Sharif Digital Repository

By employing the image theory the Er doped microsphere coupled to an external cavity made by a metallic mirror is simulated by a bimicrosphere laser. The symmetric structure causes the formation of odd and even modes corresponding to the TE and TM mode of the microsphere and splitting the oscillation frequencies. The oscillation frequencies are dependent on the coupling coefficient. The coupling coefficient is obtained near the mirror-microsphere distance. The ohmic mirror loss also is determined as a function of the mirror distance. The total optical loss experienced in these resonators is exceptionally low. In fact,quality factor as high as 108 − 1011 have already been demonstrated for... 

Blending can be used as one of the ways of producing materials with appropriate properties, which have many relative advantages in comparison with other methods like polymerization. Among the existing blends in the market and scientific areas, blends of polyurethane thermoplastic and polypropylene have been also studied because of its commercial importance and scientific interest. This blending can improve the mechanical properties, friction resistance, improvement of impact strength at low temperatures and improvement of plasticity properties. In this research, blends with different ratios of TPU/PP is produced by melt mixing, and for improving properties of blends, two kinds of nano fumed ... 

In this study, thermal and rheological properties of nanofluids of water/carbon nanotubes, water/spherical silica nanoparticles and water/hybrid nanoparticles (hybrid of carbon nanotubes and spherical silica nanoparticles) have been investigated. To do so, carbon nanotubes have been synthesized by CCVD process and spherical silica nanoparticles and hybrid nanoparticles by wet chemical method. After synthesis of nanomaterials, nanofluids have been prepared by using SDBS as a dispersant with the concentration of 1.5 times of concentration of nanomaterials and then thermal conductivity, kinematic viscosity, dynamic viscosity and density of nanofluids have been investigated. As the results show,... 

In this research UHMWPE/FUMED SILICA nanocomposites with different concentrations of nano fumed silica (0.5, 1.5, 2.5, 4.5 wt %) were prepared via in situ polymerization using a novel Bi-supported Ziegler-Natta catalytic systems. Magnesium etoxide and Fumed Silica functionalized by hydroxyl groups were used as supports of catalyst. TiCl4 accompanied by triethylaluminum constituted Ziegler-Natta catalytic system. Preparation of catalyst and polymerization were done in slurry phase under the argon atmosphere. Scanning Electron Microscopy (SEM) images also certified very good dispersion of fumed silica throughout PE matrix. Intrinsic viscosity measurements showed high molecular weight for... 

Mesoporous silica nanoparticles (MSNP) have attracted lots of attentions because of their particular characteristics. Physical characteristics such as structure, morphology, porosity, and size of these nanoparticles have strong impact on their function and it can be conceived a wide range of applications for them by manipulating these characteristics. In this research, monodispersed MSNPs with a controllable size in the range of 50-130 nm and pore size in the range of 4-24 nm were synthesized and positively functionalized in order to develop a carrier for the delivery of nucleic acids (siRNA and pDNA). The MSNPs were synthesized by the template removing method.In this method, sodium... 

Zinc oxide thin films due to special specification and properties have variable application in different industries. Recently because of wide application of zinc oxide doped SiO2 in optoelectronics and sensors, lots of investigation have been focus on it. Meanwhile due to the SiO2 hydrophilic properties, doping of ZnO with SiO2 can improve self-cleaning properties zinc oxide membrane.It this project zinc oxide and ZnO doped SiO2 thin films with different composition were made by sol-gel and dip-coating process used for coating of mentioned sol over the quartz surface(15*25 mm). At first point different sol with different components was mixed with each other to make composite films but due to... 

This research aims to develop a drug delivery system based on mesoporous silica nanoparticles (MSNPs) for hydrophobic drugs and evaluating their cytotoxicity. The internal environment of the body is aqueous, while most of effective drugs display poor aqueous solubility, resulting in insufficient bioavailability. Due to their several unique properties, such as a large surface area, tunable pore size, facile surface multi functionalization and excellent biocompatibility, MSNPs are recognized as promising and powerful tools to overcome this hurdle. In the present study, MSNPs were synthesized using template removing method and then were functionalized through grafting procedure. They were... 

Concrete is the second most structural material in the world. So attention and promotion of the concrete mix design with respect to variable issues and requirements, is very important. On the other hand, these days environment and its pollution has become very popular discussion. Waste-glass which is produced by human products is one of the environmental pollutants. In this thesis it replaces some aggregate in concrete and it can reduce the level of this material in the world. Also we study effects of silica-fume as cement replacement and properties enhancer in our concrete mix design and see how it can ... 

In this research, a review on fluoride adsorption revealed that the modification of the adsorber surface with ions like Ca2+ results in great enhancement of the fluoride adsorption. It seems that the enhancement in fluoride adsorption by the modified adsorber, is mainly due to the selective chemical binding of the fluoride ion with the surface-bound ion (Ca2+), regardless of the base material itself. In order to confirm this hypothesis, two different adsorber materials namely, γ-alumina (a material, conventionally used for fluoride removal from water and wastewater) and Micro-silica (a mineral with small adsorption capacity for fluoride) were selected for further study. It was found that the... 

In this study Ni-P-Al2O3-SiO2 nano composite coating developed on aluminium alloy 6061 using electroless method. Due to oxidation of aluminium, a double zincate pretreatment performed to obtain proper adhesion of coating on substrate. Effect of solution temperature and heat treatment on thickness and property of nano composite coating was studied. Furthermore, effect of concentration of nano particles in electroless solution on thickness, morphology, micro hardness, wear behavior, corrosion resistance and particle content in coating were investigated. Field emission scanning electron microscopy (FESEM, Hitachi S-4160) with energy dispersive spectroscopy (EDS) was used to evaluate morphology... 

