Fumed silica/polymer hybrid nanoparticles prepared by redox-initiated graft polymerization in emulsions

Hybrid particles comprising aggregated fumed silica nanoparticles as the core and hydrophobic polymers existing around the nanoparticles were prepared by ‘grafting from’ polymerization in emulsions. The emulsion polymerization employed cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant, respectively, to stabilize the emulsion polymerization. The polymerization was initiated by the redox reaction between ceric ion Ce(IV) and the amine groups on the surfaces of aminated fumed silica nanoparticles that were modified by 3-aminopropyltriethoxysilane. Infrared spectroscopy and thermogravimetric analysis demonstrated that both poly(methyl methacrylate) (PMMA) and polystyrene (PS) were successfully grafted onto the fumed silica surface. The type of surfactant greatly affected the grafting ratio, monomer-to-polymer conversion, and morphology of the product. When CTAB was used as the surfactant, both the grafting ratio and monomer-to-polymer conversion were lower than when SDS was used, but transmission electron microscopy and light scattering analysis indicated that most of the resultant particles were sub-100 nm hybrid nanoparticles with a non-spherical shape and particles sizes of 75–90 and 57–85 nm for PMMA and PS-grafted fumed silica, respectively. Whereas, when SDS was used as the surfactant, the particles agglomerated to form large irregular clusters or even networks, possibly due to the electrostatic attractions between SDS and Ce(IV) and/or the aminated fumed silica nanoparticles in aqueous solution.     

Surfactant effect on functionalized carbon nanotube coated snowman-like particles and their electro-responsive characteristics

The core–shell structured snowman-like (SL) microparticles coated by functionalized multi-walled carbon nanotube (MWNT) were prepared in the presence of different surfactants including cationic surfactant-cetyl trimethylammonium bromide (CTAB) and anionic surfactant-sodium lauryl sulfate (SDS). The effect of surfactants on adsorption onto SL particles was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and conductivity. The cationic surfactant is found to be more effective than anionic surfactant for helping nanotube adsorbed onto microparticle due to the presence of electrostatic interaction between the functionalized MWNT and the surfactant. Furthermore, the MWNT/SL particles dispersed in silicone oil exhibited a typical fibril structure of the electrorheological characteristics under an applied electric field observed by an optical microscope (OM), in which the state of nanotubes wrapped on the particles strongly affects their electro-responsive characteristics.     

A sol-powder coating technique for fabrication of yttria stabilised zirconia

Yttria stabilised zirconia has been prepared using a simple sol-powder coating technique. The polymeric yttria sol, which was prepared using 1,3 propanediol as a network modifier, was homogeneously mixed with nanocrystalline zirconia powder and it showed a dual function: as a binder which promoted densification and a phase modifier which stabilised zirconia in the tetragonal and cubic phases. Thermal analysis and X-ray diffraction revealed that the polymeric yttria sol which decomposed at low temperature into yttrium oxide could change the m → t phase transformation behaviour of the zirconia, possibly due to the small particle size and very high surface area of both yttria and zirconia particles allowing rapid alloying. The sintered samples exhibited three crystalline phases: monoclinic, tetragonal and cubic, in which cubic and tetragonal are the major phases. The weight fractions of the individual phases present in the selected specimens were determined using quantitative Rietveld analysis.     

A sol–gel preparation of silica coated zirconia microspheres as chromatographic support materials

Four silica–zirconia composites were prepared using a sol–gel process and compared with zirconia, which was prepared under the same conditions but without the addition of sodium metasilicate pentahydrate. Spherical particles (1–2 μm) resulted which were free from aggregation and hollow spheres. Raman spectroscopy, differential thermal analysis, thermal gravimetric analysis and electron microscopy were used to evaluate the properties of these composites. Addition of the silica onto the zirconia microspheres prevented the formation of monoclinic zirconia and increased the temperature of crystallization into the tetragonal form. Calcination of the composites at 1300°C produced zircon. This revised version was published online in November 2006 with corrections to the Cover Date.     

