Fe3O4/PMMA纳米复合材料的制备及其磁流变性能

采用水热法以简单原料一步合成出Fe3O4/PMMA纳米复合材料，由于聚甲基丙烯酸甲酯（PMMA）的作用，Fe3O4由十几纳米部分聚集形成几百纳米的粒子，并在PMMA中分散较为均匀．复合粒子具有较高的饱和磁化强度，为超顺磁性。由合成的复合粒子制备得到的磁流变液具有较高的剪切屈服应力和储能模量，分别可达十几kPa和几MPa，其值随外加磁场的增大而增大。     

酞菁钴-Fe_3O_4纳米复合粒子的表征及其电磁流变液的研究

制备了粒径为微米级的酞菁钴（CoPc）－Fe3O4纳米复合粒子,并用它与氯化石蜡油组成了活性较高的无水电磁流变（EMR）液,同时用IR、XRD、SEM对（CoPc）－Fe3O4纳米复合粒子进行了表征。结果表明,CoPc在Fe3O4纳米粒子表面形成了单层分散层,其阈值（最大单层分散容量）为0．06gCoPcc／g（Fe3O4）。CoPc通过一定程度的化学键作用与Fe3O4纳米粒子形成了有效的复合,提高了其抗氧化能力和稳定性。该EMR液既具有电流变效应又具有磁流变效应,当同时施加电场和磁场时,它表现出显著的协同效应。     

PEI-b-PLA/Fe_3O_4磁性复合微球的制备及其性能表征

分别采用化学共沉淀法和开环聚合法合成了Fe3O4纳米粒子和星状聚合物PEI-b-PLA,然后采用自组装的方法合成了磁性复合微球PEI-b-PLA/Fe3O4。扫描电镜分析表明磁性复微球的粒径约为10nm,粒径大小主要取决于Fe3O4纳米粒子的粒径。热性能分析表明,PEI-b-PLA/Fe3O4复合微球的聚合物含量为6.6%。产物中Fe3O4含量较高。磁性能分析和紫外分析表明,磁性复合微球PEI-b-PLA/Fe3O4和聚合物PEI-b-PLA一样,可以包裹客体分子,同时具有超顺磁性。     

纳米Fe3O4/聚苯胺复合粒子的制备及其磁性能研究

用水解沉淀法制备纳米Fe3O4,然后在其溶液中原位合成聚苯胺,得到纳米Fe3O4/聚苯胺复合粒子.通过XRD、TEM、JDM等测试对纳米复合粒子的形态、结构及磁性能进行了研究.实验制备的纳米Fe3O4粒子粒径为30nm左右,在其表面沉积聚苯胺后,复合粒子的粒径达到了50nm左右.与纳米Fe3O4粒子相比,纳米Fe3O4/聚苯胺复合粒子的XRD峰形变得更为明锐.纳米复合粒子的磁性能表现出软磁性,与纳米Fe3O4粒子相比,矫顽力减小为0,这可以大大减小材料的磁滞损耗和退磁难度,性能得到改善.     

改性Fe3O4纳米粒子在磁性复合超滤膜中的应用

为解决Fe3O4纳米粒子在磁性复合超滤膜中发生团聚和分布不均匀的问题,文中以市售20nm的Fe3O4粒子为对照,添加自制的改性Fe3O4纳米粒子制备出Fe3O4-聚砜(PSF)磁性复合超滤膜(改性复合超滤膜)。经扫描电镜观察膜表面形貌、能谱仪扫描复合膜中Fe元素分布以及铸膜液中Fe3O4纳米粒子分布情况分析和复合膜孔径分布测试后表明,改性后复合超滤膜中纳米粒子的分布较改性前更为均匀,且未出现粒子团聚现象,改性效果明显。由改性前后的复合膜在不同磁场下对聚乙二醇6000和10000的截留率呈现几乎相同的变化趋势可知,添加改性粒子并未改变磁性复合膜的分离特性。     

核/壳型Fe/Y_2O_3纳米复合粒子的制备及微结构分析

以Fe和Y2O3的微米粉为原料,压制成块体靶材,利用物理气相蒸发法原位合成了核/壳型Fe/Y2O3纳米复合粒子,并对其成分、形态和微结构进行了研究。高分辨透射电镜和暗场成像分析结果表明Fe/Y2O3纳米复合粒子具有清晰的核/壳结构,其内核及外壳分别为-αFe和体心立方相Y2O3。通过定量氧辅助-气-液-固机制对纳米复合粒子的形成过程进行了探讨。实验结果表明,本文所采用的物理气相方法实现了稀土氧化物包覆异质金属纳米胶囊的合成,为多组元纳米结构的复合提供了实验依据。     

