Thermal conductivity of polyurethane composites containing nanometer- and micrometer-sized silver particles

Polyurethane composites containing spherical and flake-shaped silver fillers of micrometer and nanometer sizes were prepared by reacting suspensions of the silver filler in tetraethylene glycol with Desmodur^? HL BA. Both the thermal conductivity and the stability of the silver composites are increased in comparison with a reference polyurethane sample without filler. Unexpectedly, the largest increases in thermal conductivity and stability are observed for the spherical silver particles of micrometer size but not for the silver nanoparticles, which is reasoned with larger aggregates of silver particles and a higher degree of crystallinity in the sample containing micrometer-sized silver particles.     

Growth of ordered silver nanoparticles in silica film mesostructured with a triblock copolymer PEO-PPO-PEO

Elaboration of mesostructured silica films with a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide, (PEO-PPO-PEO) and controlled growth of silver nanoparticles in the mesostructure are described. The films are characterized using UV-visible optical absorption spectroscopy, TEM, AFM, SEM, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Organized arrays of spherical silver nanoparticles with diameter between 5 and 8 nm have been obtained by NaBH₄ reduction. The size and the repartition of silver nanoparticles are controlled by the film mesostructure. The localization of silver nanoparticles exclusively in the upper-side part of the silica-block copolymer film is evidenced by RBS experiment. On the other hand, by using a thermal method, 40 nm long silver sticks can be obtained, by diffusion and coalescence of spherical particles in the silica-block copolymer layer. In this case, migration of silver particles toward the glass substrate-film interface is shown by the RBS experiment.     

Influence of laser illumination during an oxidation-reduction cycle on the surface structure of silver: Implications for the mechanism of SERS

The structural changes produced by oxidation and reduction of a silver surface in 1 M CKl with and without illumination were examined by scanning electron microscopy. Laser illumination (632.8 nm) during the oxidation-reduction cycle (ORC) produces a surface covered with a high density of sub-μm sized particles. The silver particles are the result of the photolytic reduction of the silver chloride made possible by the presence of the applied electric field within the silver chloride layer which prevents the recombination of the photoelectrons and holes. As the maximum anodization voltage of the ORC is increase to +100 mV vs. SCE, the number of photolytically produced silver particles increases. As the maximum anodization voltage is increased from +100 mV to +200 mV, the individual particle size increases from ≈200 nm to ≈800 nm. The intensity of Raman scattering from water adsorbed on the silver surface was maximized by a laser illuminated ORC with a maximum anodization voltage of +100 mV.Since recent theoretical studies indicate an optimum particle size of r≈50 nm for maximizing the electromagnetic component of the enhancement, the present results indicate that either the individual silver particles contain small scale (≈50 nm) roughness features or the electromagnetic factors are not the sole contributors to the enhancement.     

Synthesis of Ag and Ag/SiO2 sols by solvothermal method and their bactericidal activity

Ag and Ag/SiO₂ sols containing nanocrystalline silver particles can be advantageously prepared by solvothermal methods using an autoclave with conventional thermal or microwave heating. In this process, the reduction of silver salts can be realized with alcohols like ethanol in the presence of polyvinylpyrrolidone at temperatures of more than 120 °C. Furthermore a combination of silver salt reduction with hydrolysis of alkoxysilanes during the solvothermal process can yield Ag/SiO₂ composite sols. Particle size and crystallinity of as-prepared particles are analyzed by means of X-ray diffraction and high-resolution transmission electron microscopy. Nanosized silver particles gained by this process exhibit antimicrobial properties that are investigated in detail after application on textile fabrics.     

