Study of the gel films of Acetobacter Xylinum cellulose and its modified samples by 1H NMR cryoporometry and small-angle X-ray scattering

Gel films of Acetobacter Xylinum cellulose and its modified samples have been investigated by 1H nuclear magnetic resonance (NMR) cryoporometry and small-angle X-ray scattering. The joint use of these two methods made it possible to characterize the sizes of aqueous pores in gel films and estimate the sizes of structural inhomogeneities before and after the sorption of polyvinylpyrrolidone and Se₀ nanoparticles (stabilized by polyvinylpyrrolidone) into the films. According to small-angle X-ray scattering data, the sizes of inhomogeneities in a gel film change only slightly upon the sorption of polyvinylpyrrolidone and nanoparticles. The impregnated material is sorbed into water-filled cavities that are present in the gel film. ¹H NMR cryoporometry allowed us to reveal the details of changes in the sizes of small aqueous pores during modifications.     

Interaction of Se0 nanoparticles stabilized by poly(vinylpyrrolidone) with gel films of cellulose Acetobacter xylinum

The sorption and desorption of poly(vinylpyrrolidone)-Se⁰ (PVP-Se⁰) nanoparticles on gel films of cellulose Acetobacter xylinum (CAX) are investigated. It is revealed that the hydrodynamic radius R _h of PVP-Se⁰ nanoparticles decreases from 57 nm in the initial solution (without CAX gel films) to 25 nm after the sorption of nanostructures on gel films and then increases to approximately 100 nm after the desorption of nanoparticles with water from dry samples of the CAX gel film-PVP-Se⁰ nanocomposite. It is found that selenium atoms do not penetrate into crystallites of the cellulose nanofibrils and replace water molecules sorbed by the primary hydroxyl groups of their walls. Poly(vinylpyrrolidone)-Se⁰ nanoclusters differ in the number and size upon their sorption inside the cellulose gel film and on the film surface.     

Low-Voltage Scanning Electron Microscopy and Energy-Dispersive X-Ray Microanalysis of the Interface of Multilayer Polymer Composite

The morphology of the layer of polyelectrolyte complex, which is formed in the composite based on chitosan and sulfoethyl cellulose during the contact of a solution of one of them with a gel film of the other one, has been investigated by the low-voltage (≤3 kV) scanning electron microscopy. A technique for eliminating the effects related to charge accumulation on the dielectric film surface is proposed.     

New chiral metal-mesogenic nanosystems “silver - thiocholesterol” and their adsorption properties

ABSTRACT

New chiral matrices for thin film chromatography were obtained using hybrid metal-mesogenic nanosystems «silver – thiocholesterol» with different metal to ligand ratio, immobilized on silica gel particles. It was shown, that heteroatomic derivative of cholesterol – thiocholesterol and its composition with small silver nanoparticles formed in the system by the chemical reduction of silver ions possess liquid crystalline cholesteric mesophase. Molar ratio between thiocholesterol ligand molecules (L) and silver (Ag) insignificantly influenced on the size of silver nanoparticles formed in the system: for molar ratio Ag : L = 1:5 the main diameter of nanoparticles was equal to (2,7 ± 0,4) nm, for molar ratio Ag : L = 1:2 – (2, 2 ± 0,4) nm, for molar ratio Ag : L = 1:0,5 – (2,1 ± 0,6) nm. The new chiral matrices for thin film chromatography possess enantioselectivity related to optical isomers of 2,2′-diamino-1,1′-binaphtol (DABN) and trifluoroantranylethanol (TFAE). We have succeeded to select optical isomers of TFAE with selecting factor equal to 1,56.     

Synthesis of monodisperse platinum nanoparticles supported on carbon gel microspheres

Monodisperse platinum nanoparticles were successfully fabricated on the porous structure of carbon gel microspheres with a narrow pore size distribution. The size of the platinum nanoparticles supported on the carbon gel microspheres was almost coincident with the pore size of the carbon gel microspheres. The results indicated the potential for controlling the size distribution of the supported platinum nanoparticles using the carbon gel microspheres with different pore size distributions.     

