共查询到20条相似文献,搜索用时 15 毫秒
1.
Since 1888, the liquid crystal display (LCD) industry is facing a fierce competition due to serious limitations such as poor contrast ratio and response time. Although some new materials have offered new applications and opened new markets for LCDs, materials with improved contrast ratio are highly desirable in LCD industry to sustain in the current market. This work reports a new behaviour in nano-material-doped liquid-crystal composite which is suitable for eradicating limitations of contrast ratio. Here, a high concentration of carbon nanotubes (CNTs) is doped in liquid crystal (LC) materials wherein the CNTs form aggregates in the LC composition. In these heavily doped samples, the phase change takes place with application of bias. This reversible process improves the contrast ratio as the material oscillates between crystalline and LC phases with field. 相似文献
2.
A. N. Samoilov S. S. Minenko L. N. Lisetski M. S. Soskin S. I. Torgova 《Liquid crystals》2018,45(2):250-261
Optical transmission and selective reflection data are reported for suspensions of single-walled carbon nanotubes (CNTs) in photoactive nematic material ZhK-440 with a mesogenic chiral dopant M5. At small concentrations of CNTs (C ≈ 0.01–0.05%), the preferential localisation of CNTs at oily sticks (cholesteric topological defects) and suppression of the network of oily streaks by CNTs were observed. At the same time, the optical density D was shown to be essentially non-linear and a minimum at certain concentration of CNTs, C ≈ 0.05–0.08%, was observed. This anomalous behaviour was explained by the presence of the structural transition from the loose (ramified) aggregates with highly anisotropic shape (oriented along the anchoring direction on rubbed polyvinyl alcohol) to the compact aggregates with denser packing. The location of this minimum, as well as the selective reflection maximum (helical pitch), was sensitive to partially reversible UV-induced trans–cis–trans isomerisation effects. The UV-controlled helical pitch variation was shown to be only slightly affected by introduction of CNTs. 相似文献
3.
Solid phase extraction of metal ions using carbon nanotubes 总被引:1,自引:0,他引:1
Anna Stafiej 《Microchemical Journal》2008,89(1):29-33
The sorption behaviour of carbon nanotubes (CNTs) toward some divalent metal ions such as Cu(II), Co(II), Ni(II), Zn(II), Pb(II), Mn(II) and Cd(II) has been investigated systematically. The affinity order of the metal ions towards CNTs at pH in the range of 7.0-9.0 was: Cu(II) > Pb(II) > Zn(II) > Co(II) > Ni(II) > Cd(II) > Mn(II). The experimental parameters for preconcentration of copper, which exhibits the highest affinity towards carbon nanotubes, on a microcolumn packed with CNTs prior to its determination by flame atomic absorption spectrometry have been investigated. Copper can be quantitatively retained at pH 8.2 from sample volume up to 150 mL and then eluted completely with 0.1 mol L− 1 HNO3. The limit of detection limit for Cu(II) determination with FAAS detection was 2.1 μg L− 1, and the RSD was 3.5% at the 50 μg L− 1 level. Under the optimal conditions for copper enrichment also Zn(II), Pb(II) and Ni(II) could be quantitatively preconcentrated from water samples. The method was validated using a certified reference materials BCR-610 and SRM 1640. 相似文献
4.
Nawel Ould-Moussa Christophe Blanc Camilo Zamora-Ledezma Oleg D. Lavrentovich Ivan I. Smalyukh Mohammad F. Islam 《Liquid crystals》2013,40(12):1628-1635
A post-synthesis alignment of individual single-walled carbon nanotubes (SWCNTs) is desirable for translating their unique anisotropic properties to a macroscopic scale. Here, we demonstrate excellent dispersion, orientation and concomitant-polarised photoluminescence of SWCNTs in a nematic chromonic liquid crystal. The methods to obtain stable suspension are described, and order parameters of the liquid crystal matrix and of the nanotubes are measured independently. 相似文献
5.
The chemical syntheses of 12 new azo dyes are reported. The optically active compounds were prepared by the Mitsunobu reaction, amide formation, and esterification with optically active alcohols or acids. Several new compounds showed liquid-crystalline properties, and their phase transition behavior was investigated. 相似文献
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The optical response time of a nematic liquid crystal (NLC) decreases due to incorporation of carbon nanotubes (CNTs) in the liquid-crystal host. Such reduction is believed to be due to an increase in the elastic constant of the nanotube-doped LC system. In this paper, we present the effect on optical response due to doping an NLC with octadecylamine functionalised single-walled carbon nanotubes (ODA-SWCNT) in a twisted alignment mode. The electro-optic switching amplitude of ODA-SWCNT nanocomposites of NLC decreases compared to pure NLC. A fast response time is observed with an increase in the concentration of ODA-SWCNT in NLC host. Additionally, optical response of pure NLC in a twisted nematic (TN) cell fabricated using mixtures of polyimide (PI) and ODA-SWCNT as an alignment layer is investigated. The optical response time decreased by ~75% in a TN cell fabricated with a mixture of PI and ODA-SWCNT compared to that of a TN cell prepared using a pure PI alignment layer. The presence of ODA-SWCNT in the alignment layer enhances the surface anchoring of the NLC molecules leading to an increase in the elastic constant and a decrease in the optical response time of NLC. 相似文献
8.
