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Dissertations / Theses on the topic 'Liquid crystals Optical properties'
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1
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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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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Kim, Sang Hwa. "Fast Switching Polymer Stabilized Liquid Crystal Devices: Morphological and Electro-Optical Properties." [Kent, Ohio] : Kent State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1101220722.
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Gleeson, H. F. "Optical and electro-optical properties of chiral mesophases." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383374.
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Chen, Lu Guang, and s3064076@student rmit edu au. "Thermo-Optical Properties of Polymer Dispersed Liquid Crystals." RMIT University. Applied Science, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080206.114823.
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Polymer dispersed liquid crystal (PDLC) films, consisting of micro-sized domains of a liquid crystal dispersing in a polymer matrix, serve as the basis of a variety of high-efficiency electro-optical effects. The thermo-optical properties of the PDLCs were investigated in this thesis. The thermal properties and the morphologies of four low molar mass mesogens were studied by DSC and polarized optical microscope (POM). There were significant super cooling/heating effects on the first order phase transitions but not on the mesophase transitions. The structural effects on the transition temperature were investigated. Between the two 4-alkoxybenzoic acids mesogens, the clearing temperature of 4-(octyloxy)benzoic acid was higher than 4-(decyloxy)benzoic acid because of the increasing chain length. Trans-4-methoxycinnamic acid had the highest melting temperature among the four mesogens despite the molar mass because the carboxylic acid termini of trans-4-methoxycinnamic acid gave rise to strong intermolecular attractions. The smectic phases of 4-(octyloxy)benzoic acid were classified as head-to-head bilayer orientational smectic structures, SmA2 and SmC2, respectively, by wide angle X-ray diffraction through measuring the d spacing of the liquid crystal. The total solubility parameter was used to evaluate matching a polymer-LC-solvent combination. PDLC films were prepared by the solvent induced phase separation method and suitable morphologies were achieved by thermal induced phase separation. The phase transition temperatures of PDLCs were shifted to a lower temperature due to the polymer dispersion effects. Different mesophases were observed in PDLC films when LC exhibited different mesophases. The LC fractions in the droplets were calculated from the nematic to isotropic enthalpies through the Smith equation. Two factors, thermal cooling rate and the LC concentration, which affect the size of the droplet dispersed in the polymer matrix, were investigated in the PVC dispersed 4,4'-azoxyanisole. The phase transitions of pHEMA dispersed 4-(octyloxy)benzoic acid and PVC dispersed 4,4'-azoxyanisole were investigated by TMDSC and quasi-isothermal TMDSC. The TMDSC results were analysed by the two approaches, reversing and non-reversing heat flow and complex heat capacity. The results of the phase transitions of the two PDLCs illustrated that in the PDLCs it involved both non-reversing, melting, and reversing, clearing and the transition between two mesophases. In the non-reversing transition, the transition temperature would be affected by super cooling/heating and the results obtained in the experiments were dependent on the experimental conditions, such as the heating or cooling rate, sample size and purge gas flow rate. However, in the reversing transition process, there were no super cooling/heating effects observed and it seemed that the experimental conditions were not so critical. Results could be monitored by Lissajous figures obtained from the quasi-isothermal TMDSC. The plots of modulated heat flow versus the derivative of modulated temperature can be used to alert to unfavorable experimental conditions where loss of system linearity could be seen.
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Addis, James. "Optical properties of bent-core nematic liquid crystals." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/optical-properties-of-bentcore-nematic-liquid-crystals(de6d40c5-a11f-4ae3-ab61-dbc55671d8b4).html.
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Much of the interest in bent-core compounds in the last few years has centred aroundtheir potential to form nematic liquid crystal phases, which may be both biaxial andpolar. These properties offer possibilities for nematic ferroelectric switching andnonlinear optics applications. In this work, two optical properties, the refractive indices and the second ordernonlinear optical response, were investigated in the high temperature (> 170 °C)nematic phase of a series of bent-core oxadiazole compounds, of varying chain typeand length. An experimental technique, based on the acquisition and analysis of reflectionspectra from liquid crystal cells, and capable of operating at the high temperaturesrequired, was used for the measurement of refractive indices. The extraordinaryrefractive index was found to range from 1.70 to 1.78 over the nematic phase of thebent-core compounds. The ordinary refractive index varied from 1.58 to 1.62. Bothranges of values are higher than is typically observed for rod-like liquid crystals. Thebirefringence took values from ~ 0.10, in the high temperature nematic phase, to~ 0.18, close to the underlying smectic phase. A new experiment was designed, constructed and tested for the second harmonic(SH) measurements. The dependences of the SH on temperature and on scatteringangle are well explained by the theory of SH generation by the flexoelectricpolarisation induced by thermal fluctuations of the director in the nematic phase. Themaximum conversion efficiency was measured to be very low, ~ 1/10000 of apercent. No evidence for the formation of macroscopic biaxial nematic phases was found byeither the refractive indices or SH experiments. However, for the compounds havinglong nematic phases of > 50 °C, different regimes of behaviour in the uniaxialnematic phase were revealed by the SH experiments. This atypical behaviour isconsistent with other reports on these compounds. This study cannot confirm the existence of nanoscale cybotactic clusters in thenematic phases of the bent-core compounds examined but neither is it inconsistentwith them.
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Shinton, S. E. "Optical and dielectric properties of polymer dispersed liquid crystals." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639025.
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Polymer Dispersed Liquid Crystals (PDLCs) are attracting considerable attention for new optical displays. This thesis describes the synthesis of PDLC materials, fabrication of cells and study of their optical and dielectric behaviour. This work includes two areas of research. Predominantly it is an investigation of the properties of PDLCs prepared using Polymerisation Phase Separation (PIPS) by UV irradiation of mutually soluble liquid crystal (LC) and pre-polymer materials, developed for use in PDLC systems. A limited study of liquid crystal gels completes the thesis. We demonstrate that the electro-optical response of a PDLC is due to alignment of the LC phase, illustrated by comparison of the dielectric behaviour of the PDLC and LC in an aligning field. It is evident from this work that there is solubility of the LC component in the polymer that forms the continuous phase. Therefore, only at higher concentrations of the LC component (above 30%) will the PDLC be formed, and in such materials, the continuous phase contains dissolved LC material. Variation of experimental conditions under which samples are prepared, by changing the composition, temperature of cure and the presence of aligning fields, leads to modifications in the structure and properties of PDLCs, which are investigated. Techniques to study the dielectric, electro-optic and optical properties have been applied to the range of samples prepared. Such studies give information on the alignment of the LC phase in a PDLC in directing electric fields. It is demonstrated that dielectric relaxation spectroscopy (DRS) provides direct information on the macroscopic orientation and voltage induced changes in the alignment of gels produced in the presence and absence of electric fields. Our studies show that DRS, in combination with optical techniques, provides a powerful means for studying the alignment of LC molecules in PDLCs and gels.
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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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Ghanadzadeh-Gilani, Ali. "Dielectric and electro-optical properties of some cyanobiphenyl liquid-crystals." Thesis, Aston University, 1995. http://publications.aston.ac.uk/9688/.