银岛膜中银颗粒间表面电磁波的耦合

自从Hartstcil。等人用衰减全反射技术（AT则得到覆盖在银岛膜上的有机超薄膜的表面增强红外吸收光谱以来山，对其增强机理及应用的研究一直是人们关注的热点．人们不论是从实验上还是从理论上都通过种种努力来探索表面增强红外光谱的机理，但仍然没有给出一个清晰的图象．一般     

Spectroscopy property of Ag nanoparticles

Three silver nanoparticles of different size characterized by the UV-vis absorbance spectra and TEM images were prepared by citrate reduction and laser ablation with excitation of 532 and 248 nm. It is proved that all of them are effective SERS-active substrates, whereas, enhancement effect of silver colloids has not too much relation with the size and shape of the Ag nanoparticles. However, different photoluminescence spectra were observed from these three particles, indicating that the photoluminescence property of silver nanoparticles is dependent on the size. The spectra shift to higher energies with decreasing particle size. In addition, we also tentatively give the assignment of the luminescence bands.     

Conditions for attainment of thermodynamic equilibrium for the Ag/Hg system

Following a previous study on the influence of the size of silver particles used in dental alloys on the conditions for the attainment of thermodynamic equilibrium, results are presented on the influence of the particle shape factor. Calorimetric results obtained using different particle forms are compared with those derived from a mathematical model in which it is considered that silver particles can assume a spherical or cylindrical (flat or narrow) shape. It appears that the thermal effects obtained by computation are closer to those obtained by calorimetric experimentation when the sphere of the model is transformed into either a disc or a rod.     

烟酸在热敏成像材料中的调色作用

本文将烟酸引入以硬脂酸银为银源的热敏成像材料中,可以明显提高显影密度,并使影像颜色由金黄色变成黑色;同时显影银粒子的尺寸变大、形貌也会发生改变,并且显影银粒子像链珠一样排成一条线,而线与线之间基本上是平行排列的.进一步实验结果表明,烟酸的引入会降低材料的pH、pAg值和银盐的相变温度,硬脂酸银与烟酸一起加热可能反应生成了新的化合物.     

Self-assembly of silver nanoparticles: synthesis, stabilization, optical properties, and application in surface-enhanced Raman scattering

Silver nanoparticle aggregates were synthesized in large scale using resorcinol under alkaline condition to obtain an assembly of silver clusters. Stable dispersion of the cluster in aqueous medium has been examined out of resorcinol-capped silver nanoparticle assemblies. The UV-vis spectroscopy during the particle evolution has been studied in detail. From the high-resolution TEM (HRTEM) image and XRD pattern it was confirmed that the particles are made of pure silver only. The capping action of resorcinol has been authenticated from the FTIR spectra. UV-vis spectroscopy and TEM images reveal that the temperature, effect of vibrational energy, heat shock, and time-dependent particle evolution have unique bearing on the stability and surface properties of the clusters. The concentrations of silver nitrate, resorcinol, and NaOH have important influence on the particle evolution and its size. TEM images incite us to examine the aggregates to capitulate surface-enhanced Raman scattering (SERS) to the single molecular level using crystal violet (CV) and cresyl fast violet (CFV) as molecular probes. The SERS intensity of CV increases with increasing the size of the silver aggregate.     

Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.     

聚合物存在下纳米银复合材料的制备与表征

以聚丙烯腈聚乙二醇嵌段共聚物PAN-b-PEG-b-PAN为稳定剂, 在超声辐照下成功地制备了分散性较好、尺寸均匀的纳米银颗粒. 用X射线衍射(XRD)、红外光谱(FTIR)、透射电镜(TEM)、紫外-可见吸收光谱(UV-Vis)和热分析(TGA)等对制备的纳米银复合材料进行了表征. 红外结果表明超声辐照并没有破坏聚合物的链结构. 聚合物的引入, 对纳米银颗粒起到了很好的分散保护作用. 用低浓度的硝酸银溶液, 得到粒径较小的纳米银颗粒; 随着硝酸银浓度增大, 纳米银颗粒粒径也增大. 而聚合物的浓度增大时, 所得银纳米颗粒粒径减小. 对银纳米颗粒的形成机理进行了讨论.     

