فهرست مطالب

Scientia Iranica
Volume:18 Issue: 3, 2011

  • Transactions F: Nanotechnology
  • تاریخ انتشار: 1390/06/06
  • تعداد عناوین: 10
|
  • Anti-scratch and adhesion properties of photo-curable polymer/clay nanocomposite coatings based on methacrylate monomers
    Sh. Mohamadpour, B. Pourabbas, P. Fabbri Page 765
    Different types of polymer/clay nanocomposite were prepared and evaluated for their application as hard and anti-scratch coating materials. Photo-curable nanocomposites, based on 2,2-bis[4-(methacryloxypropoxy)-phenyl]propane (Bis-GMA (2,2-bis[4-(methacryloxypropoxy)-phenyl]propane)) and tri (ethylene glycol)dimethacrylate (TEGDMA (tri(ethylene glycol)dimethacrylate)) (50/50 wt%) were prepared using three types of clay at different loading levels. The adhesion properties and scratch resistivity of the coatings on polymethymethacrylate slabs were investigated. The results were correlated with the clay dispersion state, determined by a transmission electron microscopy, X-ray diffraction and the surface morphology by atomic force microscopy. It was concluded that exfoliation or intercalation plays an important role, primarily in surface roughness, which in turn affects adhesion by changing the characteristics of the coating-substrate interface. The highest scratch resistivity with appropriate adhesion quality was obtained for a sample containing 1 wt% of more compatible clay, Cloisite® 30B in the nanocomposite resin mixture.
  • Degradation of malachite green oxalate by UV and visible lights irradiation using nanophotocatalyst
    S. Afshar, H. Samari Jahromi, N. Jafari, Z. Ahmadi, M. Hakamizadeh Page 772
    Titania sol was modified with SiO2 and platinum ion to prepare TiO2/SiO2, Pt/TiO2 and Pt-TiO2/SiO2 nano-photocatalysts. The samples were characterized by means of UV-visible Diffuse Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD) patterns, Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM) images, Energy Dispersive X-ray spectroscopy (EDX) and Brunauer–Emmett–Teller (BET) techniques. The prepared catalysts exhibited photocatalytic activity for degradation of malachite oxalate green (MG) in water under UV light irradiation. BET analysis confirmed a significant increase in surface area, which enhanced photocatalytic activity. In comparison with anatase TiO2 nanoparticles and the commercial Degussa P-25, the prepared photocatalysts showed an improved photoactivity in comparison with anatase TiO2 nanoparticles and the commercial Degussa P-25. The results show that the reduced form of platinum deposited is important for modifying TiO2/SiO2 to be able to operate as a photocatalyst under visible light irradiation.
  • Dehydration kinetics of polyvinyl alcohol nanocomposite hydrogels containing Na-montmorillonite nanoclay
    M. Sirousazar, M. Kokabi, Z.M. Hassan, A.R. Bahramian Page 780
    A series of freeze-thawed, polyvinyl alcohol nanocomposite hydrogels were prepared using various loading levels (0–15 wt%) of hydrophilic natural Na-montmorillonite nanoclay. The morphology of nanocomposite hydrogels, their dehydration kinetics at different temperatures and the effect of Na-montmorillonite on the gelation process were investigated. The results showed a partially exfoliated morphology for the prepared nanocomposite hydrogels. Also by increasing the amount of nanoclay incorporated into the specimens, the gel fraction values of nanocomposite hydrogels were increased. According to the dehydration tests, the dehydration rates of nanocomposite hydrogels exhibited an inverse dependency on the nanoclay loading level and a direct dependency on the dehydration temperature. Finally, it was concluded that the dehydration mechanism of all specimens prepared is non-Fickian at 20 °C, while it is Fickian at 37 °C and 55 °C.
  • The influence of silica synthesis on the morphology of hydrophilic nanocomposite coating
    S. Gharazi, A. Ershad-Langroudi, A. Rahimi Page 785
    A nanocomposite coating, based on Glycidioxypropyltrimethoxysilane and Aminoethylaminopropyltrimethoxysilane, was prepared using silica nano particles in a sol-gel process by the addition of silica suspension. The good level of adhesion was attributed to the formation of Si-O-Si bonds between the coating and the substrate. Moreover, another factor in improving adhesion was linked to the tendency of silica particles to form aggregates in the continuous phase. This morphology enhances the organic phase mobility of the coating, which leads to flexibility of the coating in stress support and improving adhesion. In order to evaluate the hypothesis, the relaxation properties of this coating were compared with those of a coating synthesized by in situ polymerization of tetramethoxysilane by means of Dynamic mechanical thermal analysis. The results proved the validity of the theory that silica particles of the coating prepared with silica suspension tend to form aggregates and produce particle-matrix morphology, which allows the organic phase to find further mobility. Scanning Electron Microscopy was employed to monitor the surface of the coating. The Atomic Force Microscopic technique was used to monitor the surface roughness of the coating. Transmission Electron Microscopy showed that the dimension of silica particles remains at nano scale.
  • Determination of silver(I) by flame atomic absorption spectrometry after separation/preconcentration using modified magnetite nanoparticles
    M.A. Karimi, S.Z. Mohammadi, A. Mohadesi, A. Hatefi-Mehrjardi, M. Mazloum-Ardakani, L. Sotudehnia Korani, A. Askarpour Kabir Page 790
    A new, simple, fast and reliable method has been developed for the separation/preconcentration of trace amounts of silver ions using 2-mercaptobenzothiazole/sodium dodecyl sulfate immobilized on alumina-coated magnetite nanoparticles (MBT/SDS-ACMNPs) and their determination by flame atomic absorption spectrometry (FAAS). Optimal experimental conditions, including pH, sample volume, eluent concentration and volume, and co-existing ions, have been studied and established. Under optimal experimental conditions, the enrichment factor, detection limit, linear range and relative standard deviation (RSD) of Ag(I) ions were 250 (for 500 mL of sample solution), 0.56 ng mL−1, 2.0–100.0 ng mL−1 and 3.1% (for 5.0 μg mL−1, n=10), respectively. The presented procedure was successfully applied for determination of silver content in the different samples of water.
