Electrophoretic deposition of nickel, iron and aluminum nanoparticles on carbon fibers

The electrophoretic deposition (EPD) of nickel (Ni), iron (Fe) and aluminum (Al) nanoparticles fabricated by an active hydrogen plasma evaporation method on the surface of carbon fibers was investigated, which will allow the obtained composites to be applied as practical catalysts or electrodes. SEM observations show that the Ni nanoparticles can build up a thick EPD coating with some cracks on the surface of carbon fibers, and the analyses of X-ray diffraction (XRD) and BET specific surface area indicate that fine particles from the as-received Ni powders were finally deposited after the EPD process without crystal growth. The surface oxidation of Fe and Al nanoparticles takes serious effect on the EPD process and the morphology of the as-prepared coatings.     

Methods for functionalization of microsized polystyrene beads with titania nanoparticles for cathodic electrophoretic deposition

Functionalization of colloidal particles based on the use of polyelectrolytes and heterocoagulation was combined with electrophoretic deposition (EPD), with the aim of depositing titania-polystyrene (TiO(2)-PS) composite particles on Ti6Al4V substrates. The composite particles were obtained by heterocoagulation of TiO(2) nanoparticles on the surface of monosized polystyrene beads of 4.6 microm in diameter. Two alternative methods were developed for the preparation of the TiO(2)-PS suspensions in organic fluids for cathodic electrodeposition. The first method was carried out in alkaline aqueous medium with the use of polyelectrolytes and intermediate control measurements of zeta potential, conductivity, and pH; the second one was carried out directly in the organic solvent used for EPD, typically isopropanol. Examples of deposits obtained by EPD in both suspensions and a comparative analysis between the two methods are presented.     

二维金纳米粒子结构的制备及影响因素

用电泳沉积方法制备了金纳米粒子的二维排列结构。研究了电场强度、沉积时间、溶胶浓度、温度和方波脉冲等对沉积结构的影响。提高外加电场强度和旋加方波脉冲可以提高金粒子结构的有序性。粒子浓度减小,温度升高不利于粒子的电泳沉积。     

Formation of thin YSZ electrolyte films by electrophoretic deposition on porous cathodes

The structure, dispersity, stability, and electrophoretic deposition (EPD) of suspensions of spherical ZrO₂ stabilized Y₂O₃ (YSZ) nanoparticles with a mean size of 10.9 nm onto the porous surface of La_0.6Sr_0.4MnO₃ (LSM) with a pore size of 3–20 μm were studied by electron microscopy, photon correlation spectroscopy, and electroacoustical analysis. The optimum conditions of deposition were attained by using a mixed isopropanol-acetylacetone dispersion medium, which provided the aggregative stability of the suspension with 95% individual particles. The maximum pore size on the covered surface should be up to 0.5 μm if nanoparticles with a mean diameter of 10–20 nm are used. When the pores are larger, the EPD of YSZ will be effective if an additional intermediate LSM layer is formed by EPD to provide the required pore size.     

Electrophoretic deposition of chiral polymers and composites

Electrophoretic deposition (EPD) method has been developed for the deposition of thin films of chiral polymers. EPD of poly-L-lysine (PLL) and poly-L-ornithine (PLO) films was performed for the first time on conductive substrates from aqueous and ethanol-water solutions. The deposition yield was monitored using a quartz crystal microbalance. The results demonstrated that the deposition yield can be varied by variation of the deposition time, voltage and polymer concentration in the solutions. It was shown that PLL and PLO provided stabilization and charging of hydroxyapatite (HA) nanoparticles in suspensions. Composite PLL-HA and PLO-HA films of controlled thickness were prepared by EPD. Electron microscopy investigations showed that the thickness of the PLL, PLO and composite films was varied in the range of 0-3 μm. The polymer and composite films can be used for biomedical applications.     

Aqueous electrophoretic deposition in asymmetric AC electric fields (AC–EPD)

Electrophoretic deposition (EPD) is a cheap and simple processing technique based on the movement of charged particles in an electrical field (electrophoresis) followed by deposition of these particles on the electrode that attracted them [O. VanderBiest, L.J. Vandeperre, Electrophoretic deposition of materials, Annu. Rev. Mater. Sci. 29 (1999) 327–352]. If not for electrolysis, water would be the solvent of choice instead of the currently commercially used organics. In this work we prove that high voltages can be used for electrophoretic deposition from aqueous suspensions without decomposition of water when applying an asymmetric alternating electric field. The experimental results show that deposits formed using these fields have a green density and surface comparable and even better than those typically obtained using the classic EPD systems. As a result volatile, expensive and environmentally unfriendly solvents are no longer a necessity.     

