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摘要:Cellulose nanofiber (CNF) is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. It has high strength comparable to steel, and it shows low environmental load during a cycle of production and disposal. Besides it has many excellent properties and functions such as high rigidity, light-weight, flexibility and shape memory effect, so it is expected as a next-generation new material. Usually it is composed of many cellulose micro fibrils (CMFs) in which molecular chains of cellulose are aggregated in a crystal structure, the knowledge of mechanical properties for each CMF unit is important. Since actual fibrils are complicatedly intertwined, it is also crucial to elucidate the transmission mechanism of force and deformation not only in one fibril but also in between fibrils. How the dynamic and hierarchical structure composed of CMFs responds to bending or torsion is an interesting issue. However, little is known on torsional characteristics (shear modulus, torsional rigidity, etc.) concerning CMF. In general, in a wire-like structure, it is difficult to enhance torsional rigidity and strength, compared with tensile ones. Therefore, in this study, we try to build a hierarchical model of CNF by multiplying CMF fibers and to conduct molecular dynamics simulation for torsional deformation, by using hybrid model between all-atom and united-atoms model. First, shear modulus was estimated for one CMF fibril and it showed a value close to the experimental values. Also, we assume a state in which two CMFs are ideally arranged in parallel, and create a hierarchical structure. We evaluate the dependence on the temperature for the bond strength and toughness in the hierarchical structures. Furthermore, we mentioned the transmission mechanism between components of a hierarchical structure....
[期刊论文] Marwa Nabil
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2019年 03期
摘要:This paper reports the feasibility of synthesis and characterization of nano-porous silicon (NPS) powder and (Nickel/nano-porous silicon, Ni/NPS) nano-composite prepared using dual techniques (alkaline chemical etching process and ultra-sonication technique). The structural and the optical properties of the fabricated structures are inspected using X-ray Diffraction, Fourier Transform Infrared Spectrophotometer, Raman Spec-troscopy, and Fluorescence Spectrophotometer Photoluminescence. All the results have agreed that NPS is one of the most suitable materials used as active material in the LED fabrication; by changing the main factors in the preparation process, so the different physical and chemical properties are obtained. NPS produces two emission regions that correspond to orange-red and dark red; on the other hand, (Ni/NPS) produce the yellow emission. So, the photoluminescence emission is controllable by adjusting the preparation conditions. The optical data recorded here are useful for the production of the nanoscale optical devices....
摘要:We consider a hybrid heterostructure containing an inorganic quantum well in close proximity with organic material as overlayer. The resonant optical pumping of Frenkel exciton can lead to an efficient indirect pumping of Wannier excitons. As organic material in such a hybrid structure, we consider crystalline tetracene. In tetracene, the singlet exciton energy is close to twice the one of triplet exciton state and singlet exciton fission into two triplets can be efficient. This process in tetracene is thermally activated and we investigate here how the temperature-dependent exciton energy transfer affects the functional properties of hybrid organic-inorganic nanostructures. We have obtained the exact analytical solution of diffusion equation for organics at different temperatures defining different diffusion lengths of excitons. The effectiveness of energy transfer in hybrid with tetracene was calculated by definite method for two selected temperatures that open possibility to operate in full region of temperatures. Temperature dependence of energy transfer opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic subsystem to the inorganic subsystem....
摘要:Silver nanoparticles of diameters 3.4 to 13.2 nm grown at the interfaces between silicate glass and some oxide crystallites exhibited about six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 80%. Sn-SnO2 nano core-shell structure prepared within a gel-derived silica glass film by electrodeposition technique followed by heat treatment showed large change in resistivity as a function of humidity. The resistivity also changed due to gas flow of CO2, C2H5OH and NO2, respectively. The latter arose because of reduction/oxidation of Sn4+/Sn2+ species present at the shell layer of the nanostructures. Nickel nanosheets of thickness ~0.6 nm grown within the interlayer spaces of Na-4 mica crystallites showed a change of dielectric permittivity (5%) for an applied magnetic field of 1.2 Tesla. An inhomogeneous model was used to explain this behavior. Two dimensional CuO phase was grown within the channels of diameter ~5 nm of mesoporous SiO2 structure. A magnetodielectric (MD) parameter M.D. of 4.4% was obtained in this case. BaTiO3 nanoparticles of diameter ~25 nm having pores with diameter 10 nm showed multiferroic behavior which arose due to the presence of oxygen vacancies as a result of large surface area present. An M.D. parameter of 11% was found. Similarly mesoporous LiNbO3 of 10 nm diameter showed an M.D. parameter of ~4.5% at a magnetic field 1 Tesla. A giant magnetocapacitance effect with a value of 44% at 1.5 T was observed in nickel zinc ferrite (NZF) impregnated mesoporous silica. A magnetocapacitance of 51% at magnetic field 1.7 T was found in the case of nanocomposites comprising of iron ion containing silica based nanoglass and mesoporous silica. In the last two examples the behavior was explained on the basis of Catalan model of space-charge polarization with extracted values of magnetoresistance of the NZF and nanoglass phases being 58%....