The investigations on hydrophobic surfaces have attracted lots of intrests in science and technology. Silica sols have been used extensively in the area of producing hydrophobic coatings. On the other hand, carbon-based materials have attracted of a great deal of scientific interest in recent years. The purpose of this research is synthesis and investigation on the properties of Silica- Graphene Oxide nanocomposite coating.Graphene Oxide synthesized by using Hummer’s method. Silica nanoparticles were prepared using sol-gel process and tetraethylorthosilicate (TEOS) as precursor. The surface hydroxyl groups of silica nanoparticles are replaced with Methyl groups by treatment with... 

The purpose of this research is producing one phase silica superhydrophobic coating by sol-gel method and drying temperature less than 200 degrees. For preparing micrometer and nanometer scaled hierarchical structure based on silica, TEOS precursor and Fumed Silica nanoparticles were used by density of 43/30 cc/lit and 6/52 gr/lit in order to provide desired roughness in the range of 40 nm. Moreover, HMDS surface modifying agent was used for reducing the surface energy of coating, which is not a danger to the environment in comparison to the same substances. The best Contact Angle is 155 degree and the best Sliding Angle is less than 5 degree. For instance, it was created with the... 

One of the most useful method in medical imaging is Magnetic Resonance Imaging. Gadolinium base contrast agents used to improve images contrast made by MRI. There are some problems with using these drugs, such as toxicity and lack of targeting. In this research, Silicon nanoparticles were produced by a new fashion of removing template method. Particle size was scanned by Dynamic light scattering (DLS), mesoporous structure was investigated by Brunauer-Emmett-Teller (BET), and amine functionalization was recognized by Fourier transform infrared (FTIR). Functionality was determined by evaluation of signal and relaxation of nanoparticles.T1 was defined by a 1.5 tesla power MRI device. The... 

Epoxy resins have good mechanical and thermal properties, high chemical resistance and low shrinkage during cure but in spite of these good properties,they are brittle and this limits the usage of them. Adding a second, soft or rigid, phase has been always an effective strategy to improve the toughness of epoxy. Rigid phase used in resins are divided into organic and inorganic. The aim of this study is to increase epoxy toughness, maintaining mechanical properties and study effect of silica and polycarbonate on fracture toughness simultaneously. Mechanical properties including yield strength and elastic modulus are evaluated by pressure test. Additionally fracture toughness and three... 

Several studies based on anti- cancer, anti- metastatic and anti- tumor effects of curcumin have been reported . Besides these benefits, the therapeutic efficacy of curcumin is limited due to its poor aqueous solubility, extensive first-pass metabolism, inadequate tissue absorption and degradation at alkaline pH, which severely diminishes its bioavailability. In this project we seek to solve some of the problems with nanoscience to work more effectively. In the past decade, mesoporous silica nanoparticles (MSNs) have found widespread application as controlled drug delivery systems. Recent reports on the design of capped and gated MSN-based systems have shown promise in preventing premature... 

In this study, polyelectrolyte-coated magnetic silica nanocomposites were prepared via the covalent attachment of polyelectrolytes onto the as-prepared magnetite-silica particles with core-shell structures and average diameter of 210±50 nm, and subsequently applied for the immobilization of lipase molecules. In this regard, polyethyleneimine (PEI) with two molecular weights of 10000 and 750000 and polyacrylic acid (PAA) with two molecular weights of 1800 and 100000 were utilized. The type and molecular weight of the polyelectrolyte molecules greatly impacted the concentration of binding sites on the particles surface and consequently on the lipase immobilization efficiency and loading... 

The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this... 

The aim of this work is fabrication of magnetite@silica@gold particles. Study of the effect of pH showed that increasing pH from 9 to 12 resulted in a decrease in the size of magnetite nanoparticles from 7.9±1.38 nm to 5±0.64 nm. The TEM results indicated that modifying magnetic nanoparticles with sodium citrate prior to coating with silica leads to a narrow particle size distribution (275±16.1nm) and less number of silica nanoparticles without any magnetite core. Three methods were applied for attachment of gold nanoparticles seeds onto the silica surface: 1) use of an electrostatic interaction between positively-charged aminated silica and negatively-charged gold nanoparticles surfaces, 2)... 

To reduce material consumption needed in production as well as avoiding thousands of tons of contaminations produced by spent materials in the battery industry, recycling was taken into consideration. In this study silica was recycled from spent lead-acid battery separators by the pyrolysis process. silica along with high-density polyethylene (HDPE), can be used as supporting material for fabricating form-stable phase change materials (FSPCM). FSPCMs are of great ability to be used as thermal energy storage (TES) in different parts of a building e. g. wallboards to reduce energy consumption. In this line, an eutectic mixture of lauric acid, palmitic acid and paraffin with the melting point... 

In this study, a series of polyoxometalates nanoclusters is synthesized and their catalytic properties have been investigated in oxidation and coupling reactions. In the first and second sections, {Mo36} nanoclusters are primarily prepared. Then, the mesoporous silica, as a solid surface with a regular chanals and cavities through electrostatic interactions between polyoxo anions and amine functional groups with positive charge, is used to stabilize the nanocluster as well as the final structure of SBA-15-NH3 +•{Mo36}- formed. As a green and environmentally friendly substrate, natural zeolite is used to stabilize the nanoclusters and the {Mo36}@zeolite obtained. Both heterogeneous catalysts...