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Synthesis of New Dibenzo[a,c]phenazine Discotic Liquid Crystal (IV)Chen, Wei-jen 10 August 2011 (has links)
We take 5,6,11,12,17,18-hexaaztrinaphthylene and dibenzo[a,c]phenazine as our central core that with dove-tailed side chains. It is shown that the size-related increase of steric interactions among the peripheral side chains substituted to the aromatic core leads to a dramatically lowered isotropization temperature.
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Design and Synthesis of the Discotic Liquid Crystalline Materials for Controlling Mesomorphic Behaviors and Supramolecular AssemblyYeh, Ming-che 16 November 2012 (has links)
Discotic liquid crystals (DLC) have been reported with a large number of discoid cores to improve the degree of intermolecular ordering because the liquid crystals own to self-assembly into columnar stacking and self¡Vhealing ability. In my research, a series of disc-like £k-conjugated molecules based on aromatic rigid cores have been newly synthesized. I focus on the hexaazatrinaphthylene (HATN) and dibenzo-[a,c]- phenazine as aromatic cores, changing different side chains to control the mesomorphic behavior and their supermolecular assembly.
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The Study of Laser-Induced Molecular Reorientation and the Enhancement of Nonlinearity of Dye in the Isotropic Phase of Guest-Host Dye-Doped Liquid CrystalHo, Chen-wei 29 January 2004 (has links)
The laser-induced molecular reorientation effect of guest-host dye-doped liquid crystals in isotropic phase has been studied by measuring the signals of optical Kerr effect using pulsed frequency-doubling Nd:YAG laser as a pumping source. The critical behavior near the isotropic-nematic transition has been observed when the temperature approaches to the phase transition of liquid crystal. The relaxation time constant is about several hundreds of ns as the temperature is far above the clearing point of liquid crystals and that is longer than 1500 ns as the temperature is close to the clearing point of liquid crystals.
According to Landau¡¦s second phase transition theory, the interaction between liquid crystal molecules will be increased and the nonlinearity effect of liquid crystal will be enhanced when the temperature is near the clearing point of liquid crystal. The relaxation time constant of molecular reorientation is a function of viscosity and temperature of liquid crystal, the relationship can be fitted as£b0*exp(f/T)*(1/T-T*),where £b0 is the viscosity coefficient and T* is the clearing point of the sample.
The optical Kerr signal is found to be proportional to the energy density of pumping source. The optical Kerr signal can be sustained as long as 20£gs when the energy density of pumping source reaches to 1J/cm sq. The enhancement of molecular reorientation effect is also observed by increasing the concentration of dye.
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Photo-alignment Effect in Liquid Crystal Film Doped with Nanoparticles and Azo-dyeChen, Wen-zheng 18 July 2009 (has links)
This work discusses the effect of photo-alignment in a liquid-crystal
film that is doped with nanoparticles and azo-dye. The vertical alignment
that is induced by nanoparticles of polyhedral oligomeric silsesquioxanes
can be changed into homogeneous alignment by the absorption of
photo-excited azo-dye. Both electro-optical and surface properties are
analyzed to confirm this phenomenon. An electrically tunable
polarization-dependent LC phase grating is produced using the method.
By this method, we also present a transflective liquid crystal display
with a single cell-gap in a dual-alignment configuration. This dual
structure was fabricated via a single-step laser-light exposure through a
photomask. The vertical alignment induced by nanoparticles of
polyhedral oligomeric silsesquioxanes can be changed into a
homogeneous alignment via absorption of photo-excited azo dye. The LC
molecules at the transmissive and reflective pixels are homogeneous and
hybrid alignment, respectively, at which optimal phase retardations of
half and quarter wavelengths are achieved.
Both nanoparticle- and azo-dye-induced vertical and homogeneous
alignments are non-contact alignment processes and have potential for
practical application.