After preparing a homologous series of tetrameric mesogenic compounds in which two U-shaped molecules were connected via a rigid benzene derivative or a flexible alkyl chain, we investigated their phase transition behaviour using optical microscopy, differential scanning calorimetry and X-ray diffraction analysis. The compounds possessing an alkyl spacer as the central group exhibited nematic and smectic A phases just as the corresponding U-shaped molecule did. The compound possessing a 1,2-benzene unit as the connecting group showed nematic and smectic A phases, although the compound possessing a 1,3-benzene unit exhibited only an anticlinic smectic C phase. Structure–property relations of the liquid crystalline tetramers are interpreted in terms of preorganised effects of the four mesogenic units. 相似文献
9.
Bruce DW 《Chemical record (New York, N.Y.)》2004,4(1):10-22
In this article, the search for the elusive biaxial nematic phase (NB) in liquid crystals is considered. The structure of the phase is described along with theoretical and computational work which suggests how it might be realised. An overview of the work of the Exeter group in this area is then given showing the different approaches adopted and illustrating how one of these has led to a new type of amphiphilicity based on shape. 相似文献
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ABSTRACTThe characteristics of the twist-bend nematic (NTB) phase of an achiral asymmetrical rigid bent-core liquid crystal (LC), the ends of which are terminated by symmetric alkyl chains, are reported. The nematic–nematic phase transition and its properties are studied by differential scanning calorimetry (DSC), polarising microscopy and the electro-optic techniques. Large domains of opposite handedness are observed in the absence of the external field in the NTB phase. Another set of periodic striped pattern consisting of domains with sharp boundaries is formed when a high-frequency electric field with a magnitude above its threshold is applied across a planarly aligned cell. The neighbouring domains are of opposite chirality. The temperature dependence of the heliconical angle θ0 is determined from the birefringence measurements using Haller’s extrapolation technique. This material shows lower values of the heliconical angle (~9.3° at a temperature of 155°C within the NTB phase) when compared with the previously reported dimer-based twist-bend nematic LCs (31°±3°). 相似文献
12.
Two‐Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules 下载免费PDF全文
Prof. Dr. Sungmin Kang Dr. Eun‐Woo Lee Tianqi Li Prof. Dr. Xiaobin Liang Prof. Dr. Masatoshi Tokita Prof. Dr. Ken Nakajima Prof. Dr. Junji Watanabe 《Angewandte Chemie (International ed. in English)》2016,55(38):11552-11556
We synthesized a novel banana‐shaped molecule based on a 1,7‐naphthalene central core that exhibits a distinct mesomorphism of the nematic‐to‐nematic phase transition. Both the X‐ray profile and direct imaging of atomic force microscopy (AFM) investigations clearly indicates the formation of an anomalous nematic phase possessing a two‐dimensional (2D) tetragonal lattice with a large edge (ca. 59 Å) directed perpendicular to the director in the low‐temperature nematic phase. One plausible model is proposed by an analogy of skyrmion lattice in which two types of cylinders formed from left‐ and right‐handed twist‐bend helices stack into a 2D tetragonal lattice, diminishing the inversion domain wall. 相似文献
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ABSTRACTThe paper reviews assignment of the low-temperature nematic phase observed in simple bimesogenic or dimeric systems based on cyanobiphenyls and difluoroterphenyls to the twist-bend nematic phase, NTB, using a range of experimental techniques. These include DSC, X-rays, Polarising Microscopy, electro-optics, birefringence and measurements of the electroclinic effect arising from flexoelectricity. An emphasis is laid on the observations of the chiral domains of opposite handedness at zero field in an otherwise achiral liquid crystalline system in this phase. These observations are a direct consequence of the structure of the twist-bend phase predicted by Ivan Dozov for achiral bent core molecules. The paper reviews the electro-optic phenomena and the observed electroclinic effect and how these observations assign it as the NTB phase. Results of the nanoscale helical pitch measurements using freeze-fracture microscopy are reviewed and discussed briefly. Results of the measurements of elastic constants especially close to the N–NTB transition are also reviewed. 相似文献
15.
