Sharif Digital Repository

Surface tension is the most important interfacial parameter of a liquid. This quantity plays a key role in many processes such as extraction, distillation, absorption and chemical reactions. Various methods are proposed for measuring this quantity among which, the laser based methods are the most accurate ones. Unlike most of the mechanical methods, laser based methods remotely measure the surface tension. The aim of the current thesis is to measure the surface tension using laser beam, more specifically using homodyne detection system. This method implemented in both reflected and transmitted modes. In each of the mentioned methods, first the laser beam was incident to the liquid-air... 

In recent years, due to greater attention scientific communities to environment and environmental friendly material, use of natural fibers as reinforcing the polymers has increased significantly. High specific strength, low density, cheap, stiffness and recycled by nature, are including promotional items using natural fibers as reinforcing in the polymer composites. In This study has tried in the first place an appropriate method for producing polypropylene composites reinforced with short jute fibers should be presented and then the physical and mechanical properties of composites will be investigated. Used MAPP and Silane for compatibility took improved between natural jute fibers as a... 

In this study, friction stir lap welding of Al-5083 alloy sheets with 3 mm thickness to St-12 steel sheets with 1 mm thickness (joint without intermediate layer) and to Al-1100 clad St-12 sheets (joint with the Al-1100 intermediate layer) was investigated. The cladding process was done by rolling. For each type of joints, the bonding mechanism, optimum process parameters to reach the joints with the highest fracture loads and also the microstructure evolutions at the joint region were studied. Furthermore, for the joints without intermediate layer, the effects of the Al-5083 annealing treatment before welding and the post-weld heat treatment of the joints on the fracture loads were explored.... 

Because of low friction coefficient, Copper-Graphite and Copper-Babbitt composites can be used as brushes and bearing materials instead of materials containing lead which cause environmental problems. So far, many methods such as powder metallurgy and centrifugal casting have been used to fabricate Copper-Graphite composites. The most important problem of these methods is agglomeration of Graphite particles. Simultaneous stirring of samples during fabrication process which is one of the features of friction stir processing (FSP), can solve the problem. Recently, FSP has been used for fabricating surface composite for the purpose of producing hard and wear resistance layers on ductile... 

The purpose of this study is fabrication and characterization of a mesoporous Perovskite solar cell using Barium Titanate as the mesoporous electron transfer layer. In this study, TiO2 nanoparticles and BaTiO3 oxide perovskites were prepared by sol-gel synthesis method and their pastes were applied to the conductive substrate by spin coating method and applied to electron transfer layer in perovskite solar cells. Then Perovskite solar cells were fabricated with different structures from the electron transfer layer.The results of X-ray diffraction analysis showed that pure Barium Titanate and Titanium dioxide nanoparticles were successfully synthesized with tetragonal and cubic crystal... 

Quince seed gum is a natural material that was used in Iranian traditional medicine for wound treatment. Alginate is a beneficial biomaterial that has been used in making commercial wound dressings for a long time. In this work, the preparation method and properties of films based on Alginate and Quince seed gum for drug delivery and wound healing have been investigated. According to the obtained results about crosslinking and plasticizing, the suitable condition of synthesis is 0.5% CaCl2 concentration, 2min soaking time, and 13% glycerol in crosslinking solution. In this crosslinking solution, a film with good mechanical properties (tensile strength: 13MPa, elongation: 27.3%, and Young’s... 

In this research, wear behaviors of 6061Al and 6061Al-20 vol% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 25- 200°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.34 m/s, an applied load of 20 N and 50N, and a sliding distance of 2450m using a pin-on-disc machine test. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects on wear rate of composite. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. Also for determining the effect of age hardening treatment on wear behavior of composite, specimens were solution treated at... 

In this project, Dissimilar Friction Stir Welding (FSW) between aluminum alloys (1100-H12 and 5083-O) and Magnesium alloy (AZ31B-O) with 3mm thickness were butt joined. Fusion welding of aluminum/magnesium alloys has failed because of forming much more intermetallic compounds. By using friction stir welded samples, effect of welding parameters such as tool travel speed, tool rotation rate, tool position respect to weld centerline, and sheet position respect to tool direction on mechanical (tensile strength, yield strength and elongation) and microstructural properties of the welds were investigated. After several tests, range of optimum parameters were obtained. In both 1100 and 5083 alloys,... 

Perovskite solar cells, with high efficiency operation, have been candidated as a cost-effective and environmentally friendly technology. Despite the great progress, there are some primarily issues remained regarding to the perovskite film and its fabrication methods. A very common perovskite cell structure is FTO/TiO2/CH3NH3PbI3/Spiro-OMeTAD/Au. Although, this structure has some advantages, lack of full surface coverage of perovskite film leads researchers to put much effort on finding other constructions. This surface inhomogeneity reduces the amount of light absorption and therefore efficiency. One way to produce a complete and uniform film is applying mixed-halide composition; such as... 