Improvement of the low-temperature stability of an aqueous colloidal ethylcellulose dispersion,Aquacoat ECD,and preparation/characterization of a redispersible Aquacoat ECD powder

Aquacoat ECD, an aqueous ethylcellulose dispersion, is susceptible to low-temperature storage, resulting in irreversible coagulation as indicated by a strong increase in viscosity and particle size. This destabilization of the ethylcellulose dispersion is caused by the anionic surfactant sodium dodecyl sulfate, which precipitates at low temperatures because of its low Krafft point. This problem could be solved by using the more hydrophilic, ethoxylated, sodium dodecyl ether sulfate, which was an effective stabilizer at low temperatures. A redispersible ethylcellulose powder was prepared by freeze- or spray-drying of the original polymer dispersion (Aquacoat ECD). The pH of the dispersion medium had a strong influence on the redispersibility of the dried ethylcellulose particles because of the dissociation behavior. At a pH > 7, polymer dispersions in the colloidal size range were obtained. At lower pH values, the dried ethylcellulose agglomerates could not be redispersed. Drug release studies from pellets coated with the redispersed and the original dispersion showed a comparable release pattern when using alkalized aqueous dispersion systems. Higher plasticizer concentration and curing of the coated pellets improved the film formation of the redispersed polymer particles.     

Effect of triethanolamine and sodium dodecyl sulfate on the formation of CuInSe2 thin films by electrodeposition

In this paper, we describe the development of a bath comprising triethanolamine and sodium dodecyl sulfate for electrodeposition of CuInSe₂ thin films, by which long-term bath stability was found to be improved and near-stoichiometric CuInSe₂ films with smooth surface morphology were obtained. Scanning electron microscopy studies reveal a dramatic improvement of the crystalline quality of CuInSe₂ films with the addition of sodium dodecyl sulfate. X-ray diffraction results and Raman spectra confirm that the improvement of the film growth is attributed to the synergistic effect of triethanolamine and sodium dodecyl sulfate. The addition of anionic surfactant sodium dodecyl sulfate can significantly improve the adherence between the CuInSe₂ layer and the substrate.     

Structural,magnetic properties,and induction heating behavior studies of cobalt ferrite nanopowders synthesized using modified co-precipitation method

Nanocrystalline cobalt ferrite CoFe₂O₄ powders have been successfully synthesized via modified co-precipitation at low temperature. Obviously, well crystalline CoFe₂O₄ phase was obtained from the precipitated precursors at pH 10 using 5?M NaOH as a base thermally treated at 80°C for 1?h in aqueous medium in the absence and the presence of 1000?ppm cetyl trimethyl ammonium bromide (CTAB) as well as sodium dodecyl sulfate (SDS) as cationic and anionic surfactants, respectively. Meanwhile, the spinel ferrite was observed with the similar conditions using ethylene glycol as an organic solvent. The microstructures of the formed powders exhibited nanospheres like structure with narrow size distribution from 6 to 10?nm. The magnetic properties of the formed cobalt ferrite powders strongly depend on the synthesis conditions. For instance, the highest saturation magnetization (M_s?=?36.2?emu/g) was achieved in the aqueous medium, whereas the lowest saturation magnetization (M_s?=?16.2?emu/g) was accomplished in the ethylene glycol medium. Indeed, heating properties of the CoFe₂O₄ samples in an alternating magnetic field (AMF) at 160?kHz were estimated. Of note, it is clear that the specific heat rate SAR values were in the range from 104.5 to 302.0?W/g at different synthesis conditions, making co-ferrite appropriate for hyperthermia treatment of cancer.     

CTAB-Assisted Synthesis of Size- and Shape-Controlled Gold Nanoparticles in SDS Aqueous Solution

Variously shaped gold nanoparticles were hydrothermally prepared by adding the cationic surfactant cethyltrimetylammonium bromide (CTAB) into the anionic surfactant sodium dodecyl sulfonate (SDS) in aqueous solution at 180°C without reducing agents and/or templates. Nanoparticle size and shape were controlled by the surfactant mixing ratio CTAB:SDS = x_CTAB:(1 − x_CTAB) and reaction time. Increasing CTAB concentration from x = 0.01 to x = 0.07 changes the nanoparticle shape from icosahedron to triangle or ellipse. The influence of the cationic/anionic ratio is presumably due to the differing catanionic micelle structures.     

