فصلنامه نانو مواد
پیاپی 17 (بهار 1393)

In the this work, the effect of nano-graphene, as a platelet reinforcement, on the mechanical (tensile and impact strength) and rheological properties of general purpose polystyrene was investigated. Styrene-butadiene-styrene (SBS), was used as a compatibilizer and its effect on the improvment of nano-graphene distribution was also studied. The range of studied concentration were 0.01, 0.02 and 0.05 wt.% for graphene and 5 and 10 wt.% for SBS. The samples were prepared by melt blending method in a corotating twin screw extruder. The morphology of the samples was characterized through transmission electron microscopy (TEM) and X-ray diffraction (XRD). Further more, the mechanical properties of the all samples were analysied by tensile and impact strength tests. The rheological properties was investigated under small amplitude oscillatory shear (SAOS). The results of XRD and TEM showed a better dispersion and distribution of nano-graphene for the compositions having SBS. For all the nanocomposites with SBS the brittle failure disappeared and cold drawing area increased. The highest elongation at break and impact strength was obtained for the composition with 5 wt.% SBS and 0.05 wt.% graphene. Also, for this system the impact strength improved more than 6 times compared to pure PS. While mechanical properties improved even with low amount of graphene in the presence of SBS, the rheological measurement showed that complex viscosity reduced in these compositions which is a favorable phenomena from processing point of view.

NiO/MgO as a catalyst and in methane reforming process for the production of synthesis gas is used in many applications chemical and metallurgical industries. In this study, NiO/MgO nanocrystalline with different content of nickel (10 and 15 wt.%) and using the modified sol-gel method was synthesized. The calcination of the precursor after get the polymeric gel was performed at 700 and 800 °C for 4 h. The formation nanocrystallines NiO/MgO of were characterization by X-ray diffraction (XRD), Thermal gravimetric and differential thermal analysis (TGA/DTA), Field emission scanning electron microcopy (FE-SEM) with the energy dispersive X-ray spectroscopy (EDX), and specific surface area of the synthesized powders was measured with a Brunauer-Emmet-Teller (BET) apparatus using N2 adsorption. Results of X-ray analysis showed that with increasing content of nickel and the calcination temperature the crystal size slightly increases (17 to 25 nm). Also, the obtained nanoparticles have mesoporous structure and the pore size distribution of nanocrystalline NiO/MgO with 10 wt.% is more homogeneous, while the specific surface area was about 30 m2/g for both. The study of the surface morphology with field emission scanning electron microscope show that the obtained nanoparticles with 15 wt.% Ni, smaller, spherical shape and have a more homogeneous distribution.

In this research, epoxy matrix nanocomposite filled with alumina nanoparticles has been prepared and its mechanical properties were investigated. Epoxy resin and alumina nanoparticles were mixed with a high shear mixer and prepared nanocompsoites with 2, 5 and 8 percent mass fraction via incorporation of hardener. Then, tensile standard and charpy impact test samples were prepared. Mechanical tests results showed that when alumina nanopowder percent was increased then Young's modulus increased, subsequently rupture stress, strain to break and impact energy were decreased. Hence, ductility of the nanocomposites in comparison with net polymer was decreased. SEM micrographs were prepared to investigate alumina nanoparticles distribution and also surface fracture of the nanocomposites. Finally, interface or interphase quality of matrix and filler were analyzed by Raman spectrum. Raman spectrum results showed that nanocomposite with 5 percent mass fraction in comparison with other samples had stronger interface.

In this article, synthesis and characterization of silica nanoparticles in order to use in fabrication of metallic nanoshells has investigated. Homogenous mono dispersion, spherical shape and size controllability are three major parameters in preparation of metallic nanoshells with the favorable optical characteristics, and therefore obtaining core nanoparticles with these three points is completely necessary. Experimental results showed that the size of silica nanoparticles was in positive relation to the concentration of TEOS and H2O in solution and that NH3 concentration has the most roll in obtaining the particles in spherical shape. Also structural and optical properties were studied using TEM set and FTIR, XRD, UV-Vis and PL spectrophotometers.

