| 1. |
- Ata Alla, Rasha Mohamed, et al.
(författare)
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Light-control of liquid crystal alignment from vertical to planar
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:23
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Tidskriftsartikel (refereegranskat)abstract
- Continuous or discontinuous transition from vertical to planar alignment was found in nematic cells, containing polyimide alignment layer exposed to linear polarized UV light, depending on whether the alignment layer was mechanically rubbed or not prior the illumination. The polyimide material is designed originally to promote vertical alignment when deposited onto the inner cell substrates' surface. The mechanism behind these observations is complicated. It includes inclination of the alkyl side chains of the polyimide alignment layer towards the rubbing direction and the bond breaking process due to UV illumination which are considered as the key factors for occurrence of such alignment transition.
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| 2. |
- Elamain, Omaima Abubakr, et al.
(författare)
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Field-induced optically isotropic state in bent core nematic liquid crystals: unambiguous proof of field-induced optical biaxiality
- 2013
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Ingår i: Journal of Physics D-Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 46:45
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Tidskriftsartikel (refereegranskat)abstract
- The behaviour of bent core (BC) nematic liquid crystals was investigated under dc applied electric field. The optically isotropic state of a sample containing BC nematic was observed under application of low dc electric fields. The quality of the dark state when the sample was inserted between two crossed polarizers was found to be superb and it did not change when rotating the sample between the polarizers. The coupling between the net molecular dipole moment and the applied dc electric field was considered as the origin of the out-of-plane switching of the BC molecules resulting in switching from the field-off bright state to the field-on dark state. The field-induced optically isotropic state is an unambiguous proof of the field-induced biaxiality in the BC nematic liquid crystal. A simple model explaining the appearance of the isotropic optical state in BC nematics and the switching of the sample slow axis between three mutually orthogonal directions under dc applied electric field is proposed.
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| 3. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Azo containing thiophene based prop-2-enoates for photoalignment of a nematic liquid crystal
- 2013
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 1:22, s. 3600-3605
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Tidskriftsartikel (refereegranskat)abstract
- The ability of suitably derived prop-2-enoates from 3-(thiophen-2-yl)- and 3-(thiophen-3-yl)-prop-2-enoic acid and appropriately fluorinated and non-fluorinated 4-[(4-alkoxyphenyl)diazenyl]phenols to promote excellent photoalignment of a bulk commercial nematic liquid crystal is reported. The performed study showed that the photoalignment of the liquid crystal is influenced by the number and disposition of fluoro-substituents and the position of attachment of the terminal thiophene moiety, either 2- or 3-substituted, in the molecular structure of the alignment material. Inclusion of a lateral fluoro-substituent(s) induces an excellent photoalignment whereas the non-fluorinated counterpart tends to give an unsatisfactory alignment. 3-Substituted thiophenes give a better photoalignment than their 2-substituted isomeric counterparts. A prototype display, which contains an alignment layer made from one of the proposed materials, possessing good alignment ability, is presented in order to demonstrate the application potential of these materials in LCDs.
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| 4. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Dual Frequency Addressable Optical Device
- 2005
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Ingår i: Journal of Applied Physics. - 1089-7550. ; 97:9
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Tidskriftsartikel (refereegranskat)abstract
- We propose a photonic switch employing a liquid-crystalline material. The material exhibits a change in the sign of the dielectric anisotropy switching from a positive to a negative value at a certain crossover frequency. By application of an electric field this phenomenon can be used to alter the orientation of the sample between two orthogonal directions leading to a large change in the optical transmission characteristics of the medium. Here we demonstrate that this feature can be realized by an unpolarized ultraviolet UV beam, owing to the photoisomerization of the constituent azobenzene molecules. Possible usage of this for optically driven display devices and image-storage applications are suggested.
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| 5. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Dynamic Self-Assembly of the Liquid Crystalline Smectic-A Phase
- 2005
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Ingår i: Advanced Materials. - 1521-4095. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- A photoinduced transition in an azobenzene-containing liquid crystal leads to a phase that does not exist in the thermal cycle. The smectic A phase is induced and stabilized only in the presence of UV light, producing fan-shaped focal conic textures typical of the SmA phase, as observed by polarized-light microscopy (see Figure). This dynamic self-assembly is explained by photoinduced nanophase segregation and a frustrated spin-gas model.