Preparation and thermal evolution of sol-gel derived transparent ZrO2 and MgO-ZrO2 gel monolith

Transparent gel monoliths of pure and MgO-doped zirconia having dopant concentrations in the range 0 to 15 mol % were prepared by chemical polymerization of zirconium n-propoxide and magnesium acetate tetrahydrate using 2-methoxy ethanol as solvent. The thermal evolution of amorphous gels was studied by differential thermal analysis, X-ray diffraction and transmission electron microscopy. The crystallization of pure and doped zirconia gels occurred in the temperature range 360 to 450° C. The first crystalline phase to appear is tetragonal for pure and 2 mol % doped zirconia, and cubic for 3 to 15 mol % doped samples. Both crystallization and decomposition temperatures are found to increase with increasing dopant concentration, approaching a saturation value for 10 mol % doped samples. It has been established that the transformation of the cubic to the monoclinic phase takes place via a metastable tetragonal phase. A linear relationship between the lattice parameter of cubic zirconia and MgO concentration has been established. X-ray diffraction studies have also revealed that the entire amount of MgO used in preparing doped zirconia gels remains in a single MgO-ZrO₂ crystalline phase formed initially by thermal treatment.[/p]     

A study on the structural properties of mesoporous silica spheres

The mesoporous silica spheres were prepared by using sodium silicate as silica precursor, and low concentration of CTAB and propanol as templating agents. The resulting spherical particles were characterised by low angle PXRD, N₂ adsorption-desorption studies, pore size distribution, BET-surface area, surface morphology analysis and FTIR. From PXRD data and electron probe microanalysis, it was observed that the propanol:CTAB molar ratio 8.5:1 is the optimum for preparing the mesoporous silica spheres. With excess of propanol the orderliness of mesoporous silica has been disturbed forming agglomerate particulates. Again the BJH pore diameter and cell parameter (a) go on decreasing with the increase in the propanol:CTAB molar ratio.     

Preparation of stable micron-sized crystalline irbesartan particles for the enhancement of dissolution rate

Purpose: In this study, micron-sized crystalline drug particles of irbesartan (IBS) were prepared to improve its stability and dissolution rate.

Method: The approach to crystalline particles was based on the liquid precipitation process by which the amorphous particles were prepared. Pharmaceutical acceptable additives were used as the crystallization agent to convert the amorphous drug into crystalline particles. High pressure homogenization (HPH) process has been employed to reduce the size of the crystalline particles, and the micron-sized particles were obtained by the freeze-drying process.

Results: Different additives show different influences on the polymorphic form of IBS. Polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) were effective in stabilizing amorphous particles instead of converting amorphous drug into crystalline particles, while poloxamer407 (F127) and tween80 (T80) could convert the amorphous drug into crystalline particles. T80 was also effective in controlling the particle size than that of F127. After HPH, crystalline particles with an average of 0.8 μm were obtained. The freeze-dried micron-sized crystalline particles exhibited significantly enhanced in vitro dissolution rate when compared to the raw drug. SEM, FT-IR, XRD, DSC and dissolution rate studies indicated that the micron-sized particles were stable during 6 months storage.

Conclusion: The preparation of micron-sized crystalline drug particles is an effective way to improve the stability and dissolution rate of irbesartan.     

阴离子表面活性剂发泡MCPA6的制备与性能表征

利用阴离子表面活性剂对单体浇铸尼龙6(MCPA6)体系进行发泡,制备具有泡孔的MCPA6,使材料轻量化。利用扫描电镜(SEM)对材料的泡孔进行观察,利用差示扫描量热(DSC)和热失重分析(TGA)表征其性能。研究结果表明:十二烷基硫酸钠(SDS)发泡MCPA6形成网络状的孔隙,显著降低了MCPA6的成型收缩率;串联的微球促进了MCPA6分子链的运动,提高了其结晶速率;同时抑制了MCPA6的六方晶系γ晶型的形成,并降低了材料的结晶度。发泡对MCPA6晶型的抑制和结晶度的降低有利于其吸收冲击能。     

