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A review on low-molar-mass carbazole- based derivatives for organic light emitting diodes
摘要： Organic light emitting diodes (OLEDs) have attracted a great deal of attention within academia and industry because of their potential applications in flat panel displays and solid-state lighting technologies. Among all low-molar-mass derivatives under investigation in OLEDs field, carbazole-based materials have been studied at length for their interesting physical properties, including good charge injection and transport, electro-luminescence, improved thermal and morphological stabilities as well as film forming properties. In addition, the relatively high triplet energy level of some substituted carbazoles makes them suitable candidates to design hosts for wide bandgap triplet emitters such as blue dopants. The article is written from structural organic chemist's point of view and is divided in several parts: V-shaped 3(2)-substituted carbazoles and derivatives with 9-carbazolyl rings, star-shaped 3,6(2,7)-substituted carbazoles and branched twin derivatives containing (di)arylcarbazolyl fragments.
关键词： Amorphous material,Ionization potential,Glass transition temperature,Organic light emitting diode,Substituted carbazole,Hole transporting material
更新于2025-09-09 09:28:46
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Tungsten doped M-phase VO2 mesoporous nanocrystals with enhanced comprehensive thermochromic properties for smart windows
摘要： The phase transition temperature (~ 68 oC) of M-VO2 film can be lowered significantly by tungsten (W) doping into the crystal lattice of VO2 due to the reduction of the strength of V-V pair interaction. However, W doping was always coupled with a serious weakening of luminous transmittance and solar modulation efficiency because W dopants can increase the electron concentration of VO2 film. Herein, the simultaneous introduction of W dopants and mesopores into M-VO2 nanocrystals was employed to prepare VO2 film. Interestingly, the obtained 0.4 at% W-doped mesoporous VO2 nanocrystals based composite films exhibited enhanced comprehensive thermochromic performance with excellent solar modulation efficiency (ΔTsol = 11.4%), suitable luminous transmittance (Tlum = 61.6%) and low phase transition temperature around 43 oC, much lower than 65.3 oC of undoped VO2. It was demonstrated that the lower phase transition temperature of VO2 can be primarily attributed to abundant lattice distortion after W doping, whereas the mesoporous structure can facilitate the uniform distribution of W dopants in VO2 nanocrystals, enhance the luminous transmittance and guarantee enough VO2 nanocrystals in the composite film to keep relatively high solar modulation efficiency. Therefore, this work can provide a new way to balance the three important parameters for the thermochromic performance of VO2 film (ΔTsol, Tlum and Tc) and probably promote the application of VO2 nanocrystals in the energy efficient windows.
关键词： thermochromic performance,phase transition temperature,mesoporous structure,W-doped VO2
更新于2025-09-09 09:28:46
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Effect of PbO–B2O3–BaO–SiO2 glass additive on dielectric properties of Ba0.5Sr0.5TiO3 ceramics for radio-frequency applications
摘要： In this work, the effects of PbO–B2O3–BaO–SiO2 (PBBS) glass addition (in increasing wt%) into Ba0.5Sr0.5TiO3 (BST0) ceramic on sintering, phase, and dielectric properties of BST0 are studied. The Ba0.5Sr0.5TiO3 (BST0) ceramic was synthesized by the conventional solid-state reaction method, and the PbO–B2O3–BaO–SiO2(PBBS) glass was formed by melting and quenching process. The PBBS glass with different weight percentages (3, 5, 8 and 10 wt%)is added to BST0 ceramic (BST3, BST5, BST8, and BST10, respectively) as a sintering aid to reduce the sintering temperature. Addition of glass helps in better sintering at lower temperatures with the presence of liquid phase at the respective sintering temperatures. The results of liquid phase-sintered ceramics are compared with the BST0 ceramic sintered at 1523 K. The BST10 with 10 wt% glass showed the lowest sintering temperature of 1148 K. Rietveld refinement analysis of BST0 ceramic confirmed the formation of single phase with cubic crystal structure. X-ray diffraction patterns of all liquid phase-sintered ceramics showed that the glass has minimal reaction with the BST0 ceramic and does not affect the crystal structure. Dielectric characterization was performed within the temperature range 20–450 K and frequency range 1 kHz to 1MHz. It is revealed that the transition temperature shifted with different weight percentage of glass addition. All the compositions exhibit the paraelectric phase at room temperature. Dielectric properties were also measured in the microwave frequency range 8.5–11 GHz at room temperature.BST10shows the stable and highest dielectric constant (average value of εr = 27) with lowest dielectric loss (tanδ = ~0.121). Fourier transform infrared (FTIR) and Raman spectroscopy confirmed the formation of desired compositions by detecting molecular vibrations and chemical bonding. The synthesized ceramic is a low-cost candidate and can have potential uses in the radio-frequency applications.