Preparation and optical properties of silver nanoparticles induced by a femtosecond laser irradiation

Silver nanoparticles were prepared by a focused femtosecond laser irradiation in a 5 mM AgNO₃ solution in the presence of TiO₂ sol. TEM analysis revealed that the size of silver nanoparticles was less than 20 nm. A mechanism for the precipitation of silver nanoparticles was proposed. Nonlinear absorptions and optical limiting properties of silver nanoparticles contained solution were also measured. It is observed that the composite material showed strong self-focused effect and significant optical limiting property.     

Preparation and analysis of multilayer composites based on polyelectrolyte complexes

A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.     

Preparation and characterisation of Ag incorporated Al2O3 nanocomposite films obtained by sol‐gel method

Sol‐gel route has been applied for a deposition of the thin films of aluminum oxide and Ag embedded in Al₂O₃ films. The films are spin‐coated on Si and quartz substrates with the film thickness of 120 nm. XRD analysis has been used for the determination of the film structure. FTIR spectroscopy is applied for studying vibrational properties of the obtained coatings. Optical characterization is done by UV‐VIS spectroscopy. The formation of Ag nanoparticles has been confirmed by XRD and optical data. The sol‐gel process is found to be useful technology for incorporation of Ag nanoparticles in the metal oxide matrices. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ordered structures based on self-organized Au and CdSe nanoparticles

Methods for obtaining cadmium selenide and gold nanoparticles have been developed. The sizes of the nanoparticles are determined and the morphology, structure, and chemical composition of these nanoparticles and their ensembles are studied by a complex of structural methods: electron diffraction, X-ray diffraction, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy, and small-angle X-ray scattering. Gold nanoparticles are mainly spherical and have an average size of 10 nm. They are single-phase and have an fcc crystal structure. Samples of synthesized CdSe nanoparticles contain monodisperse spherical particles 12 nm in size with a wurtzite structure. The deposition of nanoparticles on a carbon substrate is accompanied by their self-organization into a closely packed two-dimensional structure with a pronounced texture in which all nanoparticles are oriented in the [001] direction perpendicularly to the carbon substrate plane.     

Localized surface plasmon enhanced microcrystalline–silicon solar cells

A novel type of substrate named “Ag–SP substrate”, in which silver nanoparticles are incorporated, is introduced and utilized as a back reflector for hydrogenated microcrystalline-silicon solar cell in a substrate-type (n-i-p) configuration. Optical and morphological analyses of Ag–SP substrates fabricated with various sizes of silver nanoparticles are systematically performed. It is shown that silver nanoparticles in Ag–SP substrate structure can lead to significant scattering of light when their diameter increases up to 300 nm. Furthermore, the photocurrent of the solar cell fabricated on an Ag–SP substrate with RMS roughness as small as 16.5 nm and a proper lateral diameter (approximately 300 nm) of silver nanoparticles is improved as compared to that of the solar cell prepared on reference textured substrate with RMS roughness of 25.3 nm, owing to strong scattering of light by silver nanoparticles in the red-infrared region.     

空气退火对ZnS薄膜结构和光学特性的影响

采用X射线衍射、扫描电子显微镜和光致发光等技术研究了空气退火对ZnS薄膜的结构和光学特性的影响.薄膜在500℃以下退火后结晶质量得到改善,仍呈ZnS立方相结构.退火温度达到550℃时,薄膜中出现ZnO六方相结构.薄膜退火后,大气中的氧掺入薄膜中,出现ZnS-ZnO复合层.随退火温度升高,薄膜晶粒尺寸增大,透过率增加,带隙逐渐接近ZnO带隙.薄膜光致发光结果表明,复合层内ZnS和ZnO绿色发光的叠加替代了来自ZnS缺陷能级间的绿色发光.     

