Sharif Digital Repository

Noble metallic nanostructures based on their localized surface plasmon resonance (LSPR) exhibit a phenomenon known as surface-enhanced Raman scattering (SERS) in which the scattering cross sections are dramatically enhanced for molecules adsorbed thereon. The enhancement factor (EF) in typical cases can reach 106 and in recent years, it has been reported that even single-molecule spectroscopy is possible by SERS, suggesting that the EF can be as much as 1014-1015. In this study, we report a simple method to synthesize nanostructures of Ag and Au on metallic wafers and semiconductor via electroless deposition method. This approaches has been demonstrated to deposit metal nanostructures, thin... 

In addition to chemical stability and biocompatibility, because of the characteristics of quantum dimensions, gold nanoparticles are used in detecting cancers, imaging and therapeutics .Atomic interactions between gold particles and bioparticles are influenced by the dimensions of gold particles .Therefore, in this project, after introduction of various water models and used potentials for modeling by the method of TIP3P, we studied gold clusters in different dimensions and densities, by using EAM potential in the aquatic environment .Then we can pave the way for studying proteins besides gold nanoparticles, in the future studies. Besides, gold particles were studied as colloid, so as to... 

The colloidal crystals are formed of spherical particles and can be fabricated using simple and low-cost chemical methods. Optical properties of colloidal crystals should be recognized properly in order to design optical devices based on these nano-structures. Reflection and transmission coefficients of these multilayer structures are very important for understanding their properties. Semi-analytical methods like Fourier Modal method (FMM) can be very useful to obtain their reflection and transmission properties of these multilayer structures. In this thesis, we try to implement Matched Coordinate (MC) and Adaptive Spatial Resolution (ASR) techniques in the FMM. These techniques increase... 

A nematic colloid is a mixture of microscopic particles dispersed in a nematic liquid crystal (NLC), which is an anisotropic fluid with long-range orientational order. This long-range order might be perturbed due to different reasons, such as confinement between flat or curved surfaces which leads to frustration of the nematic director in some singular points or lines called ”topological defects”. The nucleation and the structure of these defects emerge from the elastic properties of NLC and leads to unique behavior of nematic colloids. The interaction between colloidal particles in simple fluids are mainly excluded volume interactions, electrostatic interactions, van der Waals interactions,... 

As contrast enhancement agent, two different structures of superparamagnetic nanoparticles were synthesized. Iron oxide nanoparticles were prepared through an alkaline coprecipitation method of Iron (II) and (III) ions. PEG-6000 was used as biocapping material and its effect on particle size, colloidal stability and cytotoxicity was evaluated. On the other hand, novel core/shell structures were produced by NaBH4 reduction process of iron (III) in an aqueous media following by further oxidation by two different methods using (CH3)3NO oxygen transferring agent and exposure to oxygen flow. In both cases, structural examinations were conducted via X-ray diffraction, electron microscopy and... 

In the current research, colloidal stability of two different types of coating on the surface of Superparamagnetic Iron Oxide nanoparticles (SPIONs) was studied. In the first triumph, a dual-layer coating was achieved by utilizing optimum amount of Dextran and different PEG (Poly(ethylene glycol)) concentrations which the weight ratios of iron oxide/PEG were 1/1, 2/1, 4/1, 8/1, and 16/1. Then, the presence of the coating was characterized by XRD, FT-IR, DLS and FE-SEM methods. These results together with the TGA ones revealed that as the concentration of PEG surfactant increases, the thickness of coating increases. Moreover, VSM test was performed to specify the effect of coating on the... 

A liquid crystal is a state of matter composed of highly anisotropic building blocks. When liquid crystals are exposed to surfaces with given shapes and anchoring conditions, the orientation of their molecules gets spatially disordered and topological defects may form in the system. The interplay between liquid crystals and the geometry and topology of the colloidal particles has motivated extensive recent studies.In this thesis, we present the numerical modeling results for two faceted colloidal particles in a thermotropic nematic liquid crystal. To obtain the equilibrium nematic field with a finiteelement method, we numerically minimize the free energy of the system that based on the... 

The main object of this thesis is synthesizing poly(vinyl acetate)/ colloidal silica nanocomposites via emulsion and in-situ polymerization methods. At the first, nanocomposites were produced in the presence of poly(vinyl alcohol) as the protective colloid, ammonium persulphate as the initiator and sodium bicarbonate as the buffer in an aqueous solution. Then, structural, thermal, rheological, mechanical and surface properties of produced nanocomposites with various colloidal silica content (0.5 %, 1 %, 1.5 %) were evaluated by DLS, FTIR, SEM-EDS, DSC, TGA, dynamic and steady rheological tests, tensile and shear mechanical tests, AFM and static water contact angle. The particle size of... 

Solution-processed quantum dots (QDs) have attracted significant attention for the low-cost fabrication of optoelectronic devices. Here, we synthesized PbS QDs via hot injection method and passivated the trap states by using short thiols and dopant elements for photovoltaic application. In order to study the effect of dopants on photovoltaic application, PbS QDs were doped by using three different cations: Cadmium, Calcium, and Zinc. The results showed that Cd dopant has a better improvement than Ca and Zn dopants in order to increase the efficiency of the PbS QDs solar cells. We achieved solar power conversion efficiencies of 5.81% using Cd therapy. Recently, hybrid nanocomposites... 

