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951.
《Polymer Degradation and Stability》2013,98(9):1744-1753
Vectran® fibers are widely used in military and aerospace industries as high performance fibers. However, they are susceptible to degradation and undergo structural changes when exposed to ultraviolet (UV) irradiation in service. The focus of this work is to investigate the photochemical aging behavior and mechanism of the Vectran® fibers. The morphologies, mechanical properties, chemical structures and behaviors against UV irradiation have been studied. The tensile test results reveal that the tensile strength decreases quickly when the fibers are exposed to Xenon lamp irradiation. The morphology of the Vectran® fiber surface is damaged after accelerated aging. Crystallinity content analysis illustrates that the degree of the fiber structural ordering is decreased due to irradiation. Fourier transformed infrared analyses (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses of the accelerated aged fibers prove the chemical structural changes of the Vectran® fibers. For the first time, the possible photodegradation mechanism of Vectran® fiber is proposed in both air and N2 environments. The rate of degradation and number of chain scissions are greater in air than in N2. The radicals generated by chain scissions can directly abstract a hydrogen atom or can react with O2 creating hydroxyl OH/COOH end groups in air atmosphere. The diaryl ethers may be formed due to the replacement of the H atoms in aromatic rings for linking up two aromatic rings. 相似文献
952.
Liping Zhao Zhenghong Guo Zhenhu Cao Tao Zhang Zhengping Fang Mao Peng 《Polymer Degradation and Stability》2013
Fullerene (C60)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C60 on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N2 the addition of C60 increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C60. When the content of C60 is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C60 can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C60 or with low C60 concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation. 相似文献
953.
954.
以经典热力学第二定律ΔG<0为依据,分析了静态高温高压触媒法合成立方氮化硼(cBN)过程中发生的可能反应.考虑温度和压强对反应物相体积的影响,计算了六方氮化硼(Li3N-hBN)体系中hBN+Li3N→Li3BN2,h BN→cBN及Li3BN2→Li3N+cBN反应在高温高压条件下的ΔG.结果证实,Li3BN2由Li3N与hBN在高温高压(T>1300 K,P>3.0 GPa)条件下反应得到,在cBN的合成(T=1600~1800 K,P=4.6~6.0 GPa)条件下,hBN和Li3BN2都有向cBN转化的倾向,但由hBN向cBN直接转变的反应自由能比Li3BN2分解生成cBN的反应自由能更负,反应的可能性更大.探讨了高温高压条件下立方氮化硼的转变机理。 相似文献
955.
Arvind K. Gathania 《Liquid crystals》2013,40(7):773-776
Critical behaviour of the order parameters has been investigated in the ferroelectric liquid crystal mixture ZLI‐3654 in a 7.5 µm thick planar cell. The temperature dependence of the primary (tilt angle) and secondary (spontaneous polarisation) order parameters is considered. The critical exponent (β) has been evaluated from the fitting of the temperature dependence of the experimental data for both tilt angle and spontaneous polarisation. Experimental results are compared with the predictions of the de Gennes and Landau models. 相似文献
956.
Xiang Ying Shi Jue Lin Ziyang Li Tao Jin-Wang Huang Liang-Nian Ji 《Liquid crystals》2013,40(2):211-214
We observed that the planar aligned nematic liquid crystal (5CB) doped with a volume fraction of 1% of FeTPPCl [5,10,15,20-tetraphenylporphyriniron(III)chloride] or MnTPPCl [5,10,15,20-tetraphenylporphyrinmanganese(III)chloride] dramatically decreased the critical magnetic field for the magnetic field induced Freedericksz transition, while 5CB doped with ZnTPP [5,10,15,20-tetraphenylporphyrinzinc(II)] revealed no such effect, when compared with pure 5CB. In the guest-host (5CB) system, FeTPPCl and MnTPPCl as guests are both strong paramagnetic materials with an interaction through coordination of the -CN group in 5CB onto the metal ion of the porphyrin. As a result, the 5CB molecules are dragged to reorientate under a static magnetic field, while ZnTPP is a diamagnetic material without such a property. This phenomenon concerning magneto-optical components could be useful in liquid crystal displays. 相似文献
957.