In this study, Nb5Si3 and Nb/Nb5Si3 nanocomposite were fabricated by self-propagating high-temperature synthesis (SHS). The mixture of Nb and Si powders as the starting materials were mixed according to Nb5Si3 stoichiometric composition with 0 and 20 mol% additional Nb. Then, the green pellets were preparedby uniaxial cold pressing of the mixed powders mixture. Green compacts were placed in a combustion reactor with argon atmosphere and were synthesized. For the investigation of pre-milling effect on synthesis, the mixture of Nb and Si powders as the starting materials were milled according to Nb5Si3 stoichiometric composition with 0 and 20 mol% additional Nb, at 6 and 10 h, with ball-to-powder ratio 10:1. Then, the green pellets were prepared by uniaxial cold pressing of the as-milled powders mixture and were placed inside reactor and were synthesized. The mixed and synthesized samples were characterized by XRD, SEM, EDS, TEM and AAS analytical techniques. The results showed that, α-Nb5Si3 and β-Nb5Si3 by SHS method and without pre-milling and hexagonal Nb5Si3 by SHS method with pre-milling were synthesized. By increasing in milling time before the combustion reaction, the crystallites size of the end product was reduced and nanostructured product was produced.

CdS/P (NIPAM-co-MMA) core/shell nanocomposite particles were prepared via surfactant free emulsion polymerization. Firstly, the Cd2 ions were coordinated with MMA and NIPAM. After the addition of initiators and heating, NIPAM and MMA was either polymerized homogeneously or copolymerized with each other. Subsequently, after the addition of TAA and heating of the reaction system, CdS on the surface copolymer particles was formed with the release of S2− ions, thus CdS/P (NIPAM-co-MMA) core/shell nanocomposite was synthesized. Fourier transform infrared spectroscopy (FT-IR) of the polymerization of monomers and C=O and N-H groups and of cadmium ions coordination confirmed. Structure and morphology of CdS nanoparticles have been characterized using X-ray diffraction and transmission electron microscopy (TEM). The XRD measurements suggest the cubic structure for CdS and the particles size was estimated to about 3.26 nm by applying Scherer's equation. Transmission electron microscope confirmed that CdS/(NIPAM-co-MMA) nanocomposite were synthesized in the form of core/shell structure. The thermal properties of the CdS/P (NIPAM-co- MMA) core/shell nanocomposite were explored by thermal gravimetric analysis (TGA). Thermal stability of nanocomposite was increased by 47% in comparison with copolymer. The higher thermal stability of nanocomposite with respect to copolymer is indicative of a interaction between the CdS nanoparticles with copolymer chain and formed this nanoparticles with core/shell structure.

In this study, carbon nanotubes with high purity were functionalized by chemical method using sulfuric acid, nitric acid and hydrochloric acid. In order to investigate the morphology of the pristine and functionalized nanotubes, scanning and transmission electron microscopy was used. Also to investigate the functional groups formed on the surface of the nanotubes, Raman spectroscopy and infrared spectroscopy methods were used. According to the results suitable acid mixtures for the functionalization of carbon nanotubes were containing sulfuric acid, nitric acid and hydrochloric acid with volume of 60, 20 and 20 ml, at concentrations of 12, 12 and 10 molar respectively in the presence of 0.1 g of carbon nanotubes. The temperature of 150 °C and time of 4 h are the optimum parameters for created the functional groups on the surface of nanotubes. According to the results carbon nanotubes functionalized with minimal structural damage weregenerated. The results of infrared spectroscopy confirmed the presence of carboxylic and hydroxyl functional groups on the surface of the nanotubes.

In this study¡ nanocomposite coatings with antibacterial properties and hydrophobic silica nanoparticles of titanium dioxide nanoparticle solution casting method was generated and optimized conditions were introduced. Of casting solution as simple and cost effective coatings could be prepared and the influence of parameters on the final properties of titanium dioxide and silica nanoparticle concentration and the hydrophobic coating. Study on antibacterial properties of coatings based on culture experiments showed that the antibacterial behavior of their displays and hydrophobicity properties of coatings by examining the contact angle was studied. Vegetative morphology of the samples using a scanning electron microscope was performed. So that the surface is rougher than the contact angle is greater than creating their own displays of antibacterial properties. The optimum concentration of silica and titanium dioxide nanoparticles cause hydrophobicity and antibacterial properties of the silica and titanium dioxide nanoparticles increases with excessive coverage was reduced and the stability of the antimicrobial properties of the nanoparticles¡ the concentrations.