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A variety of methods have been reviewed for obtaining parallel or perpendicular alignment in liquid-crystal cells. Some of these methods have been selected and developed and were used in polarised spectroscopy, dielectric and electro-optic studies. Also, novel dielectric and electro-optic cells were constructed for use over a range of temperature. Dielectric response of thin layers of E7 and E8 (eutectic mixture liquid-crystals) have been measured in the frequency range (12 Hz-100 kHz) and over a range of temperature (183-337K). Dielectric spectra were also obtained for supercooled E7 and E8 in the Hz and kHz range. When the measuring electric field was parallel to the nematic director, one loss peak (low-frequency relaxation process) was observed for E7 and for E8, that exhibits a Debye-type behaviour in the supercooled systems. When the measuring electric field was perpendicular to the nematic director, two resolved dielectric processes have been observed. The phase transitions, effective molecular polarisabilities, anisotropy of polarisabilities and order parameters of three liquid crystal homologs (5CB, 6CB, and 7CB), 60CB and three eutectic nematic mixtures E7, E8, and E607 were calculated using optical and density data measured at several temperatures. The order parameters calculated using the different methods of Vuks, Neugebauer, Saupe-Maier, and Palffy-Muhoray are nearly the same for the liquid crystals considered in the present study. Also, the interrelationship between density and refractive index and the molecular structure of these liquid crystals were established. Accurate dielectric and dipole results of a range of liquid-crystal forming molecules at several temperatures have reported. The role of the cyano-end group, biphenyl core, and flexible tail in molecular association, were investigated using the dielectric method for some molecules which have a structural relationship to the nematogens. Analysis of the dielectric data for solution of the liquid-crystals indicated a high molecular association, comparable to that observed in the nematic or isotropic phases. Electro-optic Kerr effect were investigated for some alkyl cyanobiphenyls, their nematic mixtures and the eutectic mixture liquid-crystals E7 and E8 in the isotropic phase and solution. The Kerr constant of these liquid crystals found to be very high at the nematic-isotropic transition temperatures as the molecules are expected to be highly ordered close to phase transition temperatures. Dynamic Kerr effect behaviour and transient molecular reorientation were also observed in thin layers of some alkyl cyanobiphenyls. Dichroic ratio R and order parameters of solutions containing some azo and anthraquinone dyes in the nematic solvent (E7 and E8), were investigated by the measurement of the intensity of the absorption bands in the visible region of parallel aligned samples. The effective factors on the dichroic ratio of the dyes dissolved in the nematic solvents were determined and discussed.
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Joshi, Vinay Joshi. "ELECTRO-OPTICAL AND FLEXOELECTRO-OPTICAL PROPERTIES ENHANCED BY BIMESOGEN-DOPED CHIRAL NEMATIC LIQUID CRYSTALS." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1543053053654711.
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Folkes, Robert L. "Controlling the morphological and electro-optical properties of polymer dispersed liquid crystals." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/3669/.
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Polymer dispersed liquid crystals have shown potential as the basis for a new display screen technology which can be used to produce flexible displays. The work presented here investigates the properties during the synthesis process of PDLCs, which affect the electro-optical properties of the films produced. An investigation is performed through the use of small angle light scattering, and small angle neutron scattering, into the thermodynamic phase properties of the initial liquid crystal monomer solution from which the PDLCs are formed. Through the use of small angle light scattering and ESEM the phase separation mechanism is determined and the morphological properties of films formed under different thermodynamic conditions are investigated and linked to the electro-optical properties of test films. It is shown that due to the rod like nature of liquid crystal molecules that the monomer/liquid crystal phase properties cannot be explained by classic polymer solution thermodynamics. Phase separation is shown to occur by one of two mechanisms depending upon whether or not a crosslinking monomer species is present, either a gel phase separation mechanism or a viscoelastic mechanism. Depending upon the initial thermodynamic properties of the system the formation of a polymer network can either act to promote (resulting in a large droplet morphology size) or suppress (resulting in small impure liquid crystal droplets) phase separation. This in turn is linked to the effectiveness of films formed under given conditions as potential display devices. With thanks to EPSRC and Sony MSL, Stuttgart for funding
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Ritcey, Anna Marie. "Chiroptical properties of cellulose derivatives." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75758.
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The chiroptical properties of isotropic solutions, cholesteric liquid crystals and solid films prepared from selected cellulose derivatives are investigated by optical rotary dispersion (ORD) and circular dichroism (CD). Optical activity from intrinsic molecular dissymmetry, polymer conformation and cholesteric reflection properties are considered.The chiroptical properties of cholesteric liquid crystals are interpreted according to deVries' theory. Lyotropic liquid crystalline phases formed by (hydroxypropyl)cellulose in methanol display anomalously high optical rotation at low wavelengths. The anomalies disappear on the addition of a dipolar aprotic solvent, and are absent for the ethyl ether derivative of the polymer, indicating a chiral hydrogen bonded structure is contributing to the optical activity.
Investigation of the chiroptical properties of cellulosics by circular dichroism requires the presence of a suitable chromophore, either as a chain substituent or as an added dye. Congo red exhibits induced optical activity in dilute aqueous solutions of methylcellulose and cellulose oligomers, providing evidence for the presence of a helical conformation. CD spectra of two new biphenyl derivatives also exhibit exciton splitting characteristic of a helical arrangement of chromophores. Conformational dissymmetry is not indicated in spectra of cellulose acetate although the sign of carbonyl CD band is solvent dependent. The sign of this band is interpreted in terms of the orientation of the ester substituent relative to the anhydroglucose ring. Congo red, bound in cholesteric cellulose films prepared by the deacetylation of cellulose acetate cast from mesophase solution, shows induced optical activity which, in this case, reflects the cholesteric nature of the matrix. Similar results for cellulose gels regenerated from LiCl/N,N-dimethylacetamide solution indicate that cellulose adopts a supramolecular helicoidal arrangement on slow precipitation from solution.
The optical properties of the thermotropic cholesteric liquid crystalline phase formed by a new cellulose derivative, (ethoxypropyl)cellulose, are examined by circular reflectivity measurements.
The cholesteric reflection properties of mesophase solutions of cellulose acetate in trifluoroacetic acid are characterized. The polymer undergoes rapid trifluoroacetylation in this solvent and the presence of trifluoroacetate substituents alters the handedness and the magnitude of the pitch. Although the pitch is sensitive to the nature of achiral substituents, it is not influenced by the addition of chiral solvents. (Abstract shortened with permission of author.)
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Willmott, Jonathan Raffe. "Linear and non-linear optical properties of highly twisted chiral nematic liquid crystals." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408981.
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Rumbaugh, Scott Hamilton. "Endless state-of-polarization control for coherent optical communication systems using nematic liquid crystals." PDXScholar, 1989. https://pdxscholar.library.pdx.edu/open_access_etds/4145.
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One of the obstacles to coherent fiber-optic communications is the unpredictable polarization drift which necessitates the use of an active polarization controlling system to match the polarizations of the signal and local oscillator. The polarization match must be maintained during the reset of any of the finite range components to prevent loss of data. We present a novel and practical system which uses three liquid crystal devices for the polarization matching process. Also, the required reset control algorithm and its derivation are described in detail.
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Bryant, Jason. "Polarised photoselection and molecular dynamics in liquid crystals and proteins." Thesis, University of Essex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313097.