Synthesis and surface chemistry of nano silver particles

In this report, we present a simple wet chemical route to synthesize nano-sized silver particles, and their surface properties are discussed in detail. Silver nano particles of the size 40–80 nm are formed in the process of oxidation of glucose to gluconic acid by amine in the presence of silver nitrate, and the gluconic acid caps the nano silver particle. The presence of gluconic acid on the surface of nano silver particles was confirmed by XPS and FTIR studies. As the nano silver particle is encapsulated by gluconic acid, there was no surface oxidation, as confirmed by XPS studies. The nano silver particles have also been studied for their formation, structure, morphology and size using UV–Visible spectroscopy, XRD and SEM. Further, the antibacterial properties of these nano particles show promising results for E. Coli. The influence of the alkaline medium towards the particle size and yield was also studied by measuring the pH of the reaction for DEA, NaOH and Na₂CO₃.     

A novel one step synthesis of silver nanoparticles using room temperature ionic liquid and their biocidal activity

This article reports the synthesis of silver Nan particles (SNPs) using 1-(dodecyl) 2 amino-pyridinium bromide ionic liquid. This is a new one phase method for the synthesis of uniform monodispersed crystalline silver nanoparticles in a water-ionic liquid system. In this work, the functionalized room temperature IL acts as stabilizing agent and solvent. Hydrazine hydrate acts as reducing agent. To the best of our knowledge, there is no report of the synthesis of metal nanoparticles using this ionic liquid. The synthesis of silver nanoparticles is very primarily studied by UV-Visible spectroscopic analysis. The TEM and particle size distribution was used to study morphology and size of the particles. The charge on synthesized SNPs was determined by Zeta potential. The silver nanoparticles have been known to have inhibitory and bactericidal effect. The investigation of antibacterial activities of ionic liquid stabilized silver nanoparticles was performed by measurement of the minimum inhibitory concentration.     

Fabrication and characterization of homogeneous surface-enhanced Raman scattering substrates by single pulse UV-laser treatment of gold and silver films

The fabrication of SERS-active substrates, which offer high enhancement factors as well as spatially homogeneous distribution of the enhancement, plays an important role in the expansion of surface-enhanced Raman scattering (SERS) spectroscopy to a powerful, quantitative, and noninvasive measurement technique for analytical applications. In this paper, a novel method for the fabrication of SERS-active substrates by laser treatment of 20, 40, and 60 nm thick gold and of 40 nm thick silver films supported on quartz glass is presented. Single 308 nm UV-laser pulses were applied to melt the thin gold and silver films. During the cooling process of the noble metal, particles were formed. The particle size and density were imaged by atomic force microscopy. By varying the fluence, the size of the particles can be controlled. The enhancement factors of the nanostructures were determined by recording self-assembled monolayers of benzenethiol. The intensity of the SERS signal from benzenethiol is correlated to the mean particle size and thus to the fluence. Enhancement factors up to 10(6) with a high reproducibility were reached. Finally we have analyzed the temperature dependence of the SERS effect by recording the intensity of benzenethiol vibrations from 300 to 120 K. The temperature dependence of the SERS effect is discussed with regard to the metal properties.     

UV‐curing synthesis of sulfonated polyaniline‐silver nanocomposites by an in situ reduction method

Sulfonated polyaniline‐silver (SPAni‐Ag) hybrid nanocomposites have been synthesized by the in situ reduction using a UV‐curing polymerization method without using any reducing or binding agent. An aqueous solution of aniline and orthoanilinic acid (OA) comonomers, a free‐radical oxidant and silver metal salts were irradiated by UV rays. Reduction of the silver salt in aqueous aniline and OA leads to the formation of silver particles which in turn catalyze the oxidation of comonomers to sulfonated polyaniline (SPAni). The resultant SPAni‐Ag nanocomposites were characterized by using different spectroscopy analyses like UV–visible (UV–Vis), X‐ray diffraction (XRD) and infrared spectroscopy. The absorption bands were revealed to be optically active and the peaks blue‐shifted due to the presence of metallic silver within the SPAni matrix. The XRD patterns displayed both the broad amorphous polymeric and sharp metallic peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposites showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the nanocomposites had a better thermal stability than the bulk SPAni. Copyright © 2008 John Wiley & Sons, Ltd.     