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Obtenció de LCT's a partir de reïnes epoxi cristall líquid amb estructura de dímerRibera Ruiz, David 17 December 2002 (has links)
El present treball té com objectiu l'obtenció de materials entrecreuats conservant una mesofase cristall líquid fixada, comunment denominats LCTs. La majoria de LCTs s'obtenen per entrecreuament de reïnes epoxi cristall líquid amb amines aromàtiques primàries. L'entrecreuament dins de la mesofase porta a materials amb un menor coeficient d'expansió tèrmica i en alguns casos amb un augment considerable del mòdul d'emmagatzematge. L'orientació dels LCTs per entrecreuament dins d'un camp magnètic porta a materials anisòtrops amb una millora de les propietats mecàniques en la direcció del camp aplicat. En aquest cas, s'han sintetitzat sis sèries de monòmers diepoxídics mesomorfs amb estructura de dímer i que contenen un grup imina dins la unitat mesogènica. S'ha estudiat la influència de la diferent llargària de l'espaciador central i la incorporació de grups èter i èster als extrems del mesògen en el comportament mesomorf. L'estudi de les característiques de cristall líquid s'han caracteritzat mitjançant calorimetria diferncial d'escombrat, microscopia òptica de llum polaritzada i difracció de raigs X. A més d'aquestes tècniques, s'han caracteritzat les propietats mecàniques dels LCTs obtinguts mitjançant anàlisi termodinamomecànica. Dues de les sèries han mostrat mesofases esmèctiques i la resta únicament una mesofase nemàtica. Els resultats obtinguts confirmen la importància de la polaritat del mesogen i de la posició del grup ester entre l'espaciador central i els mesògens per a la formació de mesofases esmèctiques.S'han obtingut LCTs a partir de l'entrecreuament d'aquest monòmers amb cantitats estequiomètriques de 2,4-diaminotoluè, 4,4'-aminoacetofenona azina, i 2,4-toluendiisocianat sol i catalitzat per 4-N,N-dimetilaminopiridina. També s'han obtingut LCTs per entrecreuament amb 4-N,Ndimetilaminopiridina i diazabiciclo[2,2,2]octà en quantitats catalítiques. Els LCTs obtinguts s'han caracterizat per fixar majoritàriament ordenacions nemàtiques i en alguns casos ordenacions esmèctiques C. En els LCTs obtinguts s'ha posat de manifest la importància de la polaritat del mesogen per l'obtenció de LCTs i de la posició del grup ester entre l'espaciador central i els mesògens per a la formació de LCTs amb ordenacions esmèctiques.S'han estudiat les propietats mecàniques dels LCTs entrecreuats amb 2,4-diaminotoluè, 4-N,N-dimetilaminopiridina i diazabiciclo[2,2,2]octà. S'han comparat tres tipus diferents de materials, materials isòtrops, orientats en microdominis i materials macroscòpicament orientats. S'han obtingut graus d'orientació petits, tot i que els materials orientats van mostrar anisotropia en el coeficient d'expansió tèrmica.Obtention of LCTs from liquid crystal epoxy resins with dimeric structure. / The search for new materials with unusual mechanical and thermal properties led to research into liquid crystalline thermosets (LCT's). LC epoxies are the monomers that have been most frequently studied to obtain LCT's. If the crosslinking is carried out in the mesophase, the LCTs obtained have unusual mechanical and thermal properties, low shrinkage upon cure, low thermal expansion coefficients, low dielectric constants and enhanced reaction rates because the ordered structures mean that the reacting groups are close to one another. Several publications describe the physical properties of oriented and unoriented LCT's. Macroscopically oriented LCTs obtained by curing in the mesomorphic state inside a magnetic field led to thermal expansion coefficient and storage modulus having anisotropic characteristics. Thus, the thermal expansion coefficient of macroscopically oriented materials must be lower than that of unoriented materials and the storage modulus must be expected to increase considerably in the direction of the orientation. I have synthesized six series of liquid-crystalline epoxy resins with aromatic azomethine groups and dimeric architecture, and varied the length of the alkyl spacer. The liquid crystal behaviour of these dimeric glycidylic compounds was studied by diferential scanning calorimetry (DSC), hot stage polarized optical microscopy (POM) and X-Ray Diffraction (WAXS). Two series of them show smectic mesophases and the other show nematic mesophase. From the results we have confirmed the importance of the polarization of the mesogenic groups and the presence of an ester group in the inner position in the formation of smectic mesophases.I obtained LCT's from these monomers by isothermal curing with equimolecular amounts of 2,4-diaminotoluene, 4,4'-aminoacetophenone azine, and 2-4-toluendiisocyanate alone and catalized with 4-N,N-dimethylaminopyridine. Another LCT's have obtained by isothermal curing with catalytic amounts of 4-N,N-dimethylaminopyridine or diazabicicle[2,2,2]octane. By curing these monomers with primary and tertiary amines we make clear the polarization of the mesogenic groups and the presence of an ester group in the inner position are also determinant to obtain LCTs with a different degree of order. Most monomers produced nematic-like networks, but in one case smectic C mesophase was also locked.Finally, the mechanical characterization of the LCTs obtained by curing with 2,4-diaminotoluene, 4-N,N-dimethylaminopyridine and diazabicicle[2,2,2]octane was studied by thermodinamicmechanical analysis. The orientation experiments were made by conducting the curing in the same conditions in a NMR probe with a magnetic field of 7.1 T. I compare isotropic materials, LCTs and LCTs obtained inside a magnetic field. Low orientation degrees have led. Macroscopically oriented
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Direct Mechanical Observation of Surface Anchoring and Disclinations Using Dynamically Reconfigurable Liquid Crystal CellAngelo, Joseph S., Angelo 30 July 2018 (has links)
No description available.
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Engineering the Uniform Lying Helical Structure in Chiral Nematic Liquid Crystal Phase: From Morphology Transition to Dimension ControlJia, Zhixuan 05 1900 (has links)
Chiral nematic liquid crystals or cholesteric liquid crystals (CLC) can be obtained by adding a chiral dopant into a nematic liquid crystal. Liquid crystal molecules spontaneously rotate along a long axis to form helical structures in CLC system. Both pitch size and orientation of the helical structure is determined by the boundary conditions and can be further tuned by external stimuli. Particularly, the uniform lying helical structure of CLC has attracted intensive attention due to its beam steering and diffraction abilities. Up to now, studies have worked on controlling the in-plane orientation of lying helix through surface rubbing and external stimuli. However, it remains challenging to achieve steady and uniform lying helical structure due to its higher energy, comparing with other helical configurations. Here, by varying the surface anchoring, uniform lying helical structure with long-range order is achieved as thermodynamically stable state without external support. Poly (6-(4-methoxy-azobenzene-4'-oxy) hexyl methacrylate) (PMMAZO), a liquid crystalline polymer, is deposited onto the silicon substrate to fine-tune the surface anchoring. By changing the grafting density of PMMAZO, both pitch size and orientation of lying helical structure are precisely controlled. As the grafting density increases, the enhanced titled deformation of helical structure suppresses the pitch size of CLC at the same cell thickness; as the cell thickness increases, the morphology transition from long-range order stripe to small fingerprint domain is facilitated.
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Wavelength Tunable Devices Based on Holographic Polymer Dispersed Liquid CrystalsZhang, Hailiang 29 February 2008 (has links)
No description available.
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Chirality in liquid crystals - from bent-cores to chromonicsBergquist, Leah Elaine 01 December 2017 (has links)
No description available.
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WAVEGUIDE LIQUID CRYSTAL DISPLAYS AND OPTICAL DIFFRACTION GRATING BASED ON FLEXOELECTRIC LIQUID CRYSTALS AND POLYMER STABILIZED LIQUID CRYSTALSShin, Yunho 24 April 2023 (has links)
No description available.
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