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Liao, Guangxun. "Mechanical and Electro-Optical Properties of Unconventional Liquid Crystal Systems." Kent State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=kent1131600449.
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Li, Jie. "Design and synthesis of organic chiroptical switches." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/27385.
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Lippert, Daniel Anreas. "The effect of morpholine and polymer network structure on electro-optical properties of polymer stabilized cholesteric liquid crystals." Thesis, University of Iowa, 2019. https://ir.uiowa.edu/etd/6791.
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Polymer stabilized cholesteric liquid crystals (PSCLCs) provide many advantages over other electro-optical materials. The unique helical structure of the cholesteric liquid crystal (CLC) creates a natural gradient for light interacting across each CLC domain layer. Not only does the CLC helical structure greatly increase the bandwidth tuning and broadening range, it also allows CLCs to act as a polarizer, notch filter, reflector, and optical rotator all in one material. However, while many novel PSCLC materials have been created, little is understood about how complex initial system interactions affect final electro-optical (e-o) properties.1,2
In this work, the principal variables affecting PSCLC blue shift electro-optical behavior have been determined through structural analysis and measurement of electro-optical properties. Typical PSCLC materials must meet both formulation and photopolymerization processing requirements to display blue shift e-o properties. Threshold photoinitiator concentrations (0.5-1.5 wt%) and morpholine containing group concentrations (0.25-1.0 wt%) were both shown to be primary factors, along with sufficient UV exposure time (10-30 min) and light intensity (500 mW/cm2, 365 nm), for PSCLC blue shift bandwidth tuning/broadening to occur. Morpholine was initially identified as a component of photoinitators Irgacure 369 and 907 and was proven to increase PSCLC ion density altering LC-polymer network interactions with several proposed theories included later in this work. The use of an appropriate morpholine containing LC monomer to directly incorporate morpholine into the LC-polymer network was shown to greatly improve PSCLC sample stability. Through the results of this research we successfully induced blue shift e-o behavior in a previous red shift only PSCLC using only 30% of the UV exposure that a model PSCLC blue shift sample required while extending the blue shift broadening range over threefold (from 75 nm to 250 nm). The fundamental understanding and design of PSCLC systems described herein serves as a starting point for engineering PSCLC materials with specific and desirable electro-optical properties.
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Stojadinovic, Strahinja. "Light Scattering Studies of Dynamics of Bent-Core Liquid Crystals." Kent State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=kent1105330884.
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Nosheen, Shabeena. "Flexo electro-optic liquid crystals for phase modulation." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289439.
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Soft matter, self-assembled 3D photonic structures such as blue phase liquid crystals have of great interest to the displays industry and are highly desirable as spatial light modulators because of their polarisation independence and fast switching. However, these types of devices suffer from multistep fabrication conditions and require high threshold voltages. To overcome these limitations, two key points were considered: High flexoelectric liquid crystals are capable of uniform 3D self-assembly, with a wide temperature range but have high threshold voltages, whereas, other classes of high dielectric liquid crystals have fast electro-optic response times with low threshold voltages but show poor 3D self-assembly. In this work, new mixture formulations have been devised having both properties in moderation in order to achieve simple yet stable 3D self-assembled blue phases with fast response times at as low as possible applied fields. Dielectric materials were considered from a commercial source whereas, miscible flexoelectric soft materials were synthesised in-house. These synthesised materials were fully characterised. Then mixtures were formulated in commercial high dielectric hosts to study their miscibility, new mesogenic transitions and electro-optic responses in terms of flexoelectric and dielectric properties. The selected mixtures were further investigated for the rapid growth of blue phases and their compatibility with reactive mesogens to form stable blue phases at room temperature. This new formulation of materials has given rise to mixtures and devices which are inherently easy to fabricate allowing the robust and resilient growth of blue phases under an hour in standard laboratory conditions. Furthermore, polarisation independent electro-optic switching has been characterised at fields < 1V micron m-1. For phase modulation studies of these stabilised blue phase devices, phase shift was measured using a modified Young's slit interferometer. The observed results were very promising, with a full 2.5 pi phase shift observed at a field of 9.25 V micron m-1 when compared to earlier reported devices (which required complicated multistep fabrication processes) giving values of full 1.8 pi phase shifts at 20 V micron m-1.
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Salili, Seyyed Muhammad. "Dynamic and Magneto-optic Properties of Bent-core Liquid Crystals." Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1479906074401674.
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Jang, Yong-Kyu. "ADVANCED UNDERSTANDING OF THE OPTICAL PROPERTIES IN PHASE COMPENSATED LIQUID CRYSTAL DEVICES." Kent State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=kent1185484614.
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ATKURI, HARI MUKUNDA. "METHODS TO ADJUST THE PHYSICAL PROPERTIES OF LIQUID CRYSTALS AND RELATED DEVICES." Kent State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=kent1343078114.
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Reznikov, Dmytro Yu. "Effect of surface alignment layer on electro-optical properties of ferroelectric liquid crystal displays." Kent State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=kent1227562895.
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Osterman, Jesper. "Investigations of Optical Properties and Photo-Alignment in Bistable Nematic Liquid Crystal Displays." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6083.
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"Nonlinear optical studies of laser induced reorientation and orientational photorefractive grating formation in nematic liquid crystals." 2006. http://library.cuhk.edu.hk/record=b5892810.
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Song Liang = 向列液晶中激光束感应的取向重联非线性光学效应和取向性光折变光栅形成 / 宋亮.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Song Liang = Xiang lie ye jing zhong ji guang shu gan ying de qu xiang zhong lian fei xian xing guang xue xiao ying he qu xiang xing guang zhe bian guang zha xing cheng / Song Liang.
Abstract --- p.i
论文摘要 --- p.iii
Acknowledgement --- p.iv
Contents --- p.v
Chapter Chapter 1 --- Introduction --- p.1
References --- p.5
Chapter Chapter 2 --- Brief review of liquid crystals and nonlinear optics of liquid crystals --- p.9
Chapter 2.1 --- Brief review of liquid crystals --- p.9
Chapter 2.1.1 --- General description --- p.9
Chapter 2.1.2 --- Types of liquid crystals --- p.11
Chapter 2.1.3 --- Order parameter --- p.14
Chapter 2.1.4 --- Liquid crystal alignment --- p.14
Chapter 2.1.5 --- Continuum theory of liquid crystals --- p.16
Chapter 2.2 --- Nonlinear optics of liquid crystals --- p.20
Chapter 2.2.1 --- Basic mechanism of nonlinear optics --- p.20
Chapter 2.2.2 --- Self-phase modulation --- p.23
Chapter 2.2.3 --- Orientational photorefractive effects --- p.29
Chapter 2.3 --- Sample preparation --- p.34
Chapter 2.4 --- Conclusion --- p.37
References --- p.39
Chapter Chapter 3 --- Domain formation in homeotropic nematic liquid crystal cell --- p.42
Chapter 3.1 --- Introduction --- p.42
Chapter 3.2 --- Domain formation under applied dc and ac electric fields --- p.44
Chapter 3.3 --- Light scattering of domains under applied dc and ac electric fields --- p.49
Chapter 3.4 --- Conclusion --- p.53
References --- p.54
Chapter Chapter 4 --- Laser induced self-phase modulation and effects of applied electric field --- p.56
Chapter 4.1 --- Introduction --- p.56
Chapter 4.2 --- Self-phase modulation without applied electric field --- p.58
Chapter 4.2.1 --- Experimental setup --- p.58
Chapter 4.2.2 --- Experimental results and discussions --- p.59
Chapter 4.3 --- Effects of applied electric field --- p.67
Chapter 4.3.1 --- Effects of applied dc electric field --- p.67
Chapter 4.3.2 --- Effects of applied ac electric field --- p.72
Chapter 4.4 --- Conclusion --- p.75
References --- p.77
Chapter Chapter 5 --- Orientational photorefractive grating in nematic liquid crystals --- p.80
Chapter 5.1 --- Introduction --- p.80
Chapter 5.2 --- Orientational photorefractive grating under dc electric field --- p.82
Chapter 5.2.1 --- Experimental setup --- p.82
Chapter 5.2.2 --- Experimental results and discussion --- p.84
Chapter 5.3 --- Orientational photorefractive grating under ac electric field --- p.90
Chapter 5.3.1 --- Raman-Nath grating --- p.90
Chapter 5.3.2 --- Quasi-Bragg grating --- p.96
Chapter 5.4 --- Conclusion --- p.98
References --- p.100
Chapter Chapter 6 --- Summary and future outlook --- p.103
List of Publications and Conference Presentations --- p.107
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Hung, Raymond Jui-pu 1969. "Organic materials for microelectronics : 157 nm photoresists and electrooptic liquid crystals." 2001. http://hdl.handle.net/2152/10586.
