from the mortar to precipitate out in to stalactites. If left unattended this would eventually lay down the fort and the buildings in a ruin, and the empty space of the urinal would be filled by a mineral structure.
Bildene er av eksamensverket "Metallfeber"
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31

Levandovsky, Artem. "Structure and dynamics of interfaces in the epitaxial growth and erosion on (110) and (100) crystal surfaces." Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3731.

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Thesis (Ph. D.)--West Virginia University, 2004.
Title from document title page. Document formatted into pages; contains vii, 129 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.
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32

Ho, Chih-Hua. "Liquid crystals in woodpile photonic crystals : fabrication, numerical calculation and measurement." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/404819.

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Both experimental and numerical studies on Liquid Crystal (LC) infiltrated woodpile Photonic Crystal (PhC) are implemented in this thesis. The most well-known optical phenomenon of PhC is photonic bandgap (PBG). It is observed either in frequency or in spatial domain. The former means for a chromatic plane wave propagating though PhC that a range of frequencies do not transmit but reflect. The later means for a monochromatic focused beam passing though PhC that certain angular components do not transmit but deflect or reflect. The most well-investigated optical phenomenon of LC is birefringence. It is due to the strong dielectric anisotropy LC possesses. When the applied stimulations (e.g. electric/ optical field or external heater) are present, the orientation of LC molecules and different refractive indices (e.g. polarization or temperature dependent) are observed. The presence of LC inside PhC not only reduces index contrast (where angular BG appears) but also brings the tunability to such LC-PhC composite device. Therefore band-stop angular filter and sensitive refractometer for liquid material are potential applications controlled by multiple external stimulations. In this thesis, the related physical properties of PhCs and LCs are introduced beforehand. The fabrication of woodpile PhC is also demonstrated. Direct Laser Writing lithography technique is adopted to build microstructures with high resolution up to hundreds of nanometers. A tunable band-stop filter controlled by polarization and temperature is investigated in linear regime. To bridge our investigation to nonlinear regime, dye-doped LC is used to create graded indices inside LC medium corresponding to intensity. Numerical calculations are conducted to the experimental observations. To sum up, LC-PhC composite device possesses very promising features as demonstrated which could be applied into tunable elements in integrated optical systems and its abundant nonlinear properties remains to be explored carefully.
Ambos estudios experimentales y numéricos en cristal líquido (LC) pila de leña infiltrado de cristal fotónico (PhC) se implementan en esta tesis.El fenómeno óptico más conocido de la PhC es la banda prohibida fotónica (PBG). Se observa ya sea en la frecuencia o en el dominio espacial. Los antiguos medios para una onda que se propaga plano cromática aunque PhC que un rango de frecuencias no transmiten sino que reflejan. El medio más tarde para un paso haz enfocado monocromática aunque PhC que ciertos componentes angulares no transmiten, pero desvían o reflejan.El fenómeno óptico más bien investigado de LC es la birrefringencia. Es debido a la anisotropía dieléctrica fuerte LC posee. Cuando los estímulos aplicados (por ejemplo campo óptico / eléctrico o calentador externo) están presentes, se observa la orientación de las moléculas de cristal líquido y los diferentes índices de refracción (por ejemplo, polarización o dependientes de la temperatura). La presencia de LC en el interior PhC no sólo reduce el contraste de índice (donde aparece angular BG), pero también trae consigo la capacidad de ajuste a dicho dispositivo compuesto LC-PhC. Por lo tanto banda eliminada del filtro angular y refractómetro sensible para material líquido son posibles aplicaciones controladas por múltiples estímulos externos. En esta tesis, las propiedades físicas relacionadas de PhC y las LC se introducen de antemano. La fabricación de pila de leña PhC se demuestra. Escritura técnica de litografía láser directa se adopta para construir microestructuras con alta resolución de hasta cientos de nanómetros. Un filtro elimina banda sintonizable controlado por la polarización y la temperatura se investiga en régimen lineal. Para salvar nuestra investigación con el régimen no lineal, LC tinte dopado se utiliza para crear índices graduadas dentro de medio LC correspondiente a la intensidad. cálculos numéricos se llevan a cabo con las observaciones experimentales.Para resumir, dispositivo compuesto LC en la PhC posee características muy prometedoras como se ha demostrado que se pueden aplicar en elementos sintonizables en sistemas ópticos integrados y sus propiedades no lineales abundantes que queda por explorar con cuidado.
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33

Pelaez, Laguno Jorge. "Atomistic simulation of biaxial liquid crystals and mixtures of liquid crystals." Thesis, Durham University, 2007. http://etheses.dur.ac.uk/2498/.