Fabrication of silica-on-titania and titania-on-silica nanoparticle assemblies

Structures of silica particles on a titania surface and titania particles on a silica surface were formed by deposition of SiO₂ or TiO₂ nanoparticles on pre-patterned substrates. Photolithography was used to create a matrix for the selective deposition of nanoparticles by immersion in a colloidal suspension. Atomic force microscopy was used to investigate the topography of these inorganic assemblies. Whereas two-dimensional colloidal patches of TiO₂ nanoparticles are obtained on silica surfaces, SiO₂ nanoparticles form three-dimensional, U-shaped channels on titania surfaces.The influence of electrostatic forces on assembly structure is vital. The isoelectric points of the particles, the pre-patterned matrix and the photo-resist are key parameters and may be manipulated to achieve various microstructures. The 2D nanoparticle arrays of titania on silica and 3D channels (built of silica nanoparticles) on flat titania surfaces are of potential interest in lab-on-a-chip applications.     

用原位液体池透射电镜技术表征金属钯在球形金纳米颗粒表面的异质沉积

采用原位液体池透射电镜技术,在扫描透射电子显微镜(STEM)中,实时观察溶液中金属钯(Pd)在金(Au)纳米颗粒及团簇周围的异质沉积过程。通过对该动态过程的定量分析,结合高分辨透射电子显微镜(HRTEM)对样品进行形貌与结构表征,研究异质沉积的机理。结果表明,电子束辐照下Au-Pd异质结构纳米颗粒的形成存在两种主要机制:第一种机制中,Pd在Au纳米颗粒表面的生长是以岛状沉积开始,随着时间推移,出现Pd岛的结构弛豫和沿着Au颗粒表面的迁移扩展。伴随Pd的不断沉积和弛豫,Au-Pd复合颗粒的外接圆直径表现为震荡生长,而Au表面的Pd覆盖率显示出随时间单调增加的趋势。第二种机制中,由于Pd单体在Au纳米颗粒上的沉积位点有限,使部分被还原的Pd在Au颗粒以外区域进行同质形核与生长形成Pd团簇,之后再与Au颗粒上的Pd岛合并。进一步的结果分析显示,Au颗粒外围的Pd沉积体为多晶结构,由随机取向的Pd纳米晶粒构成。     

One-step synthesis of water-soluble AgInS2 and ZnS-AgInS2 composite nanocrystals and their photocatalytic activities

The parameters that control the stability of ZnO-nanoparticles suspensions and their deposition by electrophoretic deposition were studied, so as to organize the assembly and compaction of nanoparticles. The addition of cationic polyelectrolyte - Polyethylenimine (PEI) - with different molecular weights was investigated, in order to study their effectiveness and the influence of the molecular weight of the organic chain on suspensions dispersion. It was found that PEI with the highest molecular weight provided better dispersion conditions. Cathodic EPD was performed under previously optimized suspensions conditions and over electropolished stainless steel substrates. Experimental results showed that the EPD process in these conditions allows obtaining dense transparent ZnO thin films. Deposition times and intensities were optimized by analyzing the resulting thin films characteristics. Finally, the deposits were characterized by FE-SEM, AFM, and different spectroscopic techniques.     

The effect of electrolyte conductivity on electrophoretic deposition

In this work, the influence of electrolyte conductivity on the electrophoretic deposition of alumina particles from ethanol suspensions was studied. Deposition experiments in a Hull cell showed that high-conductivity ethanol-based suspensions yield uniform deposits, while low-conductivity suspensions result in nonuniform deposits. The difference in the deposition, behavior is due to the resistance increase over the deposit during polarization. Impedance measurements during electrophoretic deposition showed that during EPD the relative deposit resistance increases much faster for the high- than for the low-conductivity suspension. The impedance measurements also showed that the resistance increase dropped almost to the suspension resistance after the electric field was turned off. This means that the resistance over the deposit is caused by the interaction of ions with the deposit and by the depletion of ions at the deposition electrode. Negatively charged ions are depleted in the deposit by migration toward the positively charged counterelectrode, while positively charged ions undergo electrochemical reactions at the deposition electrode. This change in ion concentrations near the deposition electrode changes the acid/base properties of the particles in the deposit, as proven by adsorbed pH indicators on the particles. The change in acid/base behavior is quasi-irreversible and results in a memory effect of the deposit resistance when the voltage is reapplied.     

