| 1. |
- 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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| 2. |
- Cifelli, M., et al.
(författare)
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The twist-bend nematic phase : translational self-diffusion and biaxiality studied by H-1 nuclear magnetic resonance diffusometry
- 2017
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Ingår i: Liquid crystals (Print). - : TAYLOR & FRANCIS LTD. - 0267-8292 .- 1366-5855. ; 44:1, s. 204-218
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Tidskriftsartikel (refereegranskat)abstract
- Recently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (N-TB) phase that is shown to be chiral even though formed by effectively achiral molecules. Although it now seems to be clear that the N-TB phase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the N-TB phase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1 '',7 ''-bis-4-(4'-cyanobiphenyl-4'-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase. [GRAPHICS] .
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| 3. |
- Dvinskikh, Sergey, V
(författare)
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Nuclear magnetic resonance studies of translational diffusion in thermotropic ionic liquid crystals
- 2020
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Ingår i: Liquid crystals (Print). - : Taylor & Francis. - 0267-8292 .- 1366-5855. ; 47:13, s. 1975-1985
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Tidskriftsartikel (refereegranskat)abstract
- The NMR methodologies employed for investigating translational diffusion in anisotropic fluids and the results of their applications to ionic liquid crystals are reviewed. Experiments on ionic liquid crystals are preferably performed using oriented samples and require magnetic field gradients in orthogonal directions. Diffusion experiments in anisotropic systems with broad NMR lines are performed using line narrowing techniques and by application of strong static or pulsed field gradients for efficient gradient encoding/decoding of the spatial locations of molecules. Self-diffusion studies on various thermotropic ion-conductive materials exhibiting smectic, cubic, and columnar phases have been reported. Diffusion rates and anisotropy characterise the translational dynamics of ions in nanostructures and reflect the molecular ordering and ion pairing/dissociation processes. Distinct diffusion behaviours were observed for cations and anions. The knowledge of molecular mobility in ionic liquid crystals is important for the understanding their dynamic properties and is, therefore, valuable for the development of anisotropic soft materials for ion transport.
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| 4. |
- Hanczyc, Piotr, 1985, et al.
(författare)
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Spontaneous formation of liquid crystalline phases and phase transitions in highly concentrated plasmid DNA
- 2011
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 1366-5855 .- 0267-8292. ; 38:4, s. 461-468
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Tidskriftsartikel (refereegranskat)abstract
- The liquid crystalline (LC) properties of two supercoiled plasmid DNA samples, pBSK (2958 bp) and pGEM (3000 bp), have been studied using polarised light microscopy (PLM), circular dichroism (CD) and UV-Vis spectroscopy. The influence of methods of isolation on plasmid LC behaviour is described, and using PLM we have demonstrated the spontaneous formation of cholesteric fingerprint-like textures. Preliminary studies of LC phase transitions in pGEM show the irreversibility of LC phase formation, as a consequence of changes in the tertiary structure of supercoiled plasmids. Using UV-Vis spectroscopy a hyperchromic effect was observed with increasing temperature. The CD spectra clearly showed structural changes, and probably mismatching of DNA bases, during cooling. Finally, we have observed an irreversible phase transition in plasmid DNA which is very different from that previously reported in linear DNA.
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| 5. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Generation of hidden bistable images in a cholesteric liquid crystal device
- 2021
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 0267-8292 .- 1366-5855. ; 48:15, s. 2076-85
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Tidskriftsartikel (refereegranskat)abstract
- Generation of hidden images in a cholesteric liquid crystal device is presented. The device operation is based on the dependence of the threshold voltage for unwinding the helical molecular order in cholesteric liquid crystal (being initially ether in Grandjean or Focal conic texture) on the surface anchoring conditions of the supporting substrates. This threshold voltage, however, is different for planar and homeotropic anchoring. By patterning the substrates' surface anchoring condition, permanently or temporarily, so-called pre-determined hidden bistable images, can be visualised and memorised by a proper electronic driving. These images are constituting of areas being either in Grandjean, Focal conic or Uniform Lying Helix (ULH) textures, that is, appearing as light reflecting, light scattering or transparent, respectively. Due to bistability of these textures (states), the visualised hidden images are bistable too. So far, the lifetime of the visualised hidden images was proven to be a decade long and being switchable to any of the other bistable states. [GRAPHICS] .
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| 6. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Tuning and turning of the liquid crystal alignment by photosensitive composites
- 2021
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 0267-8292 .- 1366-5855. ; 48:15, s. 2117-2129
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Tidskriftsartikel (refereegranskat)abstract
- To improve the characteristics and quality of the photoalignment of liquid crystals has been a main goal of many relevant studies. We demonstrate in this work, following the general concept of composite materials, that the photoalignment of liquid crystal can substantially be improved when using alignment layers made from photoalignment composite materials. These composites contain at least one photoalignment material. The other components of the photoalignment composite material may or may be not photosensitive, as conventional polyimide materials, for instance. We show that by a proper choice of the components, the properties of the photoalignment materials, made by photoalignment composites, can be tailored in a broad range, resulting in higher sensitivity, and thus shorter exposure time, uniform and smooth photoalignment topography (without domains and sandy structures) resulting in high image contrast. High-quality photo-patterning of the liquid crystal alignment is demonstrated in this work with a photoalignment composite material containing one of our photoalignment materials and a conventional polyamide alignment material.