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In this thesis molecular dynamics (MD) simulations at a fully-atomistic level have been undertaken to study the biaxiality and the structure of the liquid crystalline phase formed by the para-heptylbenxoate diester of 2.5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP-Ph-C(_7)), which is a bent-core mesogen. This has been the first time the transition between isotropic and liquid crystalline phases has been achieved using a fully atomistic (all-atom) potential. Simulations at five different temperatures covering the nematic range of ODBP-Ph-C(_7) have been undertaken to study the temperature dependence of the biaxial ordering. Ferroelectric domains have been observed in all the systems. Simulations started from the biaxial nematic phase have been performed with the partial charges turned off to study the influence of the electrostatic interactions on the behaviour of the system. A system composed of ODBP-Ph-C(_7) and the deuterated molecule hexamethylbenzoate-d10 (HMB) has also been simulated to check the validity of the (^)2HNMR method, which is often employed to study biaxiality. MD simulations at a fully-atomistic level have been also performed for the mixture of liquid crystals E7， commercialized by Merck. The nematic phase for this mixture is grown from an isotropic phase using an fully atomistic (all-atom) potential, and in order to study the temperature dependence of the order parameter simulations at six different temperatures covering the nematic range have been performed. The internal structure of the mixture, alongside some of its material properties such as rotational viscosity and flexoelectric coefficients have been studied. Finally, ab initio calculations involving several molecular fragments which are components of some of the most common mesogens have been carried out to calculate torsional energies of key dihedral angles. Subsequently, torsional energies have been fitted using a Fourier series expansion to obtain torsional parameters for an atomistic force field. These will be used in future atomistic simulations of liquid crystals.
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34

Zhou, Shuang. "LYOTROPIC CHROMONIC LIQUID CRYSTALS: FROM VISCOELASTIC PROPERTIES TO LIVING LIQUID CRYSTALS." Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1460397447.

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35

Denisov, Alexey. "Reconfigurable photonic crystals : external field structuring of liquid crystals - polymer composites." Télécom Bretagne, 2009. http://www.theses.fr/2009TELB0104.

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Cette thèse concerne l'étude des composites cristaux liquides (CL) / polymère. Notre but est de concevoir et de fabriquer des cristaux photoniques dont la structure soit reconfigurable par l'action d'un champ appliqué, électrique ou lumineux. Notre première réalisation se base sur l'utilisation de cristaux liquides cholestériques (CLC) stabilisés par un polymère. Les CLC présentent naturellement une structure hélicoïdale périodique, et sont donc des cristaux photoniques à une dimension pour certaines longueurs d'ondes. Pour former un cristal photonique bidimensionnel, nous avons induit une modulation périodique de la structure CLC dans une seconde direction en appliquant un champ électrique. Cette structure a permis de montrer expérimentalement un effet de bord de bande et la possibilité d'ajuster la résonance en modifiant le champ appliqué. Notre deuxième approche se base sur l'effet photoréfractif dans les composites cristaux liquides / polymères dopés par des fullerènes. Dans ces matériaux, nous avons photo-inscrit des réseaux unidimensionnels reconfigurables. Pour améliorer l'efficacité et la résolution, nous avons étudié l'influence de la concentration du dopant, utilisant le fullerène C70 ou le dérivé PCBM-60. Nous avons observé une amélioration de la résolution due à l'effet conjoint d'une augmentation de la concentration en dopant et du mécanisme de piégeage des charges dans le réseau polymère. Nous présentons également une nouvelle façon expérimentale d'exploiter l'effet photoréfractif dans des composites cristaux liquides / polymère, permettant d'améliorer l'efficacité de diffraction, pour mieux satisfaire à des besoins d'applications pratiques.
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36

Burnham, Kikue Sugiyama. "Phototriggers for a liquid crystal-based optical switch." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/27900.

