| 1. |
- Alexe-Ionescu, Anca-Luiza, et al.
(författare)
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Anchoring of nematic liquid crystals on a thin polymeric film
- 2008
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Ingår i: PHYSICAL REVIEW E. - 1539-3755. ; 77
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the influence of a thin polymer layer with lateral side groups on the anchoring of a nematic liquid crystal. We show that the effective anisotropic part of the anchoring energy depends on the coupling of the nematic with the polymer side groups, as well as on the coupling of the polymer side groups with the surface. The relaxation time for the nematic orientation induced by an external field is evaluated by considering the surface dissipation connected to the relative motion of the nematic director with respect to the polymer side groups.
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| 2. |
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| 3. |
- Barbero, Giovanni, et al.
(författare)
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Continuum description of the interfacial layer of nematic liquid crystals in contact with solid surfaces
- 2009
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Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- We investigate when it is possible to introduce surface physical parameters characterizing the nematic/substrate interface. The analysis is performed by solving the problem assuming that the presence of the surface introduces a spatial variation, mainly localized close to the limiting surfaces, of the bulk properties of the nematic (delocalized model). The results of the calculation are compared to the prediction of a model in which the presence of the surface is taken into account by means of new physical parameters, localized to the surface (localized model). We show that if the viscous dissipative effects or the surface alignment effects are considered, the two models predict the same relaxation times and the same threshold for the Freedericksz transition is obtained. From these results we deduce that the localized models are equivalent to the delocalized ones. A continuum description of the interfacial layer of nematic liquid crystals in contact with solid surface in terms of surface properties is then correct, which makes the solution of this kind of problems simpler. Also a softening of the elastic constants near the surfaces can be represented by a localized surface energy term.
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| 4. |
- Barbero, Giovanni, et al.
(författare)
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Nonmonotonic behavior of the nematic tilt angle in a temperature-induced surface transition
- 2008
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Ingår i: PHYSICAL REVIEW E. ; 77
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Tidskriftsartikel (refereegranskat)abstract
- We report on a nonmonotonic temperature behavior of the pretilt in cells containing polymers as alignment layers. The latter are very promising since they enable control of the anchoring of the liquid crystal. We show that such a behavior cannot be interpreted by the standard Landau or mean-field theory. We propose a generalization of the mean-field model, including the temperature dependence of the anchoring due to the polymer layer that enables a description of the nonlinear behavior. The agreement between the predictions of the model and the experimental data is good.
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| 5. |
- Barbero, Giovanni, et al.
(författare)
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Temperature-induced tilt transition in the nematic phase of liquid crystal
- 2009
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105
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Tidskriftsartikel (refereegranskat)abstract
- A temperature-induced transition from homeotropic to tilted alignment in the nematic phase of a liquid crystal with smectic C-nematic phase sequence was observed. The homeotropic alignment of the nematic phase at temperatures near the nematic-isotropic transition was found to undergo a continuous change to tilted one on decreasing the temperature. The appearance of smectic-C-like order at the solid surface on approaching the smectic C-nematic transition is assumed to be the origin of this temperature-induced alignment transition.
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| 6. |
- Bubnov, Alexej, et al.
(författare)
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Polar liquid crystalline monomers with two or three lactate groups for the preparation of side chain polysiloxanes
- 2006
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 0267-8292 .- 1366-5855. ; 33:5, s. 559-566
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Tidskriftsartikel (refereegranskat)abstract
- Two new chiral liquid crystalline monomers with bilactate or trilactate chiral units were synthesized and studied. The monomers show the paraelectric SmA and ferroelectric SmC* phases. The antiferroelectric phase was detected only for the monomer possessing the bilactate unit. The temperature dependences of the spontaneous polarization and spontaneous tilt angle were measured. Real and imaginary parts of the complex permittivity were studied as a function of frequency and temperature. The synthesized monomers contain a double bond at the end of the achiral terminal chain, and were used to prepare liquid crystalline polysiloxanes.
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| 7. |
- Drevensek-Olenik, I., et al.