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| 6. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Electrically Controlled Birefringence Colors in Deformed Ferroelectric Liquid Crystals
- 2008
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Ingår i: Liquid Crystals. - 0267-8292. ; 35:9
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Tidskriftsartikel (refereegranskat)abstract
- A short helix pitch (p050.45 mm) ferroelectric liquid crystal (FLC) mixture was found to provide four electrically switched birefringence colours: blue, green, yellow and red. The contrast ratios of the birefringence colours were measured as functions of both driving voltage amplitude and frequency. The FLC mixture, which had a relatively high birefringence, Dn>0.2, was controlled by a voltage less than 5V. A simple model is proposed, which was confirmed by experiments. A possible application is discussed in field-sequential colour displays, where fast switching times are required.
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| 7. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Electrically controlled birefringent colors of Smectic C* Deformed Helix Ferroelectric Liquid
- 2008
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Ingår i: Ferroelectrics. - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 365
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Konferensbidrag (refereegranskat)abstract
- Short helix pitch (p0 = 0.45 μm) ferroelectric liquid crystal (FLC) mixture possessing high birefringenc under the action of applied voltage not more than 5 V provides four electrically switched birefringent colors: blue, green, yellow and red, while before only two [1] or three [2] colors were switched. Contrast ratio of birefringence colors were measured dependently on the driving voltage frequency. A possible application in field sequential color display where fast switching time is required has been proposed.
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| 8. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Electrooptical modes of ferroelectric liquid crystal display based on bi-and multistability
- 2007
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Ingår i: Euro Display. ; S11:1
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Konferensbidrag (refereegranskat)abstract
- The multistability effect exists under certain conditions in ferroelectric liquid crystal display cells (FLCDC) that means memorization of any light transmission level after the driving voltage switching off. This effect is responsible for three new electrooptical modes with continuous, memorized and reversible gray scale. The modes differ among themselves under the shape of the gray scale curve that can be either S (double or single) or V-shaped dependently on boundary conditions and crystallooptical parameters of the cell. Origin of these modes is under consideration.
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| 9. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Evidence of Worm-like micellar behavior in Chromonic liquid Crystals: Rheological, X-ray
- 2007
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Ingår i: J.Phys.Chem.B. ; 111:33
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Tidskriftsartikel (refereegranskat)abstract
- We report rheological, X-ray, and dielectric investigations on a chromonic liquid-crystalline system formed by aqueous solutions of a food coloring agent, Sunset Yellow, in the absence and upon addition of salt. The salt-concentration dependence of the steady-state viscosity at low shear rates has a non-monotonic variation and is qualitatively similar to the behavior seen in wormlike micellar systems, a surprising result since chromonic systems are expected to be non-micellar in character. More interestingly, for a particular low concentration of the salt (20 mM), the viscosity increases by 3 orders of magnitude in comparison with that of the pure chromonic material. The dynamic (oscillatory) rheological data bring out features which can be described in terms of a microstructure formation. X-ray and dielectric studies show that certain characters of the aggregates formed by the Sunset Yellow molecules are not altered by the addition of salt.
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| 10. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Fast liquid crystal light shutter with polymer stabilisation
- 2021
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Ingår i: Journal of Physics D-Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 54:42
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Tidskriftsartikel (refereegranskat)abstract
- We present a fast-switching liquid crystal device comprising fringe field switching (FFS) electrode structure deposited onto one of the device substrates. Initially, the liquid crystal in the device has a homeotropic alignment. The generated periodic electric field by the FFS electrode results in a periodic splay/bend elastic deformation, thus giving rise to flexoelectric polarization along the substrate normal. At low applied voltages, this periodic elastic deformation, is substantially localized in a very thin portion of the liquid crystal layer adjacent to the substrate surface bearing the electrode and it is stabilized by a polymer network. Thus, the flexoelectric polarization becomes permanently present in the device and has non-zero value at field-off state. The polymer network with splay/bend configuration occupies very small part of the liquid crystal layer (similar to 0.5 mu m), which is thinner than the light wavelength and therefore is optically invisible. Simultaneously with the formation of the polymer network, possessing splay/bend configuration, a polymer network with polymeric bundles oriented preferably along the substrates' normal is formed. As we will show, the presence of the polymer network, consisting of surface and bulk parts, reduces substantially the switching times of the liquid crystal device more than one order bringing them to mu s range.
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