Optical tweezer is a highly focused laser beam that could be used to trap micro and nano particles in three dimensions. It could be used to measure(or apply) piconewton range forces. Most of the optical tweezers experiments have been done in liquid mediums. In last few years, trapping particles which are floating in gas mediums(called aerosols) have been considered extensively. In this thesis, the changes in trap stiffness and conversion factor due to changes in laser power, trapping depth and particle are evaluated. It is shown that changing these three parameters, cause considerable changes in trap stiffnes and conversion factor. Linear behavior of trap stiffness versus laser power,... 

Microfluidics is a field of science that studies micron-scale characteristics of fluids. In this scale fluids show fascinating behavior far beyond our expectation compared to their large-scale counterparts. One of such peculiar behavior is the mixing of two different liquids flowing inside a microchannel. Due to low Reynolds number, the flow inside such a channel would be dominated by laminar behavior. In this regime mixing of the fluids is only mediated by molecular diffusion which is a rather slow process. In the current thesis, we utilized the rotating ability of optical tweezers to construct an active micromixer for Microfluidics. In order to do this we used birefringent microbeads. The... 

Intensity or phase Modulation of a wavefront is possible by means of optical devices. Placing a grating or lens on the way of a wavefront, will alter the phase or intensity of it and this will make a diffraction pattern. Spatial Light Modulator (SLM) is an optical device which is the most important part of a video projector. One can apply grating, lens and other phases on the wavefront using this device.In this project we used SLM to modify phase of laser beam and then we made many focal points such that they could displace independently. The result of this project can be used in designing and creating a holographic optical tweezers.Moreover, A. Einstein proved that the light could be... 

Viscoelastic properties of biological fluid play an important role on biological organs. As an example we all know that Red blood cells must have high flexibility to pass thorough thin capillary.This high flexibility come partially from cytoplasm and 2 dimensional membrane and partially from polymeric fluid inside the cell(hemoglobin). So, for recognizing mechanical properties of a whole cell we also need to study the same properties just for fluid inside the cell. for this general purpose through this project we are going to measure viscoelastic properties of any polymeric fluid by optical tweezers which has an ability for measuring displacement of micron particle with accuracy of nm. first... 

Optimizing optical tweezers and achieving powerful traps has always been a challenging topic for researchers , since the trap stiffness increases with increasing laser power which may damage specimens , especially biological ones and cells . In this thesis , we introduce a special geometry and structure of particles that , have the possibility to increase the stiffness (strength) of the optical trap and cause the magnetic response of particles at optical frequencies . Special geometries such as a combination of dielectric particles with magnetic nanoparticles that emphasize the role of the laser magnetic field and lead to changes in the electrical and magnetic properties at the laser... 

Optical tweezers consist of a tightly focused laser beam. Particle with refractive index grater than that of the surrounding medium are eligible for optical trapping. This device is used for measuring forces from pico-newton to nano-newton, and displacements from nanometer to micrometer. In biopolymers, for example, it is used for studying the elasticity of DNA molecules, mechanical properties of cell membrane; and also in Microfluidics, it can is used for mixing two liquids flowing in a micro-channel by rotating a trapped particle. In general, physics of optical tweezers (or interaction of the trapped particle with the tightly focused laser beam) is treated in three different regimes:1)... 

Blood is one of the most important fluids in the human body, consisting of three parts: red blood cells, white blood cells and platelets. The mechanical properties of red blood cells are important in many diseases. The study of viscosity and other mechanical properties of red blood cells in recent years has attracted the attention of scientists in this field. The mechanical properties of red blood cells are related to the outer membrane and its cytoskeleton, and the study of these components can predict the behavior of red blood cells in diseases. The thyroid gland is located in front of the neck and secretes hormones that control many chemical processes in different parts of the body.... 

Red blood cells are one of the most important parts of blood and their mechanical properties are so important in some diseases. Red blood cell is mostly consisted of membrane, cell skeleton, and cytoplasm which contains hemoglobin proteins. Studying these properties separately not only could give us pieces of information about cell mechanics, but also reveals a way to predict their behavior after illnesses. Optical tweezers as a tool, which can produce and measure Piconewton to Nanonewton forces, has been interesting in red blood cell parts' studying. In this thesis, at first hemoglobin is taken out gradually by using Saponin (which is enable to make some pores in the membrane) and the... 

In this study, Aluminium based nanocomposite with Al3Ti and Al2O3 nanoparticles have been elaborated by mechanical alloying. For this purpose, Al and TiO2 powders have been blended with weight ratios of 10, 20 and 30 percents and were milled using a planetary mill. Morphological variations in different timing periods of mechanical milling process was investigated by Scaning Electron Microscopy (SEM) and The optimal times for alloying were determined for each combination. The pure Aluminium and the powder with 10, 20 and 30%wt reinforcement had coax morphology after respectively for 44, 30, 24 and 14 hours. after studing phase transformations by XRD analysis, the final powders were cold... 

Digital holographic microscope is a microscope based on interferometry, which allows us to simultaneously have the information of the phase in addition to the intensity information. In this research, we intend to measure the thickness of the red blood cell with the help of an interferometer and prepare a three-dimensional microscopic image of the blood cell. After contamination, a laser beam hits an optical beam splitter that can divide the light into two parts with equal intensities. Each of these wave fronts, after hitting the mirror, is directed to another beam splitter to be recombined. . Since the incident lights have traveled different optical paths, they have a phase difference with...