磁性羧甲基化壳聚糖纳米粒子的制备与表征

以化学共沉淀法制备了Fe3O4纳米粒子,壳聚糖经羧甲基化改性后接枝在Fe3O4颗粒表面,得到了磁性羧甲基化壳聚糖(Fe3O4/CMC)纳米粒子.利用透射电镜(TEM)、X射线衍射(XRD)、傅立叶红外光谱(FT-IR)及磁性测试对产物进行了表征.TEM表明Fe3O4纳米粒子被CMC包覆,粒径约10 nm;XRD分析表明复合纳米粒子中磁性物质为Fe3O4;FT-IR表明壳聚糖发生羧甲基反应以及在Fe3O4表面的接枝反应.Fe3O4/CMC纳米粒子具有超顺磁性,比饱和磁化强度25.73 emu/g,有良好的磁稳定性.     

磁场诱导和晶种联合法制备链状Fe_3O_4

以粒径为700nm的球形Fe3O4为晶种,将晶种加入到含有FeSO4.7H2O、FeCl3.6H2O与尿素的混合溶液中,在磁场诱导下制备链状Fe3O4。研究了磁场强度、晶种添加量、分散剂聚乙烯吡咯烷酮(PVP)质量浓度以及反应时间对产品形貌的影响。研究结果表明,随着磁场强度的增大、晶种量的增加,链状粒子数目显著增多;适量的PVP能使链状粒子分散平行排列。合成链状Fe3O4粒子的最佳工艺条件为磁场强度0.35T,晶种用量10%,PVP质量浓度7.5g/L,反应18h。磁性能测试表明,该链状Fe3O4粒子具有亚铁磁性,磁饱和强度为72.3emu/g,矫顽力为381Oe。     

溶胶-凝胶法制备核壳SiO2/Fe3O4复合纳米粒子的研究

采用溶胶-凝胶法,以尺寸约10nm的Fe3O4纳米粒子为种子,碱催化正硅酸已酯(TEOS)水解、缩合,制备了磁性可控的核壳结构SiO2/Fe3O4复合纳米粒子.系统研究了醇水比、NH4OH及TEOS的浓度对复合纳米粒子形貌和性能的影响,并分析了SiO2/Fe3O4复合纳米粒子的生成机理.结果表明,SiO2的生长主要是SiO2初级粒子在Fe3O4表面的聚集生长,醇水比为4∶1、NH4OH浓度为0.3mol/L和TEOS浓度低于0.02mol/L时,随TEOS浓度的增大,SiO2壳层增厚,复合粒子饱和磁化强度下降,矫顽力基本不变,仍具有良好的超顺磁性.     

羧甲基纤维素-Fe_3O_4复合纳米磁性材料的制备及其渗透性能

采用改进的氧化沉淀法在羧甲基纤维素(CMC)溶液中制备了以磁性纳米Fe3O4为核心,外包CMC的复合磁性纳米粒子。用透射电镜、X射线衍射、红外光谱、Zeta电位和震动样品磁强计对复合粒子进行了表面形貌、结构和磁学的表征。实验结果表明,CMC-Fe3O4复合纳米粒子为反尖晶石型,平均粒径约为40 nm;CMC在Fe3O4粒子表面是化学吸附;在相同pH值下,CMC-Fe3O4的表面Zeta电位低于纯相Fe3O4;CMC-Fe3O4的饱和磁化强度为36.74 emu.g-1;CMC-Fe3O4复合粒子在土壤介质中的过滤系数约为0.03 cm-1;在10 cm土柱渗透实验中,72%的CMC-Fe3O4复合粒子悬浊液穿过了土壤介质。     

Novel Magnetorheological Suspensions Based on Co-Phthalocyanine/Fe Nanocomposite Particles

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Nanostructured magnetic particles with polystyrene and their magnetorheological applications

Magnetorheological (MR) fluids are known to be colloidal suspensions of magnetic particles in a non-magnetic fluid, and exposure to a magnetic field transforms the fluid into a plastic-like solid in milliseconds. To improve the stability against sedimentation and uniform dispersion, two different MR candidates, soft magnetic carbonyl iron (CI) microspheres and magnetite (Fe3O4) particles were modified with polystyrene to be applied for MR fluids in this study. After modification, their unique morphology, crystalline structure and magnetic properties were examined in addition to MR performance and sedimentation characteristics. It was found that this embedded morphology not only effectively prevents direct contact of the magnetic species thus improving particle dispersion but also leads to obvious change in their density, compared with the traditional polymer coating method with a core-shell structure.     

