Preparation of Nanoparticles of Barium Ferrite from Precipitation in Microemulsions

Magnetic nanoparticles of barium ferrite (BaFe₁₂O₁₉) have been synthesized using a microemulsion mediated process. The aqueous cores of water-in-oil microemulsions were used as constrained microreactors for the precipitation of precursor carbonate and hydroxide particles. These precursors were then calcined at 925°C for 12h, during which time they were transformed to the hexagonal ferrite. The pH of reaction was varied between 5 and 12, and it was found that the fraction of non-magnetic hematite (-Fe₂O₃) in the particles varied with the pH of reaction, thus affecting the magnetic properties of the particles. The same precursor particles were also prepared by bulk co-precipitation reaction for comparison. It was found that the microemulsion derived nanoparticles of barium ferrite had both higher intrinsic coercivity (H_c) and saturation magnetization (_s) than the particles derived from bulk co-precipitation. Particles were analyzed by electron microscopy, X-ray diffraction, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The best barium ferrite particles produced by the microemulsion synthesis method yielded an intrinsic coercivity of 4310Oe and a saturation magnetization of 60.48emu/g.     

Preparation of AgBr Nanoparticles in Microemulsions Via Reaction of AgNO<Subscript>3</Subscript> with CTAB Counterion

Nanoparticles of AgBr were prepared by precipitating AgBr in the water pools of microemulsions consisting of CTAB, n-butanol, isooctane and water. An aqueous solution of AgNO₃ added to the microemulsion was the source of Ag⁺ ions. The formation of AgBr nanoparticles in microemulsions through direct reaction with the surfactant counterion is a novel approach aimed at decreasing the role of intermicellar nucleation on nanoparticle formation for rapid reactions. The availability of the surfactant counterion in every reverse micelle and the rapidity of the reaction with the counterion trigger nucleation within individual reverse micelles. The effect of the following variables on the particle size and size distribution was investigated: the surfactant and cosurfactant concentrations, moles of AgNO₃ added, and water to surfactant mole ratio, R. High concentration of the surfactant or cosurfactant, or high water content of the microemulsion favored intermicellar nucleation and resulted in the formation of large particles with broad size distribution, while high amounts of AgNO₃ favored nucleation within individual micelles and resulted in small nanoparticles with narrow size distribution. A blue shift in the UV absorption threshold corresponding to a decrease in the particle size was generally observed. Notably, the variation of the absorption peak size with the nanoparticle size was opposite to those reported by us in previous studies using different surfactants.     

Preparation of Ultrafine Colloidal Gold Particles using a Bioactive Molecule

Synthesis of nanometer-sized particles with new physical properties is an area of tremendous interest. In metal particles, the changes in size modify the electron density in the particles, which shifts the plasmon band. The most significant size effects occur when the particles are ultrafine (size is <10 nm). Thus the synthesis of ultrafine metal particles is enormously important to exploit their unique and selective application. Here we report a novel method for the synthesis of ultrafine gold particles in the size range of 0.5–3 nm using dopamine hydrochloride (dhc), an important neurotransmitter. This is the first time where such an important bioactive molecule like dhc has been used as a reagent for the transformation of Au(III) to Au(0). The synthesis is carried out, for the first time, either in simple aqueous or in a nonionic micellar (for example Triton X-100 (TX-100)) medium. The gold sol has a beautiful yellow–brown color showing _max at 470 nm. The appearance of the absorption peak at substantially shorter wavelength (usually gold sol absorbs at 520 nm) indicates that the particles are very small. The method discussed here is very simple, reproducible and does not involve any reagent, which contains 'P' or 'S' atoms. Also in this case no polymer or dendrimer or thiol-related stabilizer is used. The effects of different parameters (such as the presence or absence of O₂, temperature, TX-100 concentration and dhc concentration) on the formation of ultrafine gold particles are discussed. The effects of 3-mercapto propionic acid and pyridine on the ultrafine gold sol are also studied and compared with those on photochemically prepared gold sol. It is observed that 3-mercapto propionic acid dampens the plasmon absorption at 470 nm of ultrafine gold particles. Pyridine, on the other hand, has no effect on the particles.     

