铁酸钴纳米晶的低温合成、谱学表征及磁性

以十六烷基三甲基溴化铵（CTAB）为模板,Fe(NO3)3·9H2O和Co(NO3)2·6H2O为前躯体,NaOH为沉淀剂,低温回流合成了磁性铁酸钴纳米晶。利用X射线衍射、透射电子显微镜、红外光谱、拉曼光谱等测试技术对产品的结构进行了表征,借助振动样品磁强计测定了样品的室温磁性能。结果表明,铁酸钴纳米晶为单相立方尖晶石结构,纳米晶的平均粒径为15-20 nm。铁酸钴纳米晶在室温外加磁场下表现出明显的磁滞现象,饱和比磁化强度MS=36.5 A.m2/kg,矫顽力HC=5.89×104 A/m。     

Electromagnetic functionalized cage-like polyaniline composite nanostructures

Novel cage-like and electromagnetic functional polyaniline (PANI)/CoFe2O4 composite nanostructures, in which the self-assembled PANI nanofibers (approximately 15 nm in diameter) entwined around the octahedral CoFe2O4 magnet acting as the nucleation site or template, were successfully prepared by FeCl3 as either oxidant and dopant via a self-assembly process. The coordination effect of the magnet as a nucleation site or template and the magnetic interaction between the PANI nanofibers and CoFe2O4 as a driving force results in such cage-like nanostructures. The cage-like composite nanostructures not only have high conductivity (sigmamax approximately 5.2 S/cm), but also show a typical ferromagnetic behavior.     

导电聚苯胺与磁性CoFe2O4纳米复合物的合成及其电磁性能

在利用HNO3处理CoFe2O4磁性纳米粒子使其表面离子化、分散性得到改善的基础上, 采用苯胺在其表面原位聚合, 制备了具有电磁功能的聚苯胺(PANI)/CoFe2O4纳米复合物. 借助TEM、XRD、FT-IR、四探针电导率仪和VSM(振动样品磁强计)等分析手段研究了复合物的形貌、结构及其电磁性能. 结果表明, CoFe2O4以25 nm左右的粒子分散于聚苯胺基体中, 被其完全包覆, CoFe2O4与PANI之间存在化学键合作用; 复合物同时具有电性能和磁性能, 其导电率随CoFe2O4含量增加而降低, 饱和磁化强度随之升高, 而矫顽力在所研究的范围内则先增大而后又减小, 且均高于CoFe2O4的矫顽力.     

一维多孔Fe-B合金纳米结构的制备及其磁性质

在十六烷基三甲基溴化铵(CTAB)的水溶液中,用NaBH₄还原FeCl₃,在反应过程中施加外部磁场,制得了一维多孔Fe-B合金纳米结构。研究表明,外部磁场对一维纳米结构的形成有重要影响,当不加外部磁场时得到的是离散的球形纳米粒子;外部磁场还影响Fe-B纳米粒子的晶体结构：外部磁场存在下得到的是无定形Fe-B合金,而不加外部磁场时则得到多晶Fe-B合金。CTAB对多孔的形成起到关键的作用,当不加CTAB时得到了实心球状纳米粒子。初步讨论了这种一维孔状Fe-B合金纳米结构的形成机理。用XRD、ICP-AES、TEM对样品进行了表征,测定了它们的磁性质。结果表明,在施加不同磁场强度条件下制得的样品具有不同的饱和磁化强度和矫顽力。     

憎水性三金属纳米粒子的合成、表征及磁性

以磺基琥珀酸二辛酯钠盐(AOT)为表面活性剂,采用反胶束法合成了憎水性CoFe/Au纳米粒子, 利用配体交换、水洗等去除AOT并使纳米粒子分级.采用紫外-可见光谱(UV-Vis)、透射电镜(TEM)、X射线衍射(XRD)、X射线电子能量散射(EDX)及等离子发射光谱 (ICP)等对产物进行了表征,通过超导量子干涉仪(SQIUD)研究了纳米粒子的磁性质.结果表明,反胶束法合成的CoFe/Au三金属纳米粒子具有较好的单分散性和稳定性,平均粒径约为4 nm.当外磁场强度为1.5×10⁴ A/m时,阻塞温度T_b为65 K,温度高于T_b时纳米粒子显示出超顺磁性,低于T_b时呈铁磁性,在5 K时其矫顽力(Hc)达4.67×10⁴ A/m.     

