Sharif Digital Repository

PVDF (polyvinylidene fluoride) magnetic nanocomposite films were prepared by solution casting using two types of nanomagnetic particles: (i) magnetic nanoparticles synthesized by using an alkaline solution of mixed ferrous/ferric salts along with oleic acid as a coating agent at 70˚C; (ii) Fe3O4 nanoparticles prepared by hydrolysis of aqueous solution of ferrous/ferric salts with potassium hydroxide at room temprature. Scanning electron microscopy (SEM) showed that the PVDF magnetic nanocomposite had a porous structure with Fe3O4 nanoparticles dispersed inside the porous polymer matrix. The presence of crystalline magnetite within the polymer matrix was confirmed by X-Ray diffraction method... 

Polylactic acid (PLA) nanocomposite films reinforced with surface-modified carbon nanotube (CNT) particles were prepared by solution-phase methods. In order to enhance the flexibility of the film, and to improve nanoparticle dispersion throughout the final material, polyvinyl acetate (PVA) was also added to the polymeric backbone during the nanocomposite preparation process. Characteristics of the former nanocomposite films were investigated by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), mechanical testing, and electrical resistance measurement. In this study, our results showed that increasing... 

Nanocomposites of PLA/Ag, PLA/PEG/Ag and PLA/PEG/Oleic acid were synthesized via chemical reduction of AgNO3.The formation of nano-silver particles (Ag-NPs) started in the aqueous phase (using NaBH4 as a reducing agent) followed by transfer of the silver nanoparticles into the organic phase (PLA solution in chloroform) due to the presence of van der waals interactions between the hydroxyl groups of the PLA and the particles charges surrounded in the surface of the Ag-NPs. The nanocomposites films were prepared by the solution casting method. The XRD patterns and UV-Vis spectra of the nanocomposites demonstrated face–centered cubic (fcc) silver crystals and spherical nanoparticles... 

Oxygen barrier properties of poly (lactic acid) (PLA) films were improved by blending it with hydrolyzed poly (vinyl acetate). Poly (vinyl acetate-co-vinyl alcohol) with vinyl alcohol contents of 0, 5, 10 and 15% was prepared using acid-catalyzed hydrolysis of poly (vinyl acetate). The Blend films of PLA/poly (VAc-co-VA) containing 0, 5, 10 and 15% of the copolymer with various degree of hydrolysis was prepared by solution-casting method. Effect of gamma irradiation on the films was examined by exposing them to radiation doses of 0, 20, 35 and 50 kGy. The films remained colorless and transparent after irradiation. Morphology of the samples characterized by optical microscopy displayed not... 

Poly (vinylidene Fluoride) (PVDF)/organoclay nanocomposite films were prepared via melt mixing, solution casting and Co-precipitation techniques. The effects of different kinds of nanoclay, sample preparation techniques and electron beam irradiation on PVDF/Nanoclay nanocomposite are reported in this research project. Differential scanning calorimetry was used to study thermal properties and crystallinity of the PVDF and its nanocomposites. The chemical and crystalline structure of the samples was analysed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) and the mechanical properties of the PVDF nanocomposite were characterized by stress strain test. The degree of... 

Biocompatible porous polymeric scaffolds provide a suitable 3-D environment for proliferation of stem cells in human body. For instance, growth and proliferation concurrent with differentiation of stem cells in such scaffolds can regenerate the tissues or organs. In this attitude we fabricated a porous Gelatin-based scaffold using both of freeze-drying and freeze-extraction methods.Also, effect fo gamma irradiation on microstructure of scaffolds was investigated. In addition, poly(ethylene glycol) was employed to make the scaffold softer. Moreover, effects of various parameters including freezing temperature, cross-linking agent concentration, gelatin and PEG concentrations and their... 

The present work investigates a novel approach for improving the oxygen-barrier property of PLA-based film using vinyl acetate-vinyl alcohol copolymer [Poly(VAc-co-VA)] and the nanoclay Nanolin DK4. The permeability, thermal and mechanical properties are studied. To synthesize poly(VAc-co-VA), the hydrolysis of PVAc was done. The nanocomposite blend of PLA/Poly(VAc-co-VA)/Nanolin DK4 was prepared by the solution casting method. The prepared nanocomposite films were optically transparent regardless of poly(Vac-co-VA) and Nanolin DK4 concentrations. The gamma irradiated Poly(VAc-co-VA) was incorporated in the PLA films to probe the effect of cross-linked copolymer on the permeability of the... 

Multiwall carbon nanotubes (MWCNTs) and carbon black (CB) reinforced polypropylene/polyamide6 (75/25) nanocomposites were prepared by melt compounding approach. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as compatibilizer. Different amount of fillers were introduced into the polymer blends. The morphology, mechanical, rheological properties and crystallization behavior of the composites were investigated. Scanning electron microscopy was employed to study the microstructure. Differential scanning calorimetry (DSC) results showed that the addition of MWNT or CB to PP/PA6 blend resultes increase in crystallinity degree of PA6. The fillers were found to be located... 

Gas hydrates are ice-like clathrate compounds. Methane and carbon dioxide can form gas hydrate and plug pipelines, in order to preventing of gas hydrate formation, inhibitors like salts and alcohols are added to the natural gas pipelines. In this work a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate formation conditions for carbon dioxide and methane in the presence of aqueous ionic liquid solutions. The statistical model of Van der Waals and Platteeuw mixed with Holder model is employed for hydrate phase. An equation of state applicable to the systems containing electrolyte developed by coupling the statistical associating fluid theory... 