Engineering the Internal Structure of Magnetic Silica Nanoparticles by Thermal Control

Calcination of hydrated iron salts in the pores of both spherical and rod‐shaped mesoporous silica nanoparticles (NPs) changes the internal structure from an ordered 2D hexagonal structure into a smaller number of large voids in the particles with sizes ranging from large hollow cores down to ten nanometer voids. The voids only form when the heating rate is rapid at a rate of 30 °C min^?1. The sizes of the voids are controlled reproducibly by the final calcination temperature; as the temperature is decreased the number of voids decreases as their size increases. The phase of the iron oxide NPs is α‐Fe₂O₃ when annealed at 500 °C, and Fe₃O₄ when annealed at lower temperatures. The water molecules in the hydrated iron (III) chloride precursor salts appear to play important roles by hydrolyzing Si? O? Si bonding, and the resulting silanol is mobile enough to affect the reconstruction into the framed hollow structures at high temperature. Along with hexahydrates, trivalent Fe³⁺ ions are assumed to contribute to the structure disruption of mesoporous silica by replacing tetrahedral Si⁴⁺ ions and making Fe? O? Si bonding. Volume fraction tomography images generated from transmission electron microscopy (TEM) images enable precise visualization of the structures. These results provide a controllable method of engineering the internal shapes in silica matrices containing superparamagnetic NPs.     

From Molecules to Particles: Quantum-chemical View Applied to Fumed Silica

An extended quantum-chemical study has been performed to examine the flame-generated silica formation at the atomic level. Starting from a set of free molecules, condensation was shown to be a non-barrier and energetically favorable. The coalescence of the formed bare-surface protoparticles can be prevented by particle surface passivation in the course of the hydroxylation reaction. The protoparticle size is determined by a balance of the fusion and hydroxylation/dehydroxylation processes. The main factors responsible for the inherent amorphicity of the fumed silica have been determined.     

室温固相反应制备纳米四水磷酸锌的热化学研究

以Na3PO4·12H2O和ZnSO4·7H2O为原料,采用室温固相反应制备纳米四水磷酸锌,用微量热法研究该反应的反应焓和四水磷酸锌的标准摩尔生成焓.根据Hess定律,设计了一个新的热化学循环:以4mol/LHCl溶液为量热溶剂,用RD496微热量计于298.15K测定了反应物与产物在量热溶剂中的溶解焓分别为(-47.180±0.084)和(-7.617±0.096)kJ/mol,同时测定两种溶液的紫外光谱、折光率和电导率.两种溶液的紫外吸收曲线重叠,稀释500倍后的电导率值分别是2180、2181μS/cm,折光率值分别是1.3679、1.3678.计算出该固相反应的反应焓为-39.530kJ/mol,同时得到纳米四水磷酸锌的标准摩尔生成焓,推荐其值为-4354.004kJ/mol.     

Effects of Metallic Silver Particles on Resonance Energy Transfer Between Fluorophores Bound to DNA

We examined the effects of metallic silver island films on resonance energy transfer (RET) between a donor and acceptor bound to double helical DNA. The donor was 4',6-diamidino-2-phenylindole (DAPI) and the acceptor was propidium iodide (PI). Proximity of the labeled DNA to the silver particles resulted in a dramatic increase in RET as seen from the emission spectra and the donor decay times. Proximity to silver particles results in an increase of the Förster distance from 35 Å an to an apparent value of 166 Å. These results suggest a new type of DNA hybridization assays based on RET over distances much longer than the free-space Forster distance.     

纳米NiO的制备及其谱学特性研究

以醋酸镍、氢氧化钠为原料,吐温80为分散剂,通过固相反应制备了纳米级NiO。 用X射线衍射仪、透射电子显微镜、傅里叶红外光谱、紫外-可见分光光度等方法对材料的粒径、晶格畸变率、形貌以及红外、紫外-可见光的吸收性能进行了表征。结果表明：制得的纳米NiO产物为球形、属立方晶系,粒径大小在9～30 nm左右;晶格畸变率随粒径的增大而减小;纳米NiO红外吸收峰出现在437 cm-1处,与普通粒径的NiO光谱纯(484 cm-1)相比,其吸收峰红移了47 cm-1,体现了纳米NiO的表面效应;不同粒径大小的NiO对紫外-可见光的吸收特性不同。普通粒径的NiO光谱纯在紫外-可见光区域没有吸收,颗粒尺寸越小吸收波长越短,10 nm NiO的紫外-可见光吸收峰位于309 nm处,直接跃迁的光学能带隙约为4.2 eV,比体相材料(3.65 eV)增加0.55 eV,表现出明显的量子尺寸效应。对纳米NiO的谱学特性研究表明该材料在光电领域具有潜在的应用价值。     

