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991.
阴离子本体开环聚合反应挤出合成聚三氟丙基甲基硅氧烷 总被引:4,自引:0,他引:4
以同向紧啮合双螺杆挤出机为反应器,硅醇钠/乙酸乙酯(EA)为引发体系,通过三氟丙基甲基环三硅氧烷(F3)阴离子本体开环聚合,制备了聚三氟丙基甲基硅氧烷(PMTFPS)。采用红外光谱(FT-IR),核磁共振(1H-NMR)和凝胶渗透色谱(GPC)确认了聚合物的结构与分子量,用电离飞行时间质谱分析了副产物的组成。研究表明,提高反应温度和EA用量可使反应平衡点提前到达。而螺杆转速对反应的主要影响在于改变聚合反应时间。因此,控制适当反应条件,使反应在平衡点到来时间之前终止,可得到高分子量以及高收率的PMTFPS。所得产物的数均分子量为2.41×105,分子量分散指数为1.12,产率为90.5%。 相似文献
992.
993.
Liu Zheng Jing Zhou Jie Shen Yanyuan Qi Sheng Li Shirley Shen 《Journal of Materials Science: Materials in Electronics》2018,29(20):17195-17200
PTFE-based ceramic-polymer dielectric composites have been widely researched in the communication field due to their good processing, wide range frequency and temperature stability and being able to provide tunable dielectric constant in a scale. In order to improve the compatibility between the ceramic fillers and polymer matrix without damage of dielectric properties, surface modifiers with less carbon remain are preferred. In this paper, tetraethylorthosilicate (TEOS) is employed as a surface modifier to improve the compatibility between the (Ca, Li, Sm)TiO3 (CLST) ceramic and PTFE, and the dispersion of the ceramic particles in the matrix. FTIR, XPS and TEM results indicate that TEOS is coated on the ceramic particles successfully and forms a silica coating layer. The surface modification improves the dispersion of particles in PTFE and interface contact between the ceramic fillers and PTFE matrix. These improve the thermal stability and reduce the dielectric loss of the dielectric composites. The CLST/PTFE composite modified by TEOS exhibits a dielectric constant of 6.22 with dielectric loss just 0.0012 at microwave frequencies (around 10 GHz). 相似文献
994.
Ji-Zhou Kong Zheng Wang Chun-Yan Luan Mei-Ling Wang Fei Zhou Xue-Mei Wu Wen-Jun Zhang Kong-Jun Zhu Jin-Hao Qiu Juan-Antonio Zapien Shuit-Tong Lee 《Journal of Materials Science: Materials in Electronics》2013,24(10):3868-3874
High-quality c-axis oriented 7 mol% Al and 1.5 mol% Er co-doped ZnO films (ZEAO) were prepared on the quartz glass substrates by using sol–gel method. The influence of the annealing temperature on the crystal orientation, microstructure and optical properties of the ZEAO thin films were studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and UV–vis transmittance spectrophotometer, respectively. XRD results revealed that all the samples were polycrystalline with hexagonal structure and exhibited (002) preferential orientation. With increasing the annealing temperature, the grain size and orientation extent increased. The optical studies showed each ZEAO film had a relatively high transmittance above 85 %. The transmittance as high as 95 % was obtained at the annealing temperature of 800 °C, and the corresponding average grain size was about 50 nm. The cathodoluminescence (CL) spectra of these films were also used to characterize the luminescence properties. Strong UV emission centered at 380 nm was observed in the CL spectra taken for the pure ZnO. For the ZEAO sample, the blue-green emission is related to the 4f shell transition in the Er3+ ions of ZnO matrices, corresponding to a transition from the excited states (4F5/2). 相似文献
995.
Enhanced Solar‐to‐Hydrogen Generation with Broadband Epsilon‐Near‐Zero Nanostructured Photocatalysts 下载免费PDF全文
Yi Tian Francisco Pelayo García de Arquer Cao‐Thang Dinh Gael Favraud Marcella Bonifazi Jun Li Min Liu Xixiang Zhang Xueli Zheng Md. Golam Kibria Sjoerd Hoogland David Sinton Edward H. Sargent Andrea Fratalocchi 《Advanced materials (Deerfield Beach, Fla.)》2017,29(27)
The direct conversion of solar energy into fuels or feedstock is an attractive approach to address increasing demand of renewable energy sources. Photocatalytic systems relying on the direct photoexcitation of metals have been explored to this end, a strategy that exploits the decay of plasmonic resonances into hot carriers. An efficient hot carrier generation and collection requires, ideally, their generation to be enclosed within few tens of nanometers at the metal interface, but it is challenging to achieve this across the broadband solar spectrum. Here the authors demonstrate a new photocatalyst for hydrogen evolution based on metal epsilon‐near‐zero metamaterials. The authors have designed these to achieve broadband strong light confinement at the metal interface across the entire solar spectrum. Using electron energy loss spectroscopy, the authors prove that hot carriers are generated in a broadband fashion within 10 nm in this system. The resulting photocatalyst achieves a hydrogen production rate of 9.5 µmol h?1 cm?2 that exceeds, by a factor of 3.2, that of the best previously reported plasmonic‐based photocatalysts for the dissociation of H2 with 50 h stable operation. 相似文献
996.