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| 7. |
- Jonas, Örtegren, et al.
(författare)
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Cone motion viscosity and optical second harmonic generation of ferroelectric liquid crystalline dendrimers
- 2001
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Ingår i: Liquid crystals (Print). - : Informa UK Limited. - 0267-8292 .- 1366-5855. ; 28:6, s. 861-868
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Tidskriftsartikel (refereegranskat)abstract
- We report second harmonic generation in a ferroelectric liquid crystalline trimer and ferroelectric liquid crystalline dendrimers of first, second and third generation. Thin cells were filled with the compounds by capillary forces at elevated temperature, and cooled from the surface stabilized ferroelectric state to below the glass transition temperature, while kept in an electric field. The cone motion viscosity and the threshold electric field for unwinding of the helix axis of the chiral tilted smectic mesophases were studied separately at elevated temperature, and these data were used to optimize the preparation of the films. The measured response time was between 0.3 and 3 ms, which corresponds to a cone motion viscosity between 0.5 and 50 Pa s. Second harmonic generation was studied both at elevated temperature with an electric field and at room temperature with and without electric field. The first generation dendrimer exhibited a strong increase in the second order non-linear optical response with time at room temperature. The d(23)-coefficient of this dendrimer was approximately four times larger than for the other macromolecules and was 0.045 pm V-1. The relatively large d-coefficient of the first generation dendrimer is ascribed to crystallization, which improved the orientation of the molecular dipoles.
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| 8. |
- Kang, S. W., et al.
(författare)
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Surface polymer-stabilised in-plane field driven vertical alignment liquid crystal device
- 2014
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 0267-8292 .- 1366-5855. ; 41:4, s. 552-557
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Tidskriftsartikel (refereegranskat)abstract
- In-plane field driven vertical alignment device using a liquid crystal with positive dielectric anisotropy has been studied. In the device, the distance between inter-digital electrodes needs to be increased to achieve higher transmittance; however, such a design results in an increase in operating voltage and slower response time. In this work, we use polymer stabilisation technique, which generates surface tilt angle other than 90(o), to improve upon these drawbacks. As a result, the proposed device shows lower operating voltage and faster response time while keeping transmittance at the same level, compared to those prior to polymer stabilisation.
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| 9. |
- Komitov, Lachezar, 1944, et al.
(författare)
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Controllable alignment of nematics by nanostructured polymeric layers
- 2009
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Ingår i: Liquid Crystals. - 1366-5855 .- 0267-8292. ; 36:6 & 7, s. 747-753
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Tidskriftsartikel (refereegranskat)abstract
- A method for a continuous control of the pretilt angle of the easy axis in the range 0-90° degrees and of the anchoring strength by using nanostructured polymers as alignment layers is described. The nanostructured polymers are blends of two different side-chain polymers each of them promoting planar and homeotropic alignment, respectively. A model to interpret the alignment of a nematic liquid crystal induced by such polymer layers is proposed. We show that in this case the anisotropic part of the surface tension can be approximated by a simple extension of the Rapini-Papoular expression. The predicted trend of the pretilt of the easy axis versus the concentration of the side-chain polymer promoting the planar alignment, for instance, is in good agreement with the experimental data. We also show that the effective anchoring strength of the system depends on the concentration of the side-chain polymer promoting planar alignment, and exhibits a minimum for a well-defined value of this quantity. The results obtained in this work seems to be of importance for liquid crystal displays technology since the control of the pretilt and the anchoring strength strongly affect the performance of liquid crystal displays.
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| 10. |
- Lagerwall, Sven, 1934
(författare)
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On some important chapters in the history of liquid crystals
- 2013
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 1366-5855 .- 0267-8292. ; 40:12, s. 1698-1729
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Tidskriftsartikel (refereegranskat)abstract
- Before 1910, the study of liquid crystals was dominated by Lehmann and the German school of chemists. The point of gravity then moved to France with Friedel as a leading figure. While there are many studies about Lehmann, there are fewer about Friedel. He has written about himself, so to speak, and more people have cited him than read his original papers. In the first part of this historical review, I will, after a close reading of the original papers, trace the development on French soil between 1910 and 1922. After 1922, the progress stopped in France, but a renewal of interest in liquid crystals came from Germany in the late 1920s and the first international symposium was organised there in 1931, closely followed by one in England 1933. After the Second World War, a new symposium in 1958 revived the field and then came a new outburst of turbulent productivity in the late 1960s. My aim is to focus on some of the most prominent persons and some turning points also in this modern era. But my foremost aim is to illustrate that nothing happened in the straightforward way in which most texts tend to outline the history.
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