关键词： Dielectric properties,Glass,Sintering,Transition Temperature,Calcination
更新于2025-09-09 09:28:46
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Fabrication of vertical alignment liquid crystal cell without forming a conventional polyimide-alignment layer
摘要： A novel preparation method of the vertical alignment polymer film (VAPF) was proposed by polymerisation of the monomers, 2,3-difluoro-4?-[2-(diacryloyl-oxy-hexyl)methyl ester-hexadecyl-oxy]-biphenyl (DFDAMHB) and 2,7-dimethacryloyl-oxy-phenanthrene (DMAPhen), being dissolved in the liquid crystal (LC) material. For obtaining the vertical alignment (VA), the ultraviolet exposure was carried out to the LC cell below the nematic to isotropic transition temperature of the LC material. The VA mode LC cell with the VAPF produced from the monomers DFDAMHB and DMAPhen exhibited enough level of electro-optical and response properties, high voltage holding ratio and low residual direct current voltage.
关键词： vertical alignment polymer film,Liquid crystals,nematic to isotropic transition temperature,monomers,polymerisation
更新于2025-09-04 15:30:14
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Quartz-enhanced conductance spectroscopy for nanomechanical analysis of polymer wire
摘要： Quartz-enhanced conductance spectroscopy is developed as an analytical tool to investigate dynamic nanomechanical behaviors of polymer wires, in order to determine the glass transition temperature (Tg). A polymethyl methacrylate (PMMA) microwire with a diameter of 10 lm was bridged across the prongs of a quartz tuning fork (QTF). With the advantage of QTF self-sensing as compared with micro-cantilevers or other resonators, the resonance frequency and Q factor can be directly determined by means of its electrical conductance spectra with respect to the frequency of the external excitation source (dI/dV vs f), and therefore, no optical beam is required. The Tg of the PMMA microwire was determined by the maximum loss modulus of the QTF, calculated from the resonance frequency and the Q factor as a function of temperature. The measured Tg of the PMMA is 103 (cid:2)C with an error of 62 (cid:2)C. Both heating/cooling and physical aging experiments were carried out, demonstrating that the technique is both reversible and reproducible.
关键词： PMMA,polymer wire,quartz tuning fork,nanomechanical analysis,glass transition temperature,Quartz-enhanced conductance spectroscopy
更新于2025-09-04 15:30:14
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Glass transition temperature of PMMA/modified alumina nanocomposite: molecular dynamic study
摘要： In this study, the effect of alumina and modi?ed alumina nanoparticles in a PMMA/alumina nanocomposite was investigated. To attain this goal, the glass transition behavior of poly methyl methacrylate (PMMA), PMMA/alumina and PMMA/functionalized alumina nanocomposites were investigated by molecular dynamic simulations (MD). All the MD simulations were performed using the Materials Studio 6.0 software package of Accelrys. To obtain the glass transition temperature, the variation of density versus temperature was obtained. The temperature at which the slope of the density-temperature curve observably changes is de?ned as the glass transition temperature (Tg). The effect of alumina nanoparticles on the Tg was related to the free volume and the mobility of chain segments and the interaction between the alumina nanoparticles and the polymer. The mobility of the chain segments was investigated based on the mean square displacement and radius gyration. The results show that the incensement the Tg of the PMMA/functionalized alumina nanocomposite is more than that of the PMMA/alumina nanocomposite due to the modi?cation of the alumina nanoparticles.
关键词： molecular dynamic,nanocomposite,glass transition temperature,gyration radius
更新于2025-09-04 15:30:14