Isabel Márquez-Sillero Eva Aguilera-HerradorSoledad Cárdenas Miguel Valcárcel 《Journal of chromatography. A》2010,1217(1):1-6
The potential of carbon nanotubes for the solid phase extraction of parabens in cosmetic products and the detection using a corona-charged aerosol detector (C-CAD) is presented in this work. The analytical procedure is based on a conventional solid phase extraction step for which 20 mg of multi-walled carbon nanotubes were packed in a 3-mL commercial SPE cartridge. Methylparaben, ethylparaben, propylparaben and butylparaben were thus isolated and preconcentrated from the pre-treated samples and subsequently separated on a RP-C18 column using acetonitrile:water, 50:50 (v/v) as mobile phase. The analytical signals for the individual parabens were obtained using C-CAD. The experimental variables affecting the extraction procedure and the instrumental detection have been deeply studied. Limits of detection were in the range of 0.5–2.1 mg L−1, while the linear range was extended up to 400 mg L−1. The average precision of the method varied between 3.3–3.8% (repeatability) and 4.3–7.6% (reproducibility). Finally, the optimized procedure was applied to the determination of the target preservatives in a variety of cosmetic products with satisfactory results. 相似文献
16.
The dielectric properties in the vicinity of the isotropic-smectic-C* phase transition in ferroelectric liquid crystals are discussed. The temperature and frequency dependence of the complex dielectric permittivity in both the phases of the transition are calculated. The theoretical phase diagram of the dielectric permittivity is studied. 相似文献
17.
A modification of the gauge-cell method for Monte Carlo studies of phase equilibrium in nano-confined systems is presented
and employed for studying the capillary phase transition of propane in single-walled carbon nanotubes as a function of tube
diameter. It is shown that if an analytical equation of state for the vapor phase is known, the acceptance rule for the trial
move of particle exchange can be modified to reference the bulk system through its chemical potential. Under these conditions,
the simulation procedure is simplified and acquires many characteristics of a Monte Carlo simulation conducted in the grand
canonical ensemble. It is also shown that the critical temperature can be estimated by interpolation of sub- and supercritical
values of the slope of the inverse isotherm at the inflection point. To enhance the sampling of propane molecules in the hollow
space of the nanotubes the configurational-bias scheme is employed. The simulation results show that the confinement of propane
increases its critical density, reduces the critical temperature and narrows the binodal curve with decreasing tube diameter
until the system approaches one-dimensional behavior. 相似文献
18.
Miroslava Trchová Elena N. Konyushenko Jana Ková?ová 《Polymer Degradation and Stability》2009,94(6):929-938
Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes. 相似文献
19.
A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO2 and H2 at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H2, CO2 and Ar and minimum adsorption of gases such as N2, O2, CO and H2O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO2 and H2 were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H2 containing 10 μL of each Ar or CO2 was 2.5% for Ar, 2.8% for CO2 and 3.6% for H2. The interfering effects of CO, and O2 were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO2 and 10-1200 ppm for H2. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO2 in air sample. 相似文献
20.
On-line solid phase extraction of Ni and Pb using carbon nanotubes and modified carbon nanotubes coupled to ETAAS 总被引:1,自引:0,他引:1
A study about the capabilities of three kinds of nanomaterials namely, carbon nanotubes (CNT), oxidized carbon nanotubes (ox-CNT) and l-alanine immobilized on carbon nanotubes (ala-CNT) to serve as sorbents for preconcentrating Ni and Pb using an on-line system coupled to electrothermal atomic absorption spectroscopy (ETAAS) technique, was accomplished. The solid phase extraction was performed in a conical minicolumn used as sorbent holder. After loading a fixed volume of the analytes, they were eluted with a discrete volume (50 μL) of nitric acid, placed directly into the platform of a L’Vov tube. After that, each analyte was determined individually. Ni and Pb retention was strongly influenced by pH but exhibiting different behaviors. The study demonstrated that the sorbent based on ox-CNTs was the one that exhibited the highest capacity and linearity for both analytes when compared with CNT or ala-CNT. The analytical performance was evaluated for the three sorbents to establish the best conditions regarding sensitivity, reproducibility and accuracy. The precision expressed as relative standard deviations (n = 6) were 3.9 and 0.5% for Ni2+ and Pb2+, respectively The limit of detection (LOD), calculated as the concentration required to yield a net peak equal to three times the standard deviation of the background signal (3σ) was 30 and 10 ng L−1 for Ni2+ and Pb2+ respectively. Alternatively, the limit of quantification (10σ) was calculated and resulted to be 0.79 and 0.07 μg L−1 for Ni2+ and Pb2+ respectively. After optimization, the method that involved the use of ox-CNT associated to an on-line preconcentration was tested in samples of relevant environmental importance. Accuracy was evaluated analyzing a certified reference material namely, Municipal Sludge (QC MUNICIPAL SLUDGE A) and a reference sample of Lake Sediment (TRAP-LRM from IJS). 相似文献