Microwave synthesis of magnetic Fe3O4 nanoparticles used as a precursor of nanocomposites and ferrofluids

Methods to synthesize magnetic Fe₃O₄ nanoparticles and to modify the surface of particles are presented in the present investigation. Fe₃O₄ magnetic nanoparticles were prepared by the co-precipitation of Fe³⁺ and Fe²⁺, NH₃·H₂O was used as the precipitating agent to adjust the pH value, and the aging of Fe₃O₄ magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe₃O₄ magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe₃O₄ crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe₃O₄ magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe₃O₄ nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe₃O₄ nanoparticles. The dispersion of Fe₃O₄ in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe₃O₄/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe₃O₄ magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe₃O₄ nanoparticles. The Fe₃O₄ magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10⁻⁸ and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe₃O₄ nanoparticles in the fluid was 36.19 nm.     

弯曲波导之间的耦合分析

采用极坐标下的光束传播法分析了两条平行变曲波导的中心间距、曲率半径等因素对模式耦合的影响,得到了耦合长度、耦合强度随中心间距、曲率半径的变化规律,并将直波导作为变曲波导的一种特殊情况进行了分析.     

Single-mode rib polymer waveguides and electro-optic polymer waveguide switches

Mode-matching and effective index methods are used to analyze single-mode operation of optical rib polymer waveguides. Their single-mode waveguiding conditions are determined. Single-mode rib waveguides fabricated from guest–host polyetherketone are presented. The estimated propagation loss of straight rib-waveguides is 0.7 dB/cm at 1.55 μm. Furthermore, by using the mode field-transfer matrix method, 2×2 and 4×4 polymer Mach–Zehnder interference switch operating at 1.55 μm wavelength has been designed based on optical multi-mode interference.     

塑料脱模剂一组分的光谱分析

柱层析色谱分离性能优良的新型塑料脱模剂，纯化后得一主要未知组分。用元素分析、红外光谱、核磁共振氢谱研究其结构特征，对其盐酸酸化前后红外光谱吸收峰及核磁带进行了归属分析并确定结构。结果表明，该组分为一表面活性剂N，N-二羟乙基十二烷基胺。这为新型脱模剂的产品开发提供了依据。     

基于随机并行梯度下降算法的光束相干合成技术

介绍了随机并行梯度下降算法的基本原理,对算法流程进行了仿真验证,并对其中随机扰动幅度和增益系数两个关键参数进行了仿真分析。分析结果表明,这两个参数存在一个最适区间,只有在此区间内取值时算法才能有效收敛。以仿真分析为依据开展了光纤激光的相干合成实验,结果表明光束相干合成效果显著,有效地验证了仿真分析的结果。     

电磁波在大气层人造等离子体中的衰减特性

利用洛沦兹模型来研究大气层人造非均匀等离子体的电磁响应特性,讨论了电磁波频率、等离子体密度及电子碰撞频率对电磁波衰减特性的影响.结果表明,电磁波在长波长区域及等离子体密度大时,其能量衰减越快.当等离子体密度高时,电子温度越低,大气层高度越高,电磁波的能量衰减越快. 关键词： 电磁波 大气等离子体 能量衰减     

水中脉冲放电的电特性与声辐射特性研究

对水中脉冲放电等离子体通道电阻与放电参数之间的关系作了研究,得到了等离子体通道电阻与电容量、初始电压、电极间距离的关系,以及通道电阻随时间的变化规律.还对冲击波的峰值压力与放电参数间的关系作了研究,并对冲击波压力的功率谱作了分析,结果表明水中脉冲放电所产生的冲击波的声辐射频率在几十赫兹到几万赫兹之间,覆盖了所有水声设备的工作频率,且在低频段具有很强的声功率,是一种理想的水下声源 关键词： 水中脉冲放电 等离子体     

电沉积处理与染料敏化纳米薄膜太阳电池的优化

采用阳极氧化水解法对染料敏化纳米TiO₂薄膜太阳电池的光阳极进行不同方式的电沉积优化处理.借助x射线衍射仪对处理后的样品进行分析，通过超高分辨率场发射扫描电子显微镜对导电玻璃以及电沉积处理前后纳米多孔薄膜表面进行了粒径和形貌的扫描.染料敏化太阳电池实验测试结果表明，电沉积处理和修饰后可以明显提高光生电子的收集率，增大短路电流密度，提高电池效率. 关键词： 2')" href="#">纳米TiO₂ 染料敏化 电沉积 太阳电池     

利用尿素热退火方法制备氮掺杂石墨

在尿素气氛中,通过热退火实验实现石墨烯的氮掺杂. 结合光电子能谱和拉曼光谱,确定了氮在石墨烯中的掺杂构型,并发现掺杂量可以通过退火温度和时间加以调控. 电性测量表明掺杂石墨烯的电导同氮掺杂量有很好的关联性.     

采用密度泛函理论研究二甲基胺-二苯甲酮的分子内电荷转移激发态氢键

利用(含时)密度泛函理论研究了二甲基胺-二苯甲酮(DMABP)及其氢键二聚物DMABP-MeOH的光物理性质和弛豫动力学过程. 结果表明,在非极性和非质子性溶剂中,DMABP分子的第一和第二激发态跃迁同时具有局域激发和分子内电荷转移的特征;在极性质子性溶剂中,分子间氢键C=O…H-O的形成增加了这两个最低激发态之间的能量差,使DMABP-MeOH的第一激发态具有较强极性的分子内电荷转移特性. 通过计算DMABP和DMABP-MeOH分子的激发态构型弛豫势能曲线研究了激发态动力学弛豫过程. 结果表明,通过扭