Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.     

碳酸钙微米球的制备与表征

采用醋酸钙和碳酸钠为原料,在反应温度为5℃和柠檬酸三钠质量百分浓度为15%的条件下,采用沉淀法合成出了粒度为1～4μm、分散性好的球形碳酸钙粉体。用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、红外光谱仪(IR)、原子力扫描探针显微镜(ASPM)、光学显微镜、粒度分析仪等对样品进行了表征,并用光学显微镜跟踪考察了碳酸钙微米球的形成过程。结果表明,碳酸钙微米球是由大量纳米级颗粒组装而成。     

Preparation of monodisperse ellipsoidal polystyrene particles

A method is described for the preparation of monodisperse ellipsoidal particles of polystyrene in the colloidal size range. Monodisperse polystyrene particles were dispersed in a solution of polyvinyl alcohol. This dispersion was then allowed to form, by evaporation, a thin film of polyvinyl alcohol containing spherical polystyrene particles. Strips of this film were clamped into a metal frame, heated rapidly in an oil bath to 200°C and stretched to a predetermined extent in order to convert the spherical particles into ellipsoids; the film was then cooled. A wide range of axial ratios for a variety of initial particle sizes was obtained by this method.     

Poly(methyl methacrylate) encapsulation of calcium carbonate particles

Dispersed calcium carbonate particles are encapsulated with poly(methyl methacrylate). The optimum condition for the polymerization is investigated; and the encapsulated particles are characterized by spectrophotometric analysis, acid decomposition, thermal analysis, and microscopic observation. From the conversion comparison of the MMA monomer it is found that the optimum concentration of polymerization initiator is 1.58 × 10^?3 mol/L. The highest yield of encapsulation is obtained at 250 rpm with a concentration of 0.5 wt % surfactant (sodium dodecyl benzene sulfonate). A comparison of the Fourier transform IR spectra distinctly indicates the formation of PMMA on the surface of the calcium carbonate particles. The outcome of an acid decomposition test proves that the PMMA coating protects the particles. In addition, thermal analyses and microscopic observation characterize the PMMA on the surface of encapsulated particles. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4063–4073, 2004     

Influence of temperature on the aggregation and sedimentation rate of monodisperse spherical silica particles

The rise in temperature of alcohol suspensions of monodisperse silica particles to 50-100^oC results in an increase in the number of coagulated particles. This phenomenon results from an increase in the degree of electrolyte dissociation, which is equivalent to the rise in its concentration under normal conditions. The suspensions with the aggregates settle at elevated temperatures with the rates that are considerably higher than it is conditioned by the decrease in the viscosity of the suspension. The aggregates and free particles settle jointly, indicating that the non-aggregated particles are held in the field of the long-range molecular attraction of aggregates. This revised version was published online in June 2006 with corrections to the Cover Date.     

碳酸钙固定化猪胰脂肪酶的制备及活性研究

本文利用市售普通碳酸钙(general calcium carbonate,GCC)作为猪胰脂肪酶(PPL)固定化的载体材料,研究了不同固定化条件对所制备的固定化酶活性的影响.结果显示PPL固定化于GCC上的最佳制备工艺为:将20 mL酶液与1.50 g GCC放入置于摇床内的三角瓶中,摇床温度设为40℃,摇床转速设为...     

Agitation requirement for synthesis of micron-sized monodisperse polymer particles in soap-free polymerization method