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Jui-Ming, Huang, and 黃瑞銘. "Electro-optical properties of ester-type bent-core liquid crystals." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/83151174126656197482.
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碩士國立臺灣科技大學
高分子工程系
92
Electro-optic properties in the antiferroelectric phase, that is, B2 phase, of ester-type bent-core liquid crystal molecules were investigated in this study. Different carbon number, on the terminal chain of bent-core liquid crystal molecules,1,3-bis[4-(4-n-alkoxybenzoyloxy)benzoyloxy] benzene (n=10,14), and play important roles in affecting the changes of spontaneous polarization. We have obtaining the homogeneously chiral domain, the racemic domain by properly choosing waveforms of electric field applied. Apply a higher electric field to this ester-type “banana- shape material”, we see that the liquid crystal state will be transformed to an optically isotropic liquid crystal state when electric field is cut off. The relationship between side-chain length and transmission, the result shows longer side-chain would be higher transmission. In the response time, we find that shorter side-chain was faster than the othe
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Hsiao, Jen-I., and 蕭仁義. "The Optical Properties of Cholesteric Liquid Crystals Doped with Dye." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/20356549840469744334.
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碩士國立臺灣科技大學
高分子工程系
91
Firstly, we mixed nematic liquid crystal with cholesteric liquid crystal to produce a liquid crystal that have two mesophases: Smectic A and Cholesteric. The reflection wavelength of the cholesteric liquid crystal is in visible region. We found the pitch will be shortened during gaining the ambient temperature and the reflection wavelength shifts to short wavelength region. After cholesteric liquid crystal doping with a Methyl Red dye, the dye is pumped by Ar laser and the reflectivity is probed by He-Ne laser. We found the reflectivity increases with gaining laser power, but the reflectivity won’t increase when laser power is too high. Conceivably Methyl Red dye occurred trans-cis transition after pumped by Ar laser, cause unhomogeneous planar texture of cholesteric liquid crystal. This investigation could be applied as optically switched display devices.
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Lin, Meng-Jie, and 林孟頡. "Electro-Optical Properties of Nanoparticle-Doped Polymer Dispersed Liquid Crystals." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/and3c9.
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碩士中原大學
物理研究所
99
Polymer dispersed liquid crystal (PDLC) are the polymer matrixes uniformly dispersed with liquid crystal droplets. When there is no electric field, PDLC appears to be white due to the mismatched refractive index of polymer and LC droplet, therefore the light is scattered from the droplets. When an electric field is applied across the cell, the LC molecules rotate to the direction of the electric field, and the PDLC is transparent. The opaque and transparent states can be switched by the external electric field through the changes of the refractive index of the LC droplet. In this thesis, we have investigated the influence of doping nanoparticals, such as Titanium dioxide, Barium titanate and Iron oxide, on the threshold voltage and the LC droplet size of PDLC. Doping nanoparticle Titanium dioxide and Barium titanate in the PDLC, the threshold voltages decrease and are saturated when the doping concentration increases. However, the size of LC droplet does not change obviously. This phenomenon is quite different when Iron oxide nanoparticles are doped in the PDLC, the changes of threshold voltage are not observed in our study and the LC droplet size is changed apparently. Finally we analyze the changes of the threshold voltage through the changes of droplet size and nanopartical concentrations.
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Guu, Fengwei, and 古峰維. "Studies of Electro-Optical Properties and Structures of Ferroelectric Liquid Crystals and Side Chain Liquid Crystal Polymers." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/00580114113987252036.
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Hsu, Chiao-Yun, and 許巧芸. "Studies of Nonlinear Optical Properties of the Blue Phase Liquid Crystals." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/64506381093764918917.
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碩士國立中山大學
光電工程學系研究所
99
This study researches the nonlinear optical properties of the blue phase liquid crystals using the Z-scan technique. The purpose is to investigate the non-linear effect of the blue phase liquid crystals induced by the thermal and the liquid crystal reorientation effect. The Z-scan technique is common method to measure the non-linear index n2 and the non-linear absorption coefficient of materials. The measurement of the optical Kerr constant using Z-scan is based on the principle of spatial beam distortion due to the self-focusing or self-defocusing. For typical nematic liquid crystals, the nonlinear effect in the nematic phase is large than that in the isotropic phase. However, due to the anisotropic properties of the liquid crystal, the light-induced nonlinear effect in the nematic phase is polarization dependency. Unlike nematic phase, the blue phase is optical isotropic duo to its symmetric structure, and therefore blue phase are polarization independent and provide a larger non-linear effect. The experiments to measure the nonlinear refractive index n2 are as follows: firstly, a linearly polarized Ar+ laser light (λ=532nm) is focused in the z direction onto the sample via lens, and the detector was set behind the sample. Sequentially, the light intensity is recorded while the sample is scanned near the beam waist of the green laser. Finally, the non-linear index n2 of the material is derived from mathematical calculation. The study investigated two kinds of material, pure blue phase liquid crystal and dye-doped blue phase liquid crystal, and measured their non-linear index n2 in the blue phase and isotropic phase, respectively. The experimental results show that the non-linear index n2 of dye-doped blue phase liquid crystal is 100~1000 times as large as this of the pure blue phase liquid crystal at the blue phase. Besides, compared with isotropic phase in the blue phase liquid crystal, the blue phase actually possesses larger non-linear index n2. This experiment confirms that the nonlinear effect can be induced using linearly polarized Ar+ laser, and the nonlinear refractive index n2 can be measured using Z-scan technique.
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Liang, Hao-Hsun, and 梁浩熏. "The electro-optical properties of binary system of banana liquid crystals." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/h45zna.