For practical guest–host applications, it is important to choose dyes with a high ability of orientation in the liquid crystal (LC) matrix. In this experimental work, two different azo-structured dyes (disperse yellow 3 and 7) were separately doped to each of two different nematic LCs (E7 and ZLI-1132). Their solubilities, textures, phase transition temperatures and order parameters were determined. At the second stage, single-walled carbon nanotubes (SWCNTs) in a small amount were separately added to each of these solutions, and the experiments were repeated as similar to the previous ones. The solubilities of dyes in the LC E7 were lower than those of ZLI-1132. Moreover, the highest order parameter value was attained with yellow 7 dye in ZLI-1132 nematic host. Co-use of nanoparticles (CNTs) as dopant resulted in notable increases in order parameters. These dyes and CNTs did not significantly destabilise the mesomorphic phase of nematic hosts. An appreciable change in textures was not monitored with addition of dopant(s). In addition, it was observed that the narrowing on the temperature range of the LC did not take place with the addition of dopants to the crystal; on the contrary, an increase was recorded. 相似文献
958.
Remko Achten Arie Koudijs Marcel Giesbers Antonius T. M. Marcelis Corresponding author Ernst J. R. Sudhölter 《Liquid crystals》2013,40(3):277-285
Two series of non‐symmetric banana‐shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3‐phenylene bis(4‐benzoyloxy)benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X‐ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC8H17 to OC16H33. The other terminal tails are OC11H23, O(CH2)9CH?=?CH2, OC10H21 and O(CH2)8CH?=?CH2. The short‐tailed compounds show monotropic or enantiotropic B1 phases and the long‐tailed compounds the B2 phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B2 phases have layer spacings that suggest a tilt of ~45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric. 相似文献
959.
Giovanni De Filpo Marialuigia MacChione Fiore P. Nicoletta Daniela Cupelli Giuseppe Chidichimo 《Liquid crystals》2013,40(12):1569-1573
Elliptic droplets of nematic liquid crystal dispersed in a fluid organic monomer were obtained by phase separation from an isotropic mixture consisting of an organic monomer and a nematic liquid crystal contained in a poly(ethylene terephthalate) cell with inner surfaces treated with rubbed polyimide. The elliptic shape is a consequence of the constraint upon droplet growth along the direction perpendicular to the cell surfaces owing to the small thickness. Then, the resulting droplets will have a contact area with the inner surfaces of the cell treated with polyimide, which will impart a planar orientation on the liquid crystal in the droplet. By means of an optical microscope, using a simple pin hole of 5 μ m, we have selected single droplets for a series of samples having different contact areas. By polarized infrared spectroscopy we have also studied the liquid crystal orientation in selected areas of the droplets. We then report the dependence of the order parameter of the liquid crystal on different contact areas with the alignment surface of the cell. The good degree of planar alignment of the liquid crystal in the elliptic droplets allows the use of such a technique for realizing electro-optical films operating in the reverse mode. We report the electro-optical transmission of reverse mode films with different sizes of elliptic droplet. 相似文献
960.
Sarah Fitzpatrick Les Ebdon Michael E. Foulkes 《International journal of environmental analytical chemistry》2013,93(11-12):835-841
A method is presented for arsenic speciation analysis of an oyster sample using ion chromatography coupled with an inductively coupled plasma mass spectrometry (ICP-MS) instrument. A strong anion exchange resin was employed with a step gradient elution of 0.1 mM/0.1 M K 2 SO 4 at pH 10.2. Arsenobetaine and dimethylarsinic acid were determined following extraction based on trypsin enzymolysis with 95-100% extraction efficiency. Limits of detection in the range 0.1-0.3 mg kg m 1 of arsenic were obtained for organic arsenic species. No inorganic arsenic was detected. Validation was performed using TORT-2 as a certified reference material. Although high performance liquid chromatography (HPLC) coupled to ICP-MS is an effective method for speciation analysis it is not always necessary to obtain such a detailed picture. A simple liquid chromatographic separation technique based upon mini-column technology is presented. It was developed to obtain a fast, efficient and reliable separation of inorganic from organic, i.e. assumed toxic from non-toxic, arsenic and selenium species suitable for use as an initial screening method for environmental analysis. Two types of strong anion exchange resin were tested. Excellent separation was obtained for both min-column resins and analysis times were within 7 min. Limits of detection obtained for inorganic arsenic, organic arsenic, selenomethionine, Se IV and Se VI were 1.6, 1.8, 66, 32 and 22 µg kg m 1 , respectively. 相似文献