CO2-expanded liquid deposition of ligand-stabilized nanoparticles as uniform, wide-area nanoparticle films

Deposition of nanoparticles into uniform, wide-area thin films using CO(2) as an antisolvent is presented. Ligand-stabilized silver particles are controllably precipitated from organic solvents by pressurizing and expanding the solution with carbon dioxide. Subsequent addition of carbon dioxide as a dense supercritical fluid provides for removal of the organic solvent while avoiding the surface tensions common to evaporating solvents that are detrimental to nanoscale assemblies and structures. This brand new CO(2)-expanded liquid particle deposition technique allows for the targeted deposition of particles and results in more uniform and lower defect metal nanoparticle thin films than are provided by conventional solvent evaporation techniques.     

Electrophoretic deposition of polyacrylic acid and composite films containing nanotubes and oxide particles

Electrophoretic deposition (EPD) method has been developed for the deposition of thin films of polyacrylic acid (PAA). This method allowed the formation of uniform films of controlled thickness on conductive substrates. It was shown that PAA can be used as a common dispersing agent suitable for charging and EPD of various materials, such as multiwalled carbon nanotubes, halloysite nanotubes, MnO(2), NiO, TiO(2) and SiO(2). The feasibility of EPD of composite films containing the nanotubes and oxide particles in a PAA matrix has been demonstrated. The kinetics of deposition and deposition mechanisms were investigated and discussed. The films were studied by thermogravimetric analysis, differential thermal analysis, X-ray diffraction and scanning electron microscopy. The results indicated that film thickness and composition can be varied. Obtained results pave the way for the fabrication of PAA and composite films for biomedical, electrochemical and other applications.     

一种复合熔融碳酸盐燃料电池基体阴极的制备和性质研究

采用电泳沉积技术将LiCoO2和CeO2两种纳米颗粒同时沉积至多孔镍基阴极表面,获得一种新型复合基体阴极材料——LiCoO2-CeO2-Ni。研究了其在模拟熔融碳酸盐燃料电池(MCFC)工作条件下的形变/溶解行为,并对其实验前后的表面进行了详细分析。结果表明,与传统多孔镍基阴极相比,新基体阴极材料在模拟MCFC启动及运行条件下形变微小,镍溶出速率低。材料表面所修饰的纳米颗粒薄层对镍基体包覆致密且与之形成稳定新相,从而有效抑制了材料的形变和溶解。     

Physical vapor deposition of one-dimensional nanoparticle arrays on graphite: seeding the electrodeposition of gold nanowires

One-dimensional (1D) ensembles of 2-15 nm diameter gold nanoparticles were prepared using physical vapor deposition (PVD) on highly oriented pyrolytic graphite (HOPG) basal plane surfaces. These 1D Au nanoparticle ensembles (NPEs) were prepared by depositing gold (0.2-0.6 nm/s) at an equivalent thickness of 3-4 nm onto HOPG surfaces at 670-690 K. Under these conditions, vapor-deposited gold nucleated selectively at the linear step edge defects present on these HOPG surfaces with virtually no nucleation of gold particles on terraces. The number density of 2-15 nm diameter gold particles at step edges was 30-40 microm-1. These 1D NPEs were up to a millimeter in length and organized into parallel arrays on the HOPG surface, following the organization of step edges. Surprisingly, the deposition of more gold by PVD did not lead to the formation of continuous gold nanowires at step edges under the range of sample temperature or deposition flux we have investigated. Instead, these 1D Au NPEs were used as nucleation templates for the preparation by electrodeposition of gold nanowires. The electrodeposition of gold occurred selectively on PVD gold nanoparticles over the potential range from 700-640 mV vs SCE, and after optimization of the electrodeposition parameters continuous gold nanowires as small as 80-90 nm in diameter and several micrometers in length were obtained.     

Cathodic electrophoretic deposition of manganese dioxide films

Cathodic electrophoretic deposition (EPD) method has been developed for the deposition of manganese dioxide films. It was shown that phosphate ester (PE) is an effective charging additive, which provides stabilization of manganese dioxide nanoparticles in suspensions. The influence of PE concentration and deposition voltage on the deposition efficiency has been studied. EPD has been utilized for the fabrication of porous nanostructured films with thickness in the range of 0.5–20 μm for application in electrochemical supercapacitors (ES). Cyclic voltammetry and chronopotentiometry data for the films tested in the 0.1 M Na₂SO₄ solutions showed capacitive behavior in the voltage window of 1 V. The highest specific capacitance (SC) of 377 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹. The SC decreased with increasing film thickness and increasing scan rate in the range of 2–100 mV s⁻¹. The deposition mechanism, kinetics of deposition and charge storage properties of the films are discussed.     