非对称矩阵结构系统固有值分析的广义逆迭代法 总被引:3,自引:0,他引:3
本文提出一种求解非对称矩阵结构的固有值的数值方法-通过广义的逆迭代过程把一个大型非对称的二次特征值问题简化为小型的标准特征值问题.算法不涉及复数运算,也不需把n阶的二次问题变换为2n阶的线性问题.迭代是在原n阶规模上进行,从而保持了系统各矩阵稀疏、带状的特点.节省了存储量和计算机时.数值实验表明本方法具有良好的稳定性和精度. 相似文献
997.
Jingwu Zheng Feifan Song Shenglei Che Wangchang Li Yao Ying Jing Yu Liang Qiao 《Advanced Powder Technology》2018,29(6):1474-1480
In the present work, the porous hollow carbon spheres loaded with NiFe2O4 nanoparticles have been successfully prepared via ultrasonic spray pyrolysis technique at 700?°C and the associated formation mechanism has been studied. The as-prepared NiFe2O4/carbon microspheres with the diameter of about 3–5?µm and the specific surface area of 236.6889?m2?g?1 exhibit good monodispersity and an abundance of mesopores of about 40?nm size. Notably, the 20?nm NiFe2O4 nanoparticles are encapsulated by carbon microspheres and disperse homogeneously inside the carbon matrix. We could tune the relative content of ferrite and carbon sphere via adjusting the composition of the solution used for synthesis and the carbonization temperature. Consequently, some interesting properties can be obtained by combining the magnetic NiFe2O4 nano powder and the electrically conductive porous carbon, which renders the resulting composite suitable for promising applications in electromagnetic wave absorption, treatment of polluted water, catalyst design, energy storage, batteries and so on. 相似文献
998.
通过脑功能磁共振技术,研究健康人参与语言的词语配对联想学习记忆任务的脑区和神经机制。对16名右利手健康志愿者进行一项词语配对联想学习记忆任务作业的同时,进行脑功能磁共振扫描。实验采用组块设计,实验任务(包括记忆编码相和记忆提取相)与对照任务(共两个相)交替进行;数据采用SPM99软件进行数据分析和脑功能区定位。结果表明:左侧额叶,特别是左侧额叶的额中下回和枕叶的18,19区在词语联想学习记忆的编码阶段中起重要作用;而左侧顶上小叶、缘上回和角回则在进行记忆提取阶段起重要作用;左侧纹状体边缘区参与了人脑词语联想学习记忆作业的编码阶段。揭示了人大脑完成语言联想学习记忆任务时,除额、顶、枕和颞叶的皮层结构参与外,还新发现有皮层下结构如纹状体参与了词语联想学习记忆。在配对词语的编码和提取阶段,激活的脑区有所变化,显示了这两个语言阶段的神经活动变化机制。 相似文献
999.
Yihui Sun Xiaoqin Yan Xin Zheng Yong Li Yichong Liu Yanwei Shen Yi Ding Yue Zhang 《Nano Research》2017,10(1):77-86
The carrier screening effect occurs commonly in dielectric materials. It reduces the electric potential gradient, thus negatively affecting the functionality of resistive random access memory (RRAM) devices. An Au/ZnO film/Al-doped ZnO device fabricated in this work exhibited no resistive switching (RS), which was attributed to the carrier screening effect. Therefore, annealing was used for alleviating the screening effect, significantly enhancing the RS property. In addition, different on/off ratios were obtained for various bias values, and the screening effect was accounted for by investigating electron transport mechanisms. Furthermore, different annealing temperatures were employed to modulate the free carrier concentration in ZnO films to alleviate the screening effect. The maximal on/off ratio reached 105 at an annealing temperature of 600 °C, yielding the lowest number of free carriers and the weakest screening effect in ZnO films. This work investigates the screening effect in RS devices. The screening effect not only modulates the characteristics of memory devices but also provides insight into the mechanism of RS in these devices. 相似文献
1000.