[期刊论文] Jia lin Wu
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2011年 03期
摘要:A basic concept in chain-particle cluster-motion, from frozen glassy state to melt state, is the 2D soft nano-scale mosaic structure formed by 8 orders of 2D interface excitation (IE) loop-flows, from small to large in inverse cascade and rearrangement structure in cascade along local one direction. IE has additional repulsive energy and extra vacancy volume. IE results from that the instantaneous synchronal polarized electron charge coupling pair is able to parallel transport on the interface between two neighboring chain-particles with antiparallel delocalization. This structure accords with de Gennes’ mosaic structure picture, from which we can directly deduce glass transition temperature, melt temperature, free volume fraction, critical entangled chain length, and activation energy to break solid lattice. This is also the inherency maximum order-potential structure in random systems....
摘要:TiO2 nanoparticles with surface hydroxyl groups are treated by trimethoxysilane (CH3O)3Si(CH2)3O(CH2CH2O)6-9CH3 and a inorganic core/organic shell hybridmaterials, which shows itself a yellow viscous fluid, is obtained. We call it solvent-free TiO2 nanofliuds. Transmission electron microscopy (TEM), Fourier transform infrared spectrum (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and rheometer are adopted to characterize the product. As a result, the content of TiO2 nanoparticles in the nanofliuds is about 5.5wt%, the functionalized TiO2 nanoparticles possess better dispersion, very low viscosity and an obvious liquid-like behavior at room temperature in absence of solvent....
摘要:A soft-chemical method has been developed for the synthesis of nano-crystalline powders of silver decamolybdate. Gas sensing characteristics of this composition both in porous pellet and thin film configurations were investigated. The compound Ag6Mo10O33 was found to sense selectively ammonia at 503 K. Above 503 K it has significant cross sensitivity to petroleum gas (PG). Spin coated thin films exhibited selective sensing towards PG....
摘要:  This paper reports a kind of banana peel carbon (BPC) containing -OH, -NH2 functional groups which prepared through controlling carbonization temperature and its application on the selective adsorption of gold from waste printed circuit boards (PCBs). The adsorption of BPC for Au(III) reached equilibrium in 30 min and the adsorption of Au(III) was favorable at pH 2.5. Meanwhile, the adsorption isotherm showed the maximum adsorption capacity of 801.7 mg/g for Au(III). The results displayed that BPC had a strong selectivity for Au(III) and a negligible affinity to base metal ions, such as Cu(II), Ni(II), Fe(III) and Pb(II). The BPC adsorbent, which absorbed gold, can be recovered completely by HCl-thiourea solution. ...
[期刊论文] F. Thiébaud
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2011年 01期
摘要:An innovative constitutive model for the rheological behavior of the polymer/carbon nanotubes composites is proposed in this paper. Based on experimental investigations, this consistent law gives the evolution of the composite shear viscosity versus the shear rate, over a large range, and the temperature with various carbon nanotubes mass fractions. Hence, this consistent could be implemented in a finite element code in order to lead many polymer/carbon nanotubes manufacturing process like injection molding or hot embossing....