Induction time of silver nanoparticles precipitation: Experiment and modeling

This paper describes the measurement of induction time in precipitation of silver nanoparticles at different temperatures and supersaturations, and models it with Smoluchowski's coagulation theory. Silver nanoparticles are synthesized by reaction of silver nitrate with hydrazine in the presence of sodium citrate as stabilizer. The rate of association between clusters is found to depend on temperature and their sizes. The activation energy for the association between two clusters and interfacial tension of silver nanoparticles were also estimated. The results also show that induction time decreases with increasing supersaturation and temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于掺杂二氧化硅包覆银纳米球的有机太阳能电池光吸收提高的研究

虽然介质包覆的金属纳米颗粒已经在试验中频繁应用到太阳能电池中,通过减少金属表面激子的猝灭和电荷的复合来提高电池性能.但是基本没有理论研究工作去解释金属颗粒的介质包覆层是如何影响器件的光学性能.本文从理论计算角度研究了二氧化硅包覆银纳米球掺杂在有机太阳能电池活性层中对活性层的光捕获的影响.研究结果表明在垂直入射的条件下,在350 nm到850 nm的波段内,加入包覆Ag纳米球的最优器件的活性层对标准太阳光谱(AM 1.5)积分后的光吸收率达到81.5;.与等效的平板结构相比,活性层的光吸收增强了9.54;.具体的场分布的分析得到光吸收增强原因主要是偶极共振、表面等离激元激发以及之间的相互耦合作用所致.经过对结构参数的研究,发现了介质包覆层越薄,增强效果越明显;包覆的介质层的折射率对光吸收性能的影响不是很明显.     

Study of polyelectrolyte complexes of chitosan and sulfoethyl cellulose

The complexing of polycation chitosan and polyanion sulphoethyl cellulose during the formation of polyelectrolyte simplex membranes using the layer-by-layer deposition of a solution of one polyion on a gel-like film of another one has been studied. The structural characteristics of the multilayer composites and their components have been analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray microanalysis. A technique is proposed for studying the structure of surface layers of thin polymer films (15–20 μm) using a portable DIFREI-401 diffractometer. It is shown that the sequence of layer deposition during the formation of membrane films does not affect their structural characteristics. The interaction between positively charged chitosan groups (-NH ₃ ⁺ ) and negatively charged sulfoethyl cellulose groups (-SO ₃ ^? ) during the growth of polyelectrolyte complexes results in a packing of chitosan chains in the multilayer film.     

Mechanical modification of β-AgI nanocrystals

A nanostructured AgI powder has been synthesized. The structure, sizes, and shapes of nanoparticles of the initial powder and a powder modified in a VIBRATOR GM-945B vibration ball mill have been investigated by SEM, X-ray diffraction, and differential thermal analysis. A hypothesis of the structure and microscopic mechanism of structural transformations in the materials under study is proposed. Particular attention is paid to the ac ionic conduction of silver iodide particles.     

Low-temperature electron paramagnetic resonance in silver-iron oxide nanoparticles

Water in oil microemulsion technique has been used to obtain silver nanoparticles with a mean size of 7 nm surrounded by a matrix of 2 nm γ-Fe₂O₃ nanoparticles. Magnetic measurements of the sample exhibit a cusp in the ZFC curve at 50 K, which corresponds to the blocking temperature. A detailed study of the thermal evolution of EPR spectra has been performed in the samples. It has been shown that the linewidth, the resonance field and the intensity of the EPR line show different behaviour near the blocking temperature.     

