فصلنامه نانو مواد
پیاپی 7 (بهار 1390)

In this study, to improve the nanoparticle dispersion and increasing possible interaction between nanoparticle and polymeric matrix in the UP/TiO2 nanocomposite, the surface of the TiO nanoparticles was modified in the new approach; first the surface of TiO2 nanoparticles was modified by a coupling agent as 3-(methacryloxy) propyl trimethoxy silane and then polymerized in the presence of ethyl acrylate and methyl methacrylate monomers with AIBN as initiator. FTIR spectroscopy confirmed the presence of the coupling molecule and consequently copolymer macromolecular chains on the surface of TiO2 nanoparticles. Transmission electron microscopy (TEM) was used to study the morphology of the particles before and after the surface grafting. Mechanical properties and ultraviolet visible (UV/Vis) spectroscopy of various samples, including the doubly modified-TiO2 nanoparticles and the unmodified-TiO2 nanoparticles were also investigated. The results showed that surface remodification of TiO2 nanoparticles improve nanoparticles dispersion, mechanical properties and UV protection of the UP/TiO2 nanocomposite.

In this research, we have synthesized Ag-TiO2 nanocomposite with an optimized concentration of 1% by sol-gel method. Rhodamin was used for photocatalytic activity. Dilatometric thermal analysis of prepared specimen was performed at different temperatures of 266, 338, 39 , 485, 600 and 700 °C for 2 hours. Using obtained results from XRD and DTA analyses, prepared specimens in 530 °С and during 0.5, 1, 2, 4 and 6 hours underwent heat treatment. The optimized specimen from decomposition point of view was that of 530 °С and 1 hour heat treatment. Additionally the specimen was operating even more efficient than Degussa P25 nanopowder. Ag2Ti4O9 phase was synthesized at room temperature and with regard to decomposition test results, it seems that the specimen has more efficiency than anatase phase. Characterizations of Ag-TiO2 nanoparticles were done by DTA, XRD, PL and SEM.

In this study, the nanopowders of hydroxyapatite (HAp) with three different materials using Ca(NO3)2.4H2O, H3PO4, P2O5, and PO(OC2H5)3 precursors have been synthesized by sol-gel and characterized by some physic-chemical approaches such as XRD, FTIR, DTA, and SEM elemental analysis and their purity have also been investigated. Followings, by the XRD data and with the aim of Scherrer equation, their particle size values have been determined. These results have good agreement with observed particle size within TEM images. It is interesting to note that based on DTA curves, the synthesized sample from PO(OC2H5)3 precursor has been crystallized at 400 ºC that is absolutely lower than the reported crystallization temperature (CT) of other samples. However, the important factors such as sol temperature, aging time and calcination temperature affect product purity. Indeed, the higher sol temperature and aging time increase the product purity. With the increase of the calcination temperature till upper than 600 ºC, calcium phosphate impurity phases transform to HAp. As expected, the mean crystalline size increased with raising in calcination temperature. By increasing temperature from 600 to 700 ºC mean particle size growed from 50 to 98 nm, hence the latter temperature assigned as suitable CT for preparing of the titled nanopowders.

The concept of nanoscale reinforcement provides opportunity for synthesis of polymer materials with unique properties. Behavior of unsaturated polyester (UP) and unsaturated polyester nanocomposites containing different nanofillers, such as Al2O3, nanoclay (Cloisite 30B) were investigated. Samples were prepared with the nano content 1, 2, 4 wt. % have been considered. Nanofillers were dispersed into a UP matrix via blending using a mechanical stirrer. Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and XRD data were in support of the formation of partially delaminated nanocomposite materials. The mechanical properties test results show that nanoclay obviously improves the Strength of UP and Al2O3 enhances its tensile, but nanoclay-Al2O3 exhibits a synergistic effect on toughening and reinforcing UP simultaneously. Increase in storage modulus and a gradual decrease in high glass-transition temperature as nanofillers loading increased.

Recently, rapid heating by microwave has been known as a significant technique for the synthesis of metal nanostructures. In this study, in order to process of silver nanoparticles from silver nitrate (AgNO3) as pre material, polyvinyl Payrolyden (PVP) as a stabilizer and water, ethylene glycol and ethanol as solvent at a temperature 25 °C were used. At first, solution with certain ratios of AgNO3 and PVP were prepared and the reaction between solvents was carried out during 90 s. During the chemical reaction between solvents, electromagnetic waves with the fixed intensity and frequency 2450 MHz were applied to the system by the microwave oven. Then intensely silver nanoparticles in the solution were obtained as a result of chemical reactions. To determine particle size distribution and concentration, the prepared nanoparticles were investigated by analysis visible spectroscopy (UV-VIS). The transmission electron microscopy (TEM) micrographs showed that the processed nanoparticles have spherical and semi-spherical morphology and size distribution of spherical particles is in the range of 10 to 40 nm. The prepared silver nanostructures show less crystallization degree and smaller particle size than the oil bath conventional methods.

In this research, mechanical properties improvement such as elongation at break and young modulus of polystyrene (PS) was investigated in presence of TiO2 and SiO2 nanoparticles. The solution method was selected for synthesis of PS/SiO2, PS/TiO2 and PS/SiO2/TiO2 nanocomposite. An ultrasonic mixer was used for higher dispersion of nanoparticle in the solvent. Morphology of produced samples was characterized through SEM, TEM and TGA. The mechanical properties of nanocomposites were studied by determination of young modulus, elongation at break and impact strength. The results showed that the elongation at break of PS is obviously enhanced in presence of both TiO2 and SiO2 nanoparticles. Also, the results indicated that in the PS/SiO2/TiO2 sample with 1 wt.% of nanoparticles, young modulus, fracture toughness and elongation at break of PS are increased simultaneously. This phenomenon was due to good breakdown structure of nanoparticles agglomeration, and also sufficient dispersion of them in PS matrix. In this case, the nanoparticles were filled in fine voids and played a roll of bridge between layers of matrix leading to improvement of elongation at break of PS. Also, thermal stability was developed in comparison with unfilled PS due to well-structural homogeneity and reduction of defected sites numbers.

In this research, siliceous nanostructures were identified and synthesized using sol-gel method. Reaction was performed in the presence of different acids and the particle size and morphology were studied. Then, pH was decreased less than 2 and the structures were re synthesized and their morphology was investigated. Then, in order to optimize the synthesis conditions and improve morphology and synthesized particle size, structural modifiers such as lanthanum nitrate hexahydrate was added to the acidic environment and the synthesis and identification were repeated. In these conditions, particle morphology improved and particle size also significantly decreased.