Controlled synthesis and magnetic properties of bimagnetic spinel ferrite CoFe2O4 and MnFe2O4 nanocrystals with core-shell architecture

A combination of hard phase CoFe(2)O(4) and soft phase MnFe(2)O(4) as the bimagnetic nanocrystals in a core-shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core-shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe(2)O(4) and MnFe(2)O(4) nanocrystals, chemically mixed Co(1-x)Mn(x)Fe(2)O(4) nanocrystals, and bimagnetic core-shell CoFe(2)O(4)@MnFe(2)O(4) and MnFe(2)O(4)@CoFe(2)O(4) nanocrystals, the bimagnetic core-shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the soft phase as the theoretical hard-soft phase model has suggested. Furthermore, switching the hard phase CoFe(2)O(4) from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core-shell nanocrystals evidently demonstrate the rational design capability to separately control the blocking temperature and the coercivity in magnetic nanocrystals by varying the materials, their combination, and the volume ratio between the core and the shell and by switching hard or soft phase materials between the core and shell. Such controls via a bimagnetic core-shell architecture are highly desirable for magnetic nanocrystals in various applications.     

EFFECT OF COMPOSITION AND PROCESSING CONDITION ON MICROSTRUCTURAL PROPERTIES AND DURABILITY OF FLUOROPOLYMER/ACRYLIC BLENDS

 Fluoropolymer blends have been widely used as binders for exterior coatings because of their excellent resistance to ultra-violet (UV) radiation as well as to many corrosive chemical agents. It is known that the fluorinated component usually has a lower glass transition temperature and easily crystallizes in the final structure depending upon the blend composition and sample annealing condition. We investigated the effect of blend composition and annealing process (slow and fast cooling) on the surface morphology and microstructure a poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blend before and after UV exposure. Surface and subsurface microstructures were studied by atomic force microscopy (AFM) and laser scanning confocal microscopy (LSCM). Bulk microstructure of PVDF-coatings before and after UV exposure were characterized using small angle neutron and light scattering. Higher PVDF content and a slow cooling process result in larger spherulite crystallite structure and rougher surface morphology. Significant ordering in the spherulite crystallite structure has been observed on the surface and the bulk films after UV exposure.     

静电纺丝法制备定向排列的铁氧体纳米纤维

以聚乙烯吡咯烷酮(PVP)和金属硝酸盐为原料,采用改进的静电纺丝法制备了直径均匀、表面光滑、定向排列的Co0.8Zn0.2Fe2O4/PVP纳米纤维前驱体,经热处理后得到定向排列的铁氧体纳米纤维.对前驱体纤维的热分解过程及Co0.8Zn0.2Fe2O4(CZFO)的结构、物相及形貌进行了表征.结果表明,在空气中经550～950℃热处理3 h后均得到纯相、结晶良好的尖晶石型钴锌铁氧体;在2000 r/min转速下收集的复合纤维形貌最佳,直径约300 nm;经750℃热处理后纤维直径约为70 nm,室温下测得饱和磁化强度为66.1 A.m2/kg,矫顽力达到最大值6.6 A/m,表明钴锌尖晶石型铁氧体单畴临界尺寸约为44 nm.与CoFe2O4相比,CZFO的饱和磁化强度升高,矫顽力下降,并且CZFO的纤维与粉末的磁特性有明显的区别.     

Properties of nanocrystalline electrodeposited CoFeP alloy with low phosphorus content

CoFe and low phosphorus containing (<4 at.%) CoFeP alloy films were electrodeposited from NaH₂PO₂ containing solutions at pH 4 on copper substrates under galvanostatic conditions. At the low phosphorus composition, nanocrystalline CoFeP alloy films are formed. The structure, composition and morphology of the thin films were studied using X-ray diffraction, energy dispersive spectroscopy and atomic force microscopy. The magnetic properties of the film were studied using superconducting quantum interference device magnetometer. The thin film performance features were explained on the basis of microstructural features developed during deposition. Whereas the electrodeposited CoFe alloy thin film exhibited mixed hcp and fcc phase structure in the absence of phosphorus, the low phosphorus containing thin film exhibited an increasing mixed bcc and hcp phase structure as its phosphorus content increases, showing modification in the grain size morphology and magnetic properties. In addition to applied current, the amount of P co-deposited in CoFeP alloy depends on the concentration of NaH₂PO₂ source in the bath. Qualitative analysis of the Tafel slope of CoFe and CoFeP deposition suggests that the presence of P in the CoFe deposit does not affect the mechanism of anomalous deposition of Co and Fe, thereby suggesting that CoFeP deposition is anomalous.     