Structure of colloidal particles in anisotropic solvent with long-range orientational ordering, such as nematic liquid crystals, has attracted great attention in science and technology. The nematic director is distorted from its uniform orientation in the bulk due to anchoring on the surface of the colloidal particles. These elastic distortions create topological defects around the particles and induce long and short range anisotropic interactions between the particles. Depending on the anchoring type and the colloidal geometry, the particle-defect can induce a long-range dipolar-dipolar, quadrupolar-quadrupolar and/or dipolar-quadrupolar potential.Experimentally, the colloidal interactions... 

Over the past two decades, several studies have been investigated on synthesis and properties of semi-conductor quantum dots because of their applications in sensors, LEDs, detectors, solar cells, etc. One of challenging issues in synthesizing these nano-particles is their size distribution. In this study, Cadmium Selenide was synthesized by the method of colloidal synthesis. X-ray diffraction showed that the crystalline nano-particles have wurtzite structure. For obtaining a uniform size distribution, effect of various parameters such as molar ratio of components and reaction temperature on the growth kinetics of these particles, were studied. Results showed that molar ratio of Selenium to... 

In the present study, a simple synthesis route was used to obtain Titanium dioxide nanoparticles with aggregates different in size. The purpose was to study the effect of TiO2 nanoparticles size on photocatalytic activity and develop it to sonocatalytic properties. Surface modification with polymeric and/or anionic agents were carried out to stabilize titania nanoparticles in aqueous media with neutral pH, specifically in SBF. Sonocatalytic properties of modified and bare particles were compared to show if the particles may be used in future studies on sonodynamic therapy. Results showed that increment in size of the aggregates, similar to primary particles, lead to lower properties due to... 

Sonodynamic therapy has been developed over the last century, now it has become more widely used as a medical tool for the treatment of various diseases such as cancer. This technique involves delivery of sonosensitizing drugs, irradiation of ultrasound waves and motivation of drugs. In this thesis surface modification process with polymer and biocompatible surfactant on TiO2 nanoparticles has been done due to stabilization of TiO2 nanoparticles in neutral pH which is similar to inside-body situation. In the last step, for cancer therapy, doxorubicin as a cancer drug was loaded on TiO2 which was surface modified by PVA. The results revealed the best ratio of (PVA: TiO2), (SDS: TiO2), (SDS:... 

The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this thesis, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the... 

In this research, the technology of fabrication and deposition of nanoparticle inks from chalcogenide compounds and then use of them in the fabrication of CuInGaS2 and Perovskite thin-film solar cells have been considered. In the first step, the synthesis of CuInGaS2 family compounds with variable In / Ga ratio and also the change of the stoichiometric ratio of Cu component using oleylamine solvent is investigated. In addition to these compounds, the synthesis of CuSnS, CuBaSnS, and CuZnSnS nanoparticles is also investigated. The synthesized nanoparticles were analyzed by XRD, DLS, UV-Vis, ICP, PL, SEM, EDX, and TEM. Then, the stability of the ink made of CuInGaS2 nanoparticles in different... 

The aim of this thesis was to study and fabricate stable inks of Cu2SnS3 (CTS), Cu2ZnSnS4 (CZTS) and Cu3SbS4 (CAS) copper-based chalcogenide nanoparticles (NPs) and their application in solar cells. Inorganic semiconductors with p-type conductivity, high stability, high hole mobility (compared to organic type), and the ability to synthesize and deposition by simple low temperature solution-based methods have the potential to provide suitable alternative for hole-transporting material (HTM) in perovskite solar cells (PSCs) and the photo-absorbers in thin film solar cells (TFSCs). The ability to adjust energy levels and optoelectrical properties is another advantage of these compounds. In... 

The use of nanofluids for direct absorption of solar irradiance to produce freshwater has received much attention. Water-based nanofluids include metals, metal oxides, and nanocarbon-based fluids, which increase collector efficiency. On the other hand, the production cost of nanofluids is high, and when discharging the brine after the desalination process, these nanofluids cause environmental issues. Therefore, water-based organic colloids of coffee, walnut shell, black tea, and madder have been studied to overcome these problems. To accurately measure the behavior of colloids, laboratory single slope solar still was used in laboratory conditions. Also, two single slope solar stills with the... 

As many oil fields are reaching their final stage of production, new technologies are required in order to maintain production and increase recovery of hydrocarbons. Among these techniques of enhanced oil recovery (EOR), chemical injection method focuses on increasing the effectiveness of waterflooding. Due to the relatively high costs and considerable adsorption on the rock formations, this method is no longer used. In Recent years nanofluids (nanoparticles dispersed in brine) have been used as a cheap, efficient and environmentally friendly alternative more than any other chemicals. It has been stated that the Smart Water method and enhanced oil recovery by SiO2 nanoparticles are effective...