Synthesis of Nanocrystalline Ceria Particles for High Temperature Oxidation Resistant Coating

Cerium oxide has been investigated to be an effective coating material for high temperature applications for various alumina- and chromia-forming alloys. The present study investigates the use of microemulsion method to obtain monodispersed, non-agglomerated nanocrystalline ceria particles in the range of 5nm using sodium bis(2-ethylhexyl) sulphosuccinate (AOT) as a surfactant. Furthermore, the use of non-agglomerated nanocrystalline ceria particles to develop improved high temperature oxidation resistant coatings on AISI 304-grade stainless steel was investigated. It was found that non-agglomerated nanocrystalline ceria particles were more effective in improving the oxidation resistance than the agglomerated nanocrystalline particles.     

Synthesis and nonlinear light scattering of microemulsions and nanoparticle suspensions

Microemulsions composed of normal or inverse micellar solutions and aqueous suspensions of pristine (uncoated) or silica-coated iron oxide nanoparticles, mainly γ-Fe₂O₃, were synthesised and their optical limiting properties investigated. The microemulsions are colorless solutions with high transparency for visible wavelengths while the aqueous suspensions of iron oxide are of pale yellow colour. Optical limiting experiments performed in 2 mm cells using a f/5 optical system with a frequency doubled Nd:YAG laser delivering 5 ns pulses with 10 Hz repetition rate, showed clamping levels of ∼3 μJ for the suspensions of both pristine and silica-coated iron oxide nanoparticles. A strong photoinduced nonlinear light scattering was observed for the water-in-oil microemulsion and the aqueous suspensions of nanoparticles while oil-in-water microemulsions did not show a significant nonlinear effect. Measurements carried out using an integrating sphere further verified that the photoinduced nonlinear light scattering is the dominating nonlinear mechanism while the nonlinear absorption of iron oxide nanoparticles is negligible at 532 nm.     

聚乙二醇光化学法制备金纳米微粒及共振散射光谱研究

采用共振散射光谱、紫外-可见吸收光谱、透射电镜对聚乙二醇(PEG)-Au3+纳米光化学反应进行了研究。讨论了金纳米粒子合成条件的影响,发现金纳米粒子的尺寸与PEG分子量大小有关。建立了一个利用不同分子量PEG制备一系列粒径为6～60 nm金纳米粒子的光化学合成新方法。根据PEG分子的空间位阻、疏水性等解释了PEG分子量不同而获得不同粒径金纳米粒子的原因。提出了一个合理的纳米光化学反应机理。     

Engineering Solution in Monitoring Nanoparticle-Fluid Flow During Nanocomposites Processing

New generation composites using nanoparticle-filled matrices have been significantly broadened to encompass a large variety of one-, two-, and three-dimensional systems made of distinctly dissimilar components mixed at the nanometer scale. Nevertheless, during the fabrication process of these novel composites, many problems potentially could arise. One such problem is the clogging of the channels of the microfiber matrix used due to strong interactions between the nanoparticle additives and the matrix walls. In this paper, a two-dimensional simulation model based on Lagrangian multiphase approach for nanoparticle-filled fluid, which flows around an aligned microfiber matrix, is introduced to investigate and predict the nanoparticles trajectories and their interactions with fluid flow and microfiber walls. An energy “imbalance” technique has been applied between the fluid and the microfiber walls to prevent any potential sticking of the nanoparticle additives on the microfiber walls. The trajectory of the nanoparticle has been predicted by integrating the force balance on it in a Lagrangian reference frame. The governing integral equations for the conservation of mass, momentum and energy have been solved in a segregated numerical fashion by a Control-Volume-Based Finite-Element Method.     