超声诱导CTAB/SDS溶液中纳米Pd粒子的形貌控制及对甲醛的电催化氧化

在十六烷基三甲基溴化铵(CTAB)-十二烷基硫酸钠(SDS)混合乙醇水溶液中,超声辐射PdCl2,合成了纳米Pd粒子,用XRD、TEM、选区电子衍射(SAED)、HRTEM和低温氮吸附-脱附等技术进行了表征,考察了CTAB/SDS组成对纳米粒子形貌的影响,纳米Pd粒子修饰玻碳电极对甲醛的电催化活性也通过循环伏安法进行了研究。结果表明:通过改变CTAB/SDS组成可以调控纳米Pd粒子的粒径和形貌;当CTAB与SDS物质的量之比为1∶1、超声反应60min时,得到呈多边形的纳米Pd粒子,粒径范围在10～20nm之间,比未添加表面活性剂样品的比表面积增大了14m2.g-1,对甲醛有较高的电催化活性。     

Synthesis and optical properties of sub-micron sized rare earth-doped zirconia particles

Sub-micron sized crystalline particles of Eu³⁺ and Er³⁺-doped zirconia (ZrO₂) were prepared via a wet chemical sol-gel route and post synthesis annealing. The doping was achieved by introduction of the respective rare earth salts into the zirconia precursor solution, with insitu generation of sodium chloride for stabilization of the particle surface during growth. A series of materials with differing europium content, nominally 0.3, 3 and 6 mol% within the ZrO₂ lattice, were prepared for respective comparison and characterization of their optical properties following annealing at 700 °C. Average emission lifetimes of up to 2.3 ms were observed for the Eu³⁺-doped particles. Particle sizes, approximated from SEM micrographs, were observed in the range 250-400 nm. The synthesis of Er³⁺-doped ZrO₂ particles (0.5 mol%) produced 300 nm sized particles which exhibited emission in the visible and infrared regions after annealing at 1000 °C. X-ray diffraction (XRD) with Rietveld analysis for phase quantification, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectra were used to characterize the samples.     

Novel sodium alginate composite membranes prepared by incorporating cobalt(III) complex particles used in pervaporation separation of water–acetic acid mixtures at different temperatures

The present paper is our continuing effort to develop a new type of sodium alginate (NaAlg) composite membrane by incorporating cobalt(III)(3-acetylpyridine-o-aminobenzoylhydrazone) (Co-APABZ) complex as filler particles in different ratios. Membranes were prepared by solution casting followed by solvent evaporation and crosslinked with glutaraldehyde. Pervaporation (PV) performance of the prepared composite membranes was assessed in terms of flux and selectivity and these data were compared with the pristine NaAlg membrane in PV dehydration of water–acetic acid mixtures. Pristine Co-APABZ particles in crystalline form were prepared and characterized by the solid state X-ray diffraction (XRD) technique, while the NaAlg/Co(III)composite membranes were characterized by thermogravimetry (TGA) and dynamic mechanical thermal analyzer (DMTA). X-ray crystal structure of Co-APABZ has shown that the complex formed was crystalline in nature with six lattice water molecules, which are interconnected by hydrogen bonds linking together to form cyclic hexamers that are analogous to cyclohexane, creating water channels for an easy transport of water molecules. TGA indicated no changes in thermal stability of the membranes due to the presence of Co-APABZ in the NaAlg matrix. DMTA confirmed NaAlg crosslinking with glutaraldehyde. Effects of Co-APABZ content, membrane thickness, temperature and feed water compositions on membrane performance were investigated to find an optimum PV performance of the membranes developed. NaAlg composite membranes in the presence of Co-APABZ particles preferentially absorbed water molecules to facilitate diffusion of water through the membranes and thus enhance the selectivity to water. However, the amount of Co-APABZ present in the NaAlg matrix and the degree of membrane swelling has an effect on membrane performance. Selectivity of 174 for water with a flux of 0.123 kg/m² h was obtained for 5 wt.% Co-APABZ containing NaAlg matrix, when tested for the feed mixture containing 10 wt % water. The present results are superior to the previously published data based on NaAlg membranes. This article is CEPS communication #110.     