Single-stage polymerization recently proposed for producing micron-sized polymer particles in aqueous media by Gu, Inukai and Konno (2002) was carried out under the control of agitation with styrene monomer, an amphoteric initiator, 2,2′-azobis [N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate and a pH buffer NH₃/NH₄Cl at a monomer concentration of 1.1 kmol/m³ H₂O, an initiator concentration of 10 mol/m³ H₂O and a buffer concentration of [NH₃] = [NH₄Cl] = 10 mol/m³ H₂O. In the polymerizations, impeller speed was ranged from 300 to 500 rpm to satisfy complete dispersion of the monomer phase and not to introduce the gas phase from the free surface. Polymerization experiments under steady agitation indicated that impeller speed was an important factor for size distribution of polymer particles. An increase in impeller speed promoted particle coagulation during the polymerization to enlarge the average size of polymer particles but widen the size distribution. To produce polymer particles with narrow size distribution, stepwise reduction in impeller speed was examined in the polymerization experiments. It was demonstrated that this method was more effective than the steady agitation. The impeller speed reduction could produce highly monodisperse particles with an average size of 2 μm and a coefficient of variation of size distributions of 2.2% that was much smaller than typical monodispersity criterion of 10%.     

无添加剂条件下文石型碳酸钙晶须制备及影响因素研究

在不加任何结晶控制剂或模板条件下,以CaCl2和Na2CO3为原料,利用复分解反应法制备了具有较好形貌和高长径比,且分布均一的文石型碳酸钙晶须,并利用扫描电镜(SEM)、X-射线粉末衍射(PXRD)和傅里叶转换红外光谱图(FT-IR)等手段对其进行了表征。研究了浓度、滴加速度、反应温度、搅拌速度以及滴加方式等因素对碳酸钙晶须的影响。结果表明最佳制备工艺为:CaC12溶液与Na2CO3溶液的浓度为0.05 mol.L-1,溶液滴加速度为1 mL.min-1,反应体系温度为80℃,搅拌速度为250 r.min-1。     

纳米碳酸钙的表面改性研究

纳米产品(材料)是当今世界高科技产品之一.纳米碳酸钙作为粉体产品中的一种,以高纯、超细、改性和功能性为标志,广泛应用于橡胶、塑料、造纸、油墨、涂料、医药、化妆品等各行各业[1-2].主要用作填充材料,因粒度超细、分散性好,可以增加填充量,降低制品成本,改善制品性能,提高制品档次,拓宽制品使用范围.近年来,随着CaCO3的超细化、结构复杂化及表面改性技术的发展,极大地提高了它的应用价值.对不同形态的超细CaCO3制备技术的研究,已成为许多先进国家竞相开发的热点[3-5].     

Production of micron-sized, monodisperse, transformable rugby-ball-like-shaped polymer particles

Micron-sized, monodisperse, “rugby-ball-like” polymer particles were produced by seeded polymerization for the dispersion of (divinylbenzene/vinylbiphenyl/xylene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method which the authors proposed in 1991. The shape of the composite polymer particle was reversibly transformed between a rugby-ball-like shape and a spherical one by absorbing/releasing toluene. Received: 24 January 2001/Accepted: 18 April 2001     

铁饼状碳酸钙的制备及性能研究

本文以氯化钙和氨水的混合溶液为水相,聚氧乙烯辛基苯酚醚-10(OP-10)为表面活性剂,正辛醇为助表面活性剂,环己烷为油相配制了反相微乳液.并通过向其中通入CO2气体制备微/纳米碳酸钙,得到了铁饼状的微米碳酸钙.采用扫描电子显微镜(SEM),X射线粉末衍射(XRD)和傅里叶变换红外光谱(FTIR)表征了微米碳酸钙的形貌...     

CaCO3超细粉末的低温水热合成与表征

超细碳酸钙有颗粒尺寸小、比表面积大和表面活性高等优良特性,在橡胶、塑料、纸张、涂料、日用化学品等领域有广泛的应用。因此,研究CaCO3超细粉末的制备方法,开发CaCO3超细微粉的用途,具有十分重要的意义。目前其制备方法主要是碳化法,本文利用水热法制备单一相超细CaCO3粉末,通过不同的反应前驱物在120℃和150℃下进行水热反应直接合成出超细CaCO3粉末,并对产品的结构和形貌进行了表征。     

Effects of PAA additive and temperature on morphology of calcium carbonate particles