Effects of quenching on the morphology and crystal structure of ZnO nanostructures

Zinc oxide nanostructures were prepared by a simple wet chemical procedure using zinc acetate and sodium hydroxide as precursors. The process was subjected to quenching treatment and the effect of the treatment on the formation of the nanostructures was studied using atomic force and scanning electron microscopies. The change in crystal structure of the nanostructures due to quenching was studied using an X-ray diffractometry that established that physical and structural properties of the nanostructures were largely influenced by the quenching treatment.     

Enhanced energy storage performance of nanocrystalline Sm-doped CoFe2O4 as an effective anode material for Li-ion battery applications

Journal of Solid State Electrochemistry - A simple modified combustion method was demonstrated in the development of cobalt ferrite (CoFe2O4) and samarium (Sm)-doped CoFe2O4 nanostructures. The...     

Supramolecular nanostructures based on bacterial reaction center proteins and quantum dots

Design of the nanostructures based on membrane proteins (the key functional elements of biomembranes) and colloid nanoparticles is a fascinating field at the interface of biochemistry and colloids, nanotechnology and biomedicine. The review discusses the main achievements in the field of ultrathin films prepared from bacterial reaction center proteins and light-harvesting complexes, as well as these complexes tagged with quantum dots. The principles of preparation of these thin films and their structure and properties at different interfaces are described; as well as their characteristics estimated using a combination of the modern interfacial techniques (absorption and fluorescence spectroscopy, atomic force and Brewster angle microscopy, etc.) are discussed. Further approaches to develop the nanostructures based on the membrane proteins and quantum dots are suggested. These supramolecular nanostructures are promising prototypes of the materials for photovoltaic, optoelectronic and biosensing applications.     

Polymeric nanocomposite materials: Preparation and characterization of star-shaped PbS nanocrystals and their influence on the thermal stability of acrylonitrile-butadiene-styrene (ABS) copolymer

Star-shaped PbS nanocrystals were synthesized via a simple hydrothermal reaction between Pb(NO₃)₂·4H₂O and thioglycolic acid at a relatively low temperature. The PbS nanostructures were then combined in a acrylonitrile-butadiene-styrene copolymer. The effect of the PbS nanostructures on the thermal stability of the nanocomposite products has been investigated. The nanostructures and nanocomposite were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, thermogravimetric-differential thermal analysis and atomic force microscopy. Cone calorimeter measurements showed that the heat release rate significantly decreased in the presence of PbS.     

Morphology-controlled fabrication of polygonal ZnO nanobowls templated from spherical polymeric nanowell arrays

We report a facile and effective strategy for synthesizing morphology-controlled patterned ZnO nanostructures. Polymeric nanowell arrays were employed as scaffold templates, followed by solution dipping and calcination process, polygonal ZnO nanobowl structures were fabricated on silicon substrate. The ordered polymeric nanowell arrays not only provided confined areas for depositing desired materials, but also induced shape transition of ZnO nanobowls from circular to polygonal. The morphology of the patterned ZnO nanostructures can be easily controlled by tuning parameters of polymeric nanowell arrays and other treatment conditions. The patterned structures were characterized by field emission scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA).     

EFFECT OF COMPOSITION AND PROCESSING CONDITION ON MICROSTRUCTURAL PROPERTIES AND DURABILITY OF FLUOROPOLYMER/ACRYLIC BLENDS

Fluoropolymer blends have been widely used as binders for exterior coatings because of their excellent resistance to ultra-violet (UV) radiation as well as to many corrosive chemical agents.It is known that the fluorinated component usually has a lower glass transition temperature and easily crystallizes in the final structure depending upon the blend composition and sample annealing condition.We investigated the effect of blend composition and annealing process (slow and fast cooling) on the surface mor...     

Magnetic antidot arrays on alumina nanoporous membranes: Rutherford backscattering and magnetic characterization

Highly ordered antidot arrays of permalloy have been prepared by sputtering onto different nanoporous alumina membranes (NAMs) and characterized by Rutherford backscattering spectrometry (RBS), SEM and Vibrating sample magnetometry (VSM). RBS spectrometry combined with SEM image analysis provides information on the in‐depth composition and porosity of the different magnetic antidot nanostructures. The coercivity increases in the antidot nanostructures as compared with that of its parent continuous film. The saturation magnetization values of the antidot nanostructures are observed to increase with increasing pore size. Our results suggest an enhanced magnetization at the Fe₂₀Ni₈₀/Al₂O₃ interface. Copyright © 2011 John Wiley & Sons, Ltd.     

