| 1. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
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Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive
- 2020
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 453
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Tidskriftsartikel (refereegranskat)abstract
- Self-discharge is being recognized as one of the main obstacles to implementing the supercapacitor (SC) in standalone self-powered systems. Strategies for addressing this issue include the modification of electrodes, electrolytes, separators, and diverse device configurations. However, an improved self-discharge behavior is often achieved with a large compromise on other prominent figures of merit such as capacitance, energy density, or cycle life of the device. In this work, a thorough comparative electrochemical investigation of SCs containing a neutral aqueous electrolyte, 1 M Li2SO4, and with a liquid crystal (LC) additive, 2% 4-n-pentyl-4′-cyanobiphenyl (5CB) in 1 M Li2SO4, has been carried out at different states of charge. The results demonstrate that the device containing the LC additive 5CB exhibits a reduced self-discharge and leakage current without compromising the capacitive performance at different nominal voltages compared to the behavior of the device without 5CB. We suggest an explanation of the difference of the self-discharge behavior between the devices through tunability of the effective conductivity of the electrolyte composite upon applied voltages. As a result, in an open circuit condition, the device containing LC shows a slower diffusion of ions that facilitates a decreased self-discharge and leakage current.
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| 3. |
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| 4. |
- Engström, David, 1976, et al.
(författare)
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Analog low-loss full-range phase modulation by utilizing a V-shaped switched ferroelectric liquid-crystal cell in reflective mode
- 2006
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:19, s. 2906-2908
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the analog (V-shaped switching) mode in ferroelectric liquid crystals in reflective mode for analog phase modulation applications. We have found that several combinations of cell thicknesses and input polarization states exist for which near-lossless analog phase modulation with a range of ~2π rad is obtained, and we demonstrate one such combination experimentally. Despite a slight deviation from the ideal conditions, e.g., the tilt angle was 38° instead of the desired 45°, virtually pure 1.6π rad phase modulation was obtained; the measured values agree very well with our numerical simulations of the real device.
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| 6. |
- Engström, David, 1976, et al.
(författare)
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Three-level phase modulator based on orthoconic antiferroelectric liquid crystals
- 2006
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:21, s. 3158-3160
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Tidskriftsartikel (refereegranskat)abstract
- Surface-stabilized orthoconic antiferroelectric liquid crystals (OAFLCs) have a director tilt of θ=45° and are, with no field applied, negatively uniaxial with the optic axis perpendicular to the cell substrates. We demonstrate that OAFLCs can be utilized to achieve lossless phase modulation with three almost equidistant phase levels. This turns out to be true also for polymer-stabilized OAFLCs, where the polymer network increases the switching speed of the device without affecting the phase modulation appreciably.
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| 7. |
- Lagerwall, Sven, 1934, et al.
(författare)
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Liquid Crystals: Cholesteric, Guest-Host, and Polymer-Dispersed
- 2015
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Ingår i: Encyclopedia of Optical and Photonic Engineering Second Edition. - 9781351247177 ; , s. 1443-1450
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- If we abandon the mirror symmetry present in the ordinary nematics, a new world opens up for applications, for photonics as well as for displays. The basic new phenomenon that now appears is scattering. In practice, we enter this domain by using cholesterics, which is the chiral form of nematics. The nematogenic molecules might themselves be chiral, but we could also, in principle, obtain the cholesteric by adding chiral dopants to the material. If we add dichroic dyes or polymerizable materials to the liquid crystal, we can create highly interesting devices based on either absorption or scattering or both. Cholesteric and nematic devices based on scattering and dichroic effects will be discussed in this entry.
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| 8. |
- Lagerwall, Sven, 1934, et al.
(författare)
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Liquid Crystals: Non-Linear Optical Effects
- 2015
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Ingår i: Encyclopedia of Optical and Photonic Engineering Second EditionP. - 9781351247177 ; , s. 1465-1472
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Today, inorganic crystals are the completely dominating materials for nonlinear optics (NLO) applications. The interest in organic materials for NLO has been constantly growing due to several factors. First of all, the polarization response to an externally applied field is of molecular electronic origin and, therefore, practically lossless and extremely rapid. Ultrafast, nonresonant nonlinearities in combination with relatively low value of dielectric permittivity can be found in organic single crystals, but these are expensive to grow. Polymer materials are cheap, but normally have very low polar order. Here, liquid crystals and liquid crystalline polymers have a particular interest due to their inherent order. While nematics show some peculiar effects which can be described as macroscopic, the polar smectics have a nonlinear response on the microscopic, electronic level which is fairly similar to what is found in crystals. We first briefly introduce the basic concepts and then discuss macroscopic and electronic effects in turn.
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| 9. |
- Lagerwall, Sven, 1934, et al.
(författare)
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Liquid Crystals: Optical Properties and Basic Devices
- 2015
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Ingår i: Encyclopedia of Optical and Photonic Engineering Second Edition. - 9781351247177 ; , s. 1473-1489
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Liquid crystals (LCs) are liquid or liquid-like states that are anisotropic. Therefore, they have less symmetry than ordinary liquids, but higher symmetry than crystals. The anisotropy makes them optically birefringent like most crystals. This entry relates the structural properties of the organic molecules that are the building blocks to the optical and the electro-optic properties of the different LC phases. The exceptional elastic properties of LCs are also described.
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