摘要:Nanosized Co<sub>3</sub>O<sub>4</sub> thin films were prepared on glass substrates by using sol-gel spin coating technique. The effect of annealing temperature (400°C - 700°C) on structural, morphological, electrical and optical properties of Co<sub>3</sub>O<sub>4</sub> thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Electrical conductivity and UV-visible Spectroscopy (UV-Vis). XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. Six prominent peaks, corresponding to the (111) phase (2θ ≈ 18.90°), (220) phase (2θ ≈ 31.29°), (311) phase (2θ ≈ 36.81°), (222) phase (2θ ≈ 38.54°), (400) phase (2θ ≈ 44.80°), (511) phase (2θ ≈ 59.37°) and (440) phase (2θ ≈ 65.27°) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the optical properties. The morphology of the sol gel derived Co<sub>3</sub>O<sub>4</sub> shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 eV to 2.07 eV with increasing annealing temperature between 400°C - 700°C. These mean that the optical quality of Co<sub>3</sub>O<sub>4</sub> films is improved by annealing. The dc electrical conductivity of Co<sub>3</sub>O<sub>4</sub> thin films were increased from 10<sup>–4</sup> to 10<sup>–2</sup> (Ω<sup>.</sup>cm)<sup>–1</sup> with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co<sub>3</sub>O<sub>4</sub> films annealed at 400°C - 700°C were estimated to be of the order of 2.4 to 4.5 × 10<sup>19</sup> cm<sup>–3</sup> and 5.2 to 7.0 × 10<sup>–5</sup> cm<sup>2</sup><sup>.</sup>V<sup>–1</sup><sup>.</sup>s<sup>–1</sup> respectively. It is observed that Co<sub>3</sub>O<sub>4</sub> thin film annealing at 700°C after deposition provide a smooth and flat texture suited for optoelectronic applications....
摘要:Two sets of gold nanoparticles (NP) embedded in amorphous BaTiO3 films were prepared by sol-gel method using spin coating. Sample (1) is having BaTiO3 sol with 0.025 gm of Chloroauric acid dissolved in 10 ml of propan-2-ol, while sample (2) is having 0.086 gm of Chloroauric acid in the same amount of propan-2-ol. The films have been deposited on various substrates like borosilicate glass and fused silica. TEM images show that the particles are of 5 and 10 nm in size for the two set of samples, and some are having elongated morphology. Optical absorption properties of these films reveal the substrate and size effect on localised surface plasmon resonance (SPR). It shows a marginal red shift in the plasmon resonance peak from 414 nm to 420 nm in the case of sample (1) and 566 nm to 568 nm for sample (2) as the substrate changed from borosilicate glass to fused silica. It also shows red shift in Plasmon peak as the size increases from 5 to 10 nm and coincides with Mie explanation for the shift with size....
摘要:Monodisperse hollow magnetite microspheres were successfully synthesized by an one-step process through a tem-plate-free hydrothermal approach employing simultaneously a mixture of FeCl3.6H2O and ferrocene as precursor and a propylene glycol-isopropanol mixture as solvent. The morphologies and properties of the magnetite microspheres were characterized by X-ray diffraction (XRD), Raman and infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), adsorption of nitrogen (BET method) and SQUID magnetometry. The results show that the microspheres consist of a single crystalline phase of magnetite. On the other hand, the size and the internal hollow of the microspheres depend on the temperature of growth and can be tuned by modifying the synthesis conditions....
摘要:The aim of the present work is to analyze the evolution of microstructural and mechanical properties of Air Plasma Sprayed (APS) CoNiCrAlY coatings after early stage high-temperature oxidation. Phase analysis and oxide scale characterization were performed by using X-Ray Diffraction (XRD). The microstructural features of CoNiCrAlY coat- ings were analyzed by Scanning Electron Microscopy (SEM), while Nanoindentation (NI) technique was employed to study the evolution of the mechanical properties....
[期刊论文] T. Prakash
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2011年
摘要:Nickel masters are widely used to produce surface relief grating like patterned antireflection coatings of polysiloxane material by simple embossing process. In the present work, patterned nickel master was prepared by using aluminium template, which is a foil peeled off from the commercial compact disk. Nickel was deposited using Watts nickel bath by pulsed electrodeposition for different relaxation times on patterned aluminium template. The deposition led to the transfer of patterns of aluminium replica to the nickel deposit. After deposition, the aluminium template was etched out chemically. Observation under an optical microscope showed that the obtained pattern was highly homogenous only for Ton = 0.1 ms, Toff = 0.9 ms duty cycles as compared with other ‘on’ and ‘off’ times of pulse cycles. This simple single step cost effective nickel master can serve as stamps for the subsequent embossing process. The preparation conditions and its salient features are discussed in this paper in detail....