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碩士國立臺灣科技大學
高分子系
94
Binary system of two mesogens exhibited antiferroelectric B2 phase (B-10)and nematic phase (B-10-Cl) was investigated. These compounds were as 1,3-Bis[4-(4-decyloxy- benzoyloxy)benzoyloxy] benzene and 4-Chloro-1,3-bis[4-(4-decyloxybenzoyloxy)benzoyloxy]benzene。When doping the molar ratio of B-10-Cl is below 60%, B2 phase appears and identified by electro-optic experiment which applied triangular wave voltage and has two peaks of response current in half period. When doping the molar ratio of B-10 is 70%, exhibited an unknown mesophase ,X phase and have no current response. When doping the molar ratio of B-10 is above 70%, only possess directional nematic phase. In the electro-optical experiment, we find that the spontaneous polarization value becomes larger but response time becomes smaller when the molar ratio of B-10-Cl rise. When apply high voltage of triangular wave, focal conic texture and fan with stripes texture were observation.
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Li, Chi-you, and 李啟佑. "Study of Structures and Optical Properties of Photonic crystals formed in Liquid crystal-Polymer Composites." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/51995372188411920970.
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碩士國立成功大學
物理學系碩博士班
97
This thesis investigates the structures and optical properties of three-dimensional (3-D) photonic crystals and quasi-periodic crystals based on liquid crystal-polymer composites. Experimentally, photonic crystals and quasi-periodic crystals were fabricated holographically using two-beam interference with four and seven exposures, respectively. The structures were studied using scanning electron microscopy, and found to be B.C.T and 7-fold quasicrystal, respectively. The size of droplets is 0.64 μm. For B.C.T, the lattice spacings were 0.796 μm, 0.806 μm, 0.8 μm, and 3.416 μm with errors of 2.1 %, 0.89 %, 1.6 %, and 5.52 % in comparison with theory, respectively. The lattice spacing of quasicrystal was 4.43μm with deviation of 5.14 % with theory. Using a diode pumped solid state laser (DPSS, λ= 532 nm)and a Xe lamp (λ=300~750 nm), we experimented the diffraction patterns from the samples with various incident angles. The results agree well with the simulsted ones obtained using Finite-Difference Time-Domain (FDTD) and Fourier Analyses. Under the application of an AC voltage, the first-order diffraction efficiency decreases, while the zoeoth-order transmission efficiency increases with the voltage. It demonstrates the fact that the fabricated photonic crystals are electrically tunable. Moreover, they possess superprism effect with a maximum dispersion angle ~24°.
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Hsu, Li-Jen, and 許力仁. "Electro-Optical Properties of Polymer-Stabilized Liquid Crystals with Negative Dielectric Anisotropy." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/15715657233604474211.
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碩士中原大學
應用物理研究所
95
In recent years, the polymer and liquid crystal mixtures have been wildly studied. The three-dimensional anchoring force by the polymer network could proved stronger support and improve the electro-optical properties. In this thesis, we mixed a liquid-crystal material possessing negative dielectric anisotropy (岛讨 < 0) with RM-257 (岛讨 < 0) together and fabricated polymer-stabilized liquid crystal cells in the vertically-aligned mode with different monomer contents prepared at distinctive curing voltages. The formation of the network direction could be parallel or perpendicular to the substrates by various applied curing voltages. Therefore, the network could either enhance or weaken the anchoring force by different experimental processes. It was found that one. can control the polymer morphology to suppress the backflow in the LC cell and a qualitative relationship between the backflow suppression and the effective elastic coefficients could be established with a DIMOS simulation software. Furthermore, we fabricated an amorphous polymer-stabilized liquid crystal cell without rubbing the alignment layers. The amorphous cell exhibited a wider viewing angle. Unfortunately, the curing voltage destroyed the viewing angle symmetry.
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Chiu, Ying-Chang, and 邱英彰. "The reflective optical properties of dye guest-host type cholesteric liquid crystals." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/82844523302246086119.
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碩士國立臺灣科技大學
纖維及高分子工程系
90
In this study, we proposed a novel dye mixed cholesteric liquid crystals devices. Experimentally, first, utilizing the nematic liquid crystal with cholesteric liquid crystal, we’ll be able to produce a cholesteric liquid crystal with a reflection wavelength in visible region. We found that the helical pitch of temperature sensitive cholesteric liquid crystal would change with the changing of temperature, and its reflectivity would have obviously changed as well. The reflectivity of cholesteric liquid crystal would not disappear due to the slow temperature rising until approach to isotropic temperature closely. To follow the temperature increase, the reflection wavelength shift to short wavelength region. After that we add dichroic dye to temperature sensitive cholesteric liquid crystal to produce dye guest-host type cholesteric liquid crystal devices. Light entering the liquid crystal is absorbed by the dye generating heat, which raises the temperature of the liquid crystal, the change of temperature caused the shift of reflective wavelength. The effect of temperature on helical pitch and reflective of helical pitch were discussed herein. When the content of dye increases, the wave of reflectivity will change. If add incident light, the wave of reflectivity changes remarkably, too.
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Her, Fung-Gyi, and 何芳吉. "Effect of Chemical Structure on Electro-optical Properties of Ferroelectric Liquid Crystals." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/33926218057033935817.
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Wang, Hung-I., and 王弘毅. "Electro-optical properties of azobenzene-doped smectic C / smectic C* liquid crystals." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/85900514118820483941.
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碩士國立中央大學
光電科學與工程學系
105
Surface-stabilized ferroelectric liquid crystals (SSFLCs) possess their unique characteristics of fast response and bistability. Many scientists have been paying much attention to this research topic in recent decade. Although SSFLCs have the advantages mentioned above, some shortcomings, such as Chevron defect, horizontal defect, and the limitation of small cell gap and uniformity, should be considered. Generally speaking, to obtain the property of bistability, the cell gap of the SSFLC cell is limited to be smaller than 2 m. As a result, the cell fabrication processes are extremely difficult so that the researches in this field gradually decrease. The rotation range in the plane of the LC cell of SSFLC molecules is dependent on the cone angles of the FLCs. According to our experimental results, the cone angle of the FLCs can be modulated by doping azobenzene materials into smectic C / smectic C*, and by illuminating with UV light. Moreover, the stability of azobenzene-doped SSFLCs can be enhanced by illuminating with UV light to get cis-azobenzenes, having relatively high electric dipole moment. To establish the mechanism of the generation of the SSFFLC stability, the electro-optical properties of SSFLCs, prepared by the mixtures of various azobenzenes and smectic C / smectic C*, have been studied before and after been treated with UV illumination. Accordingly, we believe that such a novel approach can improve the developments of the SSFLC in LC technology.
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Tsai, You-Jhe, and 蔡佑哲. "Electro-Optical Properties of Polymer-Dispersed Liquid Crystals Doped with Carbon Nanosolids." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/38423156267948407374.