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37

Dong, Shaosheng. "Liquid Crystal Polymers And Dendritic Liquid Crystals: Synthesis, Morphology, Rheology And Binary Mixtures." online version, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1094584392.

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38

Zhang, Guoqiang. "Stressed Liquid Crystals: Properties and Applications." [Kent, Ohio] : Kent State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1184972979.

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Thesis (Ph.D.)--Kent State University, 2007.
Title from PDF t.p. (viewed Mar. 4, 2009). Advisor: John West. Keywords: liquid crystal, polymer, shear, structure, application Includes bibliographical references (p. 252-267).
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39

Hu, Zhen. "Modeling photonic crystal devices by Dirichlet-to-Neumann maps /." access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ma-b30082559f.pdf.

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Thesis (Ph.D.)--City University of Hong Kong, 2009.
"Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [85]-91)
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40

Xu, Peizhi. "Electrooptical modes of liquid crystal for shutter and display applications /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202005%20XU.

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41

Yeung, Fion Sze Yan. "Variable liquid crystal pretilt angles by nanostructured surfaces and their applications /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20YEUNG.

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42

Chen, Peng 1960. "Precipitation and Pattern Formation under Far-From-Equilibrium Conditions." Thesis, University of North Texas, 1995. https://digital.library.unt.edu/ark:/67531/metadc278650/.

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Precipitates of a series of alkaline earth metal (barium and strontium) carbonates, chromates, phosphates, and sulfates were formed at high supersaturation by diffusion through silica hydrogel, agarose hydrogel, and the freshly developed agarosesilica mixed gels. The reaction vessels could be a small test tube, a recently designed standard micro slide cassette and a enlarged supercassette. Homogeneous nucleation is thought to have taken place, and particle development led to the formation of an unusual category of materials, known as Induced Morphology Crystal Aggregates [IMCA], at high pH under far-from-equilibrium conditions. Standard procedures were developed in order to produce homogeneous gels. Particle development led to characteristic style of pattern formation, which I have called monster, spiral, and flake. Among these IMCA, barium carbonate, chromate, and sulfate were moderately easy to grow. Barium phosphate was very difficult to grow as IMCA due to formation of poorly crystalline spherulites. IMCA of strontium carbonate, chromate and sulfate could be developed at high basic pH in the presence of silicate. Strontium carbonate sheet morphology displays a unique property, double internal layer structure, which was identified by backscattering electron imaging (BEI). Selected electron diffraction (SAD) revealed a new crystal phase which was called "Dentonite". Precipitate particles were isolated using a non-destructive isolation technique. Optical microscopy was widely used to examine particles in situ and scanning electron microscopy and X-ray dispersive energy (EDX) spectroscopy were applied to particles ex situ, together with ESCA for surface analysis. Growth patterns were found to be strongly dependent on pH. Other related pattern formation processes were also investigated including normal and dendritic structures, spherulitic structures and periodic pattern formation. Some interpretations were proposed in terms of mechanism. Chemical additive effects were examined experimentally in the calcium phosphate system. The effect of external ionic strength was investigated, and it was found that a certain concentration of sodium chloride (0.2 M) approximately equals a fraction of pH unit (-0.2).
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43

Du, Tao. "Single cell gap transflective liquid crystal displays and the use of photoalignment technology /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?ECED%202009%20DU.

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44

Huang, Danding. "Ferroelectric liquid crystal display based on photo-aligned azo-dye layers /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202004%20HUANGD.

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45

Amombo, Noa Francoise Mystere. "Crystal engineering of selected phenolic acids." Thesis, Cape Peninsula University of Technology, 2014. http://hdl.handle.net/20.500.11838/734.

