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991.
Two new series of styrene monomers with different alkyl chain length were successfully synthesised. The chemical structures of synthetic intermediates and monomers were confirmed by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. Their thermal stability, transition temperatures and phase sequences were investigated by polarised light microscopy, thermogravimetric analysis, differential scanning calorimetry and one-dimensional wide-angle X-ray diffraction. The birefringent and photoelectric properties, UV–vis and fluorescence spectroscopy were also measured using Abbe refractometer and fluorescent apparatus. The results indicated that all the monomers exhibited a liquid crystalline phase at higher temperature, high birefringence values between 0.4 and 0.7, and good photoluminescence properties. Optical anisotropy of homologous molecules was reduced with the increase of alkyl chain length due to the decrease of molecular polarisation. Moreover, a significant effect of the chemical structure on the photoluminescence properties was also found and discussed according to the length of π-conjugation. 相似文献
992.
Chong-Kwang Lee Andrew Primak Antal Ja kli E.-Joon Choi Wang-Cheol Zin Liang-Chy Chien 《Liquid crystals》2013,40(9):1293-1299
A new banana-shaped achiral molecule, 1,3-phenylene bis[4-(3-chloro-4-n-octyloxyphenyliminomethyl)benzoate] (PBCOB) has been synthesized, and its ferroelectric properties and homeotropic alignment investigated. The presence of a lateral chloro-substituent in the Schiff 's base moiety prevents the regular stacking of molecules and results in lowering the transition temperature and the degree of crystallinity of the switchable banana phase. Their smectic mesophases, including a switchable banana phase B7, were characterized by differential scanning calorimetry, X-ray scattering and polarizing optical microscopy. Both the left- and right-handed helical domains are spontaneously formed upon cooling from the isotropic liquid to the switchable banana phase B7. By X-ray study, the smectic phases showed a layer spacing of 38.1 Å, compatible with the end-to-end distance of the molecule with a bent conformation. Significantly, the smectic B7 phase exhibited a periodicity of 292 Å that corresponds to a helical structure with periodicity about 7.5 times 38.1 Å. The spontaneous polarization for PBCOB is about 50 nCcm-2 and shows a temperature dependence. The ferroelectric lyomesophase of PBCOB showed a ferroelectric electro-optical switching range extending more than 50°C, switchable at room temperature. 相似文献
993.
Toshio Itahara 《Liquid crystals》2013,40(9):1157-1163
Liquid crystal trimers and tetramers containing two kinds of flexible spacers, namely O(CH2) m O and COO(CH2) n O, were divided into four classes according to the odd/even nature of the number of atoms in the flexible spacers: specifically, even–even, odd–odd, even–odd, and odd–even trimers, and even–even–even, odd–odd–odd, odd–even–odd, and even–odd–even tetramers. The transition properties of the four types of trimers and of tetramers were compared. Although the nematic–isotropic transition temperature and the associated entropy changes were primarily related to the number of the even-membered flexible spacers in these molecules, the different combinations of the flexible spacers significantly affected their transition properties. 相似文献
994.
S. Sreehari Sastry S.T. Ha B. Gowri Sankara Rao K. Mallika T. Vindhya Kumari 《Liquid crystals》2013,40(11):1414-1419
An image analysis technique in conjunction with polarising optical microscopy (POM) is proposed for assessment of the thermo-optical properties of homogeneously aligned chiral ester liquid crystals of the type ((S)-(-)-2-methylbutyl 4′-(4″-n-alkanoyloxybenzoyloxy) biphenyl-4-carboxylates, where n?=?16 or 18. Chiral ester textures are recorded as a function of temperature using POM provided with a hot-stage and a high-resolution colour camera. Temperature-dependent optical parameters, or thermo-optical properties such as optical transmission, degree of polarisation, absorption coefficient and birefringence are computed for chiral esters by analysing the texture of samples using MATLAB software. This is a simple experimental technique for observing how the optical parameters of liquid crystals change with temperature. 相似文献
995.
Rasika Prabhu Rasmus Klitkou Grigori A. Medvedev James M. Caruthers 《Journal of Polymer Science.Polymer Physics》2013,51(8):687-697
The linear viscoelastic behavior in dynamic shear and tensile creep at temperatures from −30 to 70 °C is measured for an styrene–butadiene rubber (SBR) elastomer cured with dicumyl peroxide to crosslinking densities between 0 and 23.5 × 10−5 mol/cm3. The G′, G″, and tan δ isotherms are analyzed by time–temperature superposition (TTS), where the tan δ master curves are consistent with those of Mancke and Ferry. However, to achieve the TTS in the lightly crosslinked SBR systems, an anomalous vertical shift is required in the narrow temperature region from 10 to 30 °C. The vertical shift factor in this temperature region is not the standard from rubber elasticity. No anomalous behavior is detected in the equilibrium modulus, which is a linear function of temperature in accordance with the classical theory of rubber elasticity. In contrast to SBR, standard vertical shifts are required to effect TTS for uncrosslinked polybutadiene and an ethylene propylene diene monomer elastomer. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
996.
