| 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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| 2. |
- Örtegren, Jonas, et al.
(författare)
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Time-dependent nonlinear optical properties of pyroelectric liquid crystalline polymers
- 1999
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Ingår i: Macromolecular Symposia. - : Wiley. - 1022-1360 .- 1521-3900. ; 148, s. 179-195
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Tidskriftsartikel (refereegranskat)abstract
- Highly oriented pyroelectric liquid-crystalline polymers were prepared by photopolymerization under the influence of a static electric field from binary mixtures of two acrylate monomers exhibiting chiral smectic C mesomorphism. Both monomers contained nitro groups to yield second order nonlinear optical properties (second harmonic generation) and one of the monomers had two functional groups to yield a crosslinked polymer. The room temperature second order nonlinear susceptibility of the polymers showed during the first two hours a 10 % decrease after which it remained constant during the next 48 days. At elevated temperatures there was a significant difference in the nonlinear optical properties over time between crosslinked and uncrosslinked polymers. The uncrosslinked polymer showed a pronounced loss of second order nonlinear optical activity with time at ≥38°C. The crosslinked polymer showed a much smaller and basically a temperature independent decrease rate in the second order nonlinear optical properties at all the ageing temperatures (23-130°C). Both the loss in mesogen order parameter, very evident for the uncrosslinked polymer, and conformational changes occurring within the mesogens (β mechanism), may account for the observations made.
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| 3. |
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| 4. |
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| 5. |
- Börjesson, Karl, 1982, et al.
(författare)
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Photon upconversion with directed emission
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Photon upconversion has the potential to increase the efficiency of single bandgap solar cells beyond the Shockley Queisser limit. Efficient light management is an important point in this context. Here we demonstrate that the direction of upconverted emission can be controlled in a reversible way, by embedding anthracene derivatives together with palladium porphyrin in a liquid crystalline matrix. The system is employed in a triplet-triplet annihilation photon upconversion scheme demonstrating controlled switching of directional anti Stokes emission. Using this approach an emission ratio of 0.37 between the axial and longitudinal emission directions and a directivity of 1.52 is achieved, reasonably close to the theoretical maximal value of 2 obtained from a perfectly oriented sample. The system can be switched for multiple cycles without any visible degradation and the speed of switching is only limited by the intrinsic rate of alignment of the liquid crystalline matrix.
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| 6. |
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| 7. |
- Caillaud, B., et al.
(författare)
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Safe and ergonomic welding masks by fast liquid crystals
- 2008
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Ingår i: Molecular Crystals and Liquid Crystals. - : Informa UK Limited. - 1563-5287 .- 1542-1406. ; 494, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in welding technology, in particular the high intensity pulsed welding arc, have sharpened the requirements on speed and adjustable attenuation for safe and ergonomic operations. With this advent the conventional welding helmets based on nematic liquid crystals are facing difficulties because the nematics are not responding fast enough to stroboscopically follow the changing intensity of the arc during pulsed welding. We propose here a new generation of welding shutters based on smectic (ferroelectric or antiferroelectric) liquid crystals which are fast enough to be synchronized to follow pulsed arc regimes and hence permitting a better visibility of the object under work. The two varieties of smectic materials used are polymer-stabilized in order to make the device shock-proof, to prevent the formation of specific defects such as stripes and chevrons, and to reduce the back-relaxation time in the antiferroelectric case.
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| 8. |
- Chesneau, A., et al.
(författare)
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Teaching nanoscience across scientific and geographical borders-A European Master programme in nanoscience and nanotechnology
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 100:Part 3
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Konferensbidrag (refereegranskat)abstract
- Within the Erasmus Mundus Master (EMM) Programme, five European Universities (KU Leuven, Belgium, Chalmers University of Technology, Sweden, Delft University of Technology and Leiden University, the Netherlands, and the University of Dresden, Germany) have joined forces to offer a unique master programme in Nanoscience and Nanotechnology, EMM-nano, at the cutting edge of state-of-the-art research. The students design and build their individual area of specialisation within nanophysics, nanotechnology, biophysics, biotechnology through their choice of trajectory between the partners. We discuss some of the challenges related to the crossdisciplinary nature of the field, educational activities in cleanrooms, and issues related to the integration of teaching programmes across the borders within Europe.
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| 9. |
- Czerwiński, Michał, et al.
(författare)
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Influence of the type of phase sequence and polymer-stabilization on the physicochemical and electro-optical properties of novel high-tilt antiferroelectric liquid crystalline materials
- 2019
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Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 288
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Tidskriftsartikel (refereegranskat)abstract
- Antiferroelectric liquid crystal (AFLC)mixtures with two types of phase sequence, isotropic - smectic A* - smectic C* - smectic CA* and isotropic - smectic CA*, respectively, have been formulated from components having biphenyl benzoate rigid cores, a non-chiral terminal chain with either alkoxy groups as well as perfluorinated parts on one side, and a chiral chain with different structures on the other side. The properties of the mixtures have been examined by means of polarized optical microscopy, differential scanning calorimetry, as well as UV–Vis-NIR spectrophotometry, and their electrooptic performance have been characterized in device cells, before and after polymer-stabilization of the structures. For all mixtures we observed unusually broad temperature ranges of the smectic CA* phase, extending from at least −30 °C to about +70 °C or more, molecular tilt angles of 42–44°, helical pitches of several micrometers, and a spontaneous polarization of about 200 nC/cm2. The polymer network has a profound impact on the relaxation to the anticlinic state, especially in the mixtures with a direct smectic SmCA*- isotropic phase transition. A symmetric electrooptic response, with both on and off response times of about 140 μs, was obtained in cell gaps of 1.5 μm, which is, to our knowledge, unique among contemporary available high tilt AFLC material systems.
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