Sharif Digital Repository

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... 

In this project, melamine formaldehyde was chosen as initial substrate for its high porosity. Then for having superhydrophobic surface, surface functional groups were silanized and deactivated as a result. It was assumed that high porosity of prepared sorbent and its nonpolar nature, can increase extraction efficiency. To study extraction efficiency of the prepared sorbent, it was filled inside a needle and used for needle-trap head-space extraction of BTEX (abbreviation for Benzene, Toluene, Ethylbenzene and Xylenes). Needle packed with sorbent was held on headspace of sample containing BTEX and head- space was pumped with a peristaltic pump. Pumping introduces fresh sample to sorbent... 

Through history, increased energy consumption has been encouraged researchers to improve the performance of energy-using devices. Some researchers believe that hydrophobic surfaces can play an important role in this regard.The encounter and the presence of water on different surfaces can have different effects on them. The surface sedimentation of these surfaces, the eating of metal surfaces, the drag force (water friction) due to water collision with the moving object in water and the attachment of algae And other marine organisms to the surfaces, including the limitations and problems faced by professionals and staff associated with this sector.In the present study, the drag reduction of... 

This dissertation argues that bi-conductive textured surfaces increase both Critical Heat Flux (CHF) and Heat Transfer Coefficient (HTC) simultaneously. Surface modification is applied to stainless steel specimens by the anodizing method in an electrolyte containing Ammonium Fluoride and DI-Water and Ethylene Glycol as the based solvent. The process of oxidation was under constant DC voltage and constant temperature. The contact angle on self-aligned Nano-porous oxide layer fabricated on the substrate substantially decreases to about 5.7 degree which has a dramatic effect on CHF. Furthermore, the oxide layer augments the boiling efficiency by increasing the number of active sites and... 

Although using solar energies have some limitations, such as low efficiency, require a large space and high starting cost, they are one of the most attractive source of energies. The reasons that cause efficiency of the solar panels decrease are contamination of dust particles on them and formation of water droplet on solar panel surface due to humidity of the air. Also, a solar panel can absorb only 25% of incident light and the others are reflected by the cover glass. Therefore, fabrication of a self-cleaning surface that can inhibit the aggregation of dust particles and also transparent that doesn’t reflect the incident light is crucial.In this work, we aim to obtain a transparent,... 

Superhydrophobic surfaces have attracted so mucha attenetions in recent years. High contact angle, Low adhesion and low friction drag are the most important features of these surfaces. Two main parameters of these surfaces are hydrophobicity and micro-( or nano) scale roughness. In this Project a 2-D simulation of flow on superhydrophobic surfaces have been considered. Shan-Chen multiphase Lattice Boltzmann Model has been used for the simulation and carnahan-starling equation of state have been used or a higher density ratio. In the first step flow in a channel with smooth walls with different hydrophobicity have been simulated and effects of hydrophobicity on pressure drop have been... 

Condensation is one of the main processes in environment and engineering systems, including thermal power plants, desalination systems and air conditioners. Thus, improvement of its performance can lead to decrease of energy consumption and the resulting air pollutions. Recently, using nanotechnology and new coating methods, there have been great researches on stable superhydrophobic surfaces and using theme as condensing surfaces which because of jumping droplet phenomena can increase condensation performance. Because of the great influence of wetting and structure properties of surfaces on condensation, in this study nucleation and growth of condensing droplets on smooth and structured... 

Superhydrophobic surfaces have attracted much attention in recent years due to their unique properties. Artificial superhydrophobic surfaces can be fabricated by employing chemical modifying a hierarchical structured surface (micro- and nanostructures) with a low surface free energy material. In this report, we used a simple one-step coating process to prepare superhydrophobic sorbents with a large surface area. Surface chemistry and porosity are fundamental parameters for an efficient sorbent capable of extracting low levels of analytes. Considering physical and chemical peroperties of chlorobenzenes, superhydrophobic materials make to be good sorbents. So in this project melamine... 

The increasing demand of energy and energy consumption, urged researchers of different fields of science to investigate different aspects of energy efficiency methods. One way of optimization of energy consumption is to reduce drag force in moving objects in fluids. Changing the geometry of objects, bubble injection, air suction and blowing on surface, using nano fluid and superhydrophobic surface are just a number of drag reduction methods. Among the mentioned methods, using superhydrophobic surface due to its simplicity, low cost and no need to change in geometry of vehicles attracted attentions of researchers of all over the world. These surfaces with micro/nano roughness combined with... 

Today, with rapid developments and advances in science and technology, different ways have been studied to reduce energy consumption in various industries. Reducing the drag force and thus reducing the friction force is one of these methods which has many applications (e. g, in submarine construction industries). Creating some microgrooves in the microchannels is one of the most effective methods in order to reduce the friction force in microchannels that has recently been studied. In this method the air is trapped within the microgrooves and when the fluid (e. g, water) enters the channel passes over the trapped air within these microgrooves instead of touching the channel walls (solid... 

Nowdays, one of the most important concerns for scientists is increasing CO2 emmisions and global warming. To overcome this problem, a large number of studies have been carried out to improve energy system performance and reducing the overall energy consumption. One solution to this problem is using the superhydrophobic surfaces with contact angle larger than 150°.In this study, we try to reduce the pressure drop through the galvanized pipes. So, by reducing the pressure drop, power required for pumps can be reduced. To this end, two different coatings by silica nano-particles which were modified with first hydrophobic agent are used. In first coating which is named as PS coating, stearic... 