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碩士中原大學
應用物理研究所
94
Since the refractive index of polymer does not match that of liquid crystals in the polymer dispersed liquid crystal (PDLC) model, a light scattering phenomenon can be obtained in the absence of an electric field. On the contrary, the refractive index of polymer matches that of liquid crystals for a uniform direction of liquid crystals within each droplet in the presence of an electric field, meanwhile, reduction of light scattering can be attained and so the PDLC bulk achieves a transparent state. This promising device can be applied to large and flexible display panels without the need for alignment layers and polarizers. The suitable concentration of prepolymer to liquid crystal is investigated in the relevant literature to possess significant light scattering and then one can observe the electro-optical effect by employing an automatic measurement system (AMS). Experimental results show that the PDLC researched in the present thesis possesses the following characteristics: Firstly, threshold and driving voltage of the PDLC bulk is larger than that of intrinsic LC bulk due to the polymer doping of LC. A reduction of the threshold voltage can be obtained by adding C60 into the PDLC as a dopant. Secondly, if more prepolymer is added into the PDLC for a higher concentration, then a higher sensitivity to the variation of frequency results. The reduction of sensitivity to the variation of frequency can be obtained by adding C60 into the PDLC. Thirdly, PDLC doped with C60 can effectively reduce total response time in comparison with that of pure PDLC. Fourthly, the degradation of the off-axis haze phenomenon can be obtained while the effective refractive index of the PDLC doped with C60 is modified, furthermore, larger domains formed by the curing process relatively reduce the light scattering effect.
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Wen-Hsian, Huang, and 黃文賢. "Electro-Optical Properties of Polymer-Stabilized Liquid Crystals Doped with Carbon Nanotubes." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/21328179029416067474.
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碩士中原大學
應用物理研究所
94
Polymer-stabilized liquid crystal (PSLC) has been extensively studied in recent years. Primarily, the formed polymer branches can stabilize the structure of the liquid-crystal molecules, confining the local domains inside the bulk and increasing the boundary anchoring, thereby improving the electro-optical display performance. To reduce the response time whereas keep the ac driving voltage to be reasonably low, we have consulted the relevant literature for an optimum concentration of prepolymer to LC. Experimental results show that the PSLC investigated in this study possesses the following characteristics: 1. The relaxation time is ca. 1/3 of that of a pristine liquid crystal. 2. The driving voltage with high frequency is greater than that with low frequency. 3. The relaxation time varies with the frequency of ac driving voltage. 4. Carbon nanotubes as a dopant can reduce the driving voltage and relaxation time effectively.
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Sha, Yi-An, and 沙益安. "Design, Synthesis, Electro-Optical Properties and Alignment Phenomenon of Ferroelectric Liquid Crystals." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/88084403049553429454.
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博士國立清華大學
化學工程學系
91
During the past decade, ferroelectric liquid crystals (FLCs) have been extensively studied because of their fast response time and memory effect toward an applied electric field. These characteristics make them suitable for electro-optical applications in liquid crystal display, fast switching devices, light shutter, memory devices and pyroelectric sensors. In this work, we demonstrate two major topics. One is the photo-aligne ferroelectric liquid crystal guest-host system and the other is the halogen containing ferroelectric liquid crystals. (1) Photo-aligned ferroelectric liquid crystal guest-host system For past years, surface stabilized ferroelectric liquid crystal (SSFLC) technology (cell gap < 2μm) was proven to be the effective method to make a high performance display. The uniform FLC display would be achieved because the thinning cell gap could provide a boundary force to unwind FLC molecules. However, this technology is not available for large scale display applications. Due to the thinning cell gap and high viscosity of FLCs, filling FLC into a large scale display would be a serious problem and production yield would be down. To circumvent the drawbacks of few gray scales and shock effect, the polymer stabilized FLC system has been developed. A polymer or network (about 1~10 wt%) was added into the FLC materials, respectively. The thermal stability, gray scales, and anti-shock properties usually increase with increasing polymer/network concentration. Nevertheless, this system was not able to resolve all the drawbacks of FLC display applications. First, the polymer could hinder the alignment and rotation of the FLC molecules. Moreover, the compatibility between the FLC molecules and polymer is still considered a serious problem. These brought about the defects of high driven voltage, low contrast ratio, and slow response, which were the major hurdles toward application. As part of our endeavor to pursue the realization of FLC commercial applications in display, it is important to resolve the aforementioned issues. Photo-alignment technique has been reported previously. This approach provides a novel way to prepare rubbing-free production of LC alignment films through photocrosslink-induced alignment. To expose the poly(vinylcinnamate) thin film under linear polarized ultraviolet light (LPUV), a uniaxial reorientation of LC layer could be induced. This is a facile method to make an alignment layer without any mechanical process. The photochemistry of cinnamates group involves two kinds of photoreactions including the (2+2) photodimerization and E/Z photoisomeization. The LC oriented direction (perpendicular or parallel) to the incident LPUV is dependent on the molecular interaction between the alignment layer and LC molecules. In this work, we present a novel photoalignment process of FLC devices which include the advantages of fast switching, high Ps value, well alignment, thick gap cell, and anti-shock properties. Instead of using photo-crosslinkable poly(vinylcinnamate) as the alignment layer, a guest-host system was used to investigate the photo-induced alignment properties of FLCs. This system was consisted of an FLC monomers and cinnamate group containing materials. Various cinnamate containing materials were synthesized via etherification, esterification, and/ or hydrosilation reactions. To realize the photo-alignment mechanisms, thin films were obtained by casting the guest-host mixture on the CaF2 plate. The alignment properties of the films induced by LPUV were investigated by a polarized FT-IR. Furthermore, these photo-induced alignment phenomenon and the variations of electro-optical properties were also discussed. Via painstaking molecular design, a series of cinnamate containing materials reveal crystal, N, SA, SC*, and/or high order smectic phases. Guest-host systems were prepared by mixing these polymers with an FLC monomer, respectively. A photo-induced anisotropy was achieved via LPUV. The FLC monomer was arranged perpendicular to the incidence angle of LPUV. Distinct domains or zigzag defects were observed by POM after filling these guest-host mixtures into test cells. These domains or defects would gradually disappear upon irradiation by LPUV. This is because the smectic layers could be aligned, unwinded and stabilized by the ordered networks. After irradiating by LPUV, these electro-optical properties would be improved. This is because the ordered cross-type network provided molecular interaction perpendicular to alignment direction that could further speed up the switching rate and promote the reorientation properties of the dipoles under the alternating electric field. It is shown that these FLC guest-host materials could exhibit excellent alignment behavior and electro-optical properties in the thick cell. The limitation on SSFLC technique could be removed by the photo-alignment technique. Moreover, the yield of the large scale display application will be increased due to the feasibility in fabricating thicker cell gap. (2)Halogen containing ferroelectric liquid crystals For FLC display, FLC materials have mostly been designed to provide a wide temperature range of FLC phase including room temperature, and large spontaneous polarization (Ps) value. These properties are influenced by the design of molecular structures of FLC mesogens. The fundamental molecular structure of an FLC includes mesogenic group, spacer chain unit, and chiral center unit (terminal chain units). The mesogenic group often consists of at least two linked rigid groups with lateral substituents. The length and chemical structure of the spacer unit appear to be an important factor in FLC phase formation and temperature range. The oxyethylene unit as the spacer unit favors reducing the phase transition temperatures. As the number of oxyethylene unit increases, the transition temperature decreases. Moreover, the chiral center is usually the major part of the terminal chain due to the fact that the Ps value is affected by the asymmetric atom and its position, and the length of the terminal chain unit. In addition, incorporating a polar group (-F, -Cl, -Br, -CN, CF3, etc) onto the chiral center close to the core can maximize the Ps value . In this work, a new series of ferroelectric liquid crystals and side chain liquid crystalline polymers were developed. These liquid crystalline materials consist of various halogens containing chiral moieties (F, Cl, and Br), oligooxyethylene spacers, and ester core unit. The influences of different halogen containing chiral tails and spacer units on formation of mesophases and electro-optical properties were also discussed. This new series of ferroelectric liquid crystal monomers and polymers exhibit chiral smectic C phase except the bromine group containing homopolymers. Wide temperature ranges of chiral smectic (SC*) phase were obtained in these monomer (~90℃ ) and polymers (~100℃). Several compounds such as the MDn12F and MDn12B (n=1 and 2) exhibited chiral smecitc F phase. When the number of oxyethylene spacer units increased, the clearing and phase transition temperatures decreased. The bromine group containing homopolymers possesses few mesomorphic phases and no chiral smectic C phase due to bulky substituted group of chiral center which disturbs the orientation of the side chain liquid crystal polymer. The dielectric properties of a series of FLCPs with different halogen chiral centers were investigated in this work. The collective and molecular relaxation of these FLCPs were also observed. The dielectric constant was enhanced remarkedly because of the occurrence of the Goldstone mode in the Sc* phase. The Goldstone mode appears in the Ch phase for homopolymers PSn12B (n= 1, 2, and 3) due to the electro-induced phase transition effect. Bulky terminal group was loosening the dense packing and increasing the mobility of the tilted smectic phase under alternative electron field. Furthermore, decreasing the size of the chiral center resulted in an increase in the relaxation intensity and decrease activity energy.