  • Raman spectroscopy and conductivity variation of nanocluster carbon thin films grown using a room temperature based cathodic arc process
    Shounak De, S. Niranjana Satyanarayana, K. Mohan Rao Page 797
    Nanocluster Carbon (NC) thin films grown at room temperature, using a cathodic arc process, under varying deposition conditions, exhibit interesting electrical and opto-electronic properties. These films are mixed phase material containing both sp2 (graphite-like) and sp3 (diamond-like) bonding. A Raman G-peak has been observed between 1585 and 1595 cm−1, which indicates graphite-like bonding. A Raman D-peak has been observed between 1355 and 1365 cm−1, which indicates disorderliness in the carbon structure of the films. The Raman spectra of the films were deconvoluted using Breit–Wigner–Fano line shapes. The Raman parameters, including intensity ratios, peak positions, Full-Width Half Maxima (FWHM) and coupling coefficients obtained from both line shapes, were described and compared with varying Helium partial pressures. The dependence on temperature of the conductivity, showing two regions of electronic transport, is explained based on a thermal-assisted tunneling process. The electrical conductivity varies from 1×10−4 S/cm to 1.66×10−5 S/cm with respect to varying deposition parameters, such as arc current, DC bias and throw distance.
  • TiO2 nanoparticles prepared without harmful organics: A biosafe and economical approach
    M.A. Shah, F.M. Al-Marzouki Page 804
    Growth of titanium oxide (TiO2) nanoparticles of varying size, ranging from 20–60 nms through a versatile and an economic route, is being reported. The approach is based on a simple reaction of titanium powder and De-Ionized (DI) water at ∼180 °C, without use of any harmful additives. Field Emission Scanning Electron Microscopy (FESEM) reveals the well defined morphology of nanoparticles, whereas X-ray Diffraction (XRD) studies reveal that the, as prepared, nanoparticles are in a mixed phase, with a dominance of a stable rutile phase. Since only water, which is regarded as a benign solvent, is used during the preparation of nanoparticles, we believe that the products so produced are biocompatible and bio-safe and can be readily used for medical applications. The biocompatibility tests are yet to be carried out and shall be reported in forthcoming publications.
  • Dynamic modeling for nanomanipulation of polystyrene nanorod by atomic force microscope
    M. Moradi, A.H. Fereidon, S. Sadeghzadeh Page 808
    Nanomanipulation, using an Atomic Force Microscope (AFM), is one of the new emerging approaches to manufacturing in nanoscale. Wide spread applications of nano-rods and lack of real time imaging in nanotechnology cause the necessity of process modelling. This article presents a new dynamic model for flexible nanorods on elastic substrate. This model presents a nine step strategy to push nanorods, considering three basic nanoforces; van der Waals, friction and contact force for quantitative analysis of effective parameters. Dynamic analysis of nanorod pushing, considering depression on elastic substrate, indention between the tip-nanorod and deflection along a straight path, is presented. Using a beam on elastic substrate assumption, the complete model up to now for nanorod manipulation is obtained. This model is verified by available (theoretical and experimental) results. A polystyrene nanorod is simulated, and the snap in/pull out distances, critical force and time, maximum deflection and safety factor of the process are obtained. Also it is determined that the dynamic mode of micro and nanorods is different. Despite the rolling mode being dominant in micro rod manipulation, the sliding mode is observed to be the dominant dynamic mode in the pushing of nanorods. Our model can be used in the mechanical behaviour of nanorods.
  • Treatment of ZnO nanowires on Si(111)
    G.Sh. Shmavonyan, S.M. Zendehbad Page 816
    We investigated vapour-phase-epitaxy grown ZnO NWs on a Si substrate by SEM. SEM investigations show that there are single NWs and ensembles of NWs, among which we found straight and bend, perfect (with regular facets and smooth surfaces) and non-perfect (with irregular facets, non smooth surfaces, variable widths, damaged and particle) NWs, as well as NWs with clean surfaces, and surfaces with dark spots and features. After FIB polishing, we found that every NW has a clean homogeneous surface, which allows us to conclude that all its dark spots and surface features are really just surface features. The FIB milling gives information regarding the deeper interior of the NWs, i.e. buried structures within them, and whether or not those structures are propagating within them. But also here we found that there are no buried structures inside the NWs and the dark spots and features are not propagating within them, which lead to the result that NWs are totally homogeneous. The hexagonal facets of the NWs were observed on SEM images, which emphasize their good crystalline quality. The sizes of NWs were determined: the length is about 2–24 μm, and the width and height are about 200–500 nm.
  • Cavity quantum electrodynamics in the ultrastrong coupling regime
    E. Ahmadi, H.R. Chalabi, A. Arab, S. Khorasani Page 820
    We revisit the mathematical formulation of the famous Jaynes–Cummings–Paul Hamiltonian, which describes the interaction of a two-level atom with a single mode of an electromagnetic cavity reservoir. We rigorously show that under the condition of ultrastrong coupling between the atom and cavity in which the transition frequency is comparable to the coupling frequency, the bosonic field operators undergo non-sinusoidal time variations. As a result, the well-known solutions to the Jaynes–Cummings–Paul model are no longer valid, even when the rotating wave approximation is not used. We show how a correct mathematical solution could be found instead.