摘要:The mixture of C12E5 microemulsion with PEG have been studied by small-angle X-ray scattering and dynamic light scattering in order to determine structure and dynamic of the system. Light scattering experiment shown an exponential relaxation for pure C12E5 microemulsion that with increasing of PEG concentration in the C12E5 microemulsion, relaxation becomes non-exponential, which demonstrates that increase of cooperativity. The study structure of the system with SAXS experiment, shown with increasing of PEG concentration, the size of the droplet doesn’t change but interaction between droplets increases that have agreement with light scattering data’s....
摘要:Oxidative polymerization of aniline in aqueous solution in the presence of trehalose was conducted. Fourier transform infrared spectroscopy confirmed successful preparation of polyaniline containing a trace amount of trehalose. Electron spin resonance spectroscopy revealed that electron spin concentration of the polyaniline increases with aniline/trehalose ratio in the polymerization. Scanning electron microscopy revealed that the polyaniline shows granular and porous morphology. Electrical conductivity of these polyanilines was in the order of 10-4 S/cm....
摘要:

Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materials are focused on. Diffusion coefficient decreases with increase of the number of shells in CNF-MF. The structure of CNF-MFs with crystalline alignment is totally stabilized with twist which is an accumulation of torsion angles at Glycosidic bonds between monomers inside CNFs. Unique fiber drawing simulation, where a single CNF fiber is taken out of CNF-MF structure, is first conducted. The CNF fiber which is drawn out stretches up to relatively large strain, with linear increase of tensile stress. The computation results show that, the larger the number of shell structure of CNF-MF is, the larger the stretch and the stress of drawn fibers are.

...
[期刊论文] Ali Rahmati
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2012年 01期
摘要: A metalloid Ti13Cu87 target was sputtered by reactive DC magnetron sputtering at various substrate temperatures in an Ar-N2 mixture ambient. The sputtered species were condensed on Si (111), glass slide and Potsssium bromide (KBr) substrates. The as-deposited films were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), optical spectrophotometry and four point probe technique. The as-deposited films present composite structure of nano-crystallite cubic anti-ReO3 structure of Ti inserted Cu3N (Ti:Cu3N) and nano-crystallite face centre cubic (fcc) structure of Cu. The titanium atoms and sequential nitrogen excess form a solid solution within the Cu3N crystal structure and accommodate in crystal lattice and vacant interstitial site, respectively. Depending on substrate temperature, unreacted N atoms interdiffuse between crystallites and their (and grain) boundaries. The films have agglomerated structure with atomic Ti:Cu ratio less than that of the original targets. A theoretical model has been developed, based on sputtering yield, to predict the atomic Ti:Cu ratio for the as-deposited films. Film thickness, refractive index and extinction coefficient are extracted from the measured transmittance spectra. The films’ resistivity is strongly depending on its microstructural features and substrate temperature. ...
摘要:A series of nanocomposites based on an ethylene vinyl acetate (EVA) copolymer with two types of inorganic clays was prepared by melt blending and film blowing.The tested clays were Hydrotalcite (a layered double hydroxide) and Dellite 72T (an organo-modified montmorillonite) in different percentage, the exfoliation degree of which has been evaluated in the presence of three types of compatibilisers. The nanocomposite morphology, thermal behaviour and mechanical properties were analysed as function of the nature and content of clays and in the presence of compatibilisers....
摘要:We show that the cytotoxic effect of carbon nanotubes (CNTs) on bacteria is mediated by mechanical damage to the cell wall and membrane. Two <i>β</i>-galactosidase-producing strains of <i>Escherichia coli</i> harboringgenomically integrated reporter gene constructs, namely pchbB:lacZand prpoS:lacZ, were used for the purpose. We first verified that CNTs result in an inhibition of cell growth. Enzyme activity was determined using a reporter gene assay in which CNTs were used without the lysis buffer (containing detergent). <i>β</i>-galactosidase activity in the presence of CNTs alone measured several fold more than the controls used (without nanotubes). This suggests that CNTs damage the cell membrane in a manner similar to the detergent in the lysis buffer and render E. <i>coli</i> cell walls porous, causing cell contents including enzymes to leak out into the medium. Our results support the hypothesis that mechanical damage to bacterial cell membranes is the prevailing cause of CNT-cytotoxicity....
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