Surfactant-assisted hydrothermal synthesis of titania nanoparticles for solar cell applications

Nanostructured anatase TiO₂ powders (~7 nm) with different microstructures have been successfully synthesized using surfactant-assisted hydrothermal route. It can be seen that different morphologies of sphere, flower petal and cauliflower were appeared for the anatase powders formed at hydrothermal temperature 100 °C for 24 h without and with sodium dodecyl sulfate (SDS) and cetyl trimethyl-ammonium bromide (CTAB) as anionic and cationic surfactants, respectively. The specific surface area S_BET was increased from 77.14 m²/g without surfactant to 177.19 m²/g in the presence of SDS as anionic surfactant. The optical properties were measured and the band gap energy of the obtained powders was ~3.3 eV. The UV-absorption band of the anatase phase was at near 295 nm without other observable bands, which proved to exhibit high optical property and might have potential application in solar cells devices.     

Surfactant assisted synthesis and spectroscopic characterization of selenium nanoparticles in ambient conditions

In this work, an attempt has been made to synthesize well-distributed stable selenium (Se) particles of nanosize dimensions via an aqueous micellar solution by the assistance of surfactants of two different polarities (anionic, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and cationic, hexadecyltrimethylammonium bromide (CTAB)). The morphology of the particles was examined with transmission electron microscopy (TEM). X-ray analysis reveals that the particles have a monoclinic structure. The band gap of the particles was determined from UV-visible optical spectroscopic results. The size variation was estimated by employing a quantum confinement effect equation. The evolution of the selenium nanoparticles in AOT and CTAB micellar media was corroborated with the time-dependent absorption spectra. The influence of hydrazine hydrate concentrations on the formation kinetics of Se nanoparticles was also investigated. The capping ability of the surfactants has been quantitatively evaluated from Fourier transform infrared (FTIR) studies.     

Electrochemical deposition of Ni–TiN nanocomposite coatings and the effect of sodium dodecyl sulphate surfactant on the coating properties

Ni–TiN nanocomposite coatings were prepared by using electrochemical deposition in a Watt’s bath containing TiN particles to increase the hardness of Ni. The effects of deposition current density, electrolyte agitation speed and the number of particles in the solution on the amount of incorporated particles in the coating process were investigated. The optimum deposition current density of 4 A dm^?2 and agitation speed of 450 rpm were obtained. The effect of sodium dodecyl sulphate (SDS) anionic surfactant on the amount of particles in the coatings was investigated. It was observed that the maximum amount of incorporated particles, with a value of 7.5% by volume, was created in the current density of 4 A dm^?2, stirring rate of 450 rpm, 30 g l^?1 TiN particles and in the presence of 0.6 g l^?1 SDS anionic surfactant.     

以正钛酸为原料制备纳米TiO2光催化剂

以正钛酸为原料，通过直接水解法制备纳米TiO2，并对样品分别进行了差热分析，X射线衍射分析和透射电子显微镜分析。结果表明，样品粒子为混晶型纳米TiO2，单分散性良好，粒径分布范围狭窄，当它应用阴离子表面活性剂十二烷基苯磺酸钠的光催化降解时，与P－25光催化剂相比，具有较好的催化活性。同时，我们用Al2O3陶瓷膜回收纳米TiO2循环再利用，这为纳米TiO2在环保方面的大规模应用创造了条件。     

以正钛酸为原料制备纳米TiO2光催化剂

以正钛酸为原料,通过直接水解法制备纳米ＴｉＯ_２;并对样品分别进行了差热分析、Ｘ射线衍射分析和透射电子显微镜分析．结果表明,样品粒子为混晶型纳米ＴｉＯ_２,单分散性良好,粒径分布范围狭窄．当它应用于阴离子表面活性剂十二烷基苯磺酸钠的光催化降解时,与Ｐ－２５光催化剂相比,具有较好的催化活性．同时,我们用Ａｌ_２Ｏ_３陶瓷膜回收纳米ＴｉＯ_２循环再利用;这为纳米ＴｉＯ_２在环保方面的大规模应用创造了条件．