Correlation between spin-orbital coupling and the superparamagnetic properties in magnetite and cobalt ferrite spinel nanocrystals

The superparamagnetic properties of CoFe2O4 and Fe3O4 nanocrystals have been systematically investigated. The observed blocking temperature of CoFe2O4 nanocrystals is at least 100 deg higher than that of the same sized Fe3O4 nanocrystals. The coercivity of CoFe2O4 nanocrystals at 5 K is over 50 times higher than the same sized Fe3O4 nanocrystals. The drastic difference in superparamagnetic properties between the similar sized spherical CoFe2O4 and Fe3O4 (or FeFe2O4) spinel ferrite nanocrystals was correlated to the coupling strength between electron spin and orbital angular momentum (L-S) in magnetic cations. Compared to the Fe2+ ion, the effect of much stronger spin-orbital coupling at Co2+ lattice sites leads to a higher magnetic anisotropy and results in the dramatic discrepancy of superparamagnetic properties between CoFe2O4 and Fe3O4 nanocrystals. These results provide some insight to the fundamental understanding of the quantum origin of superparamagnetic properties. Furthermore, they suggest that it is possible to control the superparamagnetic properties through magnetic coupling at the atomic level in spinel ferrite nanocrystals for various applications.     

Electric field induced AC alignment and realignment, a study of a liquid-crystalline copolymer having longitudinally and laterally attached mesogenic groups as side chains monitored through dielectric spectroscopy and optical thermomicroscopy

A study of a liquid crystal side chain copolymer with a siloxane backbone has been carried out using dielectric relaxation spectroscopy and optical microscopy. We have found that this particular copolymer, a mixture of longitudinally and laterally attached mesogens, can be aligned both homeotropically and planarly between two electrodes using a directing AC field of specific frequency by cooling from the melt or more importantly at temperatures below the clearing point (T_c). The switching of the material from homeotropic to planar and the reverse has been studied at temperatures below T_c. It is shown that the kinetics of realignment are strongly dependent on the electrical/thermal history of the sample. The dielectric data allows the state of alignment of the sample to be monitored and the molecular dynamics to be studied. The optical textures of the polymer which were subjected to different AC electric fields have been observed and provide complementary information to the dielectric work on the state of the aligned sample.     

NixPb1-x nanowire arrays: effects of annealing

Ni(x)Pb(1-x) nanowire arrays were successfully fabricated by AC electrodeposition within the nanopores of ordered porous alumina films prepared by a two-step anodization. Transmission electron microscopy analyses showed that the Ni-Pb nanoarrays are polycrystalline with dimension uniformity around 20 nm in diameter and lengths up to several micrometers. X-ray diffraction results revealed that the face-centered-cubic (fcc) Ni and fcc Pb peaks are detected when the Ni component (x) is below 0.71, indicating that the Ni(x)Pb(1-x) nanoarrays do not form metastable phase alloy. Hysteresis loops determined by vibrating sample magnetometer indicated that the Ni(x)Pb(1-x) nanoarrays obtained possess obvious magnetic anisotropy, and the perpendicular coercivity was lower than that of pure Ni nanowries before and after annealing. Annealing under magnetic field was carried out to examine the effect of a magnetic field on magnetic properties using an electromagnet field up to 0.3 T.     

Photoactive Nanostructures of Polypyrrole

The creation of nanostructures of the photoactive polymer polypyrrole (PPy) on glass substrates with the spin‐coating method is described. No additional post‐production treatment is necessary to obtain uniformly distributed photoactive nanostructures on macroscopically scaled substrates. Based on X‐ray reflectivity measurements, the critical solution concentration of PPy below which these nanostructures develop is determined. The PPy nanostructures are displayed with atomic force microscopy (AFM) measurements, which prove that the nanostructures form directly on the substrate. With UV/Vis spectroscopy the absorption behavior of the nanostructures is probed in comparison to PPy films and PPy solutions. A linear dependence of the absorption of the nanostructure on the surface coverage measured with AFM is detected. The influence of confinement on the conjugation length results in a modified absorption behavior of the nanostructures.