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Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Chemistry in the Faculty of Applied Science at the CAPE PENINSULA UNIVERSITY OF TECHNOLOGY 2014
Crystal engineering based upon acid: base compounds have been studied in this thesis. Selected phenolic acids such as: vanillic acid (VA), phenylacetic acid (PAA), 4-hydroxyphenylacetic acid (HPAA), 3-chloro-4-hydroxyphenylacetic acid (CHPAA), caffeic acid (CFA), p-coumaric acid (pCA), trans-ferulic acid (tFER), 2-phenylpropionic acid (PPA) and 2-phenylbutyric acid (PBA) were the main compounds investigated. These phenolic acids have formed co-crystals/co-crystal hydrates, salts/salt hydrates and hybrid salt-co-crystals with acridine (ACRI), caffeine (CAF), cinchonidine (CIND), isonicotinamide (INM), isonicotinic acid (INA), nicotinamide (NAM), quinidine (QUID), quinine (QUIN), theobromine (THBR), theophylline (THPH) and urea (U). The two racemic compounds 2-phenylpropionic acid (PPA) and 2-phenylbutyric acid (PBA) were used to study chiral discrimination leading to the understanding of separation enantiomers. Compounds were prepared in different solvents (alcohols, ketone and distilled water) to investigate the relationship between solvents used and the crystalline product obtained. (If there is any effect on the crystalline compound obtained by changing the solvent). The structures were elucidated using single crystal X-ray diffraction. Ground products of obtained compounds were characterized by powder X-ray diffraction (PXRD). Thermal analyses like thermogravimetry (TG), differential scanning calorimetry (DSC) and hot stage microscopy (HSM) were used for the determination of thermal character of the new compounds. IR was also performed to characterize the new compounds. Non-isothermal TG was utilised to obtain kinetic parameters for the water and the methanol release in (pCA−)(QUIN+)•pCA•MeOH•H2O. A selective experiment was done in which quinidine and quinine were used to compete between selected phenolic acids (PAA and HPAA). viii The comparison of the crystal structures determined showed that, changing the phenolic acid while using the same co-crystal former has a significant effect on the type of compounds obtained. The obtained crystal structures were either co-crystal/co-crystal hydrates, salts/salt hydrates or hybrid salt-co-crystals which formed network via means of supramolecular interactions.
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46

Benedetti, Cesare. "Defects in thermosensitive colloidal crystals." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/4322/.

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Poly-N-Isopropylacrylamide (PNIPAM) colloidal particles form crystal phases that show a thermosensitive behaviour and can be used as atomic model systems. This polymer has both hydrophilic and hydrophobic character and has interesting stimuli-responsive properties in aqueous solution, of which the most important is the temperature response. Above a certain temperature, called Lower Critical Solution Temperature (LCST), the system undergoes a volume phase transition (VPT). Above the LCST, the water is expelled from the polymer network and the swollen state at low temperature transforms into a shrunken state at high temperature. The thermoresponsive behaviour of PNIPAM can be influenced by pH and ionic strength, as well as by the presence of copolymers, such as acrylic acid. In a system formed both by particles of PNIPAM and PNIPAM doped with acrylic acid, one can control the size ratio of the two components by changing the temperature of the mixture, while keeping particle interactions relatively the same. It is therefore possible to obtain thermoresponsive colloidal crystal in which temperature changes induce defects whose formation processes and dynamics can be analysed in an optical microscope at a convenient spatial and temporal scale. The goal of this thesis project was to find the conditions in which such a system could be formed, by using characterization techniques such as Static Light Scattering, Dynamic Light Scattering and Confocal Laser Scanning Microscopy. Two PNIPAM-AAc systems were available, and after characterization it was possible to select a suitable one, on the basis of its low polydispersity and the lack of a VPT, regardless of the external conditions (system JPN_7). The synthesis of a PNIPAM system was attempted, with particles of dimensions matching the JPN_7 system and, unlike JPN_7, displaying a VPT, and one suitable candidate for the mixed system was finally found (system CB_5). The best conditions to obtain thermoresponsive crystal were selected, and the formation and healing of defects were investigated with CLSM temperature scans. The obtained results show that the approach is the correct one and that the present report could represent a useful start for future developments in defect analysis and defect dynamics studies.
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47

Narvaez, Morales Jackeline. "Flexoelectricity in single crystals." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/384638.