Nanodiamond (ND)/polylactic acid (PLA) nanocomposites have the potential for biomedical applications and bone tissue engineering. In this research, nanodiamond/poly lactic acid nanocomposites were prepared by mechanical mixing solution method and applying ultrasonication. Also, PLA-based nanofiber scaffold reinforced by nanodiamond were prepared by electrospinning methods. To find the optimum value of parameters to prepare this nanocomposite sample, the effect of nanofiller concentration, mixing rate and duration, the role of solute and ultrasonication, and solvent evaporation conditions were investigated and then it compared to the neat polylactic acid sample. By means of Fourier transform... 

Polymeric membranes based on polyaniline and PVDF were prepared by using cast-solvent film method. The effects of various parameters including polyaniline synthesis temparature, thickness of the PANI/PVDF films and feed pressure were investigated. The results obtained from exprimental data showed increasing permeability with reducing the thickness of the film and increasing feed pressure. Increasing polyaniline synthesis temprature increased the permeability of PANI/PVDF films. Reducing the films thikcness and increasing the feed pressure decreased the selectivity of films for the , and . The results showed increasing selectivity for PANI/PVDF films by using PANI produced at 10°C.... 

Semi-crystalline polylactic acid (PLA) and amorphous polymethyl methacrylate can form a soluble and miscible alloy in which the crystalline regions in the polylactic acid act as the fixed and immutable region and amorphous regions of the two polymers act as the changeable region. The two polymers can form a lattice structure with physical connections having shape-memory. So that the deformed polymer returns to its original shape above a certain temperature. These materials are used in sensors, smart materials, and medicine. On the other hand, Polyethylene glycol (PEG) is compatible with polylactic acid (PLA) and it seems that adding it will increase the ductility of polylactic acid (PLA). In... 

Theory says that prudential fiscal policies can mitigate the unintended consequences of business cycles. Does evidence support the effectiveness of fiscal policies is still a challenging question. In this thesis, I focus on the relationship between fiscal policies and aggregate movements in oil producing countries. I found significant pro-cyclicality in these countries in which questions the goal of their policy making. Furthermore, I show that in my sample of oil producers,data doesn’t support the poorer is the country, the higher is the pro-cyclicality of their fiscal policies  

The Reliability of substation structures with consideration of earthquake uncertainties is one of the most important subjects in structural analysis in recent years. In this project we first introduce IEEE-693-2005, which is the most effective and comprehensive seismic design code for electronic substations. Also in second chapter the rudimentary aspects of Reliability Theory and methods for evaluating the reliability of substation structures is introduced. Then with modeling the most common and most important electronic substation devices in Iran, with consideration of all seismic parameters and their uncertainties, the reliability of these structures evaluated. In this project for... 

In this thesis behavior of intermediate steel moment frames and intermediate steel moment frames equipped with knee element are investigated. The knee element attaches to the beam element by inverted-V type concentric braces. The knee element acts as a fuse to dissipate input energy during an earthquake by the formation of plastic hinges. On the other hand, brace elements remain in the elastic range without buckling and provide suitable lateral stiffness. Main object of this investigation is reducing deteriorations in the main frame in intermediate and sever earthquake by concentrating deteriorations in knee element. Whereas knee element is not a main element of the frame, retrofitting of the... 

A particular kind of concentric bracing system composed of three members arranged in y-shaped geometry is examined in this thesis. The non-straight diagonal strut of this off-centre bracing causes eccentricity to the system and is connected to the frame corner through a third member. Providing adequate openings in braced bays accompanied by improved energy dissipation are resulted in positive attitude toward using y-bracing frame as a lateral load resisting system. However, lacking of specific design codes could be problematic for engineers. To overcome this incompetency, seismic performance factors including the response modification coefficient, the system overstrength factor, and... 

Developing new micro and nano devices, help us instruction micro and nano devices in very small scales. Also nano technology improved in recent decades especially in century 21th. These devices contained many important members, such as micro and nano filters, micro channels, sensors, and electrical chipsets. Navier-Stockes equations with slip and no-slip conditions can not used in transition and free molecular regimes. Since most of the MEMS and NEMS devices working in slip and transition regimes, then we must using DSMC for simulation these devices. DSMC is a physically method and working on the physics bases. Also it was derived from Boltzmann equations by Bird. In this study, we want... 

Use of micro/nanoelectromechanical systems has become increasingly prevalent in recent years. Therefore, the development of technologies and understanding of fundamental physics associated with them is necessary.In micro-and nano-scale different behavior is often observed and it is due to Knudsen number that forms different types of flow regimes. When the flow is considered to be continuum; for it is in the slip-flow regime, for it is called the transition-flow regime. When , the flow is considered to be free molecular and is sufficiently rarefied to allow molecular collisions to be completely neglected in analysis. For continuum and slip flow regime the Navier-Stokes equations with... 

Steel plate shear walls are lateral load resisting systems, especially against earthquake excitation. They are constructed with or without stiffeners. Stiffened walls are more ductile than without stiffeners walls. In this research, nine thin steel plate shear walls models were considered in three groups of 5story, 01story and 05 story walls. In each group different yield point steel for the infill plate was used. The results showed that, using low yield point(LYP) steel will increase energy dissipation of models up to %36. LYP also improve shear capacity of models up to %96. The results showed that using LYP will cause lower lateral displacement in models  

This thesis presents the investigation and development of a Finite Element Model (FEM) for a new type of Beam-Column Semi-Rigid steel connection. One of the main parts of this connection is a steel T profile inserted on top of a beam connecting it to a column by bolts. It seems that changes in the geometry of the T profile and its bolt positions can have a great influence on the rigidity or flexibility of the connection. Therefore, meaningful categories of the T profile geometry with different bolt positions have been modeled and analyzed by means of a Finite Element Modeling software ABAQUS, and their moment-rotation curves were driven. Also the Initial and Nonlinear Stiffness and the...