(författare)
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Ferroelectric switching of electrically commanded alignment layers for liquid crystal displays
- 2006
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Ingår i: J.Appl.Phys.. - : AIP Publishing. - 0021-8979. ; 100
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Tidskriftsartikel (refereegranskat)abstract
- Optical second harmonic generation (SHG) was used to probe the structural and dynamic properties of electrically commanded alignment layers for liquid crystal displays. The layers were 200 nm thick and were made of siloxane-based side chain ferroelectric liquid crystal polymer (FLCP). The effect of an external dc electric field in the range of 0–2 V/µm on the SHG signal was probed in an empty sandwich cell and in a cell filled with an isotropic liquid (hexadecane). In both cases the nonlinear induced polarization shows characteristics of the "V-shaped" switching, which is associated with a relatively minor reorientational perturbation of the film. This signifies a presence of domain structure, which is strongly pinned to the substrates. The values of switching times deduced from the SHG response are two orders of magnitude larger from the values obtained by optical birefringence measurements. This observation suggests that in the top surface layer of the FLCP, which is mainly responsible for the birefringence and also for the so-called electrically commanded surface effect, the reorientation of the polymer side chains takes place much faster than in the regions close to the substrate. ©2006 American Institute of Physics
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| 8. |
- Helgee, Bertil, et al.
(författare)
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Liquid crystal device and its manufacture
- 2005
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- The invention relates to a liq. crystal device comprising a liq. crystal bulk layer and a dynamic surface-director alignment layer, wherein the liq. crystal bulk layer comprises a liq. cryst. material possessing a phase sequence consisting of isotropic phase, nematic phase and optionally cryst. phase (s), and the surface-director alignment layer comprises a chiral smectic liq. cryst. polysiloxane. The invention also relates to a method for its manufg.
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| 9. |
- Hu, Qui-Hong, et al.
(författare)
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Field emission display with ZnO-nanostructures
- 2009
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention relates to a method for the manufg. of a field-emission display, comprising the steps of arranging an electron-emission receptor in an evacuated chamber, arranging a wavelength converting material in the vicinity of the electron-emission receptor, and arranging an electron-emission source in the evacuated chamber, the electron-emission source adapted to emit electrons towards the electron-emission receptor, wherein the electron-emission source is formed by providing a substrate, forming a plurality of ZnO-nanostructures on the substrate, wherein the ZnO-nanostructures each have a first end and a second end, and the first end is connected to the substrate, arranging an elec. insulation to elec. insulate the ZnO-nanostructures from each other, connecting an elec. conductive member to the second end of a selection of the ZnO-nanostructures, arranging a support structure onto of the elec. conductive member, and removing the substrate, thereby exposing the first end of the ZnO-nanostructures. Advantages with the invention include for example increased lifetime of the field-emission display as there will be a smaller sections of the nanostructures that will be non-height-aligned. Furthermore, by not having to height align the nanostructures using an expensive etching, grinding, or similar method step, it is possible to achieve a less expensive end product. The present invention also relates to a corresponding field-emission display.
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| 10. |
- Kim, Sang Hwa, et al.
(författare)
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Effects of polymer concentration and localization on the electro-optical performance of cholesteric flexoelectro-optical devices
- 2005
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Ingår i: Proceedings of the SPIE. - 0277-786X. ; 5741, s. 15-22
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Tidskriftsartikel (refereegranskat)abstract
- We discussed the effect of polymer concentration and localization on flexoelectro-optical device using short pitch cholesterics oriented in uniform lying helix texture. By using a small concentration of photoreactive liquid crystal monomer with various concentrations and selecting the illumination conditions, we have been able to create a localized polymeric network at both substrate surfaces. We can stabilized the two switching modes and eliminating at the same time the effect of the residual birefringence of the polymeric network in the field-unwound state of the sample. The device has two operating modes: amplitude and phase modulation mode, respectively. The amplitude modulation mode is a fast in-plane switching of the device optic axis that enables to achieve a 100 % modulation of the transmitted light intensity whereas the phase mode gives a continuous change of the refractive index and thus of the phase shift of the transmitted light.
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