Dr. Jiwei Liu Junjie Xu Prof. Renchao Che Huajun Chen Mengmei Liu Zhengwang Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6746-6752
A facile and efficient strategy for the synthesis of hierarchical yolk–shell microspheres with magnetic Fe3O4 cores and dielectric TiO2 shells has been developed. Various Fe3O4@TiO2 yolk–shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk–shell microspheres, such as the complex permittivity and permeability, were investigated. The electromagnetic data demonstrate that the as‐synthesized Fe3O4@TiO2 yolk–shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe3O4 and our previously reported Fe3O4@TiO2 core–shell microspheres, which may result from the unique yolk–shell structure with a large surface area and high porosity, as well as synergistic effects between the functional Fe3O4 cores and TiO2 shells. 相似文献
997.
Gadolinium(III)‐Hydroxy Ladders Trapped in Succinate Frameworks with Optimized Magnetocaloric Effect
Yan‐Cong Chen Fu‐Sheng Guo Prof. Dr. Yan‐Zhen Zheng Jun‐Liang Liu Ji‐Dong Leng Róbert Tarasenko Prof. Dr. Martin Orendáč Dr. Jan Prokleška Prof. Dr. Vladimír Sechovský Prof. Dr. Ming‐Liang Tong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13504-13510
Two kinds of inorganic gadolinium(III)‐hydroxy “ladders”, [2×n] and [3×n], were successfully trapped in succinate (suc) coordination polymers, [Gd2(OH)2(suc)2(H2O)]n ? 2n H2O ( 1 ) and [Gd6(OH)8(suc)5(H2O)2]n ? 4n H2O ( 2 ), respectively. Such coordination polymers could be regarded as alternating inorganic–organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (ΔH=70 kG) 42.8 J kg?1 K?1 for complex 1 and 48.0 J kg?1 K?1 for complex 2 . The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm?3 K?1 for complexes 1 and 2 , respectively. 相似文献
998.
Haiquan Tian Dr. Lang Zhao Haifeng Lin Prof. Dr. Jinkui Tang Prof. Dr. Guangshe Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13235-13241
Two new “butterfly‐shaped” pentanuclear dysprosium(III) clusters, [Dy5(μ3‐OH)3(opch)6(H2O)3] ? 3 MeOH ? 9 H2O ( 1 ) and [Dy5(μ3‐OH)3(Hopch)2(opch)4(MeOH)(H2O)2] ? (ClO4)2 ? 6 MeOH ? 4 H2O ( 2 ), which were based on the heterodonor‐chelating ligand o‐vanillin pyrazine acylhydrazone (H2opch), have been successfully synthesized by applying different reaction conditions. Single‐crystal X‐ray diffraction analysis revealed that the butterfly‐shaped cores in both compounds were comparable. However, their magnetic properties were drastically different. Indeed, compound 1 showed dual slow‐relaxation processes with a transition between them that corresponded to energy gaps (Δ) of 8.1 and 37.9 K and pre‐exponential factors (τ0) of 1.7×10?5 and 9.7×10?8 s for the low‐ and high‐temperature domains, respectively, whilst only a single relaxation process was noted for compound 2 (Δ=197 K, τ0=3.2×10?9 s). These significant disparities are most likely due to the versatile coordination of the H2opch ligands with particular keto–enol tautomerism, which alters the strength of the local crystal field and, hence, the nature or direction of the easy axes of anisotropic dysprosium ions. 相似文献
999.
1000.
Daniel Tordera Andreas M. Bünzli Antonio Pertegás Dr. José M. Junquera‐Hernández Prof. Edwin C. Constable Dr. Jennifer A. Zampese Prof. Catherine E. Housecroft Prof. Enrique Ortí Dr. Henk J. Bolink 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8597-8609
A new approach to obtain green‐emitting iridium(III) complexes is described. The synthetic approach consists of introducing a methylsulfone electron‐withdrawing substituent into a 4‐phenylpyrazole cyclometalating ligand in order to stabilize the highest‐occupied molecular orbital (HOMO). Six new complexes have been synthesized incorporating the conjugate base of 1‐(4‐(methylsulfonyl)phenyl)‐1 H‐pyrazole as the cyclometalating ligand. The complexes show green emission and very high photoluminescence quantum yields in both diluted and concentrated films. When used as the main active component in light‐emitting electrochemical cells (LECs), green electroluminance is observed. High efficiencies and luminances are obtained at low driving voltages. This approach for green emitters is an alternative to the widely used fluorine‐based substituents in the cyclometalating ligands and opens new design possibilities for the synthesis of green emitters for LECs. 相似文献