Many researches have been made on super hydrophobic and photocatalyst nano coatings in the last decades as a solution to some environmental issues. Among all semiconductors chosen for this property, titanium dioxide is often used because of it's low cost, ease of accessibility and stability in different chemical circumstances to break up organic pollutions. Mixing this property of TiO2 with hydrophobic manner of SiO2 causes a superhydrophobe & photocatalyst nano coating. Doping TiO2 with another semiconductor may also improve photocatalytic behavior of coating by increasing surface area of reaction or decreasing the band-gap.In this research TiO2-SiO2 hybrid nano coating is made via... 

This thesis is a research corresponding to Super-Hydrophobic condensation substrates with Nanometer texture. In this study, the foresaid surfaces are fabricated by two methods that are Nano-composite paint and Electrophoretic coating. As a summary for the first method (the Super-Hydrophobic Nano-composite paint), the hybrid coating contains two mineral and organic phases; The organic phase is a two-part clear-coat polyurethane and plays the role as a polymer matrix in Nano-composite structure. Silica Nano-particles are the mineral phase and the two phases of Nano-composite have made connection with silane compounds. Also, surface-modification in Nano-particles for giving hydrophobicity... 

In the first work, a superhydrophobic polystyrene hollow fiber (PS–HF) was synthesized by electrospinning and used in microextraction of trazine herbicides from aquatic media followed by gas chromatography mass spectrometric (GC–MS) determination. Effects of different parameters influencing the extraction efficiency including the solvent extraction and its amount, the desorbing solvent and its amount, extraction time and ionic strength were optimized. The characteristic properties of the hollow fiber were studied by scanning electron microscopy (SEM). The limits of detection and quantification of the method under optimized condition were 2 and 6 ng L-1, respectively. The relative standard... 

Rehabilitation usually involves physical therapy, occupational therapy and counseling for the patient's morale to help to restore his power and performance. Considering the economic outlook and the costs of rehabilitation methods and due to the increasing prevalence of stroke and the need to recover the patients in a short period, only the use of robotic systems opens the door to the medical community. Since a large rehabilitation robots designed and built and each been used according to their advantages and shortcomings. In this project, the major shortcomings examined and exoskeleton designed on two major features including portability and covering shoulder workspace. Shoulder movement was... 

In this research we developed a superhydrophobic and anti-wear coating on a glass substrate using SiO2 nanoparticles to form a transparent superhydrophobic thin film and SiC nanoparticles to improve the wear resistance of coating.
Silica nanoparticles were produced via a simple sol gel method from Tetraethylorthosilicate (TEOS) as precursor. Hexamethyldisilazane (HMDS) and Tetramethylclourosilane (TMCS) were used as hydrophobic inducing agents and at last SiC nanoparticles were dispersed in the solution in order to provide wear resistance. The final results indicate the contact angle (CA) of water droplet on the surface was about 158° and sliding angle (SA) lower than 9°. Studying the... 

Phase change processes have been used in heat transfer industries for decades. However, the heat transfer rate enhancement of the surfaces is still a challenging issue for the researchers. In this path, emerging nanostructured surfaces have shown great potentials. We demonstrate that using nanostructured surfaces in the condensation processes enhances the heat transfer behaviour of the fluid through interfacial contact area increase. In the present study molecular dynamics simulation have been employed to monitor the atomic behaviour of the system components at nanoscale. The argon liquid is considered as the working fluid and the copper surfaces as the phase change site. The effect of... 

Titanium nano-oxide (TiO2) coatings have been used for self-cleaning, antimicrobial, and dust-proof designs. The degree of wetting of a solid surface with water in humid air depends on how the surface tension of the existing phases relates. The ratio between these tensions estimates the contact angle between a drop of water and the surface on which it is placed. A contact angle above 150 º is essential for surface overflow. In this study, 18 different combinations of titanium oxide and FAS, PDMS and PMS nanoparticles were obtained with a static contact angle of 165 to 150 º and a dynamic contact angle of 7 º.1 to 4.5 º. Following the measurement of water droplet slip speed on a sloping... 

Ice accretion may cause malfunction or serious performance degradation in outdoor facilities and structures, such as aircraft, ship, locks and dams, offshore platforms, solar panels, wind turbines, power transmission towers and lines, and sports facilities, leading to huge economic loss or even loss of human lives. Icephobic materials, typically applied in the form of coatings, have received growing attention in the last decade. This work focuses on surfaces with a surface tension gradient which has icephobic properties. various surface tension gradients such as linear, exponential, cycloid and parabola have been imposed on a surface in order to achieve the shortest time for a droplet to... 

Due to their unique characteristics, such as drag reduction, anti-fouling, and enhancing condensation, hydrophobic and superhydrophobic surfaces have attracted a lot of attention in the past decades. Since approximately 4% of the fossil fuel usage and 14-19% of the air pollution (including greenhouse gases, sulfur, and so forth) are attributed to naval activities, and the dominant form of drag on vessels is friction, drag reduction will not only reduce the cost and usage of fossil fuels, but it will also have numerous environmental benefits