Unusual Behavior of Nanocrystalline Strontium Oxide Toward Hydrogen Sulfide

The thermodynamically favored reaction of solid strontium oxide with gaseous hydrogen sulfide is kinetically enhanced to a large degree by the use of higher surface area nanocrystalline SrO in the form of brush-like collections of metal oxide fibers. An unusual feature is that the reaction SrO + H₂S SrS + H₂O proceeds stoichiometrically at room temperature, but at higher temperatures the reaction efficiency goes down, apparently due to rapid temperature induced crystal growth of the nanocrystalline SrO. The samples studied vary in crystallite size from 20 to 27nm, while average particle size (nanocrystal aggregates) varies in the following order; aerogel prepared SrO (100nm) 相似文献   

Simulation of Dynamic Light Scattering Signals of Ultrafine Particles

In order to conveniently obtain dynamic light scattering (DLS) signal, a simulation method of DLS signal is proposed in this paper. This method regards the light intensity fluctuation of DLS as a stationary random process. According to autocorrelation function (ACF) of DLS signal, the stationary random process of DLS can be generated by auto‐regressive (AR) model. Signal simulations of several kinds of distribution particles and comparison of simulations and experiment prove that AR model can be used for DLS signal simulation. Moreover, by analyzing effect of simulation parameters on simulation precision, we obtained the relationship between simulation parameters and simulation precision. Finally, application of simulation signal verifies the effectiveness and convenience of this simulation method.     

双大涡模拟方法模拟提升管内气固两相流动

基于Smagorinsky涡黏模型以及颗粒动理学理论,建立了气固两相流双大涡模拟模型。考虑大涡模拟中过滤尺度的影响,给出颗粒相亚格子压力和热传导系数计算模型。考虑颗粒聚团对两相作用的影响,给出了考虑颗粒聚团作用的气固两相多尺度曳力系数模型。数值模拟了提升管内气固两相流动特性,合理地预测出了提升管内气固两相环-核流动结构。模拟结果与Knowlton等实测结果相吻合。     

ZnO∶Tb3+纳米晶的制备及发光性质研究

利用溶胶-凝胶法（Sol-Gel）制备了不同浓度的ZnO∶Tb3+纳米晶，测量了样品的光致发光谱(PL)和激发谱(PLE).在ZnO宽的可见发射背景上，观察到样品在485 nm、544 nm、584 nm和620 nm附近出现了稀土Tb3+的特征发射.给出了ZnO∶Tb3+纳米晶光致发光的峰值强度随掺Tb3+浓度的变化关系，分析了稀土Tb3+的激发态5D4→7F6、5D4→7F5和5D4→7F4的发射机制，证实了稀土Tb3+的特征发射来源于稀土离子内部4f电子的f-f跃迁和ZnO基质与稀土Tb3+离子之间能量传递.     

Preparation of Polycaprolactone Tissue Engineering Scaffolds by Improved Solvent Casting/Particulate Leaching Method

The classic solvent casting/particulate leaching method to fabricate PCL scaffolds was improved by using a centrifugal technology, a direct bonding process in preparing salt matrices and a technology of vacuum treatment under heating in the desolvation process. Series operations of preshaping, centrifuging, casting and desolvating were employed during the scaffold's manufacture. The scaffold's properties were characterized including micro‐structures, pore dimensions, porosity and hydrophilicity. The results show that centrifugal technology can improve the pore uniformity of scaffolds. In the bonding process, well‐interconnected porous structures were formed if water content was between 2～7%. The distribution of pore dimensions was from 10 to 80 μm, and the porosities were about 89%. Generally, the porosities formed by vacuum treatment at high temperature are greater than those formed by vacuum treatment at ambient temperature in the desolvation process. The fabricated porous PCL scaffolds with good elasticity and desired thickness could be a good choice for application in soft tissue engineering.     

Efficient Cellular Internalization and Transport of Bowl-Shaped Polydopamine Particles

In drug delivery applications, particle-based systems have been used widely due to their physicochemical properties such as size, shape, and surface charge to achieve desirable properties in intracellular environments. The way in which nanoparticles enter a biological cell is an important factor in determining their efficacy as drug carriers, their biodistribution, and toxicity. Most research thus far has focused on the comparison of spherical and rod-like particles on cellular internalization and transport. Here, the synthesis of bowl-shaped polydopamine (PDA) mesoporous nanoparticles with an average diameter of 200 nm and well-controlled radially oriented mesochannels are reported. By incubating bowl-shaped PDA nanoparticles and spherical nanoparticles with HeLa cells, their internalization behaviors are investigated using a suite of characterization techniques. Extensive experimental results demonstrate that bowl-shaped PDA nanoparticles adhere to the cell more efficiently and a faster rate of cellular uptake of bowl-shaped nanoparticles compared to their spherical counterparts. Overall, the cellular internalization behavior of particles is shape-dependent, and such information is crucial in designing nanoparticles for biomedical applications.