Calcium carbonate particles with various shapes were prepared by the reaction of sodium carbonate with calcium chloride in the absence and presence of a polyacrylic acid (PAA) at 25°C and 80°C, respectively. The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. The effects of pH, temperatures, aging time and concentration of PAA and CaCO₃ on the crystal form and morphologies of the as-prepared CaCO₃ were investigated. The results show that pH, temperatures, concentration of PAA and CaCO₃ are important parameters for the control of morphologies of CaCO₃. Various crystal morphologies of calcite, such as, plates, rhombohedras, rectangles, ellipsoids, cubes, etc. can be obtained depending on the experimental conditions. Especially, the monodispersed cubic calcite particles can be produced by PAA addition at 80°C. Moreover, higher temperature is beneficial to the formation of monodispersed cubic or rectangular calcite particles. This research may provide new insight into the control of morphologies of calcium carbonate and the biomimetic synthesis of novel inorganic materials.     

Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Silver nanoparticles were synthesized by UV irradiation of [Ag(NH₃)₂]⁺ aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag₂O was much quicker than that from AgNO₃, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength (λ_max) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH₃)₂]⁺ (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (25 °C).     

Preparation and properties of gluten/calcium carbonate composites

Environment friendly thermosetting composites were prepared by blending wheat gluten （WG） as matrix, calcium carbonate （CaCO3） as filler and glycerol as plasticizer followed by compression molding the mixture at 120 ℃ to crosslink the WG matrix. Morphology observation showed that the CaCO3 particles were finely dispersed in matrix. Incorporation of CaCO3 up to 10 wt% into the composites caused Young＇s modulus and tensile strength to increase markedly. On the other hand, the moisture absorption and elongation at break decreased slightly.     

Preparation of hemispherical hollow silica microcapsules with different affinity surface by using spherical vaterite calcium carbonate as template

We developed a method to prepare hemispherical hollow silica microcapsules (HHSM) with different affinity surfaces using spherical vaterite calcium carbonate (SVCC) as a template. The preparation process composed of the adhesion of calcium carbonate onto the surface of methyl methacrylate (MMA) droplets followed by suspension polymerization, the partial etching of calcium carbonate on the polymethyl methacrylate (PMMA) mother particle, the formation of silicon dioxide powder by sol–gel reaction and their deposition onto the etched flat surface of calcium carbonate, the surface modification of deposited silicon dioxide with silane coupling agent, the removal of the mother particle with acetone, the formation of silicon dioxide powder by sol–gel reaction and deposition onto the exposed hemispherical surface of calcium carbonate, and the surface modification of deposited silicon dioxide with silane coupling agent. The synthesized microcapsules had a complete hemispherical structure and both hydrophilic and hydrophobic surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate

Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product.     

Formation of CaO from thermal decomposition of calcium carbonate in the presence of carboxylic acids

Effect of 5% tartaric, succinic and citric acids on the decomposition of CaCO₃ have been studied by TG-DSC and X-ray diffraction techniques. The decomposition temperature of CaCO₃ is not decreased and at the same time particle size distribution and morphology of CaO are changed as determined by laser granulometer and SEM studies.     

Preparation of poly(methyl methacrylate) microcapsules by in situ polymerization on the surface of calcium carbonate particles

Poly(methyl methacrylate) (PMMA) microcapsules were prepared by the in situ polymerization of methyl methacrylate (MMA) and N,N′-methylenebisacrylamide on the surface of calcium carbonate (CaCO₃) particles, followed by the dissolution of the CaCO₃ core in ethylenediaminetetraacetic acid solution. The microcapsules were characterized using fluorescence microscopy, atomic force microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. The average sizes of the CaCO₃ particles and PMMA capsules were 3.8 ± 0.6 and 4.0 ± 0.6 μm, respectively. A copolymer consisting of MMA and rhodamine B-bearing MMA was also used to prepare microcapsules for fluorescent microscopy observations. Fluorescein isothiocyanate-labeled bovine serum albumin was enclosed in the PMMA microcapsules and its release properties were studied.