纳米复合磁流变液的流变特性

在不同的磁场强度H、剪切速率γ和温度T下,测试了纳米复合磁流变(MR)液的磁致剪切应力△τ以及响应时间△tο结果表明,H、γ和T对纳米复合MR液的△t的影响较小,纳米复合MR液对撤消磁场的响应比施加磁场的响应略慢;随H增加,△τ增加;随户提高、△τ出现最大值;随T升高,△τ缓慢降低。它们之间的定量关系可用公式△τ=kHH+(Kγ1-kγ2γ)γ-kt△T来描述,其中:kH=28.32,kγ1=2.85,kγ2=0.0013,kt=3.8。用它能较全面地评价纳米复合MR液的性能,并可作为设计磁流变液智能器件的基础。     

Synthesis and characterization of SiO2/(PMMA/Fe3O4) magnetic nanocomposites

Magnetic silica nanocomposites (magnetic nanoparticles core coated by silica shell) have the wide promising applications in the biomedical field and usually been prepared based on the famous St?ber process. However, the flocculation of Fe3O4 nanoparticles easily occurs during the silica coating, which limits the amount of magnetic silica particles produced in the St?ber process. In this paper, PMMA/Fe3O4 nanoparticles were used in the St?ber process instead of the "nude" Fe3O4 nanoparticles. And coating Fe3O4 with PMMA polymer beforehand can prevent magnetic nanoparticles from the aggregation that usually comes from the increasing of ionic strength during the hydrolyzation of tetraethoxysilane (TEOS) by the steric hindrance. The results show that the critical concentration of magnetic nanoparticles can increase from 12 mg/L for "nude" Fe3O4 nanoparticles to 3 g/L for PMMA/Fe3O4 nanoparticles during the St?ber process. And before the deposition of silica shell, the surface of PMMA/FeO4 nanoparticles had to be further modified by hydrolyzing them in CH3OH/NH3 x H2O mixture solution, which provides the carboxyl groups on their surface to react further with the silanol groups of silicic acid.     

Non-Settling Super-Strong Magnetorheological Fluids

A magnetorheological (MR) fluid is generally called a suspension in which magnetic particles are dispersed in a non-magnetic medium. When an external magnetic field is applied, a pseudo-phase transition occurs within a short time to generate yield stress, and when the magnetic field is released, it returns to the suspended state. Due to these unique characteristics, it is classified as a smart material to be widely applied in various industries. High performance MR fluids require high yield stress and stability for long-term use. However, it is very difficult to improve performance and stability simultaneously due to the limited amount of magnetic particles in the suspension and particle sedimentation caused by the density mismatch between the suspending particles and the liquid phase. In this study, an MR slurry is developed that is completely different from the MR suspension, starting from the opposite concept. An innovative non-settling (i.e., permanently stable) magnetorheological slurry is successfully created that exhibits unprecedented ultra-high yield stress. This result is expected to be a turning point for applying MR fluids to more diverse industries. In addition, a simple fitting equation expressing the yield stress as a function of the particle volume fraction is proposed.     

Fe3O4/聚苯乙烯磁性微球的合成与表征

用化学共沉淀法合成了Fe3O4纳米微粒,并用双层表面活性剂对其进行表面修饰,得到了以水和乙醇为分散介质的磁流体。在磁流体的存在下,用改进的乳液聚合方法合成了Fe3O4/聚苯乙烯磁性微球。X射线衍射研究表明,Fe3O4纳米微粒的平均粒径约为10 nm;在透射电镜下观察磁性微球的粒径在140 nm左右;并用红外光谱和热失重方法表征了复合微球的化学成分及其所含Fe3O4的百分数。阐述了双层表面活性剂改性的机理,并对聚合过程中单体、磁流体及引发剂的用量的影响进行了讨论。     