Magnetic resonances of Fe and Ni nanoparticles in films of silicon suboxide produced by ion irradiation of triethoxysilane gels containing Fe or Ni solute atoms

The structure and magnetic properties of composite films obtained by ion irradiation or thermal treatment of triethoxysilane gels containing iron or nickel in solution are investigated by means of X-ray diffraction, electron microscopy and electron spin resonance. Ion irradiated gels are converted into silica glasses containing metallic nanoparticles with a narrow range of sizes. These particles exhibit a magnetic resonance with a preferential alignment of magnetic moments perpendicular to the surface. This unusual out of plane anisotropy seem to be ascribed to an interaction of the moments with radiation defects. The magnetization in irradiated film is comparable to that in films of same materials submitted to a thermal conversion at 1000 °C in vacuum. But the latter films are porous and contain particles of metal and silicide or silicate with a wider range of sizes.     

Facile synthesis of silver‐nanobeadwire transparent conductive film by organic‐precursor paint reduction

A new facile process has been developed to synthesize silver nanowire transparent conductive films by reducing high‐aspect‐ratio, needle‐shaped silver carboxylates, prepared as the precursor, while retaining their morphology. Nanowire precursors are simply obtained by ultrasound irradiation when silver (I) oxide and carboxylic acids are used as starting materials. The aspect ratio of the precursors is increased when the ultrasound irradiation is followed by microwave irradiation. Silver nanowires can be easily obtained by reducing these precursors with hydrazine gas or irradiating them with Ar plasma for a short time. The morphology of the resulting nanowires is different from that of typical nanowires that have been reported. The nanowires have porous morphology, where small nanoparticles are connected to form nanobeadwire. The nanobeadwire is considered to increase the transparency of the film because of its rough morphology. This new method can synthesize silver nanobeadwires and fabricate the transparent conductive film simultaneously, in one‐step, so that it can significantly simplify manufacturing processes.     

Er photoluminescence enhancement in Ag-doped sol-gel planar waveguides

This paper reports on the study of the effects of silver (Ag^o) nanoparticles on the optical and spectroscopic properties of Er³⁺-doped silica-based gels and glasses, including active bulk materials and planar waveguides for integrated optics. Two different procedures for silver and erbium ion incorporation into the glassy matrices have been investigated: the direct incorporation of a metal salt (AgNO₃ and/or Er(NO₃)₃) into the sol-gel solution, as well as a modified sol-gel process, based on pore-doping of a precursor gel with AgNO₃ and/or Er(NO₃)₃ solutions. The study of the parameters determining the average size and size distribution of the nanoparticles, together with their influence on the sol-gel material densification and Er³⁺ photoluminescence at 1.5 μm, has been performed by means of transmission electron microscopy, plus ultra-violet/visible and photoluminescence spectroscopies. The Ag^o colloidal nanoparticles, obtained by thermal precipitation, were approximately spherical, homogeneously distributed and they exhibited an average size between ∼2 and 15 nm, depending on the silver content and heat treatment performed. They are shown to be responsible for a remarkable enhancement of the Er³⁺ photoluminescence intensity, which is mainly due to the increase of the local electric field around the Er³⁺ ions, due to the surface plasmon resonance of the Ag^o nanoparticles.     

HNTs/SiO2复合气凝胶制备及其性能研究

采用正硅酸乙酯(TEOS)为硅原,以硅烷改性的埃洛石纳米管(HNTs)为增强相,利用CO2超临界干燥技术制备具有优良力学和隔热性能的HNTs/SiO2复合气凝胶.利用傅立叶红外光谱、扫描电镜、比表面积与孔径分析仪、万能试验机和导热率测量仪等手段对HNTs改性后的表面状态、HNTs/SiO2复合气凝胶的微观形貌、孔结构、力学和导热性能进行了测试分析.结果表明:改性后的HNTs均匀分散到二氧化硅气凝胶基体中,并与SiO2纳米颗粒实现良好的结合,HNTs/SiO2复合气凝胶呈三维网络结构,当HNTs含量为15wt;时,平均孔径为10.47 nm;随着HNTs含量的增加,复合气凝胶的力学性能不断增强,同时其导热系数也不断增大,当HNTs含量为15wt;时,HNTs/SiO2复合气凝胶的抗压强度为0.85 MPa,导热系数为0.024 W/mK.