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Li, Min-Shuang, and 李明霜. "Studies on the Synthesis and Electro-Optical Properties of Antiferroelectric Liquid Crystals." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/79650791274350960092.
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碩士國立清華大學
化學工程學系
88
Abstract The purpose of this research work was an attempt to elucidate the structure-property correlations in the chiral smectic liquid crystals, because the exciting results have been obtained the field of study. A homologous series of chiral materials MDn2Nx (n = 1, 2, 3; x = 1b, 2b, 2p, 3p) was designed for the synthesis and investigation of the structure-property relationship in the chiral liquid crystal system. The target compounds were independently modified by the length of the oligo(oxyethylene) chain (n) and terminal chiral alkyl chain (x) for the study. A chiral swallow-tailed compounds MDn2N3p (n = 2, 3) have the same phase sequence: Iso-Ch-SA-SCA*-Cr, suggesting that the extending the oxyethylene repeat unit from n=2 to n=3 oligo(oxyethylene) chain length has no remarkable effect on the formation of tilted smectic phases, compound with shorter oxyethylene chain length(n =1; MD12N3p) have the phase sequence: Iso-Ch-SA-SB-Cr. The thermal analysis shows that as n increases, the clearing point falls, and the SA-SCA* transition temperature decreases, resulting in a suppress of the SA phase stability, the temperature range of SCA* phase are generally increased as the n increased. In addition, The MD32N3p material SCA* phase range can be achieved about 50℃(including room temperature). The optical responses in the SCA* phases have been measured. The thresholdless phenomena are found and characterized in these phases. In addition, the maximal spontaneous polarization value (131 nC/cm2) and fast response time (140 μs) are found in MD22N3p, and also found MD32N3p material have maximal spontaneous polarization value (127 nC/cm2) and fast response time (270μs). The dielectric properties for the compounds MD22N3p and MD32N3p were also measured and two different relaxation processes were obtained and characterized as soft mode in the SA phase, and Goldstone mode in the SCA* phases. The results of dielectric investigations indicate that oligo(oxyethylene) chain length has no remarkably effect on the collective or non-collective molecular motions. On the other hand, the molecular modeling shows a similar result with the experimental X-ray diffraction of smectic liquid crystals to demonstrate the correct AFLC structures. Investigating the effect of terminal chiral alkyl chain (x) on the mesomorphic properties show that the stability of tilted smectic phases and the magnitudes of spontaneous polarization in the SC* phases are enhanced as the introduction of second anchiral methyl substitutent at chiral tail. In addition, the phase sequence for compounds MDn2Nx (n = 1, 2, 3; x = 1b, 2b, 2p) is depended on the oligo(oxyethylene) chain length n. A Iso-SA-SB-Cr sequence was obtained at shorter chain length (n = 1). A Iso-SA-SC*-Cr* sequence was obtained at longer chain length (n = 2 and 3).
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Chen, Jr-Hong, and 陳志宏. "Design, synthesis and electro-optical properties of ferroelectric liquid crystals and side chain liquid crystalline polymers." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/15864895761152596358.
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博士國立清華大學
化學工程研究所
84
The goal of this research is to develop the ferroelectric liquid crystal and ferroelectric liquid crystalline polymers which can exhibit wide chiral smectic C phase range (including room temperature), and excellent electro-optical properties. These FLC/FLCPs'' structures contain the flexible spacer chain, mesogenic group, chiral moiety and polymeric backbone. Several different chiral moieties with 1-3 asymmetric centers on the butyl or heptyl alkyl chains are used. The polymeric backbones are polymethylhydrosiloxane or copolydimethylsiloxane. The electro-optical properties (for example the spontaneous polarization, response time, tilt angle, and dielectric analysis) of FLC/FLCPs were also examined. Results obtained here show that the most suitable liquid crystalline structures for the formation of chiral smectic C phase are those which consist of oligo(oxyethylene) spacer, chiral butyl chain length coupling with three to four phenyl rings of ester mesogenic cores. The Sc* phase range can be achieved about 90.The high spontaneous polarization value and quite fast response time are found in some FLC system with two asymmetric centers on the chiral moiety. Finally, the copolysiloxane as the polymeric backbone is quite helpful for lowering the viscosity and shift the Sc* phase range to room temperature of ferroelectric side chain liquid crystalline polymer system. That is due to the microphase separation of side chain liquid crystalline copolysiloxane. The spontaneous polarization value (~200nC/cm2) and less 1ms response time were also achieved. These materials exhibiting the broad temperature range of Sc* phase and excellent electro- optical properties simultaneously are highly potential for the E-O applications.
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Chen, Li-Jun, and 陳力榮. "Optical Properties of Polymer Dispersive Liquid Crystal." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/83194006508298575643.
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碩士國防大學理工學院
材料科學與工程碩士班
100
In this study, Polytron Technologies Inc. cooperated with us. Uniform resin system that using heat-hardenable epoxy resin and hardener as major components is adopted in this project. Following the process, liquid crystal is mixed with uniform resin system to form uniform solution, which is hardened by PIPS method. As the reaction proceeded, liquid crystal gradually separated out and dispersed in substrate to form PDLC. Influencing factors including epoxy composition, heat-hardening time and temperature can be changed to fabricate five different samples to be analyzed. Change of transmittance is measured by UV/Visible spectrometer under different applied voltage, wavelength, and temperature. Variable temperature system combined with optical path system is used to analyze the refraction index change of ITO coating layer having different area resistance. The capacitance, Cp and dissipation factor, D of the PDLC samples were measured by LCR meter. Using different methods to analyze our experimental data, the activation energy of PDLC samples were determined. It is found out that the result is totally fitted into Arrhenius activation energy and macromolecule viscosity theorem. Finally, electrical and heat treatment are conducted through successive switch on/off and heating to accomplish the reliability analysis. The results indicate that the reliability is fine, and as it possesses the most extraordinary transmittance and sensitivity toward temperature, sample No. 08-HA is probably the most suitable one to be put in mass production.