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En términos generales, la flexoelectricidad es la respuesta de la polarización a un gradiente de deformación. A diferencia del efecto piezoeléctrico, este efecto está presente en todos los materiales independientemente de su estructura cristalina. En esta tesis doctoral, hemos estudiado la polarización inducida por deformación en cristales dieléctricos y semiconductores, la cual surge desde dos mecanismos: flexoelectricidad macroscópica y flexoelectricidad superficial. Los dos mecanismos son del mismo orden en dieléctricos normales y hasta ahora sus respectivas contribuciones han sido indistinguibles entre ellas. La investigación desarrollada en esta tesis muestra que es posible separar las dos contribuciones, además de mostrar que la deformación induce reorientación de las nanoregiones polares las cuales también pueden incrementar el coeficiente flexoelectrico efectivo sobre el valor intrínseco. La polarización puede ser generada por la separación de las cargas enlazadas entre los átomos o la celda unidad, pero también por la separación de cargas superficiales debido a las cargas libres. Hasta ahora cuando se refiere a flexoelectricidad, únicamente es tomada en cuenta la respuesta de las cargas enlazadas; sin embargo, en esta tesis doctoral se ha reportado que la polarización debida a las cargas libres también pueden contribuir, generando una gran respuesta flexoeléctrica efectiva en materiales semiconductores. Antes de esta investigación, habían numerosas controversias respecto a la verdadera magnitud del coeficiente flexoelectrico y el origen de la discrepancia entre los valores predichos teóricamente y experimentalmente. En el presente trabajo hemos buscado dilucidar esta situación y cuantificar el valor intrínseco del coeficiente flexoelectrico e identificar el origen de contribuciones adicionales a este. El mensaje principal de esta tesis es que el coeficiente macroscópico flexoeléctrico efectivo permanece en valores relativamente pequeño con un riguroso límite superior de f ≈ 10V para el coeficiente de flexoacoplo de incluso los mejores materiales, pero hay otra gran cantidad de fenómenos de polarización inducida debida a gradientes de deformación que pueden incrementar la respuesta total de este: nanoregiones polares, piezoelectricidad superficial y movimiento de cargas libres son las tres que hemos identificado, pero no descartamos la existencia de otras. Entre estos, la incorporación de cargas libres a la respuesta flexoeléctrica total en semiconductores es cuantitativamente la más grande y la más prometedora dando lugar a aplicaciones macroscópicas debida a su elevada magnitud del coeficiente flexoeléctrico y permitiendo a su vez que compita con la piezoelectricidad.
In general terms, flexoelectricity is the response of polarization to a strain gradient. In contrast to the piezoelectric effect, this effect is present in all materials regardless of their crystal structure. In this doctoral dissertation, we studied the bending-induced polarization in dielectric and semiconductor single crystals that arises from two mechanisms: bulk flexoelectricity and surface flexoelectricity. Both mechanisms are of the same order in ordinary dielectrics and, before this work, their respective contributions were considered indistinguishable one from another. The research in this thesis shows that it is possible to separate the two contributions. Additionally, we show that bending-induced reorientation of polar nanoregions can also enhance the effective flexoelectric coefficients well above the intrinsic value. Polarization can be generated by dielectric separation of bound charge within atoms or unit cells, but also by a space charge separation of free carriers. Until now, when referring to flexoelectricity, only the response from bound charge was taken into account; however, in this thesis dissertation we report that free charge also can also contribute, generating very big effective flexoelectric responses in semiconductor materials. Before this research, there were numerous controversies regarding the true magnitude of flexoelectricity and the origin of discrepancies between theoretically predicted values and actual experimentally measured ones. The present work has seeked to address this situation by quantifying the true value of the intrinsic flexoelectiricy and identifying the origin of additional contributions. The take-home message from this thesis is that true bulk flexoelectricity remains a relatively small effect with a stringent upper bound of f ≈10V for the flexocoupling coefficient of even the best materials, but that there are a number of other gradient-induced polarization phenomena that can greatly enhance the total response: polar nanoregions, surface piezoelectricity and movement of free charges are the three we have identified, but we do not discard the existence of others. Among these, the incorporation of free carriers to the total flexoelectric response in semiconductors is quantitatively the largest, and it also offers most promising route to elevating flexoelectricity to a level where it can compete with piezoelectricity even in bulk applications.
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48

Dzibrou, Dzmitry. "Complex Oxide Photonic Crystals." Licentiate thesis, KTH, Microelectronics and Applied Physics, MAP, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11068.