A novel nanoscale catalyst system composed of nanosized Pd catalysts immobilized on Fe(3)O(4)@SiO(2)-PAMAM

This study reports the syntheses of Fe(3)O(4)@SiO(2)-Gn-PAMAM-Pd(0) composites and their applications as magnetically recoverable catalysts for the hydrogenation of allyl alcohol. The controlled growth of polyamidoamine (PAMAM) dendrimers with different generations on Fe(3)O(4)@SiO(2) surfaces was monitored by FT-IR spectra. Subsequently, Pd nanoparticles with diameters of about 2.5?nm were stabilized homogeneously on the surface of Fe(3)O(4)@SiO(2)-Gn-PAMAM (n = 1-4), investigated by thermogravimetry (TG) and transmission electron microscopy (TEM) measurements. The?Fe(3)O(4)@SiO(2)-Gn-PAMAM-Pd(0) have high catalytic activity for the hydrogenation of allyl alcohol and the rate of the reaction can be controlled by changing the generation of PAMAM. In particular, the composites made of superparamagnetic Fe(3)O(4) nanocrystals with diameters of about 10?nm are very suitable as catalyst supports for catalyst separation under a relatively low external magnetic field and catalyst re-dispersion after removing the external magnetic field.     

Fe_3O_4@胺甲基改性植物多酚磁絮凝收集能源微藻

对落叶松植物多酚进行胺甲基化改性,将其包覆于磁性Fe_3O_4颗粒表面,制备了功能化Fe_3O_4@胺甲基改性植物多酚(Fe_3O_4@A-PP),用于能源微藻-普通小球藻的收集。采用FTIR、磁滞回线、zeta电位的方法对Fe_3O_4@A-PP磁性材料的物理化学性质进行了测定,并研究了投加方式、包覆比例对Fe_3O_4@A-PP收集微藻效能的影响。FTIR显示Fe_3O_4@A-PP具有来自A-PP的C—H、N—H和—OH等官能团。A-PP包覆对Fe_3O_4的磁性无改变。与A-PP的zeta电位相比,Fe_3O_4@A-PP的zeta电位增大了5~10mV。Fe_3O_4@A-PP中两者配比影响微藻的收集效率,当配比为20/200时,收集率达到最大值84.2%。采用Fe_3O_4@A-PP可以将磁絮凝收集时间从A-PP的30min缩短至0.5 min以内。显微图像显示,与A-PP絮凝后絮体呈片状松散团聚的状态相比,Fe_3O_4@A-PP收集的微藻细胞呈链状被Fe_3O_4包裹或团簇在其四周。吸附电中和在Fe_3O_4@A-PP磁絮凝收集微藻的机理中发挥重要作用。     

磁场作用下磁流变液剪切性能的实验分析

本文研究了磁流变液的力学性能,制备了羰基铁粉体积分数为20%的硅油基磁流变液,观察了磁流变液在磁场作用下的微观变化,测试了磁流变液的剪切性能。实验表明,无磁场作用下,磁流变液为牛顿流体;在磁场作用下,随着剪切速率的增加,剪切应力趋于稳定,表观粘度呈现指数式下降,磁流变液具有剪切稀化效应,符合广义Bingham模型。磁流变液剪切应力和外加电流的依赖关系为:在电流较小时,剪切应力表现为指数增长,指数值约为1.5;随着外加电流的增大,剪切应力表现为线性增长,最终达到稳定值。     

Influence of grain boundaries and voids on the saturated magnetization in Fe/sub 3/O/sub 4/ films at a low magnetic field

We report the magnetic behaviors of Fe/sub 3/O/sub 4/ thin films grown by zero field growth (ZFG) and field growth (FG) techniques during the sputtering process. In FG conditions, an in situ 300 Oe field during growth is applied to a substrate, inducing an easy axis of magnetization. Structural observations obtained by high-resolution transmission electron microscopy measurements clearly depicted a significant reduction of the grain boundaries and voids in the Fe/sub 3/O/sub 4/ films grown under FG conditions, thus explaining the saturated magnetization of the Fe/sub 3/O/sub 4/ films at about 0.01 T. This behavior was expected due to a remarkable reduction of the antiferromagnetic exchange couplings between grains for FG conditions. In addition, the zero-field-cooled magnetization of the ZFG samples showed an abrupt change at about 285 K, confirming the existence of defects or other phases in the ZFG films.