Directed assembly of BaFe12O19 particles and the formation of magnetically oriented films

We have studied the preparation of oriented BaFe(12)O(19) films produced using electrophoretic deposition (EPD). Highly anisotropic, platelike BaFe(12)O(19) particles were synthesized under hydrothermal conditions, and from these particles, stable suspensions were prepared in 1-butanol by the addition of dodecylbenzene sulfonic acid as a surfactant. The interplay of the interaction forces between the suspended particles and the forces acting on the particles during the EPD directed the particles' assembly in the plane of the substrate. The most significant effect on the orientation of the films was the diameter-to-thickness ratio of the particles, which was experimentally confirmed with X-ray analyses, electron microscopy, and magnetic measurements. The abnormal grain growth that accompanied the sintering at 1150 °C further improved the overall orientation of the films, which showed highly anisotropic magnetic behavior with a remanent-to-saturation magnetization ratio exceeding 0.8.     

Facile fabrication of hollow mesoporous silica nanospheres for superhydrophilic and visible/near-IR antireflection coatings

A series of hierarchically mesostructured silica nanoparticles (MSNs) less than 100 nm in size were fabricated by means of a one-step synthesis using dodecanethiol (C(12)-SH) and cetyltrimethylammonium bromide (CTAB) as the dual template, and trimethylbenzene (TMB) as the swelling agent. Silica nanoparticles with varied morphologies and structures, including mesoporous silica nanoparticles with tunable pore size, mesoporous silica nanoparticles with a thin solid shell, hollow mesoporous silica nanoparticles with tunable cavity size, and hollow mesoporous silica nanoparticles with a thin solid shell, were obtained by regulating the TMB/CTAB molar ratio and the stirring rate with the assistance of C(12)-SH. Silica particulate coatings were successfully fabricated by using MSNs with varied morphologies and structures as building block through layer-by-layer dip-coating on glass substrates. The thickness and roughness of the silica particulate coatings could be tailored by regulating the deposition cycles of nanoparticles. The silica particulate coatings composed of hollow mesoporous silica nanoparticles with a thin shell (S2) increased the maximum transmittance of slide glass from 90 to 96%, whereas they reduced its minimum reflection from 8 to 2% at the optimized wavelength region that could be adjusted from visible to near-IR with a growing number of deposition cycles. The coatings also exhibited excellent superhydrophilic and antifogging properties. These mesostructured silica nanoparticles are also expected to serve as ideal scaffolds for biological, medical, and catalytic applications.     

Controllable zeolite films on electrodes—comparing dc voltage electrophoretic deposition and a novel pulsed voltage method

We report here a novel application of pulsed voltage electrophoretic deposition (EPD) of zeolite 13X particles on glassy carbon surfaces. Our initial studies employing dc voltage EPD indicated that while adjustments of solution parameters (pH, supporting electrolyte concentration) and other experimental parameters (dc voltage, deposition time) allowed control of the amount of zeolite coated (from sub-monolayer to multilayer), difficulties of surface deactivation, controllability, uniformity, and reproducibility occurred under conditions suitable for the various films. These difficulties can be alleviated by utilizing a pulsed voltage program for EPD, an approach which has not been previously used for the fabrication of zeolite modified electrodes.     

Electrodeposition and characterization of Pd nanoparticles doped amorphous hydrogenated carbon films

Palladium (0) nanoparticles incorporated hydrogenated amorphous carbon (Pd/a-C:H) films were synthesized on single crystal silicon (100) substrates by electrochemical deposition route using methanol and camphor as carbon source, and Pd nanoparticles as dopant. The characterization results indicate that Pd nanocrystalline particles with diameter in the range of 1–5 nm dispersed in the amorphous carbon matrix. Compared with pure a-C:H films, the introduction of Pd nanoparticles didn't change the structure of carbon films. At the end, the growth mechanism of the Pd/a-C:H composite films was discussed.     

Silver metal nanosized particles: Control of particle size,self assemblies in 2D and 3D superlattices and optical properties

Water in oil droplets are used to control the size of silver metal nanoparticles. After synthesis, the silver metal particles are extracted from reverse micelles and redispersed in a non polar solvent. By increasing the size of the water droplets the average size of silver nanoparticles increases from 2 nm to 7 nm with a rather high size distribution. To narrow the panicle distribution a size selected precipitation method is used. By deposition of a dilute solution containing the coated particles on a carbon grid, the particles arrange themselves in a monolayer organized in a hexagonal network. At high particle concentration, the particles are organized in multilayers forming microcrystals arranged in a face centered cubic structure. The optical properties of the silver nanoparticles isolated in micellar solution or self-assembled in 2D or 3D supperlattices are reported.