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Microphotonics has been offering a body of ideas to prospective applicationsin optics. Among those, the concept of photonic integrated circuits (PIC’s) has recently spurred a substantial excitement into the scientific community. Relisation of the PIC’s becomes feasible as the size shrinkage of the optical elements is accomplished. The elements based on photonic crystals (PCs) represent promising candidacy for manufacture of PIC’s. This thesis is devoted to tailoring of optical properties and advanced modelling of two types of photonic crystals: (Bi3Fe5O12/Sm3Ga5O12)m and (TiO2/Er2O3)m potentially applicable in the role optical isolators and optical amplifiers, respectively. Deposition conditions of titanium dioxide were first investigated to maximise refractive index and minimise absorption as well as surface roughness of titania films. It was done employing three routines: deposition at elevated substrate temperatures, regular annealing in thermodynamically equilibrium conditions and rapid thermal annealing (RTA). RTA at 500 oC was shown to provide the best optical performance giving a refractive index of 2.53, an absorption coefficient of 404 cm−1 and a root-mean-square surface roughness of 0.6 nm. Advanced modelling of transmittance and Faraday rotation for the PCs (Bi3Fe5O12/Sm3Ga5O12)5 and (TiO2/Er2O3)6 was done using the 4 × 4 matrix formalism of Višňovský. The simulations for the constituent materials in the forms of single films were performed using the Swanepoel and Višňovský formulae. This enabled generation of the dispersion relations for diagonal and off-diagonal elements of the permittivity tensors relating to the materials. These dispersion relations were utilised to produce dispersion relations for complex refractive indices of the materials. Integration of the complex refractive indices into the 4 × 4 matrix formalism allowed computation of transmittance and Faraday rotation of the PCs. The simulation results were found to be in a good agreement with the experimental ones proving such a simulation approach is an excellent means of engineering PCs.

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49

Bergenius, Sara. "GLAST CsI(Tl) Crystals." Licentiate thesis, KTH, Physics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1775.

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50

Jackson, Daniel. "Flexoelectricity in Liquid Crystals." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487116.

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A rich variety of symmetric and non-symmetric liquid crystal dimers have been synthesised . and studied in order to investigate their structure property relations; in particular their flexoelectric properties. The project is introduced in Chapters 1 and 2 where Chapter 1 gives a brief general background to liquid crystals and liquid crystal synthe~is, and Chapter 2 gives a more detailed background to the flexoelectric effect. The research can be broadly divided into two parts. Chapters 3 and 4 focus on seven conventional non-symmetric liquid crystal dimer series containing two mesogenic groups ether linked through a flexible spacer. These non-symmetric dimers all contain a ( . cyanobiphenyl mesogenic group at one end and either a poly-fluorinated biphenyl or a phenyl-cyclohexyl-alkane mesogenic group at the other. Almost all these materials possess nematic phases (and in one series a smectic phase) and show strong flexoelectric coupling to an applied field with some experiments yielding very large values for the flexoelastic ratio. Chapter 5 focuses on two series of bent core liquid crystal dimers, wher~ the long chain spacer is divided by a catechol or resorcinol based disruptor group. The disruptor is located in the centre of the molecule and symmetric cyanobiphenyl mesogenic groups are at each end. These materials show a curious odd-even effect in the nematic-isotropic transition temperatures which is further investigated in Chapter 6 by reducing the symmetry of the compounds and studying the changes in the transitional ·properties. 1.ills was achieved in one series by changing the relative position of the catechol linking group along the spac~r chain or, in a different series, by altering one of the mesogenic end groups to a di-fluorinated biphenyl (a mesogenic moiety studied in Chapter 3). The liquid crystal properties were investigated by·optical microscopy, differential scanning calorimetry and deuterium NMR spectroscopy. The flexoelastic ratios were determined from thed~pendence of the tilt in the optic axis on an applied electric field
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