فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 8 (بهار 1393)

Polypyrrole (PPy) was electrochemically synthesized on AZ31 Mg alloy in a solution containing sodium salicylate and pyrrole using cyclic voltammetry. Through taking advantage of electrochemical impedance spectroscopy and potentiodynamic polarization measurements, the effect of some electropolymerization parameters like potential, monomer concentration and number of cycles on the quality and protective performance of the PPy coating applied on the Mg alloy was studied. In the presence of the PPy coating synthesized in the optimal conditions, the charge transfer resistance and corrosion current density encountered a significant increase and drop, respectively. Furthermore, corrosion potential shifted toward more noble values. Scanning electron microscopy (SEM) studies revealed a cauliflower morphology for the PPy film synthesized on the Mg alloy. The grain size ranged from 30 to 50 nm.

In this research, uniform LaF3 nanoparticles have been successfully synthesized via co-precipitation route in which ethylenediaminetetraacetic acid (EDTA) was used as an effective size-controlled chelating agent. The appropriate analyses were carried out to characterize final nano-crystallites such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results revealed that the nanoparticles were well-crystallized with hexagonal structure and were coated with an organic additive. From the scanning electron microscopy (SEM) micrographs, the spherical particles in the presence of EDTA were more uniform with higher detectable boundary phase. The dynamic light scattering (DLS) results showed that the mean diameter for samples with and without EDTA is 66.1 and 106 nm, respectively. Furthermore, from up-conversion luminescence (UCL) spectrum under excitation at 980 nm, the La0.85Yb0.12Er0.03F3 nanoparticles exhibit the bright orange emission photo-physically originated from separate transitions: 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 at 520, 538 and 658 nm, respectively. Consequently, as prepared LaF3:Yb,Er with relatively bright up-conversion luminescence can be a promising candidate for use as bio-labels.

In this paper the thermal stability and properties of resole type phenolic resin is investigated. Thermoset phenolic resins have good physical and mechanical properties up to 250 ˚C temperature; however, for high temperature applications modification of thermal stability of resin is very important. Nano silica (SiO2) effect as a filler on thermal stability of the resin is investigated. Thermal properties was studied by means of thermo gravimetric analysis (TGA) to evaluate char yield and differential scanning calorimetric (DSC) to evaluate the resin curing behavior and SiO2 effects on curing reaction heat. Results showed increase of char yield and curing reaction heat in the presence of SiO2. Fourier transform infrared spectroscopy (FTIR) was used to investigate the variation of absorption bands in the presence of SiO2. The results indicated that with an increase of temperature from 200 ˚C to 800 ˚C resin structure was decomposed and volatile compounds including CH4, CO, CO2 and H2O were released out and the resin was carbonized and converted into amorphous carbon. Finally, the microstructure evolution of modified resin and distribution of nano silica in resin matrix were investigated using scanning electron microscopy (SEM). Results showed that silica particles are completely and uniformly distributed in the resin.

In this work, undoped and cobalt doped titanium dioxide nanoparticles in different molar ratio of 6, 12, 18 and 24, was prepared through the sol-gel method. We investigated the effect of cobalt doping on the magnetic properties of our samples.X-Ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the increase of cobalt doping produce a CoTiO3 phase and the particle sizes increase.Vibrating sample magnetometer (VSM) showed that cobalt doped TiO2 nanoparticles behaved paramagnetically and their magnetic susceptibilities enhanced of 0.7516×10-5 to 2.847×10-5 by increasing the doping level.

In this study, hyperbtanched polyester amid (H1500) with hydroxyl surface functional groups was end-capped with a saturated fatty acid. The molecular structure of the modified hyperbranched polymer was characterized with HNMR and FTIR spectroscopies and GPC analysis. Decrease of peak intensity of –OH groups in FTIR spectra proved substitution of these functional groups with saturation fatty acids. HNMR spectra also demonstrate substitution of hydroxyl groups with fatty acid chains. GPC results show the higher percent of modification in hyperbranched polymers with lower molecular weight. Thermal properties of modified hyperbranched polymer were investigated by DSC analysis. For characterized of surface modification effect on the interaction of these polymers, the effect of modified and unmodified hyperbranched polymer on the viscosity of epoxy diacrylate oligomer were investigated. The results show that the replacement of OH groups with fatty acid chains can decrease the strength of hydrogen bonding and cause lower viscosity

Toner acts as the image producer in digital electrophotographic printing methods. There are several ways for the fabrication of toners that one new method among them is the emulsion aggregation technique. The control and tuning of toner shape, its size, and size distribution is a key in producing toner. The aim of this work is to study the effect of processing variables including mixing speed, mixing time, and heating rate on the shape, size, and particle size distribution of toners synthesize by emulsion aggregation method. The quality of resulting toner is evaluated based on its size and colorimetric study. Optimization of process employing Response Surface Methodology by designing and performing 15 experiments was carried out varying processing variables and the trends in the size and color of produced toner was detected to give a deep understanding of production process. The main practical aspect of this research was attributed to reduction in the size of toner particles over increasing mixing intensity.

Discovery of conducting and semiconducting property of organic materials (especially in polymers), has created several applications for them like photovoltaic devices. In this study, bulk heterojunction polymer solar cells based on donor-acceptor P3HT:PCBM active layer have been investigated. It was seen that through the heat treatment at 1200 C in time duration of 0-45 min on the active layer of the cells with structure of ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al, series resistance reduces and current density and power conversion efficiency significantly and continuously increase from 3.78 to 12.01 mA/cm2, and from 1.09% to 5.5% respectively. The reason for the progress in the performance of the cells with the mentioned structure under the heat treatment for 0-45 min is attributed to the increase in the size of nanostructure crystals in the active layer, resulting in decrease in series resistance and increase in current density. Role of LiF buffer layer in electron collection was also investigated.