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WANG, XIU-RU, and 王秀如. "The effect of polymer matrix on the electro-optical properties of polymer dispersed liquid crystals and synthesis of tolane liquid crystals." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/03049143740652287460.
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Jagadish, K. N. "Studies on optical and electrical properties of pure and mixtures of liquid crystals." Thesis, 1998. http://hdl.handle.net/2009/1483.
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Cheng-Feng, Tang, and 唐振峰. "Synthesis of Achiral liquid crystals and the Electro-optical Properties in Binary Mixtures." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/23626629174938832889.
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碩士國立臺灣科技大學
高分子工程系
92
Two different structural achiral liquid crystals [2-methyle- thyl4-(4-decyloxy- biphenyl-4-carbonyloxy)benzoate] ,h ;[2-methylethyl4-(4’-decyloxybiphenyl-4-carbonyloxy)-3-fluorobenzoate], f had been synthesized. Utilized melting point apparatus and 1H-NMR to make sure molecular structure and all the final products were further confirmed with 13C-NMR and element analysis(EA). Polarizing microscope was used to observe texture of the mesophases and DSC was used to find out phase transition temperature. The study of electro-optical behavior for the binary mixture indicated that the electro-optical behavior critically depended on the mixture ratio, frequency, and temperature.
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Liao, Chien-Tung, and 廖健同. "Design, Synthesis, Characterization and Electro-Optical Properties of Ferroelectric and Antiferroelectric Liquid Crystals." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/38x72a.
Full textAbstract:
博士國立臺灣科技大學
材料科學與工程系
99
A series of novel liquid crystals containing different shapes and mesogenic groups was designed and synthesized by attaching different types of mesogenic units, terminal chiral and achiral segments to investigate the structure-property relation of liquid crystals and the electro-optical properties. The structures of the synthesized compounds were identified using 1H-NMR, MASS, and elemental analyses. The thermal properties of these compounds were analyzed using DSC, X-ray and POM. The electro-optical properties of the compounds, such as tilt angle, V-T curve, dielectric permittivity and switching behavior were also measured. The research work was carried out in two parts. In Part I, two series of rod shaped ferroelectric liquid crystals were synthesized. In the series I, the ferroelectric liquid crystals that have a 4'-hydroxybiphenyl-4-yl 4-hydroxybenzoate core 、a chiral butyl 2-hydroxypropanoate unit and an oligomeric siloxane end-group were synthesized, and the mesophases exhibited were compared. We examined the influence of the addition of a trisiloxane end-group on one side-chain of an achiral alkyl chain on the phase transition. In the series II, we report the synthesis and characterization of new ferroelectric liquid crystal material which have a 4-hydroxyphenyl 4'-hydroxybiphenyl-4-carboxylate core 、a chiral octan-2-ol unit and an oligomeric siloxane end-group. We examined the influence of the addition of different length of siloxane and achiral alkyl chain in the end-group on the phase transition. The target compounds with large tilt angle and wide temperature range of SmC* phase were also measured. In part II, two series of bend shaped antiferroelectric liquid crystals were synthesized. In series I, the series bent-core materials were based on a 3,4′-biphenyldiol central core containing salicylaldimine-based and two terminal tetradecyloxy tails. In addition, the effects of lateral substituents (R = F and Cl) at the biphenyl core into 3′-position were examined. These substituents have a strong influence in reducing the clearing temperatures and increasing temperature range of SmCP phase. In series II and III, the bent-shaped mesogens have been synthesised and their mesomorphic properties studied. We examined some novel series of bent-core compounds containing 3,4′-positions of a diphenol ring as the central unit with the side wings containing a cinnamoyloxy group and a methyl cinnamoyloxy group. We have to investigated the relation between the structure and the mesomorphic properties. Besides, we added the halogen (F and Cl) in 3′-position of the diphenol, and researched the effect in the mesomorphic properties. In conclusion, the molecules are then developed large amount of ferroelectric liquid crystals, and subsequently, the structure-property correlation for the formation of ferroelectric liquid crystals is established. The establishment of this correction will be beneficial for the future design and synthesis of more ferroelectric liquid crystals. A large amount of ferroelectric liquid crystals developed in the present work demonstrates that there is a potential for the preparation of suitable ferroelectric mixtures for the display devices.
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Pang, Chin-Poh, and 彭進寶. "Linear and Nonlinear Optical Properties of Soft Matters: Liquid Crystals, Ferrofluids and Liquids Suspended with Silica Microspheres." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/31575744926971333823.
Full textAbstract:
博士國立清華大學
物理學系
93
Assisted with Monte Carlo simulation, linear optical properties of soft matters such as liquid crystals, ferrofluids and liquids suspended with silica microspheres were investigated by transmittance, Faraday rotation and attenuated total reflection by exciting surface plasmons resonance. The microscopic structure of a thin liquid crystal film embedded between two glass plates when applying with electric fields was studied by the grand-canonical-ensemble Monte Carlo simulation. The time duration to reach the equilibrium state is successfully verified from the direct experimental measurement of light transmissions. The Kretschmann–Raether and the Otto configurations are implemented to generate surface plasmons and to examine the change of the refractive index of liquid crystals (LCs) by an applied field. The change of the minimum ATR angles does not agree with the calculation based on field-induced refractive-index change suggesting that the orientation of LC molecules adjacent to an electrode surface is unaffected by the external field because of the strong-anchoring effect. The aggregation and rearrangement of nanoparticles embedded in a thin cell of ferrofluid at various applied magnetic fields was studied by Monte Carlo simulation. Our model successfully simulate the reported experimental results by which the column size decreases as the ramp speed increases, implying that the time to arrive the final assembling state diminishes for a given final magnetic field. Physical parameters such as dielectric constant and susceptibility of dilute Fe3O4 ferrofluids derived directly from ATR and ferromagnetic resonance, respectively, were exploited to delineate the corresponding Faraday rotation angles with respect to the applied magnetic fields. Theoretical estimation was compared with experimental measurements ensuring that the effective medium theory is admittedly correct. Finally, the linear refractive indices of hydrated and dehydrated silica micro-spheres were studied under Kretschmann configuration to excite surface plasmons (SP), while the nonlinear second-order susceptibility was measured in direct transmission. An inconspicuous change for the case of dehydrated silica spheres is expected to be due to the small electro-optic (Pockels) effect, which is measured to have a linear electro-optic coefficients of . The SHG emission comes from the third-order susceptibility , which is a coupling of two photons and the electrostatic field induced by the surface –OH charges as characterized by the Gouy-Chapman model. The vanishing of SH signal from the dehydrated silica results from the loss of -OH group on the particle surfaces. Optical properties of dried silica spheres do not recover to its original hydrated state when pure water is refilled.
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楊世斌. "Study the synthesis of ester system ferroelectric liquid crystals and their electro-optical properties." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/73105932132613991405.
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