钴岛膜上对巯基苯甲酸的表面增强红外吸收光谱

通过置换反应在金属铝表面制备了表面没有任何保护剂且具有红外增强作用的钴岛膜,用SEM、XRD和表面增强红外光谱对其形貌和性质进行表征。 结果表明,铝片上沉积出的钴呈岛状结构,钴岛膜由二次钴粒子和一次钴粒子通过密堆积的方式构成;首次发现具有这种特殊结构的钴对吸附于其表面的有机分子的红外吸收光谱有较大的增强作用,用此钴岛膜对1 mmol/L的对巯基苯甲酸的红外光谱研究时得到很好的红外增强信号,使得表面增强红外光谱可以用于痕量分析、检测。     

Epoxy‐based composite adhesives: Effect of hybrid fillers on thermal conductivity,rheology, and lap shear strength

Thermal management is an important parameter in an electronic packaging application. In this work, three different types of fillers such as natural graphite powder (Gr) of 50‐μm particle size, boron nitride powder (h‐BN) of 1‐μm size, and silver flakes (Ag) of 10‐μm particle size were used for thermal conductivity enhancement of neat epoxy resin. The thermal properties, rheology, and lap shear strength of the neat epoxy and its composite were investigated. The analysis showed that the loading of different wt% of Gr‐based fillers can effectively increase the thermal conductivity of the epoxy resin. It has also been observed that the thermal conductivity of the hybrid filler (Gr/h‐BN/Ag) reinforced epoxy adhesive composite increased six times greater than that of neat epoxy resin composite. Further, the viscosity of hybrid filler reinforced epoxy resin was found to be increased as compared with its virgin counterpart. The adhesive composite with optimized filler content was then subsequently subjected to determine single lap shear strength. The degree of filler dispersion and alignment in the matrix were determined by scanning electron microscopy (SEM) analysis.     

A thermal decomposition route for synthesis of silver ribbons

In the presence of dodecylamine, which can serve as the medium and at the same time as the stabilizing reagent, ribbons made of metallic silver were produced by thermal decomposition of silver phthalate. As the reaction mixture was heated up to 170°C, thermal reduction took place in parallel. Silver ribbon is produced if growth proceeds by regular addition of silver atoms to the edges of nuclei. However, seed-form particles will be produced if growth proceeds by irregular addition of silver atoms to the nuclei. Synthesized silver ribbons were characterized by energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and UV-Vis spectroscopy. Surface morphological survey of silver particles was conducted by using SEM image, confirming the formation of agglomerated silver particles as well as silver ribbons.     

Silver nanoparticles capped by oleylamine: formation, growth, and self-organization

Nearly monodisperse silver nanoparticles have been prepared in a simple oleylamine-liquid paraffin system. Intensive study has found that the formation process of silver nanoparticles could be divided into three stages: growth, incubation, and Ostwald ripening stages. Ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM have all demonstrated the occurrence of Ostwald ripening, which could result in better control over the size and size distribution of silver nanoparticles. SAXS (small-angle X-ray scattering) results show that the as-obtained silver nanoparticles can self-assemble into ordered arrays. The possible reduction mechanism of silver ions by oleylamine is related to the Ag+-mediated conversion of primary amines to nitriles.     

Production and structural characterization of crystalline silver nanoparticles from Bacillus cereus isolate

To date, biosynthesis of metal nanoparticles has been intensively studied using bacteria and fungi. We have isolated and identified metal resistant bacterial strains from electroplating industries, they produce silver nanoparticles. The reduction reaction of aqueous silver nitrate with bacterial biomass was carried out for 120 h. Bacteria produced metallic nanoparticles showed a strong absorbance at surface plasmon resonance wavelength around 420 nm. The size and morphology of these nanoparticles were typically imaged using high resolution transmission electron microscopy, the particles size ranges between 4 and 5 nm and are spherical in shape. The crystal structure of the particles was characterized by X-ray diffraction pattern. The full width half maxima from X-ray diffraction measurements indicated that the particles exhibited face-centered cubic phase.